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Rifapentine is a cyclopentyl derivative of rifampin under development for the treatment of Mycobacterium tuberculosis and Mycobacterium avium complex infections. These studies were designed to investigate the disposition and biotransformation of single iv and oral doses of 14C-rifapentine in mice, bile duct-cannulated and uncannulated rats, and monkeys. Mass balance studies included 14C analyses of urine, feces, bile, cage wash, carcasses, and cage air collected for up to 120 hr postdose. Separation of radioactive compounds extracted from urine, bile, and feces was conducted using high-performance liquid chromatography and radioisotope detection. The mass spectra of selected chromatographic peaks were obtained. Disposition results were similar for all three species. Less than 5% of the radioactive dose of 14C-rifapentine was recovered in urine, indicating that renal excretion is a minor route of elimination in these species. The major route of elimination of radioactivity was into the feces, where more than 75% of the radioactivity was recovered. Biliary excretion was the major route of elimination of radioactivity in bile duct-cannulated rats dosed either po or IV. Radiochromatograms were similar for fecal samples from animals dosed by IV or orally. Ten regions of radioactivity were observed in mouse and rat fecal sample radiochromatograms, and seven regions of radioactivity were observed in monkey fecal sample radiochromatograms. The most abundant compound identified in feces was usually intact rifapentine (27%-41% of dose in mouse, 3%-35% of dose in rat, and 17%-29% of dose in monkey). Other peaks identified or characterized in feces based on liquid chromatography/ultraviolet/14C and/or liquid chromatography/mass spectrometry methods included 25-desacetyl-rifapentine, 3-formyl-25-desacetyl-rifapentine, and 3-formyl-rifapentine. The compounds rifapentine, 25-desacetyl-rifapentine, and 3-formyl-rifapentine were present in rat bile samples. These studies show that the metabolism and disposition of rifapentine in mice, rats, and monkeys were similar.

Rifapentine is a long-acting cyclopentyl-derivative of rifampin. This study was designed to investigate the mass balance and biotransformation of 14C-rifapentine in humans. Four healthy male volunteers received a single 600-mg oral dose of 14C-rifapentine in a hydroalcoholic solution. Whole blood, urine, and fecal samples were collected before and at frequent intervals after drug administration. Amount of radioactivity recovered in urine and feces was assessed for up to 18 days postdose. Metabolite characterization in urine and feces was conducted using high-performance liquid chromatography with radiometric detection and liquid chromatography/mass spectroscopy. The total recovery of radioactive dose was 86.8%, with the majority of the radioactive dose recovered in feces (70.2%). Urine was a minor pathway for excretion (16.6% of the dose recovered). More than 90% of the excreted radioactivity was profiled as 14C chromatographic peaks and 50% was structurally characterized. These characterized compounds found in feces and urine were rifapentine, 25-desacetyl-rifapentine, 3-formyl-rifapentine, and 3-formyl-25-desacetyl-rifapentine. The 25-desacetyl metabolite, formed by esterase enzymes found in blood, liver, and other tissues, was the most abundant compound in feces and urine, contributing 22% to the profiled radioactivity in feces and 54% in urine. The 3-formyl derivatives of rifapentine and 25-desacetyl-rifapentine, formed by nonenzymatic hydrolysis, were also prominent in feces and, to a lesser extent, in urine. In contrast to the feces and urine, rifapentine and 25-desacetyl-rifapentine accounted for essentially all of the plasma radioactivity (99% of the 14C area under the concentration-time curve), indicating that 25-desacetyl-rifapentine is the primary metabolite in plasma. It appears, therefore, that the nonenzymatic hydrolysis of rifapentine to 3-formyl byproducts occurs primarily in the gut and the acidic environment of the urine.

A new high-performance liquid chromatograhic procedure for simultaneous determination of pyrazinamide (PZA) and its three metabolites 5-hydroxypyrazinamide (5-OH-PZA), pyrazinoic acid (PA), and 5-hydroxypyrazinoic acid (5-OH-PA), in rat urine was developed. 5-OH-PZA and 5-OH-PA standards were obtained by enzymatic synthesis (xanthine oxidase) and checked by HPLC and GC-MS. Chromatographic separation was achieved in 0.01 M KH2PO4 (pH 5.2), circulating at 0.9 ml/min, on a C18 silica column, at 22 degrees C. The limits of detection were 300 microg/l for PZA, 125 microg/l for PA, 90 microg/l for 5-OH-PZA and 70 microg/l for 5-OH-PA. Good linearity (r2>0.99) was observed within the calibration ranges studied: 0.375-7.50 mg/l for PZA, 0.416-3.33 mg/l for PA, 0.830-6.64 mg/l for 5-OH-PZA and 2.83-22.6 mg/l for 5-OHPA. Accuracy was always lower than +/- 10.8%. Precision was in the range 0.33-5.7%. The method will constitute a useful tool for studies on the influence of drug interactions in tuberculosis treatment.

