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Urate transporter 1 (URAT1) and glucose transporter 9 (GLUT9) are important targets for the development of uric acid-lowering drugs. We previously showed that the flexible linkers of URAT1 inhibitors could enhance their potency. In this study we designed and synthesized CDER167, a novel RDEA3710 analogue, by introducing a linker (methylene) between the naphthalene and pyridine rings to increase flexibility, and characterized its pharmacological and pharmacokinetics properties in vitro and in vivo. We showed that CDER167 exerted dual-target inhibitory effects on both URAT1 and GLUT9: CDER167 concentration-dependently inhibited the uptake of [(14)C]-uric acid in URAT1-expressing HEK293 cells with an IC(50) value of 2.08 ± 0.31 μM, which was similar to that of RDEA3170 (its IC(50) value was 1.47 ± 0.23 μM). Using site-directed mutagenesis, we demonstrated that CDER167 might interact with URAT1 at S35 and F365. In GLUT9-expressing HEK293T cells, CDER167 concentration-dependently inhibited GLUT9 with an IC(50) value of 91.55 ± 15.28 μM, whereas RDEA3170 at 100 μM had no effect on GLUT9. In potassium oxonate-induced hyperuricemic mice, oral administration of CDER167 (10 mg·kg(−1) · d(−1)) for 7 days was more effective in lowering uric acid in blood and significantly promoted uric acid excretion in urine as compared with RDEA3170 (20 mg·kg(−1) · d(−1)) administered. The animal experiment proved the safety of CDER167. In addition, CDER167 displayed better bioavailability than RDEA3170, better metabolic stability and no hERG toxicity at 100 μM. These results suggest that CDER167 deserves further investigation as a candidate antihyperuricemic drug targeting URAT1 and GLUT9.

Background Dotinurad is a novel selective urate reabsorption inhibitor that reduces serum urate levels in hyperuricemic patients with or without gout by selectively inhibiting urate transporter 1. This study was conducted to compare the efficacy and safety of dotinurad with those of benzbromarone. Methods In this 14-week, randomized, multicenter, double-blind, parallel-group, dose escalation, benzbromarone-controlled, phase 3 study, hyperuricemic patients with or without gout were randomized to two groups that received either dotinurad 2 mg or benzbromarone 50 mg. Dotinurad or benzbromarone was administered once a day for 14 weeks. The primary endpoint was the percent change in serum uric acid level from the baseline to the final visit. Results A total of 201 Japanese hyperuricemic patients with or without gout (dotinurad: 102, benzbromarone: 99) received at least one dose of the study drug. The mean percent change in serum uric acid level from the baseline to the final visit in the dotinurad and benzbromarone groups was 45.9% and 43.8%, respectively. Non-inferiority of dotinurad 2 mg to benzbromarone 50 mg in lowering serum uric acid was verified by the predefined non-inferiority margin (95% CI − 1.27 to 5.37%). The incidence of adverse events and adverse drug reactions was comparable between the two groups. Conclusion Dotinurad 2 mg was verified to have a non-inferior serum uric acid lowering effect compared with benzbromarone 50 mg, in Japanese hyperuricemic patients with or without gout. ClinicalTrials.gov Identifier NCT03100318.

Background Dotinurad, a novel selective urate reabsorption inhibitor, exerts a serum uric acid-lowering effect by selectively inhibiting urate transporter 1 (URAT1) in patients with hyperuricemia. It is generally known that the progression of renal dysfunction is associated with a reduction in the serum uric acid-lowering effects of uricosuric drugs. We, therefore, investigated the pharmacokinetics (PK), pharmacodynamics (PD), and safety of dotinurad in subjects with renal dysfunction. Methods This was a parallel-group, open-label, single-dose clinical pharmacology study. Dotinurad (1 mg) was administered once, orally to subjects with mild (estimated glomerular filtration rate [eGFR], ≥ 60 to 2) or moderate (eGFR, ≥ 30 to 2) renal dysfunction or normal (eGFR, ≥ 90 mL/min/1.73 m2) renal function. Results The time-course of mean plasma concentration of dotinurad had similar profiles across the groups. Regarding PK, there was no significant difference between the renal dysfunction groups and normal renal function group. Regarding PD, the maximum reduction rate in serum uric acid levels and the fractional uric acid excretion (FE) ratio (FE0–24/FE−24–0) were significantly lower in the moderate renal dysfunction group than in the normal renal function group. However, other PD parameters were not significantly different among the groups. No notable adverse events or adverse drug reactions were observed in this study. Conclusion These results suggested that no dose adjustment might be necessary when administering dotinurad to patients with mild-to-moderate renal dysfunction. ClinicalTrials.gov Identifier: NCT02347046.

Gout is more prevalent than ever and is associated with multiple chronic comorbidities, including Chronic Kidney Disease (CKD). While goals of treatment are the same as in those without renal impairment, co-morbid CKD poses a challenge in treatment selection and requires a solid understanding of potential drug-drug interaction and drug-related toxicity. In acute gout complicated by CKD, NSAIDs should be avoided, and colchicine used with caution. Systemic corticosteroids are effective but may be replaced by anakinra, in particular in inpatients with additional comorbidities that may make corticosteroids less desirable. Allopurinol remains the first line urate lowering therapy (ULT), starting at a low dose followed by careful goal driven up-titration. Febuxostat is a reasonable alternative, though second line in light of recent cardiovascular data. Uricosuric drugs are generally less effective, while pegloticase is reserved for refractory cases of polyarticular tophaceous disease. Gout treatment must be guided by renal function but in spite of renal disease can be successfully managed.

