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Introduction Paclitaxel micellar is a novel formulation of paclitaxel in which retinoic acid derivates solubilize paclitaxel. The aim of the present study was to compare the unbound and total plasma pharmacokinetics of the new formulation with those of nanoparticle albumin-bound (nab)-paclitaxel and to further assess its safety. Methods In this open, randomized, cross-over study, 28 female patients with breast cancer were given paclitaxel micellar and nab-paclitaxel as a 1-h intravenous infusion at a dose of 260 mg/m2. Plasma samples were collected during 10 h, which were projected to cover at least 80% of the area to infinite time, AUCinf. Unbound paclitaxel was measured in ultrafiltrate of plasma. Total paclitaxel in plasma was measured after protein precipitation with acetonitrile. Both assays used ultra-performance liquid chromatography (UPLC) followed by MS/MS for drug quantification. The unbound fraction, fu, was calculated as the ratio between the unbound and the total concentration. Results No difference in fu of paclitaxel between the two formulations was observed. Statistical comparison of AUC0–10h and Cmax of unbound paclitaxel demonstrated that the two formulations met the criteria for bioequivalence. Regarding total paclitaxel levels, Cmax but not AUC0–10h met the criteria. This study supports a safe administration of paclitaxel micellar. Conclusion The two formulations, paclitaxel micellar and nab-paclitaxel, behaved similarly following infusion. Probably, both formulations dissociate immediately in the blood, whereupon released paclitaxel rapidly distributes into tissue. Judged from the bioequivalence demonstrated for unbound paclitaxel, the two formulations are considered clinically equivalent. Trial Registration EudraCT no.: 2010-019838-27. Funding Oasmia Pharmaceutical AB.

Introduction A water-soluble Cremophor EL-free formulation of paclitaxel, in which retinoic acid derivates solubilize paclitaxel by forming micelles (paclitaxel micellar), was studied for the first time in man to establish the maximum tolerated dose (MTD) and to characterize the pharmacokinetics (PK). Methods This was an open-label, one-arm, dose-escalating study in patients with advanced solid malignant tumours, for which no standard therapy was available or had failed. Paclitaxel micellar was given as 1-h intravenous infusion every 21 days for 3 cycles, mainly without premedication. Plasma samples were collected during 24 h at the first cycle and paclitaxel concentrations were assayed by high-performance liquid chromatography. PK was evaluated using a two-compartment model. Results Thirty-four patients received paclitaxel micellar at doses ranging between 90 and 275 mg/m2. MTD was established as 250 mg/m2. Fatigue and neuropathy were the most frequent dose-limiting toxicities. No hypersensitivity reactions were observed. PK of paclitaxel was evaluated in 25 data sets. Paclitaxel micellar had a rapid initial distribution phase, mean half-life 0.55 h, estimated to be completed 3 h after dosing and a mean terminal half-life of 8.8 h. Mean clearance was 13.4 L/h/m2 with fivefold interindividual variability. The residual areas after 10 h and 24 h were 15.7 ± 8.6% and 5.7 ± 3.9% of the area under the plasma concentration–time curve to infinite time (AUCinf), respectively. Conclusion No new side effects unknown for paclitaxel were observed. Maximum plasma concentration (Cmax) and AUCinf showed a tendency to increase linearly with dose within the 150–275 mg/m2 dose range. The possibility to administer paclitaxel micellar without steroid premedication makes it an attractive candidate for further studies in combination with immunotherapy. Trial Registration EudraCT no: 2004-001821-54. Funding Oasmia Pharmaceutical AB.

Many drugs undergo first-pass metabolism both in the gut mucosa and the liver, but little is known about the relative efficiency of these two pathways. The objective of this study was to differentiate between mucosal and hepatic metabolism using budesonide as a probe. After a light breakfast, budesonide, 3 mg, was infused locally in the proximal jejunum of eight healthy men on seven occasions, on six occasions after administering the CYP3A4 inhibitor ketoconazole 5 min before in the same jejunal position. The dose range of local inhibitor was 1–128 mg, the highest dose also preceded by an oral dose of 200 mg given 12 h earlier. Simultaneously with intrajejunal budesonide, deuterium-labelled budesonide (0.2 mg) was administered intravenously. Pharmacokinetics of unlabelled and labelled budesonide in plasma was evaluated after LC–MS/MS analysis. Bioavailability of budesonide without inhibition was 27(12–42)%. All ketoconazole doses increased budesonide bioavailability. However, systemic clearance of labelled budesonide was unaffected by ketoconazole doses up to 16 mg but decreased significantly at doses of 64 mg and above. At the two highest doses (128 mg and above) bioavailability approached 100%, showing that budesonide was completely absorbed from jejunum. Ketoconazole doses up to 16 mg appeared to inhibit only mucosal enzymes, while higher doses inhibited also hepatic metabolism. Applying sigmoid E max -models of the mean inhibitions in mucosa and liver indicated that, in this study performed under fed conditions, their uninhibited extraction ratios of budesonide were approximately 0.32 and 0.60, respectively. Ketoconazole doses that inhibited half the metabolism were estimated at about 1 mg in the mucosa and about 50 mg in the liver. In conclusion, this study gave a rough estimate of the relation between mucosal and hepatic first-pass metabolism of budesonide.

