rifampin and 25-deacetylrifampicin

Clarithromycin (CLA) is a well established macrolide antibiotic which is frequently used in therapy of airway diseases in foals. It is extensively metabolized by CYP3A4 resulting in the antimicrobial active metabolite 14-hydroxyclarithromycin (OH-CLA). Rifampicin (RIF) is often comedicated to prevent resistance and augment therapy. RIF is a known inducer for metabolizing enzymes and transporter proteins. Therefore, comedication might bare the risks of pharmacokinetic drug interactions which were investigated in a clinical trial. As no adequate method to determine CLA, RIF and their main metabolites OH-CLA and 25-O-desacetylrifampicin (DAc-RIF) were described so far, we developed a selective and sensitive assay to measure concentrations of all four substances simultaneously in plasma, epithelial lining fluid (ELF) and broncho-alveolar cells (BAC) of foals. Drugs were measured after extraction with methyl tert-butyl ether using roxithromycin as internal standard and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for detection. The chromatography was done isocratically using 25mM ammonium acetate buffer (pH 4)/acetonitrile (45%/55%, flow rate 200μl/min). The MS/MS analysis was performed in the positive ion mode (m/z transitions: CLA, 748.5-590.1; OH-CLA, 764.1-606.1; RIF, 823.1-791.2; DAc-RIF, 781.1-749.1 and 837.3-679.2 for the internal standard). The method was validated according to selectivity, linearity, accuracy, precision, recovery, matrix effects and stability. The validation ranges for all substances were 2.5-25 for the low and 25-250ng/ml for the high validation range. The described assay was shown to be valid and successfully applied to measure disposition of CLA, OH-CLA, RIF and DAc-RIF in plasma, ELF and BAC of foals in a clinical trial.

Topics: Animals; Anti-Bacterial Agents; Biotransformation; Bronchioles; Bronchoalveolar Lavage Fluid; Chromatography, High Pressure Liquid; Clarithromycin; Drug Interactions; Drug Stability; Horse Diseases; Horses; Limit of Detection; Pulmonary Alveoli; Reproducibility of Results; Respiratory Tract Infections; Rifampin; Spectrometry, Mass, Electrospray Ionization; Tandem Mass Spectrometry

Low serum concentrations of anti-tuberculosis drugs have occasionally been associated with treatment failure.. To determine the prevalence of low serum concentrations of anti-tuberculosis drugs and to identify the determinants of drug concentrations.. Venous blood was obtained 2 h after drug ingestion, and serum levels of isoniazid (INH), rifampicin (RMP), ethambutol (EMB), pyrazinamide (PZA), acetyl INH and 25-desacetyl RMP were analysed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Patients with human immunodeficiency virus co-infection and gastrointestinal disease or diarrhoea were excluded.. Among 69 enrolled TB patients, the prevalence of a low 2 h serum concentration of at least one anti-tuberculosis drug was 46.4%. Prevalences of a low concentration of INH, RMP, EMB or PZA were 15.2%, 23.5%, 22.4% and 4.5%, respectively. By multivariate linear regression analysis, the serum concentrations of INH, RMP and PZA were positively associated with dose per kg of body weight (P < 0.05). Moreover, INH concentration was associated with acetyl INH/INH ratio (beta = -8.588, P < 0.001) and EMB concentration was associated with calculated creatinine clearance (beta = -0.025, P < 0.001).. Low concentrations of anti-tuberculosis drugs are common, and although the clinical significance of low concentrations remains uncertain, it may be necessary to optimise drug doses by therapeutic drug monitoring, especially in patients with an inadequate clinical response to chemotherapy.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Antitubercular Agents; Chromatography, Liquid; Drug Monitoring; Ethambutol; Female; Humans; Isoniazid; Linear Models; Male; Mass Spectrometry; Middle Aged; Pyrazinamide; Rifampin; Tuberculosis