Hyperuricemia is the main cause of gout, an inflammation induced by uric acid deposition in joints. Drugs available present side effects, so there is a need for new treatment alternatives. Lychnophora species are used in folk medicine to treat inflammation, rheumatism and muscle pain. Goyazensolide (10 mg/kg), eremantholide C (25 mg/kg) and lychnopholide (25 mg/kg), sesquiterpene lactones isolated from Lychnophora species were previously studied and showed anti-hyperuricemic effects in mice. However, the mechanisms of this effect were not elucidated. The methodology of this study consisted in treatment of hyperuricemic-induced rats, and comparison between control groups, clinically used anti-hyperuricemic drugs and sesquiterpene lactones. Urine and blood were collected for uric acid quantification. Xanthine oxidase inhibition was measured in liver homogenates. Results showed that all evaluated sesquiterpene lactones presented anti-hyperuricemic activity at the doses of 5 and 10 mg/kg and can act through one or both mechanisms, depending on the dose administrated. Goyazensolide and lychnopholide at dose of 5 mg/kg showed important uricosuric effect. Goyazensolide and lychnopholide at dose of 10 mg/kg, and eremantholide C (5 and 10 mg/kg) presented notable inhibition of hepatic xanthine oxidase activity and uricosuric effect. Thus, these sesquiterpene lactones are promising hypouricemic agent to treat hyperuricemia and gout. Keywords: Sesquiterpene lactones, Hyperuricemia, Xanthine oxidase, Uricosuric effect, Gout

Our goal was to establish a model for the evaluation of the effects of uricosuric agents and to clarify the underlying mechanism(s). The effects of a uricosuric agent co-treated with pyrazinamide, an anti-tubercular agent, on urate handling were examined in rats. Furthermore, the effects of uricosuric agents on urate uptake were evaluated using the vesicles of rat renal brush-border membrane. Treatment with probenecid, at a dose of 100 mg/kg, significantly increased the urinary urate to creatinine ratio (UUA/UCRE) in pyrazinamide-treated rats although the same treatment did not produce any uricosuric effects in intact rats. In this model, the urinary excretion of pyrazinecarboxylic acid (PZA), an active metabolite of pyrazinamide, was decreased by probenecid and indicated an inverse correlation between urinary excretion of urate and PZA. Furthermore, in the examination using FYU-981, a potent uricosuric agent, a more than 10-fold leftward shift of the dose–response relationship of the uricosuric effect was observed in pyrazinamide-treated rats when compared with intact rats. In the in vitro study, the treatment of the vesicles of rat renal brush-border membrane with PZA produced an increased urate uptake, which was inhibited by uricosuric agents. The pyrazinamide-treated model used in the present study seems to be valuable for the evaluation of uricosurics because of its higher sensitivity to these drugs when compared to intact rats, and this is probably due to the enhanced urate reabsorption accompanied with trans-stimulated PZA transport at the renal brush-border membrane.

Uric acid (UA) has been associated with hypertension, renal disease and cardiovascular disease. The aim of the present study was to compare the UA-lowering effects of a standard dose of the UA synthesis inhibitor febuxostat to a standard dose of the uricosuric agent benzbromarone, and to investigate the effects of a low-dose combination of both agents in hypertensive patients with hyperuricemia. Twenty hypertensive patients with inadequate UA control were administered febuxostat 40 mg (Feb), benzbromarone 50 mg (Ben) and febuxostat 20 mg and benzbromarone 25 mg (feb/ben) for 3 months each in a randomized modified crossover manner. UA metabolism, blood pressure (BP) and the indices of organ damage were assessed at baseline and the end of each treatment period. No significant changes were observed in BP or estimated glomerular filtration rate (eGFR) after the treatment with each UA-lowering regimen. The change in UA was significantly greater with feb/ben than with Feb. The excretion of UA and clearance of UA were higher with Ben than with Feb and feb/ben. Urinary 8-hydroxydeoxyguanosine and liver-type fatty-acid-binding protein levels were slightly lower with Ben, whereas flow-mediated dilation was slightly higher with feb/ben and Ben. The UA-lowering effects of the low-dose combination of the UA synthesis inhibitor and uricosuric agent were greater than those of the standard dose of each agent alone. The uricosuric agent may be more effective at improving vascular function than the UA synthesis inhibitor. Thus, the appropriate management of hyperuricemia with uricosuric drugs appears to be useful for hypertensive patients with hyperuricemia.

Probenecid was initially developed with the goal of reducing the renal excretion of antibiotics, specifically penicillin. It is still used for its uricosuric properties in the treatment in gout, but its clinical relevance has sharply fallen and is rarely used today for either. Interestingly, throughout the last 60 years, there have been a host of apparently unrelated studies using probenecid in the clinical and basic research arena, including its potential use in the diagnosis and treatment of depression and its use to prevent fura-2 leakage in calcium transient studies. Recently, it has been shown that it is also an agonist of the Transient Receptor Potential Vanilloid 2 channel. Due to its unique action and new findings implicating TRPV channels in physiology and in disease, probenecid may have a new future as a research tool, and perhaps as a clinical agent in the neurology and cardiology fields. We review the history of probenecid in this paper and its potential future uses.

Benzbromarone, a potent uricosuric drug, was introduced in the 1970s and was viewed as having few associated serious adverse reactions. It was registered in about 20 countries throughout Asia, South America and Europe. In 2003, the drug was withdrawn by Sanofi-Synthelabo, after reports of serious hepatotoxicity, although it is still marketed in several countries by other drug companies. The withdrawal has greatly limited its availability around the world, and increased difficulty in accessing it in other countries where it has never been available.

In 2003, the uricosuric drug benzbromarone was withdrawn from the market. The first alternative drug of choice was the xanthine oxidase inhibitor allopurinol. The purpose was to (1) investigate the efficacy of allopurinol (standard dosage) compared with previous treatment with benzbromarone; and (2) investigate the combination therapy allopurinol-probenecid as an effective alternative treatment compared with previous benzbromarone treatment. A prospective, open study was carried out in a cohort of 51 gout patients who discontinued benzbromarone therapy because of market withdrawal. Patients were given 200-300 mg allopurinol (stage 1). When allopurinol failed to attain the target serum urate (sUr) levelsor=0.30 mmol/l, probenecid 1,000 mg/day was added (stage 2). Treatment with benzbromarone monotherapy (range: 100-200 mg/day; mean 138 mg/day) resulted in 92% of patients reaching target levels sUror= 0.30 mmol/l with a decrease of 61[11]% compared to baseline. In stage 1, 32 patients completed treatment with allopurinol monotherapy (range 200-300 mg/day; mean 256 mg/day), which resulted in 25% of patients attaining sUr target levels. Decrease in sUr levels was 36[11]%, which was significantly less compared to treatment with benzbromarone (p0.001). In stage 2, 14 patients received allopurinol-probenecid combination therapy, which resulted in 86% of patients attaining target sUr levels (after failure on allopurinol monotherapy), which was comparable to previous treatment with benzbromarone (p = 0.81). Decrease in sUr levels was 53[9]% (CI 95%: 48-58%), which was a non-significant difference compared to previous treatment with benzbromarone (p = 0.23). Benzbromarone is a very effective antihyperuricemic drug with 91% success in attainment of target sUr levelsor=0.30 mmol/l. Allopurinol 200-300 mg/day was shown to be a less potent alternative for most selected patients to attain target sUr levels (13% success). In patients failing on allopurinol monotherapy, the addition of probenecid proves to be an effective treatment strategy for attaining sUr target levels (86% success).