The CYP3A4 substrate budesonide was used to investigate gut wall first-pass metabolism in jejunum, ileum and colon of eight healthy men. Three milligram budesonide in solution was installed at each location by intubation, with or without immediate prior local administration of 16 mg ketoconazole. Simultaneously, deuterium-labelled budesonide (0.2 mg) was administered intravenously. Pharmacokinetics of unlabelled and labelled budesonide in plasma was evaluated using LC-MS/MS. Ketoconazole increased budesonide systemic availability significantly in jejunum (from 11.8 to 21.7%) and ileum (from 15.9 to 31.8%). T max and MAT were unaffected. No significant effects were noted after colon administrations, nor were there any effects on the pharmacokinetics of intravenously administered budesonide. The increased bioavailability is most probably explained as inhibition of gut wall metabolism. The data are in accordance with the well-known CYP3A activity in the small intestine, evidently capable of metabolising at least half the absorbed dose of budesonide. In contrast, the results indicate that this enzyme activity is insignificant in the colon.

NXY-059 is a novel free-radical trapping neuroprotectant. Digoxin treatment is common in acute ischaemic stroke, the intended patient population for NXY-059. Since both digoxin and NXY-059 are eliminated primarily renally, with a substantial contribution by active renal secretion, and because digoxin has a narrow therapeutic window, this open, randomised, crossover, two-period study investigated whether NXY-059 affects the pharmacokinetics (PK) of digoxin.Twenty-two healthy subjects received 0.5 mg oral digoxin 2 h after the start of 60-h intravenous infusions of NXY-059 and placebo separated by a 14-day washout. Blood and urine were collected for 60 h. Digoxin concentrations were measured by a novel liquid chromatography-mass spectrometry assay.The ratio of the geometric mean (90% confidence interval) between NXY-059 and placebo for the digoxin area under the concentration-versus-time curve was 0.91 (0.83-0.99) and was within the predefined range for no interaction (0.80-1.25). No safety concerns were raised in the study. No serious adverse events were recorded. The most common adverse event was headache with similar frequencies in the two treatments.NXY-059 had no clinically significant effect on the PK of digoxin.

Background: Intranasal and oral antihistamines are effective in treating allergic rhinitis. Studies comparing these routes of administration of an antihistamine regarding efficacy and pharmacokinetic profile are lacking. Objective: To compare topical and oral routes of administration of cetirizine regarding efficacy, plasma exudation, and systemic drug levels in a repeated allergen challenge model of allergic rhinitis. Methods: Oral cetirizine dihydrochloride, 10 mg once daily, and topical cetirizine dinitrate in a dose corresponding to 4.4 mg of the dihydrochloride salt twice daily were given to grass pollen-sensitive individuals for 12 days in a double-blind, placebo-controlled, crossover design. Timothy grass pollen allergen challenges were given once daily for 7 days using a nasal spray device. Nasal symptoms and peak inspiratory flow were recorded in the morning, 10 minutes after allergen challenge, and in the evening. The pharmacokinetics of the treatments was monitored in 8 patients. The remaining 28 patients were challenged topically with histamine 12 and 24 hours after the final topical and oral cetirizine doses, respectively. Nasal lavage levels of alpha(2)-macroglobulin were determined to evaluate histamine-induced mucosal plasma exudation. Results: During the last 3 days of the repeated allergen challenge model, chronic symptoms were established. Both treatments reduced symptoms 10 minutes after allergen challenge (P < .001 vs placebo). Neither treatment reduced morning and evening symptoms or nasal peak inspiratory flow. Topical, but not oral, cetirizine reduced histamine-induced plasma exudation (P < .01 vs placebo) when systemic drug levels were similar in the 2 treatment regimens. Conclusions: Topical and oral cetirizine reduced acute nasal symptoms produced by allergen challenges in patients with established chronic symptoms. There were also antihistaminic effects of topical cetirizine not related to systemic drug levels.

SUMMARY Methods: The retrograde spread of two budesonide enema formulations with different viscosities was investigated. The study design was open, randomized and two-period crossover. Three female and two male patients (age range: 35-45 years) with distal ulcerative colitis or proctitis participated. Both enema formulations contained a dose of 2 mg budesonide/ 100 mL. An unabsorbable radioactive marker ( 99mTc-labelled human serum albumin microcolloid) was added to the enema just before administration. All doses were given in the evening with the patients lying in a supine position during the whole investigation. The intestinal spread was followed for 8 h using scintigraphic imaging. Plasma samples for budesonide assay were taken during the 12 h after administration of the low viscosity enema. Results : Budesonide plasma levels were measurable for up to 4-6 h. C,,, was 2.5 nmol/L (range: 0.9-4.5 nmol/L) and was attained in 1.5 h (range 1-3 h). The patients had no difficulty in retaining the enemas. There was a statistically significant difference in spread between the low and high viscosity enema. The low viscosity enema spread over an area situated between the rectum and the splenic flexure. The spread occurred mainly in the first 15 min after administration. In contrast, the high viscosity enema, in most cases, spread only over a minor part of this area and the rate and extent of spreading was also more variable with this formulation. Conclusion: The spread of a low viscosity enema appears to be well suited for the treatment of proctitis and distal colitis.