The benefits of fixed-dose combination (FDC) formulations of rifampicin, isoniazid and pyrazinamide over individual formulations are well recognised.. To evaluate the comparative bioavailability of antituberculosis drugs in FDC formulations and the same doses in separate formulations of antituberculosis drugs, using a simplified protocol developed by the World Health Organization (WHO).. Twenty healthy volunteers were included in the study and evaluated for bioequivalence of rifampicin in a cross-over experimental design. After administration of drugs the plasma concentration of rifampicin and desacetyl-rifampicin was measured repeatedly up to 8 hours in both plasma and urine. Various pharmacokinetic parameters of rifampicin, such as Cmax, Tmax, elimination rate constant, area under the curve (AUC) up to 8 hours and absorption efficiency were calculated.. No significant differences were observed between the FDCs and separate formulations when Cmax, Tmax, AUC and absorption efficiencies were compared by parametric test and Hauschke's analysis.. The WHO simplified protocol is suitable for evaluating bioequivalence of antituberculosis drugs.

Topics: Adolescent; Adult; Antibiotics, Antitubercular; Antitubercular Agents; Area Under Curve; Biological Availability; Clinical Protocols; Creatinine; Cross-Over Studies; Drug Combinations; Humans; Male; Middle Aged; Rifampin; Therapeutic Equivalency; World Health Organization

In the bioavailability studies with drugs biotransformed to biologically active metabolities only the concentrations of the parent drug (PD) are usually taken into account even when the pharmacokinetic data on the metabolite(s) (M) are available. However, such data may be useful as an alternative source for the bioavailability determination. Moreover, the clinical outcomes often depend on both the PD and M concentrations. The aim of the study performed with two rifampicin formulations, tablets and dragee, was to correlate the pharmacokinetic parameters of the PD and 25-O-deacetylrifampicin, a microbiologically active M of rifampicin, and to examine whether the bioavailability parameters based on the PD and M concentrations were compatible. The serum concentrations of the PD and M were determined in 8 healthy volunteers by HPLC. Despite different patterns of the PD and M pharmacokinetic profiles the PD peak concentration (Cmax) and especially the AUC correlated with Cmax or the AUC of the M (r = 0.76 and 0.92 respectively). Moreover, the extent of the absorption expressed as the AUC ratio for the PD correlated with the AUC ratio for the M (r = 0.86). However, neither the time to reach the maximum (tmax), nor the Cmax/AUC ratio, a measure of the absorption rate, based on the PD pharmacokinetic data correlated with the respective parameters calculated with using the M concentrations. Thus, only the estimates of the extent of the absorption and not of the absorption rate based on the PD and M data may be considered as compatible.

Topics: Antibiotics, Antitubercular; Biological Availability; Chromatography, High Pressure Liquid; Drug Evaluation; Female; Humans; Male; Reference Values; Rifampin

We investigated the pharmacokinetics of rifampicin and its major metabolites, 25-desacetylrifampicin and 3-formylrifampicin, in two groups of six patients with active pulmonary tuberculosis, who received either multiple oral or intravenous rifampicin therapy in combination with intravenous isoniazid and ethambutol. Serum concentrations of rifampicin were each determined after a single oral and intravenous test dose of 600 mg rifampicin at the beginning and after 1 and 3 weeks of tuberculostatic treatment. Analysis of rifampicin and its metabolites was performed by high-pressure liquid chromatography. It was found that, due to autoinduction of its metabolizing hepatic enzymes, the systemic clearance of rifampicin increased from 5.69 to 9.03 l/h after 3 weeks of multiple dosing. The volume of distribution of the drug was constant over the period of this study. The bioavailability of the active, orally administered rifampicin decreased from 93% after the first single oral dose to 68% after 3 weeks of oral and intravenous rifampicin therapy. Relating to the increase in systemic (hepatic) clearance, a bioavailability no lower than 90% can be predicted. The reduction to 68% indicates that, in addition to an increase of hepatic metabolism, an induction of a prehepatic "first-pass" effect resulted from multiple rifampicin doses. Our study of rifampicin metabolites confirm that prehepatic metabolism was induced, since a higher metabolic ratio resulted after the oral doses than after the intravenous rifampicin test doses. A preabsorptive process can therefore be excluded as a cause of reduced bioavailability.