Allopurinol is the drug most widely used to lower the blood concentrations of urate and, therefore, to decrease the number of repeated attacks of gout. Allopurinol is rapidly and extensively metabolised to oxypurinol (oxipurinol), and the hypouricaemic efficacy of allopurinol is due very largely to this metabolite. The pharmacokinetic parameters of allopurinol after oral dosage include oral bioavailability of 79 +/- 20% (mean +/- SD), an elimination half-life (t((1/2))) of 1.2 +/- 0.3 hours, apparent oral clearance (CL/F) of 15.8 +/- 5.2 mL/min/kg and an apparent volume of distribution after oral administration (V(d)/F) of 1.31 +/- 0.41 L/kg. Assuming that 90 mg of oxypurinol is formed from every 100mg of allopurinol, the pharmacokinetic parameters of oxypurinol in subjects with normal renal function are a t((1/2)) of 23.3 +/- 6.0 hours, CL/F of 0.31 +/- 0.07 mL/min/kg, V(d)/F of 0.59 +/- 0.16 L/kg, and renal clearance (CL(R)) relative to creatinine clearance of 0.19 +/- 0.06. Oxypurinol is cleared almost entirely by urinary excretion and, for many years, it has been recommended that the dosage of allopurinol should be reduced in renal impairment. A reduced initial target dosage in renal impairment is still reasonable, but recent data on the toxicity of allopurinol indicate that the dosage may be increased above the present guidelines if the reduction in plasma urate concentrations is inadequate. Measurement of plasma concentrations of oxypurinol in selected patients, particularly those with renal impairment, may help to decrease the risk of toxicity and improve the hypouricaemic response. Monitoring of plasma concentrations of oxypurinol should also help to identify patients with poor adherence. Uricosuric drugs, such as probenecid, have potentially opposing effects on the hypouricaemic efficacy of allopurinol. Their uricosuric effect lowers the plasma concentrations of urate; however, they increase the CL(R) of oxypurinol, thus potentially decreasing the influence of allopurinol. The net effect is an increased degree of hypouricaemia, but the interaction is probably limited to patients with normal renal function or only moderate impairment.

The prevalence of gout has increased markedly in the United States in the past two decades, and new treatments for hyperuricemia are being developed. Recent molecular identification of urate transporter-1 (URAT1) as the central mediator of renal urate reabsorption has provided novel understanding of the pathogenesis of hyperuricemia, and the target site for current and possibly future primary uricosuric agents. Recent studies have also highlighted uricosuric effects of several drugs (losartan, atorvastatin, fenofibrate) that are prescribed for primary indications other than hyperuricemia. The niche of these agents in current management of hyperuricemia is discussed. We also review the ongoing development of recombinant uricase preparations and of novel xanthine oxidase inhibitors exemplified by febuxostat. These agents should provide novel options for patients with chronic, refractory gout and hyperuricemia, particularly in association with allopurinol hypersensitivity and renal insufficiency.

There are three stages in the management of gout: (i) treating the acute attack; (ii) lowering excess stores of uric acid to prevent flares of gouty arthritis and to prevent tissue deposition of urate; and (iii) providing prophylaxis to prevent acute flares. It is important to distinguish between therapy to reduce acute inflammation in acute gout and therapy to manage hyperuricaemia in patients with chronic gouty arthritis. During the acute gouty attack nonpharmacological treatments such as topical ice and rest of the inflamed joint are useful. NSAIDs are the preferred treatment in acute gout. The most important determinant of therapeutic success is not which NSAID is chosen, but rather how soon NSAID therapy is initiated. Other treatments include oral and intravenous colchicine, intra-articular and systemic corticosteroids, and intramuscular corticotropin. Optimal treatment of chronic gout requires long-standing reduction in serum uric acid. The urate-lowering drugs used to treat chronic gout are the uricosuric drugs, the uricostatic drugs, which are xanthine oxidase inhibitors, and the uricolytic drugs. Xanthine oxidase inhibitors such as allopurinol, oxipurinol and febuxastat should be used as first-line treatment in patients with renal calculi, renal insufficiency, concomitant diuretic therapy and ciclosporin (cyclosporine) therapy, and urate overproduction. Uricosuric drugs include probenecid, benzbromarone, micronised fenofibrate and losartan. They are the urate-lowering drugs of choice in allopurinol-allergic patients and underexcretors with normal renal function and no history of urolithiasis. The use of recombinant urate oxidase in patients with chronic gout is limited by the need for parenteral administration, the potential antigenicity and production of anti-urate oxidase antibodies, and declining efficacy. The effectiveness of colchicine prophylaxis as an isolated therapy is still to be confirmed by placebo-controlled trials. Another issue is prophylaxis with NSAIDs. There are no comparative studies with colchicine.