NXY-059 is a free radical-trapping neuroprotectant that reduces infarct size and preserves brain function in animal models of acute ischemic stroke. Acute ischemic stroke patients receiving NXY-059 may also be exposed to diuretics for treatment of heart failure or hypertension. NXY-059 and furosemide are partly eliminated by active tubular secretion via an organic anion transporter. This double-blind, randomized, crossover, placebo-controlled study investigated whether an infusion of NXY-059 (15 mg/mL) during 12 hours affects the diuretic and saluretic effects of a 30-mg intravenous bolus dose of furosemide (10 mg/mL) administered after 6 hours' infusion, in 13 male and 11 female healthy subjects. The net increase in urine volume and sodium excretion in the interval of 6 to 12 hours was 4.15 L and 178 mmol/L, respectively, during NXY-059 treatment (P = .93) and 4.34 L and 190 mmol/L, respectively, during placebo treatment (P = .54). NXY-059 reduced the renal clearance of furosemide by 19% (P = .019), and furosemide reduced the renal clearance of NXY-059 by 8% (P = .005). NXY-059 was well tolerated.

Clomethiazole is virtually completely eliminated by hepatic metabolism. This study was designed to assess the impact of liver impairment on its elimination and sedative effects.Eight patients with mild liver impairment (Child-Pugh grade A), eight patients with moderate/severe liver impairment (Child-Pugh grade B/C) and eight healthy subjects of similar age were given 68 mg/kg clomethiazole edisilate according to a 24-h infusion scheme aimed at producing minimum sedation as it was intended for clinical use in patients with stroke. Concentrations of clomethiazole and its active alpha-carbon hydroxylated metabolite NLA-715 were followed in plasma and urine for 96 h and 24 h, respectively. Sedation was monitored using a scale from 1 to 6.The fraction excreted unchanged in urine was less than 0.2% for clomethiazole and less than 0.4% for NLA-715. Urine concentrations of clomethiazole were strongly correlated (r(2)=0.60) to plasma concentrations and approximately equal to unbound plasma concentrations. Plasma levels of NLA-715 increased steadily during the infusion, eventually reaching mean levels exceeding those of clomethiazole in all groups. Plasma clearance of clomethiazole in subjects with mildly impaired liver function was not statistically different from that of healthy controls (40 l/h vs 44 l/h). In subjects with moderate/severe liver impairment, there was a 50% reduction in clearance. Sedation was not observed except in two subjects in the Child-Pugh A group showing mild sedation.The reduced clomethiazole clearance in patients with moderate/severe liver impairment seems to call for a reduction of clomethiazole dosage. However, sedation was not observed in this group at the investigated dose level.

Objective. NXY-059 is a nitrone-based, free-radical trapping agent being developed for the treatment of acute ischaemic stroke. Elimination of NXY-059 is primarily renal. The objective of the study was to investigate the pharmacokinetics of NXY-059 in subjects with renal impairment. Methods. Twenty-four subjects with a glomerular filtration rate (GFR) ranging from 19 ml/min to 100 ml/min received NXY-059 intravenously over a 24-h period. Drug in plasma and urine was measured for 72 h. One-hour loading infusion rates were proportional to body weight, while maintenance infusion rates were proportional to GFR. Target plasma levels were 60 µmol/l for subjects with mild (GFR 50–100 ml/min) and moderate (GFR 30–49 ml/min) renal impairment, and 30 µmol/l for subjects with severe renal impairment (GFR

The tolerability, safety, and pharmacokinetics of NXY-059, a nitrone-based free radical trapping agent under development for the treatment of acute ischemic stroke, were investigated in 2 double-blind, placebo-controlled dose-escalation studies in healthy subjects. In the first study in 6 panels of young male subjects (n = 48, 22-45 years), constant rate infusions lasted 8 hours and ranged from 0.16 to 5.25 μmol/kg/h (0.06 to 2.0 mg/kg/h). In the second study, elderly male and female subjects (n = 24, 57-72 years) were infused over 24 hours or 72 hours to reach target plasma levels of 30 μmol/L or 60 μmol/L, respectively, using doses in the range 1.4-4.0 μmol/kg/h. With a 1-hour loading infusion set at 3 times the maintenance infusion rate, the target plasma level was reached in 1 hour. Adverse events were mild or moderate, and no clinically relevant changes in vital signs, ECG recordings, or laboratory values were noted. Steady-state levels in both studies increased proportionally to the infusion rate, indicating linear kinetics. Renal elimination was predominant, the recovery of unchanged drug in urine being 80% to 90% irrespective of age. The average plasma clearance in young and elderly subjects was 7.0 L/h and 4.1 L/h, respectively. It was estimated that glomerular filtration and active tubular secretion of NXY-059 accounted for approximately two-thirds and one-third of its renal clearance, respectively. In the elderly, clearance of NXY-059 was significantly correlated to creatinine clearance. The renal clearance was insensitive to variations in urine pH and urine flow rate. It appears that NXY-059 is well tolerated and has a highly predictable pharmacokinetic profile. Copyright © 2002 by National Stroke Association