Background: This study highlights the importance of antitubercular chemoprophylaxis with isoniazid to control and prevent tuberculosis in prisons. The relationship between compliance with the chemoprophylaxis and study factors was evaluated and we examined whether health education given in our prison motivated the prisoners to comply with this treatment., Methods: Compliance with chemoprophylaxis using isoniazid by 52 inmates of the Jaén Penal Institution was studied for the period February to May 1995. The dose of isoniazid taken was calculated by means of the spectrophotometric determination of isoniazid metabolites in urine using the Eidus Hamilton method. Likewise, the influence of variables such as sex, HIV infection, legal situation and cultural level on compliance was studied., Results: Out of 52 inmates, 23 (44.23%) were taking a daily dose of isoniazid that was considered to be effective and 29 inmates (55.77%) were taking less than the effective isoniazid dose for the chemoprophylaxis. With regard to the variables studied, greater compliance with the chemoprophylaxis was recorded among men (sex variable) and those inmates with a higher educational level (cultural level) although no significant differences were found., Conclusions: Compliance with the chemoprophylaxis among our inmates is inadequate although it matches similar studies that have been carried out on the prison population. This is not the case for the community population where compliance with chemoprophylaxis is greater. This low compliance forces us to review our current health education programme and to take steps that might increase this degree of compliance such as direct observation of treatment, a system of intermittent treatment, etc.

Objectives: To determine the efficacy of isoniazid 300 mg daily for 6 months in the prevention of tuberculosis in HIV-1-infected adults and to determine whether tuberculosis preventive therapy prolongs survival in HIV-1-infected adults., Design and Setting: Randomized, double-blind, placebo-controlled trial in Nairobi, Kenya., Subjects: Six hundred and eighty-four HIV-1-infected adults., Main Outcome Measures: Development of tuberculosis and death., Results: Three hundred and forty-two subjects received isoniazid and 342 received placebo. The median CD4 lymphocyte counts at enrolment were 322 and 346 x 10(6)/l in the isoniazid and placebo groups, respectively. The overall median follow-up from enrolment was 1.83 years (range, 0-3.4 years). The incidence of tuberculosis in the isoniazid group was 4.29 per 100 person-years (PY) of observation [95% confidence interval (CI) 2.78-6.33] and 3.86 per 100 PY of observation (95% CI, 2.45-5.79) in the placebo group, giving an adjusted rate ratio for isoniazid versus placebo of 0.92 (95% CI, 0.49-1.71). The adjusted rate ratio for tuberculosis for isoniazid versus placebo for tuberculin skin test (TST)-positive subjects was 0.60 (95% CI, 0.23-1.60) and for the TST-negative subjects, 1.23 (95% CI, 0.55-2.76). The overall adjusted mortality rate ratio for isoniazid versus placebo was 1.18 (95% CI, 0.79-1.75). Stratifying by TST reactivity gave an adjusted mortality rate ratio in those who were TST-positive of 0.33 (95% CI, 0.09-1.23) and for TST-negative subjects, 1.39 (95% CI, 0.90-2.12)., Conclusions: Overall there was no statistically significant protective effect of daily isoniazid for 6 months in the prevention of tuberculosis. In the TST-positive subjects, where reactivation is likely to be the more important pathogenetic mechanism, there was some protection and some reduction in mortality, although this was not statistically significant. The small number of individuals in this subgroup made the power to detect a statistically significant difference in this subgroup low. Other influences that may have diluted the efficacy of isoniazid include a high rate of transmission of new infection and rapid progression to disease or insufficient duration of isoniazid in subjects with relatively advanced immunosuppression. The rate of drug resistance observed in subjects who received isoniazid and subsequently developed tuberculosis was low.