A major obstacle to the treatment of hyperuricemia in patients allergic to allopurinol is the limited availability of suitable, equally effective, alternative, urate-lowering drugs. Conventional uricosuric drugs, including probenecid and sulfinpyrazone, are recommended for allopurinol- intolerant patients with gout and "underexcretion" hyperuricemia who have normal renal function and no history of nephrolithiasis. Therapeutic options in those in whom traditional uricosuric drugs are contraindicated, ineffective, or poorly tolerated include slow oral desensitization to allopurinol and cautious administration of oxipurinol. Allopurinol desensitization is useful particularly in those who have failed other treatment modalities. If available (as in Europe, South Africa, and Japan), benzbromarone may be tried in patients with gout and mild-to-moderate renal insufficiency. Recombinant urate oxidase can be used in the short-term prophylaxis and treatment of chemotherapy- associated hyperuricemia in patients with lymphoproliferative and myeloproliferative disorders. Hyperuricemia and gout occur with increased frequency in cyclosporine-treated allograft transplant recipients. The management of gout in these patients is complicated by two main factors: cyclosporine-induced renal impairment, and interactions with medications used to preserve the allograft.

Gout in the elderly differs from classical gout found in middle-aged men in several respects: it has a more equal gender distribution, frequent polyarticular presentation with involvement of the joints of the upper extremities, fewer acute gouty episodes, a more indolent chronic clinical course, and an increased incidence of tophi. Long term diuretic use in patients with hypertension or congestive cardiac failure, renal insufficiency, prophylactic low dose aspirin (acetylsalicylic acid), and alcohol (ethanol) abuse (particularly by men) are factors associated with the development of hyperuricaemia and gout in the elderly. Extreme caution is necessary when prescribing nonsteroidal anti-inflammatory drugs (NSAIDs) for the treatment of acute gouty arthritis in the elderly. NSAIDs with short plasma half-life (such as diclofenac and ketoprofen) are preferred, but these drugs are not recommended in patients with peptic ulcer disease, renal failure, uncontrolled hypertension or cardiac failure. Colchicine is poorly tolerated in the elderly and is best avoided. Intra-articular and systemic corticosteroids are increasingly being used for treating acute gouty flares in aged patients with medical disorders contraindicating NSAID therapy. Urate-lowering drugs are indicated for the treatment of hyperuricaemia and chronic gouty arthritis. Uricosuric drugs are poorly tolerated and the frequent presence of renal impairment in the elderly renders these drugs ineffective. Allopurinol is the urate-lowering drug of choice, but its use in the aged is associated with an increased incidence of both cutaneous and severe hypersensitivity reactions. To minimise this risk, allopurinol dose must be kept low. A starting dose of allopurinal 50 to 100mg on alternate days, to a maximum daily dose of about 100 to 300mg, based upon the patient's creatinine clearance and serum urate level, is recommended. Asymptomatic hyperuricaemia is not an indication for long term urate-lowering therapy; the risks of drug toxicity often outweigh any benefit.

Gout is a common disease with a worldwide distribution. The major risk factor for the development of gout is sustained asymptomatic hyperuricaemia. Although pharmacological therapy of asymptomatic hyperuricaemia is not recommended, primary prevention of gout can be achieved through lifestyle changes including weight loss, restricting protein and calorie intake, limiting alcohol consumption, avoiding the use of diuretics in the treatment of hypertension, and avoiding occupational exposure to lead. The arthritis of gout can be readily managed with the use of nonsteroidal anti-inflammatory drugs (NSAIDs); systemic steroids or corticotrophin (adrenocorticotrophic hormone; ACTH) should be used in patients with contraindications to NSAIDs, or who are intolerant of them. Because of potential toxicity, colchicine should not be used to treat acute gout, but should be used in low dosage (0.6 to 1.2 mg/day) for prophylaxis of recurrent attacks of gout. The other cornerstone of prevention of recurrent gouty attacks is control of hyperuricaemia, which can be effectively accomplished with antihyperuricaemic therapy. The choice of agents, either uricosuric drugs or xanthine oxidase inhibitors, is based on the level of urinary uric acid excretion, renal function, age of patient, history of renal calculi and presence of tophi. Treatment and prevention of gout are exceedingly effective and patients can usually be managed by their primary care physician.

Irtemazole 12.5 to 50 mg in 6 healthy, normouricaemic subjects caused a maximal decrease in plasma uric acid (after 8 to 12 h) of 46.5%. The uricosuric effect began during the first 60 min after drug administration and it lasted for 7 to 24 h. Renal uric acid excretion returned to its base line value after 8 to 16 h and uric acid clearance after 10.0 to 12.0 h. Doses of irtemazole between 12.5 and 37.5 mg produced a dose-related rise in the uricosuric effect. There was no essential difference between the uricosuric effect of 37.5 mg and 50 mg irtemazole. The D50 dose (that producing a half-maximal effect) was between 16.3 mg and 34.2 mg, (average 24.7 mg). The value of irtemazole in the management of hyperuricaemia and gout remains to be determined.

The uricosuric effect of DuP-753, a novel, specific angiotensin II receptor antagonist, has been explored in a healthy male Japanese volunteers, given single oral doses of 25, 50, 100 or 200 mg (n = 6), or 100 mg (n = 6) or placebo (n = 3) once daily for 7 consecutive days. In the single-dose study, serum uric acid measured at 4 h after dosing showed a dose dependent decrease; the reductions from the corresponding pre-dose values were: 0.32 (25 mg), 0.77 (50 mg), 1.25 (100 mg) and 1.33 mg.dl-1 (200 mg). The urinary excretion of uric acid within the first 4 h after treatment was also increased in a dose-dependent manner, whereas the urinary excretion of creatinine remained unchanged. In the multiple-dose study, DuP-753 significantly decreased the serum uric acid concentration measured 4 h both after the first (pre-dose value: 5.68 vs 4 h after: 4.48 mg.dl-1) and last administrations (4.42 mg.dl-1). Simultaneously, the ratio of urinary uric acid to creatinine excretion was significantly increased within the first 4 h both after the first (DuP-753: 1.190 vs placebo: 0.576) and last administrations (1.02 vs 0.576). The findings suggest that DuP-753 possesses a uricosuric effect both after single and multiple doses in healthy subjects. The effect should be further examined in hypertensive patients.