Topics: Administration, Oral; Adolescent; Adult; Aged; Biological Availability; Drug Therapy, Combination; Ethambutol; Female; Humans; Infusions, Parenteral; Isoniazid; Male; Metabolic Clearance Rate; Middle Aged; Rifampin; Rifamycins; Tuberculosis, Pulmonary

Measurement of rifampin levels is not part of routine practice. However, low levels are associated with failure of tuberculosis treatment. The clinical relevance of serum levels in daily practice is unclear. The objective was to evaluate rifampin serum concentrations and factors associated with insufficient concentrations.. Patients with at least one rifampin concentration drawn 3 hours after intake (C3) between 2005 and 2014 were included. Data on demographic and clinical characteristics were collected, including side effects and dose adjustments. Two different criteria were used to define adequate concentrations (criterion 1: C3 a nd C 6 ≥ 3 mg/l; criterion 2: C3 or C6 ≥ 5 mg/l).. Of 63 patients, 66% and 76% had a sufficient level according to criterion 1 or 2, respectively. C3 exceeded C6 in most patients, while a late maximum was significantly associated with diabetes mellitus (p = 0.003). A dose adjustment was made in 19% of cases, more frequently in patients with insufficient levels (p = 0.02) or with ≥ 2 side effects (p = 0.03).. Rifampin levels varied but were mostly adequate and a single measurement at 3 hours after intake provided the required information in most cases, indicating that full AUC0-24 measurements could be limited to specific situations.

Topics: Adolescent; Adult; Aged; Antibiotics, Antitubercular; Child; Child, Preschool; Drug Monitoring; Female; Humans; Infant; Infant, Newborn; Male; Middle Aged; Retrospective Studies; Rifampin; Time Factors; Tuberculosis, Pulmonary; Young Adult

Rifampicin (RIF) and isoniazid (INH), first line drugs for the treatment of tuberculosis, are known to cause hepatotoxicity as a serious adverse side effect. To further understand the pharmacokinetic parameters of these two drugs, we have developed and validated a rapid, sensitive and selective LC-MS/MS method for simultaneous quantification of RIF, INH and their metabolites 25-desacetylrifampicin (DRIF), acetylisoniazid (AcINH) and isonicotinic acid (INA). Analytes were extracted from 20 μl of plasma using solid-phase extraction (SPE) followed by chromatographic separation on Zorbax SB-Aq column (50 mm × 4.6mm, particle size 5 μm) using stepwise gradient elution of 5mM ammonium acetate and 90% acetonitrile with 0.1% formic acid. Separation of all analytes was achieved in the total run time of 6 min. The analytes were detected under positive ionization mode by multiple reaction monitoring (MRM) and quantification of analytes was performed by using deuterium-labelled internal standard. Excellent linearity (r(2) ≥ 0.995) was achieved for the analytes at different concentration ranges. The method was accurate (90-115%), precise (CV %<14) and specific. Matrix effect was in the range of 93-111% except for INA (40-42%) while recovery from SPE was reproducible (CV %<7.4) in the range of 60-86%. Post-preparative stability (48 h, 6°C autosampler) and freeze-thaw stability (3 cycles) were assessed with mean recovered concentration of >85%. The method was successfully applied to a clinical study of 33 healthy subjects to evaluate the effect of concomitant of INH on the pharmacokinetic parameters of RIF as well as the segregation of the subjects into slow or fast acetylators of INH.

Topics: Antitubercular Agents; Chromatography, High Pressure Liquid; Humans; Isoniazid; Rifampin; Solid Phase Extraction; Tandem Mass Spectrometry

Rifampicin is known to be deacetylated in vivo, resulting in its metabolite 25-desacetyl rifampicin, but the enzyme metabolizing rifampicin and the association of this process with any genetic variation have not yet been elucidated. In this study, genetic variations of a surrogate enzyme, carboxylesterase 2 (CES2), and their association with the metabolism of this drug, were investigated.. Plasma concentrations of rifampicin and 25-desacetyl rifampicin were measured in 35 patients with tuberculosis receiving a first-line antituberculosis treatment. Direct PCR-based sequencing of the CES2 gene, covering all 12 exons, the 5'-untranslated region (UTR), the 3'-UTR and intronic and promoter regions, was performed. A dual luciferase reporter assay was carried out to assess whether variations in the promoter region affected the transcription of this gene.. Ten variations were detected, of which two were in the candidate promoter region, five in introns and three in the 3'-UTR. One of the variations in the 3'-UTR was a novel variation. Genotypes at three closely linked variations (c.-2263A > G, c.269-965A > G and c.1612 + 136G > A) and c.1872*302_304delGAA were associated with significantly different plasma rifampicin concentrations. The mean plasma rifampicin concentration significantly increased with the number of risk alleles at the three closely linked variations, while the plasma concentration decreased along with an increase in the number of risk alleles at c.1872*302_304delGAA. When HepG2 cells were transfected with a luciferase reporter construct bearing the c.-2263G allele, luciferase activities were consistently decreased (by 5%-10%) compared with those harbouring the c.-2263A sequence.. Variations in CES2, especially c.-2263A > G in the promoter region, may alter rifampicin metabolism by affecting expression of the gene.