The in vivo disposition and in vitro metabolism of rifabutin, a new spiropiperidylrifamycin, were studied in rats and in microsomes from rat liver and enterocytes, respectively. After i.v. doses of 1,5, 10 and 25 mg/kg the systemic clearance was 0.7 to 1.0 liters/hr/kg; the volume of distribution was 4.4 liters/kg for the 1 mg/kg dose and 7.4 to 7.7 liters/kg for the 5 to 25 mg/kg doses, and the half-life ranged from 4.4 to 9.1 hr. Urinary and fecal excretion over 0 to 96 hr after i.v. administration of 25 mg/kg [14C]rifabutin accounted for 40.1 and 52.2% of the dose, respectively. Exteriorization of the bile duct showed that approximately 24% of the dose was eliminated in bile, > or = 98% as metabolites. Bioavailability after oral administration of 25 and 1 mg/kg rifabutin was > 90% and 44%, respectively, suggesting significant first-pass metabolism of the lower dose. Concentrations of rifabutin in gastric juice were 10 to 17 times higher than in blood, indicating extensive secretion into the stomach. Experiments with the isolated small intestinal loop demonstrated direct exsorption of the drug into the lumen. The rate of rifabutin metabolism by enterocyte microsomes was > 10 times higher than that by liver microsomes, i.e., 84 and 8 pmol/min/mg protein, respectively. Biotransformation of rifabutin in vivo and in vitro was markedly induced by dexamethasone and inhibited by erythromycin, suggesting that CYP3A is involved in the metabolism of rifabutin. Several metabolites, including 20-OH-rifabutin and 27-O-demethyl-rifabutin, isolated from urine and microsomes were identified by mass spectrometry and nuclear magnetic resonance spectroscopy.

New methods for detecting the acetylation phenotype have been developed for therapeutic monitoring using isoniazid as the pharmacogenetic marker. The study is carried out with 4-chloro-5,7-dinitrobenzofurane by direct spectrophotometry, high performance liquid and thin-layer chromatography. The methods proved to be highly sensitive, selectively detecting isoniazid, simple, and requiring no sophisticated equipment. The methods were tried in examinations of patients with visceral diseases. Effects of various inductors on the acetylation rate were assessed.

A sensitive and selective HPLC method for the determination of ethambutol in human plasma and urine was developed. Ethambutol was extracted from basified plasma samples (0.2 ml) with diethyl ether, back-extracted into 0.01 M phosphoric acid and derivatized with 4-fluoro-7-nitrobenzo-2-oxa-1, 3-diazole. After 30 min at 80 degrees C and elimination of the reactive excess, the compound was determined by reversed-phase liquid chromatography. urine was analysed for ethambutol after dilution 1:200 with distilled water and derivatization as described for plasma. Quantification in plasma and urine was achieved by fluorescence detection of the eluate. The linearity, precision and accuracy of the method were evaluated. No interference from the constituents of human plasma and urine was observed. The limit of quantification was 10 ng/ml in plasma and 10 micrograms/ml in urine. The suitability of the method for in vivo samples was checked by analysis of plasma and urine samples drawn from healthy volunteers who had received a 1200-mg oral dose of the test compound.

Study Objective: To determine the bioavailability and renal elimination of isoniazid, acetylisoniazid, monoacetylhydrazine, diacetylhydrazine, aconiazide, and 2-formylphenoxyacetic acid., Study Design: Randomized, double-blind, two-period, crossover phase I study., Setting: Pharmacokinetics unit at a referral hospital that specializes in the treatment of mycobacterial infections., Subjects: Twelve healthy volunteers selected from the hospital staff., Interventions: Subjects received aconiazide tablets 650 mg (containing isoniazid 300 mg) and isoniazid tablets 300 mg. Blood and urine samples were collected over 24 hours after the dose., Measurements and Main Results: Intact aconiazide and 2-formylphenoxyacetic acid were not detected in the serum. Compared with isoniazid tablets, aconiazide's relative bioavailability (based on the area under the serum concentration-time curve) was 50.7%; its relative maximum serum concentration was 13.4%., Conclusions: Isoniazid is less bioavailable after aconiazide tablets than after isoniazid tablets. The optimum dose of aconiazide remains to be determined.