We evaluated the uricosuric action of AA-193 by comparing it with the effect on PAH secretion in rats, using in vivo and in vitro techniques. The i.v. administration of AA-193 elevated the fractional excretion of urate (FEurate) significantly in a dose-dependent manner at doses from 0.1 to 10 mg/kg. Only at the highest dose of 10 mg/kg did AA-193 cause a momentary decrease in FEPAH. On the other hand, tienilic acid and probenecid reduced FEPAH at uricosuric effective doses. To compare the inhibitory effects of uricosurics on urate reabsorption and PAH secretion more directly, we investigated the effects of uricosurics on the OH- gradient-dependent urate uptake in brush border membrane vesicles and the net PAH accumulation in cortical slices. The relation between the affinity of uricosuric drug for urate and PAH transporters corresponds well with the difference between the effect on FEurate and that on FEPAH. The relative affinity of AA-193 for the urate uptake is 83-fold greater than that for the PAH accumulation. These results support the assumption that, in contrast with the other uricosurics, AA-193 has a much higher affinity for urate reabsorption system than that for the common pathway of weak organic acids in rats.

In a recent article entitled ‘‘Effect of treatment of hyperuricemia with allopurinol on blood pressure, creatinine clearence, and proteinuria in patients with normal renal functions’’ in this journal [1], the authors attributed the benefits of allopurinol on blood pressure and renal function to the decrease of the level of uric acid. As we know, there are two types of drugs which are used to decrease the level of uric acid: xanthine oxidase inhibitors (XOI), which can decrease the production of uric acid, and uricosuric drugs, which can increase the excretion of uric acid. Xanthine oxidase (XO) has been established as an important source of oxygen free-radical production in humans [2–4]. It can cause oxidative stress and endothelial dysfunction [3, 4], which have a close relationship with hypertension and chronic renal disease [5–7]. Therefore the benefits of allopurinol on blood pressure and renal function may be partly attributed to the inhibition of XO. Of course, this needs to be confirmed by comparing the effects of uricosuric drugs with those of allopurinol. References

Although dietary, genetic, or disease-related excesses in urate production may contribute to hyperuricemia, impaired renal excretion of uric acid is the dominant cause of hyperuricemia in the majority of patients with gout. The aims of this review are to highlight exciting and clinically pertinent advances in our understanding of how uric acid is reabsorbed by the kidney under the regulation of urate transporter (URAT)1 and other recently identified urate transporters; to discuss urate-lowering agents in clinical development; and to summarize the limitations of currently available antihyperuricemic drugs. The use of uricosuric drugs to treat hyperuricemia in patients with gout is limited by prior urolothiasis or renal dysfunction. For this reason, our discussion focuses on the development of the novel xanthine oxidase inhibitor febuxostat and modified recombinant uricase preparations.

The pharmacokinetics and metabolism of tienilic acid (ticrynafen) a new diuretic with uricosuric properties, were studied in human volunteers following single ingestion of 250, 500 or 1000 mg. Tienilic acid was found to be extentively (more than 98%) bound to plasma proteins but not to displace the fraction of urate bound to plasma proteins at the usual therapeutic dosage (250 to 500 mg). The uricosuric and natriuretic effects of the drug lasted 8 to 12 hours. A peak concentration of 2.5, 4.5 or 10.1 mg/dl was noted in the plasma 2 hours following ingestion of each dose. The apparent volume of distribution of the drug was close to that of plasma volume. Tienilic acid disappeared rapidly from the plasma according to a first order kinetics and the plasma half-life ranged from 1.6 to 2.4 hours. Gas chromatography and mass spectrometric studies revealed that 21% of the ingested tienilic acid is excreted as such in the urine over 24 hours. Three major metabolites of the drug were identified in the urine: a monohydroxylated, a dihydroxylated and a diacid product. Including metabolites, 36 to 47% of the drug was excreted in the urine within 24 hours. No significant glucuro or sulfoconjugation of the drug or its metabolites could be detected in the urine. Excretion of the drug and its metabolites was also noted in the bile. It is concluded that tienilic acid is rapidly metabolized and excreted in humans with normal kidney and liver function.

To compare the clinical and metabolic effects of a new diuretic uricosuric agent, tienilic acid, with those of hydrochlorothiazide, a multicentre double-blind trial was performed in 56 hypertensive patients. Twenty — eight patients were randomly assigned to take tienilic acid and 28 to take hydrochlorothiazide. The diuretic and anti-hypertensive actions of the two compounds were similar. No significant differences were observed between tienilic acid and hydrochlorothiazide in their effects on urinary and serum electrolytes, hepatic and renal function tests, and fasting lipids. The patients who received tienilic acid showed a significant fall in serum uric acid, mediated by the uricosuric effect. The availability of an agent combining diuretic, anti-hypertensive and hypouricemic effects offers promise in the treatment of arterial hypertension.

Sulphinpyrazone is a derivative of Phenylbutazone. It was originally introduced as a uricosuric agent but in recent years it has been investigated for effects on platelet function. Sulphinpyrazone and its metabolites can be measured in blood and urine using high performance liquid chromatography and gas chromatography-mass spectrometry. It is almost completely absorbed and maximum plasma concentrations are found about 2 hours after oral administration. The decay of the plasma concentration of sulphinpyrazone when administered intravenously is best described by an open 3-compartment model with half-lives of the α-, β-and γ-phases at about 0.3, 3 and 6 hours, respectively. The volume of distribution has been calculated to be 60ml/kg. Sulphinpyrazone and its unconjugated metabolites are strongly (98 to 99%) bound to plasma proteins. The total clearance of sulphinpyrazone has been estimated at 20 to 25ml/min. 25 to 50% of a sulphinpyrazone dose is excreted in the urine in unchanged form. The remainder is metabolised via several pathways; a sulphide metabolite is the predominant circulating metabolite reaching levels about 25 % of that of sulphinpyrazone. The sulphide is probably important for the antiplatelet effect of sulphinpyrazone, but not for the uricosuric action. The sulphone metabolite and parahydroxylated metabolites are of minor quantitative significance. All metabolites are excreted as C-glucuronides;onlya small proportion of metabolites is excreted in O-glucuronidated or in unconjugated form in urine. Decreased renal function apparently does not influence plasma concentrations of sulphinpyrazone, and dosage changes in patients with renal dysfunction do not seem warranted. Several drug interactions have been reported involving displacement from plasma proteins, inhibition and induction of hepatic microsomal metabolism, and influence on renal tubular secretion. Clinically the most important interactions seem to be potentiation of the effects of oral anticoagulants, Phenytoin and tolbutamide, and inhibition of the uricosuric effect of probenecid and salicylate. No data comparing plasma concentrations and clinical effects are available.