The objective of this work was to study the role of regional intestinal efflux activity of P-glycoprotein (Pgp) in situ in anesthetized rats in limiting the absorption of digoxin. A 10-cm portion of duodenum or jejunum, or 5-cm of colon was perfused single-pass with saline containing [(3)H]digoxin while the appearance of radioactivity in the blood was measured. Verapamil in the perfusate was used as a modulator of Pgp in the intestinal mucosa. Net water absorption, mucosal integrity, and intestinal motility of the isolated segment were monitored, as well as heart rate and blood pressure. Excretion of i.v. administered unlabelled digoxin, 1 mg/kg, into the intestine while perfusing the duodenum-proximal jejunum region, was studied for comparison. At a perfusate concentration of 1 mM, verapamil caused a dramatic increase in [(3)H]digoxin absorption rate from duodenum and jejunum, while the effect in colon was insignificant. At concentrations of 0.1, 1, and 2.5 mM in the duodenal perfusate, verapamil increased the absorption rate of [(3)H]digoxin in a dose-dependent manner. The lowest concentration almost doubled the rate without having any significant effects on the cardiovascular system, intestinal motility, or net absorption of water. The excretion rate of unlabelled digoxin from the blood into the gut lumen was found to be halved in the presence of 0.5 mM verapamil in the perfusate. Absorption rate of [(3)H]digoxin in the rat is likely limited by Pgp-mediated efflux. The data indicate that Pgp plays an important role for digoxin efflux in the small intestine only.

The unbound fraction in serum, fu, is a critical parameter in describing and understanding the pharmacokinetics of NSAIDs. We compared fu for 6 different NSAIDs using ultrafiltration of pooled serum at pH 7.4 and 24C. Measurements covered a wide concentration range in order to define binding affinity and number of binding sites. HPLC was used to measure drug concentrations in serum and ultrafiltrate. Direct injection of ultrafiltrate and serum (diluted 250 x) permitted quantitation down to approximately 70 nM for most of the NSAIDs, i.e., approximately 15-20 ng/ml. Assuming binding only to albumin, the data were fitted to a model of two classes of binding sites with dissociation constants K1 and K2. The lowest K1 (highest affinity) was found with flurbiprofen, 0.0658 microM, the highest with ketoprofen, 5.23 microM, an 80-fold difference. At low drug concentrations, fu becomes virtually constant and approaches a lower limit, fumin. The following fumin values were calculated: diclofenac 0.21%; fenoprofen 0.25%, flurbiprofen 0.022%, ketoprofen 0.52%, naproxen 0.039%, and tolmetin 0.37%. Thus the least bound NSAID, ketoprofen, had a value 24-fold that of the most highly bound, flurbiprofen. The NSAIDs also differed widely with regard to the extent of variation in fu within the range of therapeutic concentrations, and hence with regard to their potential as displacers of other drugs.

For local administration of drugs or enzyme inhibitors in the human gut, a small-bore, smooth tube was introduced through the nose, retrieved from the pharynx, equipped with a firm radio-opaque capsule, and swallowed. Peristalsis moves the capsule to the desired location in the gut where it is anchored before administration via the tube. Drug uptake is followed by plasma sampling. One capsule type is used for solutions, another for solid formulations. With solutions, repeated administrations could be done with the capsule being anchored for 24 h or longer or, alternatively, at several locations along the gut. This communication presents the method and an overview of 13 uptake and enzyme/transporter localization studies. Altogether, 268 intubations were undertaken in a total of 128 subjects. Plasma concentrations found with terbutaline and metoprolol are presented showing that terbutaline has its best uptake in the upper small intestine, whereas metoprolol shows the same bioavailability along the whole gut. Subjects could undertake most of their normal activities while carrying the equipment. No serious adverse events (AEs) occurred. Possibly intubation-related AEs were abdominal pain (n = 8) and constipation (n = 5). In conclusion, the method has been found to be safe, convenient and multifunctional for studies of drug uptake at predetermined gut locations in healthy subjects. (Less)

The cerebrospinal fluid (CSF) and plasma levels of demethylchlorimipramine (DMCI) were determined during treatment of depression or obsessive-compulsive disorders with chlorimipramine. In 18 patients the mean CSF/plasma ratio of DMCI was 2.6% +/- 0.7 SD with fourfold variation (1.1% to 4.0%). In spite of this variation, the levels in CSF and plasma at steady state correlated closely (r = 0.91; p less than 0.001). With equilibrium dialysis for the determination of the protein binding of DMCI, a much higher free fraction was found in patients (8.0 +/- 1.6%) and in control subjects (8.2 +/- 1.4%). It was shown that part of the plasma binding capacity was lost during the incubation. Results obtained by ultrafiltration (3.9 +/- 1.0% unbound drug) were closer to the in vivo results, but this method also had disadvantages; much of the drug was absorbed on the ultrafiltration dialysis membrane. Our results suggest that there is a need for care in the selection of a technique for studies of drug protein binding.

To assess the importance of disease-induced increases in plasma concentrations of alpha1 acid glycoprotein (an acute-phase plasma protein that binds cationic drugs), we determined binding of propranolol in plasma from 53 patients and 25 healthy volunteers. Binding was increased in 10 patients with Crohn's disease (P less than 0.002), nine with inflammatory arthritis (P less than 0.002) and eight with chronic renal failure with superimposed inflammatory disease (P less than 0.01) as compared with healthy controls. The plasma binding of control subjects did not differ from that of 12 patients with chronic hepatic disease (P greater than 0.45) or 14 with uncomplicated renal failure (P greater than 0.80). Chlorpromazine binding, determined in 60 subjects, yielded similar results. Percentage of free drug and alpha1 acid glycoprotein concentration were inversely correlated (r = -0.77 with propranolol, P less than 0.001, and r = -0.69 with chlorpromazine, P less than 0.001). Increases in plasma protein binding in patients with inflammatory disease appear mediated by increases in alpha1 acid glycoprotein concentration, which may influence drug kinetics.