14C-Rifabutin was given orally to rats, rabbits and monkeys at a dose of 25 mg/kg and to healthy volunteers at a dose of 270 mg. Radioactivity was eliminated by both the renal and faecal routes in all species, with a predominance of the renal route in man and monkeys (50.19% and 46.73% of the dose, respectively, in urine at 96 h), whereas in rats and rabbits a slight predominance of faecal excretion was observed (48.09% and 45.01% of the dose, respectively, at 96 h in faeces; 42.22% and 36.37% in urine). Radioactivity as expired 14CO2 was detected in the rat and accounted for less than 0.5% of the dose within 96 h. The drug was rapidly absorbed and peak plasma radioactivity levels were reached from 1 to 4 h after dosing. Rifabutin was the predominant compound circulating in plasma at the first sampling times, but significant levels of 31-OH rifabutin were detected up to 8-24 h in all species studied. 25-O-deacetyl rifabutin was detected only in rat and man. Polar metabolites were also present, particularly at the later sampling times. The urinary metabolism was studied by radio-HPLC. Rifabutin accounted for 8.5% and 4.6% of the dose in 0-24 h urine of rats and man respectively, whereas in rabbit and monkey urine only traces of this compound were detected. The main known metabolite in all animal species was 31-OH rifabutin; 25-O-deacetyl rifabutin was detected only in rat and man. The remaining urinary radioactivity was mainly due to polar compounds.

The quantitative aspects of the disposition in man of 12 antituberculosis drugs [isoniazid, rifampicin, (rifampin), ethambutol, para-aminosalicylic acid, pyrazinamide, streptomycin, kanamycin, ethionamide, cycloserine, capreomycin, viomycin and thiacetazone] are reviewed. Isoniazid appears to be the only agent for which plasma concentrations and clearance are related to hereditary differences in acetylator status and for which there is an appreciable 'first-pass' effect. Recent data cast doubt on the suggestion that isoniazid may be more hepatotoxic for rapid as opposed to slow acetylators. Continuous administration of rifampicin leads to induction of enzymes in the liver with a concomitant decrease in maximum plasma concentrations, the time required to achieve this level, elimination half-life, and area under the plasma concentration-time curve (AUC). Coadministration of para-aminosalicylic acid leads to increases in the serum concentrations and elimination half-life of isoniazid. With a few exceptions, the metabolites of the antituberculosis drugs are devoid of antimicrobial activity; the exceptions are 25-desacetylrifampicin which accounts for approximately 80% of the drug's antimicrobial activity in human bile, the acetylated and glycylated metabolites of para-aminosalicylic acid, and the sulphoxide metabolites of ethionamide. The effect of renal impairment is relatively unimportant for the excretion of isoniazid, rifampicin and para-aminosalicylic acid, but the elimination half-life of streptomycin increases to 100 hours when the blood urea nitrogen level is greater than 100mg/100ml, and ototoxicity is strikingly more frequent. In states of malnutrition, such as kwashiorkor, the protein binding of para-aminosalicylic acid decreases from 15% to essentially zero and in the case of ethionamide and streptomycin binding decreases by 6% and 16% respectively. Of the data concerning age-related effects, most notable are the prolonged elimination half-life of isoniazid in neonates (up to 19.8 hours), and the lower peak serum concentrations of rifampicin in children of one-third to one-tenth those of adults following a similar dose on a weight basis. For kanamycin, the maximum plasma concentration varies inversely with age but is not influenced by birthweight; however, the clearance is directly dependent upon birthweight and postnatal age. For the elderly, age is an insignificant factor for the elimination of isoniazid when compared with young adults of similar acetylator status, and the metabolism of rifampicin may be considered globally unaltered in this age group.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Metabolites of the antimycobacterial agent 4-deoxo-3,4-[2-spiro-(N-isobutyl-4-piperidyl)]-(1H)-imidazo-(2,5-dihydro )- rifamycin S (rifabutin) were isolated from human urine after administration of a single oral dose of the drug. Some of these metabolites were identified by direct inlet mass spectrometry, 1H-n.m.r. spectrometry and, in two cases, by chromatographic comparison with reference compounds. 2. Unchanged drug, 25-O-deacetyl rifabutin and four other metabolites were identified in human urine. 25-O-Deacetyl rifabutin was the main urinary metabolite, other metabolites were characterized as oxidized, and oxidized-deacetylated derivatives. 3. Routes of metabolic transformation were: (a) deacetylation at position 25, (b) oxidation of methyl groups 31 or 32 or at the piperidine nitrogen, and (c) combination of these.