Following a single dose of 50 mg irtemazole per os, plasma uric acid levels decreased after 1 h and fell to 53.5% of the original value within 6-12 h. Renal uric acid excretion increased up to 66 mg/h 30 min after drug application and reached its maximum of 151 mg/h 30 min later. Uric acid clearance also increased after 30 min and reached its maximum of 56 ml/min after 60 min. The response of the kidney to irtemazole is faster than to benzbromarone or probenecid. Lowering of plasma uric acid has a shorter-lasting effect than benzbromarone or probenecid. At 24 h after the application of 50 mg irtemazole the decrease of the plasma uric acid was between 15.4% and 30.0%, or 24.7% on average. Three days after the application the basic plasma uric acid levels were reached again.

Previous studies have described a pharmacokinetic interaction between probenecid, a uricosuric drug, and oxipurinol, the major metabolite of allopurinol. In single dose studies, no interaction was found to occur between benzbromarone, another uricosuric agent, and oxipurinol. A cross over study was conducted in 12 volunteers to compare the kinetics of allopurinol and oxipurinol following treatment for 7 days with allopurinol alone or combined with benzbromarone 20 or 100 mg. The pharmacokinetic parameters of allopurinol were not modified by the uricosuric therapy, but those of oxipurinol were markedly altered by concurrent administration even of the lower dose of benzbromarone; the average plasma level fell by 30% and the renal elimination rate was increased by 50%. A parallel increase in the renal elimination rate of uric acid was observed (significant only with the higher dose of benzbromarone) and a positive linear correlation between the fractional excretion of uric acid and that of oxipurinol was established.

The action of ketoprofen on the calciuric and uricosuric effects of porcine calcitonin in man is reported. The drug is capable of inhibiting both effects. This action is considered like an effect on CT receptors in the kidney or a competitive action on prostaglandin synthesis.

When six normal men took probenecid with ketoprofen in a two-treatment crossover study, steady-state plasma concentrations of ketoprofen and ketoprofen conjugates rose, but plasma protein binding of ketoprofen and urinary excretion of ketoprofen conjugates decreased. Probenecid decreased protein binding of ketoprofen by 28 +/- 7%, total ketoprofen clearance by 67 +/- 11%, clearance of unbound ketoprofen by 74 +/- 10%, clearance of unbound ketoprofen by conjugation by 91 +/- 5%, and renal clearance of ketoprofen conjugates by 93 +/- 4%. An apparent decrease (22 +/- 29%) in unbound ketoprofen clearance by mechanisms other than conjugation might have been established in a study of more than six subjects. Probenecid, which reaches plasma concentrations that approach 100 times those of ketoprofen or its conjugates, appears to inhibit both the conjugation of ketoprofen and the renal excretion of ketoprofen conjugates. An alternative explanation to inhibition of conjugation involves cumulation and subsequent hydrolysis of ketoprofen conjugates as a result of the renal action of probenecid. In addition to the advantages of obtaining simultaneous uricosuric and anti-inflammatory effects, there may be clinical kinetic advantages of administration of probenecid with ketoprofen, because the large interdose concentration swings of ketoprofen are then substantially reduced.

The uricosuric effect of tiaprofenic acid was evaluated in a group of normouricaemic inpatients with various rheumatic disorders. Six patients aged 26 to 60 years were maintained on a standardised low-purine diet and, after a washout period of 72 hours, tiaprofenic acid was administered in 3 oral doses of 300 mg 12-hourly. A normal renal function, as assessed by serum creatinine and creatinine clearance determinations, was considered mandatory for entry into the study. The following parameters were evaluated before and after treatment: haematological values, blood urea nitrogen (BUN), serum and urinary creatine concentrations, serum uric acid concentration and the fractional excretion rate of uric acid. Our preliminary results showed a substantial increase of urinary uric acid excretion in the samples collected after treatment, especially in the first 4 hours.

Hyperuricaemia carries with it a high risk of tophi development affecting connective tissue in kidney, skin and joints, its overt clinical expression being gout. Diuretics, which are invariably prescribed in congestive heart failure and widely used for the treatment of essential hypertension, may cause hyperuricaemia and predispose to gout by inducing renal retention of urate. The angiotensin I converting enzyme inhibitors captopril and enalapril have been found to augment renal urate excretion both in normal volunteers and in hypertensive patients. Current evidence appears to indicate that the uricosuric effect of captopril and enalapril could be due to the rises in renin and angiotensin I these drugs elicit by angiotensin I converting enzyme inhibition, and/or to pharmacological actions not related, at least directly, to the renin-angiotensin-aldosterone system. Serum urate levels have been significantly reduced by monotherapy with captopril in hypertensive patients suffering from hyperuricaemia. Diuretic-induced hyperuricaemia in hypertensive patients can be prevented or counteracted by the administration of captopril and enalapril. Available clinical data support the argument that captopril and enalapril should be used as first choice drugs for the treatment of hyperuricaemic hypertensive patients. When diuretic-induced hyperuricaemia develops in patients suffering from congestive heart failure, captopril or enalapril should be added to the therapeutic regime in doses capable of countering the shift in plasma urate concentration, provided the clinical condition of the patients permits such additional pharmacological treatment. Therapy with captopril and enalapril should preferably be instituted in a gradual manner, especially in patients with hyperuricaemia, in order to prevent the precipitation of urate in the kidney and in the urinary tract.