Acetylsalicylic acid in daily doses from 3 to 6g was prescribed to 8 patients with rheumatoid arthritis. Various assessments of clinical effect, as well as steady-state plasma concentrations and degree of plasma protein binding, were determined at each dose. The unbound fraction of salicylate increased with the dose, resulting in very high free concentrations of drug in some patients. No statistically significant relationship between total or unbound plasma concentration and the measurements of clinical efficacy were obtained. The marked increase with the dose in unbound salicylate concentration is interpreted as the result of the saturable elimination known to occur for this drug.

The protein binding of diazepam, indomethacin, salicylic acid, sulfadimetoxine and warfarin in serum of uremic patients has been studied by equilibrium dialysis and circular dichroism measurements and compared with that in normal serum. Comparisons have also been made with isolated human serum albumin (HSA) from uremic patients and healthy individuals. The binding of diazepam, salicylic acid, sulfadimetoxine and warfarin is impaired in the uremic sera, while the binding of indomethacin is apparently unchanged. The apparent binding constants of salicylic acid and warfarin in both uremic and normal sera are affected by dilution of the sera in buffer. The binding constants obtained with isolated albumins, however, are unaffected by dilution. The albumin isolated from uremic serum shows lower binding affinity for salicylic acid and warfarin than normal HSA, but the affinity was normalized by charcoal treatment at pH 3.0. It is shown that the binding both in normal and uremic sera is impaired compared with isolated defatted serum albumin due to the presence of competitive inhibitors. The inhibition is more pronounced in uremic serum. In addition, the binding to albumin in uremic sera is impaired by strongly bound allosteric inhibitors. It is also emphasized that determinations of association constants have to be related to the dilution of the serum, plasma or blood, respectively.

Five healthy subjects performed submaximal physical exercise approximately 20 h after a single oral dose of phenytoin (5 mg/kg of the sodium salt). The plasma levels of free fatty acids (FFA) increased 2- to 3-fold in the post-exercise period. In spite of this, the degree of plasma binding of phenytoin and its total concentration in plasma were unaffected. Thus FFA at the levels reached (1.5-2.9 mEq/l), did not displace phenytoin from its binding sites on albumin. Furthermore, during the FFA peak the plasma protein binding of warfarin, as measured in vitro, did not decrease as compared to the pre-exercise period. These findings contrast to previous observations in rats and dogs, where FFA caused a considerable displacement of warfarin and phenytoin at relatively low FFA/albumin molar ratios.

The protein binding of two basic drugs, alprenolol and imipramine, and the acidic drug, naproxen, was determined in plasma obtained from 23 healthy subjects. A 2jold variation was found between individuals in the free fraction of the two bases, while the range was even greater with naproxen. The free fraction correlated with the plasma concentration of ai-acid glycoprotein for alprenolol (r = -0.75, p 0.1). This confirms recent experiments which showed that isolated ai-acid glycoprotein avidly bound both alprenolol and imipramine. Drug binding, however, did not correlate with albumin concentration, although experiments with isolated albumin demonstrated its unusually high affinity for naproxen.

Protein binding of salicylate was studied by equilibrium dialysis at 37 degrees C in plasma from uremic patients and healthy subjects. The protein binding was considerably lower in the uremic plasma at all salicylate concentrations studied (14 to 1,400 mug/ml). Scatchard plots of the data were computer-analyzed assuming binding to the classes of binding sites. According to this analysis, the binding to the class of primary binding sites was considerably decreased in the uremic plasma. In addition to the effect of the uremic state, the binding was considerably decreased at high therapeutic plasma levels and at low albumin levels. The combined effect of two or three of these factors may lead to unexpectedly high unbound fractions of salicylate, which should be considered in the monitoring of plasma salicylate levels in patients.

With the intention of studying the fate of transplacentally transferred diphenylhydantoin (DPH, phenytoin) in the newborn infant, a mass fragmentographic analytic method has been developed, in which deuterium-labeled DPH is used as internal standard. The analytic procedure permits precise determinations of DPH in 100 µl plasma samples in concentrations down to 0.01 µg per milliliter. Seven newborn infants of epileptic mothers treated with DPH throughout the pregnancy were studied during the first 4 to 9 days of life. The rate of plasma disappearance of DPH in the newborn infants was of the same order of magnitude as previously reported in adults. The initial parts of the plasma concentration curves indicated zero-order disappearance of DPH. Nursing did not seem to affect the rapid plasma level decline in the babies until extremely low concentrations (0.1 p.g per milliliter) were reached. The arr,wunts of unchanged drug excreted in the urine were inSignificant. It is therefore concluded that babies born by mothers treated chronically with DPH are able to metabolize this drug effectively immediately after birth.