It has been recognized that primary disorders of uric acid metabolism result from impaired renal excretion or increased endogenous production of uric acid. It has also been found that these two mechanisms do not comprise two distinct syndromes, but may each constitute a group of syndromes. Contrary to earlier as well as currently published reports we conclude from our clinical and experimental experience that the fraction of so-called over-producers is less than 1% of all patients with primary hyperuricaemia and gout. A procedure for the diagnosis of uric acid overproduction is suggested. The manifestation of hyperuricaemia and gout mainly depends on renal uric acid clearance and is greatly influenced by dietary habits in most of the patients. An impaired renal uric acid excretion results in an increased intestinal excretion; this partly compensates for the defect. Normalization of serum uric acid should be achieved by dietary regimens with or without additional drug treatment, but not by drug treatment alone. With drug treatment xanthine oxidase inhibitors are preferable to uricosurics; no other xanthine oxidase inhibitor besides Allopurinol has been in clinical trial, however. Due to the enhancement of uric acid clearance with uricosurics, there are groups of patients who should not be treated with these drugs. Fixed combinations of Allopurinol and uricosurics should not be used. Drugs which have uricosuric as well as other pharmacologic properties are under investigation. So far they have not reached general clinical application.

Summary: The pathogenesis of familial hyperuricemia has been investigated in two kindreds in whom hyperuricemia was present in members of successive generations. Enzymatic and metabolic studies, including the incorporation of isotopically labeled glycine into urinary uric acid and assessment of the total excretion of oxypurines in one family, excluded a metabolic etiology. No secondary cause of hyperuricemia was identified in either family. Fractional excretion of uric acid was less than 6.2% in all hyperuricemic individuals studied, while creatinine clearances were normal. Tubular secretion of uric acid and tubular reabsorption of uric acid were studied in an affected teenager from each family while receiving a purine-free diet. Inhibition of secretion of uric acid with pyrazinamide decreased fractional excretion of uric acid to 0.6% in patient S and to 0.7% in patient B. Tubular secretion of uric acid at maximal response to pyrazinamide in these patients was 0.393 and 0.410 mg/dl glomerular filtration rate (nl response 0.300 to 1.30 mg/min/100 ml inulin clearance). Probenecid, an inhibitor of uric acid reabsorption, increased uric acid excretion by 3.9 rag/min and by 3.2 mg/min (nl response 1.7 ± 03 mg/min) in patients S and B. Tubular reabsorption of uric acid distal to secretory sites was determined by assessing the uricosuric response to probenecid plus pyrazinamide. Uric acid excretion increased by only 0.08 mg/min in patient A and by 0.17 mg/min in patient B (nl response 0.9 mg/min). Ascorbic acid increased fractional excretion of uric acid by 7.2% in patient S but was not uricosuric in patient B or any hyperuricemic member of his family. These data suggest that hyperuricemia in these families is due to diminished renal clearance of uric acid and that the reduced clearance is due to increased tubular reabsorption of uric acid distal to secretory sites. Speculation: The pathogenetic mechanism in individuals with familial hyperuricemia may differ from patients with sporadic gout. In some families, hyperuricemia may be due to increased tubular reabsorption of uric acid distal to secretory sites in the nephron. Such patients might benefit from judicious therapy with agents which inhibit tubular urate reabsorption.

The response to indacrinone, a new indanone diuretic, was studied in 12 healthy subjects. Ten milligrams alone and in combination with either 2.5 mg or 5 mg amiloride was given in a randomized double-blind study with placebo control to study its action and to assess the optimum combination. Indacrinone alone induced an increase in urine flow rate and in sodium, potassium, and hydrogen ion excretion for at least 8 hr. Indacrinone also induced an initial uricosuria in the first 4 hr, followed by urate retention in the subsequent 12 to 24 hr, with no resultant change in the mean 24-hr urate excretion and minimal changes in the serum urate concentrations. The addition of 2.5 mg amiloride to the 10 mg indacrinone lowered potassium excretion to control levels, whereas addition of 5 mg amiloride resulted in net retention of potassium. With both doses of amiloride, the increased free hydrogen ion excretion after indacrinone returned to placebo levels. There were minor increases in serum creatinine, consistent with volume depletion due to the diuresis. There was a reduction in urinary calcium excretion. Our study shows that the combination of 10 mg indacrinone and 2.5 mg amiloride induces useful diuresis with minimal overall effect on urate, potassium, and hydrogen ion excretion.

A simple and reliable HPLC method for the determination of tienilic acid ((TA) Selacryn, Selcryn, Diflurex, Ticrynafen) and its alcoholic metabolite in plasma and urine has been developed. In 8 healthy adult volunteers the plasma and urinary levels of tienilic acid and its alcoholic metabolite, and plasma and urinary levels of sodium, creatinine and uric acid were measured after oral administration of tienilic acid 250 mg. The pharmacokinetic parameters found differed only slightly from those reported in the literature, as there was faster absorption and a shorter half-life. TA is probably excreted by a saturable renal tubular transport mechanism. The pharmacodynamic effects of tienilic acid developed quickly, the uricosuric effect being very impressive and the natriuretic effect moderate. These effects disappeared in about 8 h. An inverse relationship was found between the starting plasma uric acid level in an individual and the maximal uric acid clearance - the higher the plasma uric acid level, the lower was the maximum effect. Plasma tienilic acid level and natriuretic effect were correlative within individuals and intra-individually (p less than 0.05). Urinary tienilic acid level and natriuretic effect were correlated, too (p less than 0.05 to p less than 0.001), but only intraindividually. No correlation between drug level and uricosuric effect was found.

The effect of furosemide on maximal reabsorption of glucose on the secretion of diodone, and on the excretion of urates was investigated in chronic experiments. After a single injection of furosemide the maximal reabsorption of glucose was found to be increased in dogs. The substance was found to have no effect on the secretory transport of diodone. Furosemide has an uricosuric action in rats and dogs.

In anesthetized rabbits, continuous infusion of methotrexate (MTX; 30 micrograms kg-1 min-1) established steady-state plasma concentrations for MTX and the metabolite 7-hydroxymethotrexate (7-OH-MTX) within 40 min. Fifty percent of the infused dose was eliminated unchanged by the kidneys and the renal MTX clearance was slightly higher than the inulin clearance. Another 15%-30% was metabolized and excreted as 7-OH-MTX in the urine. Infusions of 7-OH-MTX, furosemide or benzarone had no influence on the clearance of MTX or 7-OH-MTX. Infusions of probenecid or piperacillin decreased the renal clearance of MTX and 7-OH-MTX mainly by reducing the tubular secretion of both compounds. In contrast, infusions of the antibiotics ceftriaxone and sulfamethoxazole increased the renal elimination of MTX and 7-OH-MTX. An increase was also observed during the infusion of the uricosuric drugs sulfinpyrazone and benzbromarone. These results are consistent with competition for tubular reabsorption between MTX, ceftriaxone and sulfamethoxazole. The pharmacokinetic drug interactions observed occurred with therapeutic drug concentrations and thus may be clinically relevant.