The effect of intravenously administered ampicillin on plasma levels and renal clearance of enprofylline was investigated in seven young and six elderly volunteers. On one occasion, each subject received 2 g of ampicillin intravenously, and serum concentrations of ampicillin were followed for 4 hours. On a separate occasion, a loading infusion of enprofylline was administered over 60 min., aiming at a plasma level of 2 micrograms/ml, and followed by a maintenance infusion. During this an infusion of 2 g of ampicillin was given for 10 min., and subsequently, renal clearance and plasma levels of enprofylline were followed for 4 hours. Plasma enprofylline levels increased significantly in the subjects after ampicillin infusion, but the effects on renal clearance of enprofylline were not statistically significant. The magnitude of the effects on enprofylline plasma levels and renal clearance from high doses of ampicillin do not suggest that interaction with beta-lactam antibiotics will be a serious problem for patients on enprofylline treatment.

The protein binding of diphenylhydantoin (DPH) and desmethylimipramine (DMI) was measured in plasma from azotemic and uremic patients by an Ultrafiltration technic. DPH binding was decreased in uremic plasma. The impairment of binding was strongly correlated (p less than 0.001) to the degree of azotemia and degree of physical disability of the patients but weakly correlated (p less than 0.05) to their concentrations of serum proteins. DMI binding was almost normal. Dialysis of normal and uremic plasma in tap water or hemodialysis solution did not alter the DPH binding. The binding of DPH by plasma proteins from azotemic patients appears to be decreased, probably owing to a change in the binding proteins. The possibility of alteration of drug binding by pathologic states should be considered when total plasma concentrations of protein-bound drugs are measured and the values used to establish or modify drug-dosage regimens.

After intravenous administration of desmethylimipramine and nortriptyline to dogs, the excretion of unchanged drug in urine or gastric juice was found to be of little quantitative importance. The renal excretion was pH dependent, indicating nonionic diffusion between blood and urine. The urinary excretion of desmethylimipramine or nortriptyline given in therapeutic doses to depressed patients was also shown to be pH dependent. At a steady-state plasma level of the antidepressant drugs, less than 5 per cent of the daily dose was excreted unchanged through the kidney. These data are discussed in relation to the treatment of tricyclic drug intoxications.

The inhibitory effect of nortriptyline (NT) on the neuronal uptake of radio labeled norepinephrine (NE) was studied with the use of the rat iris preparation in Krebs-Ringer solution or human plasma. When added to the incubation medium, NT inhibited the uptake of NE approximately ten times as effectively in buffer as in human plasma within the tested concentration range of NT (10−8 to 10−6M). This result is in good agreement with the 94 per cent binding (at NT concentration of 1.1 10−6M) obtained by the ultrafiltration method. Plasma from patients treated with NT also inhibited the uptake of NE. Correlation between the inhibitory effect and the “endogenous” plasma level of NT in the 14 patients studied was significant (p < 0.001). When NT was added in different concentrations to control plasma the inhibitory effect observed was close to that obtained with patient plasma containing the same “endogenous” concentration of NT.

A quantitative method has been developed for the determination of the tricyclic antidepressant drug nortriptyline in plasma, utilizing a combined technique of gas chromatography - mass spectrometry called mass fragmentography. A metabolite, desmethylnortriptyline, may be analyzed in the same run. The compounds are first converted to their heptafluorobutyranide derivatives. A complete chromatogram takes less than five minutes. Quantitive determinations under the present conditions are possible down to a few nanograms of nortriptyline per milliliter. There is a good correlation between the new method and that previously used which was based upon in vitro 3 11-acetylation labelling.

Six patients undergoing diagnostic lumbar myelography were studied with respect to plasma and cerebrospinal fluid (CSF) concentrations of two xanthine drugs--enprofylline and theophylline. Three patients received enprofylline and three patients received theophylline, 200 mg t.i.d., and plasma and CSF were sampled on the morning of the third day of treatment. CSF plasma ratios averaged 0.095 with enprofylline (range of 0.094-0.097) and 0.36 with theophylline (range of 0.35-0.37). The different ratios of the two drugs contrast to their similar plasma protein binding, about 50%. Different lipophilicity or differences with regard to transport out of the CSF may explain the discrepancy.

The kinetics of enprofylline, a novel antiasthmatic xanthine derivative, were studied. Eight healthy subjects received three different single enprofylline doses, 0.5, 1, and 1.5 mg/kg, injected as an infusion over 10 min. Plasma and urine levels of unchanged enprofylline were observed 3 to 7 and 21 to 24 hr after dosing. Plasma t½ varied among individuals from 1.2 to 1.9 hr. Volume of distribution (Vβ orarea) and volume of distribution at steady state (Vss) averaged 0.57 and 0.511 · kg'−1. Total clearance averaged 0.25 l · hr−1 · kg−1. Renal clearance ranged from 200 to 400 ml · min−1, indicating a large contribution by active tubular secretion. The mean recovery of unchanged drug in the urine was 89%. Thus, unlike theophylline, enprofylline was eliminated mainly by the kidney. Clinical Pharmacology and Therapeutics (1983) 34, 799–804; doi:10.1038/clpt.1983.252

Plasma protein binding of phenytoin (diphenylhydantoin) in 63 epileptic patients was investigated with an ultrafiltration technique at room temperature using 14C-labelled phenytoin. A strong correlation was found between the total and the unbound drug concentration (r = 0.97, p less than 0.001). The unbound phenytoin fraction was 7.1 +/- 1.0% with a range of 4.9 to 10.2%. This variation is considerably less than that reported recently by different authors. Individual phenytoin binding was reproducible when the determination was repeated several weeks later. Salivary phenytoin concentrations in 33 epileptic patients were significantly correlated to the unbound (r = 0.83) and total concentrations (r = 0.82) of phenytoin in plasma. This study confirms that the clinical practice of monitoring total phenytoin plasma concentrations is sufficient, since the unbound phenytoin fraction has only a 2-fold interindividual variation in epileptic patients, provided that they do not suffer from renal or hepatic disease.

Enprofylline concentrations were measured on 3 consecutive days in milk and plasma from six nursing mothers who were treated twice daily with 150-mg enprofylline slow-release tablets. The mean plasma concentration was 0.89 mg/L and the mean milk concentration was 0.71 mg/L, the average milk/plasma ratio being 0.80. The mean milk/plasma ratio ranged from 0.67 to 0.98 in the six mothers. It was estimated that a maximum of approximately 10% of an adult dose of enprofylline, on a per-kilogram body-weight basis, may be transferred to the suckling infant.

Drug concentrations in plasma and urine were determined in 5 healthy subjects after intravenous infusion of 1 gm cephapirin and cephaloridine. Sampling of blood and urine was frequent and prolonged. Specimens were analyzed by high-pressure liquid chromatography (HPLC). Renal clearance of cephapirin decreased to less than 5% of control in all subjects when drug concentrations in plasma and urine declined. Cephaloridine clearance decreased to a lesser extent. Our findings suggest that, besides tubular secretion and glomerular filtration, a saturable and probably active tubular reabsorption is also involved in the renal handling of these two cephalosporins. The saturable reabsorption process was characterized by its Michaelis-Menten constant Km and its maximum transport capacity Tm.

The plasma kinetics of phenytoin were studied in pregnant and nonpregnant rats after a single intravenous dose. The apparent volume of distribution was greater in the pregnant rats resulting in lower plasma concentrations in these rats within the first hour of injection. The beta half-life in pregnant rats (5.0 hours) was prolonged compared to the non-pregnant rats (2.2 hours). The plasma clearance values which take the altered volume of distribution into account, showed a smaller but still significant difference between the two groups of rats. This indicates a lower capacity of the pregnant rats to metabolize the drug.

Therapeutic drug monitoring is based upon determination of the total drug concentration in plasma or serum. This is, of course, acceptable only as long as the fraction of unbound drug remains virtually constant within the patient population and within each patient. However, under certain circumstances, protein binding may vary several-fold between subjects because of differences in the following: (1) primary structure of the binding proteins; (2) concentration of the binding proteins; (3) concentration of endogenous and exogenous binding inhibitors; (4) concentration of the drug to be measured. These factors (with the exception of (1)) may cause intraindividual as well as interindividual variability, since they may be influenced by, for example, age, physical activity, other drug therapy and diet. On the other hand, it appears that the primary structure of a binding protein is under genetic control (Wilding et al., 1977). Furthermore, dramatically increased or decreased binding has been observed in several disease states, for example renal and liver disease (Piafsky, 1980).

Plasma levels of nortriptyline and perphenazine were measured in six patients on continuous nortriptyline treatment before, during and after oral administration of perphenazine 4 mg t.i.d. In four patients the plasma levels of the conjugated and unconjugated principal metabolite 10-hydroxy-nortriptyline were also measured. Urinary excretion of conjugated and unconjugated 10-hydroxy-nortriptyline and plasma levels of perphenazine were determined in all six patients. During treatment with perphenazine two patients showed a slight increase in the plasma level of nortriptyline. The changes in metabolite excretion rate were inconclusive. Thus, there did not appear to be any important pharmacokinetic interaction between the two drugs at the doses used, which were normal therapeutic doses. The previously reported inhibitory effect of perphenazine on the metabolism of nortriptyline probably depended therefore, either on administration of a higher dose of perphenazine, or on treatment in the reverse sequence — a single dose of nortriptyline was given to patients already receiving perphenazine.

Enprofylline, a new potent bronchodilator xanthine drug, was given orally as an aqueous solution to 6 healthy subjects in single doses of 2, 4 and 6 mg/kg. The two lower doses produced plasma concentrations in the range 1-4 mg/l, i.e. in the assumed "therapeutic interval" according to previous animal studies. A high 24 h urine recovery of unchanged drug, with mean values for the three dose levels ranging from 85 to 91% of the given dose, indicated good absorption and little metabolism. The dose-corrected area under the plasma concentration-time curve rose with dose as the latter was increased from 2 to 6 mg/kg. This indicates that the elimination of enprofylline is capacity-limited at high doses. Double peaks in the plasma concentration-time curves at the higher dose levels suggested intermittent and delayed gastric emptying as a possible explanation. This hypothesis was confirmed by studies in 6 other healthy subjects, who received the drug solution by three different routes; by mouth, via a catheter in the duodenum, and rectally via a catheter in the colon. The corresponding time to peak values (mean +/- SEM) were 32.5 +/- 8.7, 13.3 +/- 2.5, and 157 +/- 23 min.