The uricosuric drug benzbromarone inhibits a number of membrane-bound mitochondrial enzymes. A strong inhibition of succinate dehydrogenase, α-glycerophosphate dehydrogenase and pyridinnucleotide transhydrogenase was found (approximately 28, 48, 45 μM benzbromarone for 50% inhibition respectively). Some possible consequences of these results for the lipid metabolism in patients during benzbromarone are discussed.

To determine whether an impaired tubular transport mechanism for urate could differentiate the pathogenesis of gouty hyperuricemia and if serum urate influences the renal handling of uric acid, we conducted metabolic studies in 56 patients with primary gout. Tubular reabsorption of urate was normal. Tubular secretory rate was 29.3 ± 8.7 percent of filtered urate as compared to 42.4 ± 4.3 percent in 10 normal subjects for a similar urate filtered load (P < 0.01). Among 30 patients examined in the basal state and at pharmacologically reduced serum urate levels, 24 showed a diminished and 6 normal tubular urate secretion in both states of uricemia. According to the probenecid test, 45 patients evidenced a diminished uricosuric response and 11 normal urate excretion rates. This classification was similar to that obtained by the 24-h urinary urate excretion and was identical to that established by means of [2-14C]uric acid in 8 selected patients. We conclude that an impaired tubular secretion of urate may differentiate gouty underexcretors from uric acid overproducers. Increased serum urate is not the cause but a consequence of the impaired tubular urate secretory mechanism in gout.

Intrarenal handling of uric acid was evaluated in five patients with diminished serum urate levels (1.4 to 2.0 mg/dl) and increased renal clearance of uric acid (22.9 to 65.3 ml/min/1.73 m2). One patient with kappa light-chain disease and Fanconi syndrome showed a blunted uric acid excretion response to both pyrazinamide and probenecid, indicating a defective tubular reabsorption of urate. Three patients had recurrent calcium oxalate nephrolithiasis and one infant bening idiopathic hematuria. In addition to hyperuricosuria the infant and two patients with recurrent urolithiasis showed renal hypercalciuria. All evidenced normal responses to pyrazinamide. Compared to normal subjects, three patients showed a diminished and one an increased uricosuric response to probenecid. The former were considered to have a defective tubular urate postsecretory reabsorption and the latter an enhanced tubular secretion of urate. These results indicate that (1) hypouricemia may provide an important clue for the existence of an underlying disease, and (2) tubular urate transport defects may be of pathogenic importance in patients with recurrent calcium nephrolithiasis.

The lower serum urate concentration of age-fertile women compared to men is thought to be related to a higher renal clearance of urate possibly detrmined by plasma estrogen levels. We assessed renal handling of uric acid in 9 normal age-fertile women compared to 9 age-matched men. Women showed significantly lower serum urate concentrations than men (3.5 ± 0.3 vs. 4.9 ± 0.7 mg/dl, P < 0.001), higher fractional excretion of urate (9.8 ± 1.0 vs. 7.3 ± 0.8 percent, P < 0.001) and lower tubular urate postsecretory reabsorption (P

The species differences in renal tubular transport of uric acid are well known. Among various nonhuman mammalian species, rats belong to a group with a reabsorptive net flux of uric acid in the renal tubules, and hence they have sometimes been used to test uricosuric activity by a clearance technique. The stop-flow technique is also regarded as a useful method for evaluating drug effects on tubular transport of uric acid. This technique has been used with rabbits, dogs and cebus monkeys, but not with rats. Reported here is the utility of a stop-flow technique using rats. The fractional excretion value of uric acid (FEua) in rats with a high urine flow rate was nearly 1.0, which was clearly higher than those in clearance experiments. On the other hand, in pyrazinoic acid (PZO)-treated rats with inhibited secretion of uric acid, the FEua value was much lower than that in non-treated rats, and the stop-flow patterns always indicated a remarkable reabsorption of urate in the proximal tubules corresponding to the secretion of p-aminohippurate. As generally accepted, uricosuric drugs inhibit bidirectional transport of uric acid in the renal tubules. We describe the characteristics of uricosuric drugs using stop-flow techniques with PZO-treated and non-treated rats, and the uricosuric properties of a new uricosuric diuretic, S-8666, which has been developed in our laboratories.

A new uricosuric agent, 5-chloro-7,8-dihydro-3-phenylfuro[2,3-g]-1,2-benzisoxazole-7-carboxylic acid (AA-193) was compared with other uricosurics in the rat, mouse and cebus monkey, because the effects of those drugs were known to be highly species-dependent. Probenecid and tienilic acid which in the human kidney block the reabsorption of filtered and secreted urate, increased the urate excretion in rats. But benzbromarone, an inhibitor of the latter reabsorption in man, did not have the uricosuric activity. Thus, the post-filtered reabsorption of urate is probably dominant in rats. We found that in rats AA-193 is the most potent uricosuric yet reported. In mice, probenecid not only had so-called paradoxical actions but stimulated the urinary urate wasting after administration of pyrazinamide. Aspirin also responded paradoxically. These data suggested that the renal transport system of urate in the mouse is similar to that in man. AA-193 as well as benzbromarone enhanced the urate excretion dose-dependently in normal condition, but the effects were different in pyrazinamide-suppression tests in mice. In cebus monkeys, the uricosuric and hypouricemic effects of AA-193 were more patent than those of probenecid and similar to those of tienilic acid, but less than those of benzbromarone. Benzbromarone had a considerable role in post-secreted reabsorption in the mokey. Conclusion: AA-193 is a new class of uricosuric agent that controls the renal reabsorption of filtrated urate particularly.