Phenytoin (DPH) and its two major metabolites, conjugated and unconjugated 5-(4-hydroxyphenyl)-5-phenylhydantoin (4-OH-DPH), have been studied in plasma and urine to 4 healthy subjects and 3 uremic patients during two weeks on DPH, 0.1 gm daily. Only 0.4% to 1.2% of the dose was excreted as unchanged DPH. The DPH concentrations in urine were in the same range as calculated unbound levels of DPH in plasma in the normal subjects; 1% to 2% of the dose was excreted as unconjugated 4-OH-DPH in the normal subjects. In the uremic patients, renal clearance of this metabolite was reduced to one-sixth that percentage. Plasma concentrations rose to values twice as high as normal, indicating increased rate of glucuronidation. Urinary recovery of conjugated 4-OH-DPH in healthy subjects was 52% to 94%. Its renal clearance was close to glomerular filtration rate when corrected for protein binding, suggesting elimination by glomerular filtration rate when corrected for protein binding, suggesting elimination by glomerular filtration only. Plasma concentrations of conjugated 4-OH-DPH reached plateau levels around day 4 in normal subjects. In the uremic patients, plasma concentrations of this metabolite accumulated to levels 10 times normal, and after 15 days of medication plateau levels did not seem to have been reached.

The plasma protein binding of phenytoin (DPH) was studied by equilibrium dialysis at 37 degrees C in plasma from uremic patients and healthy subjects. Scatchard plot analyses demonstrated a decreased association constant Ka for the DPH-albumin interaction in the uremic plasma (mean 1.76 - 10(3) M-1 +/-SD 0.12 and a mean 4.10 - 10(3) M-1 +/- SD 0.24 in normal plasma). Studies on separated fractions of serum did not indicate any significant binding of DPH to proteins other than albumin. The nonlinear mathematical relationship between bound DPH and serum albumin could be linearized at low drug concentrations by plotting the ratio of bound/unbound DPH against albumin concentration. The displacement effect of salicylic acid at a concentration of 276 mug/ml (2mM) and DPH was considerable in plasma from normal subjects. In uremic plasma the effect was of much smaller magnitude.

The protein binding of diazepam, salicylic acid and warfarin in serum of patients with liver cirrhosis has been studied by equilibrium dialysis and circular dichroism measurements and compared with that in normal serum. Diazepam and warfarin are mainly bound to two separate sites on the serum albumin molecule and salicylic acid to both sites. The binding of diazepam and salicylic acid was impaired in serum from the patients when compared with the binding in serum from healthy individuals, while the binding of warfarin was unchanged. The results were the same when the binding was studied with albumin isolated from patient serum and normal serum. After treatment of the albumin with charcoal at pH 3, however, the binding was improved. The apparent binding constants of the drugs in serum both from patients with liver cirrhosis and from healthy persons were increased by dilution of the sera in buffer. This effect is due to the presence of competitive inhibitors in the sera. The decreased binding of diazepam and salicylic acid in the serum from the patients with liver cirrhosis can in addition be related to the presence of allosteric inhibitors specifically affecting the diazepam binding site on albumin, while the warfarin site apparently is unaffected.

Wahrend der letzten Jahre versuchten wir an unserer Klinik immer mehr, die Patienten vom chemotherapeutischen Gesichtspunkt aus individuell zu behandeln. Wir halten uns nicht an das von den pharmazeutischen Firmen empfohlene standardisierte Dosierungsschema, das sich im allgemeinen auf umfangreiche klinische Untersuchungen stutzt, in denen der Patient aber als Durchschnitt „des untersuchten Krankengutes betrachtet wird“. Der einzelne Patient verhalt sich bezuglich Resorption, Verteilung, Metabolismus und Ausscheidung individuell.

5-(3,4-Dihydroxyphenyl)-5-phenylhydantoin, a diphenolic metabolite of diphenylhydantoin, has been identified by use of gas chromatography/mass spectrometry in urine from rats and man. The metabolite i

The binding of various tricyclic antidepressants to human plasma and the effects thereupon of other drugs were studied by an ultrafiltration technique utilizing labeled compounds. At a total concentration of 0·29 μ/ml the percentage of unbound desmethylimipramine(DMI) was found to be 9·5 ± 1·4 in 41 individuals. The unbound fraction of DMI in plasma increased only twofold when the total concentration of the drug was increased a thousand times. The degree of binding over the entire range of therapeutic plasma drug concentration was relatively constant. The binding of various tricyclic antidepressants was compared at a drug concentration of 1·1 μM. The percentage of unbound drug was for nortriptyline (NT) 5·5 ± 0·6, for amitriptyline (AT) 3·6 ± 0·8, for imipramine (I) 4·2 ± 0·8, for protriptyline (PT) 8·0 ± 0·6 (tested at a cone, of 7·7 μM) and for Leo 640, an imipramine analogue, 0·7 ± 0·7. The acetyl derivatives of DMI, NT and PT were much more bound than the parent compounds. The addition of NT, PT or AT in a “therapeutic” concentration of 0·2 μg/ml didnot displace DMI, nor did chlorpromazine in supratherapeutic concentration. Diphenylhydantoin was found to displace DMI, NT, PT, AT and particularly I.