Topics: 3' Untranslated Regions; Alleles; Anti-Bacterial Agents; Asian People; Carboxylesterase; Chromatography, High Pressure Liquid; Dealkylation; Gene Frequency; Genetic Variation; Humans; Luciferases; Mass Spectrometry; Polymerase Chain Reaction; Polymorphism, Genetic; Promoter Regions, Genetic; Rifampin

Clarithromycin and rifampicin are used for the treatment of Mycobacteria. Pharmacokinetic drug interaction is possibly due to the influence of the two drugs on the liver enzymes. Using a Hypurity Aquastar C18 column (50mm×2.1mm×5μm) for liquid chromatography including a polar end-capped phase for the determination of clarithromycin, rifampicin and their metabolites together in plasma using LC-MS/MS resulted in a substantial carry-over. As a consequence, the throughput of the method is not assured. Using a step-by-step troubleshooting procedure, such carry-over was found originating from column memory effect. With the use of another type of C18 column, the carry-over is eliminated. Due to the absence of carry-over, the analytical concentration ranges are extended and are therefore more appropriate for the analysis of patient samples. The method was re-validated for linearity, reproducibility and dilution integrity.

Topics: Chromatography, Liquid; Clarithromycin; Humans; Linear Models; Reproducibility of Results; Rifampin; Sensitivity and Specificity; Tandem Mass Spectrometry

The drug combination rifampicin and clarithromycin is used in regimens for infections caused by Mycobacteria. Rifampicin is a CYP3A4 inducer while clarithromycin is known to inhibit CYP3A4. During combined therapy rifampicin concentrations may increase and clarithromycin concentrations may decrease. Therefore a simple, rapid and easy method for the measurement of the blood concentrations of these drugs and their main metabolites (14-hydroxyclarithromycin and 25-desacetylrifampicin) is developed to evaluate the effect of the drug interaction. The method is based on the precipitation of proteins in human serum with precipitation reagent containing the internal standard (cyanoimipramine) and subsequently high-performance liquid chromatography (HPLC) analysis and tandem mass spectrometry (MS/MS) detection in an electron positive mode. The method validation included selectivity, linearity, accuracy, precision, dilution integrity, recovery and stability according to the "Guidance for Industry - Bioanalytical Method Validation" of the FDA. The calibration curves were linear in the range of 0.10-10.0 mg/L for clarithromycin and 14-hydroxyclarithromycin and 0.20-5.0 mg/L for rifampicin and 25-desacetylrifampicin, with within-run and between-run precisions (CVs) in the range of 0% to -10%. The components in human plasma are stable after freeze-thaw (three cycles), in the autosampler (3 days), in the refrigerator (3 days) and at room temperature (clarithromycin and 14-hydroxyclarithromycin: 3 days; rifampicin and 25-desacetylrifampicin: 1 day). The developed rapid and fully validated liquid chromatography-tandem mass spectrometry (LC/MS/MS) method is suitable for the determination of clarithromycin, 14-hydroxyclarithromycin, rifampicin and 25-desacetylrifampicin in human plasma.

Topics: Anti-Bacterial Agents; Chromatography, Liquid; Clarithromycin; Humans; Rifampin; Tandem Mass Spectrometry

Monitoring of anti-tuberculosis drug concentrations and dose adjustment can be helpful in cases that show poor response to treatment. Here, we describe a method that can rapidly and simultaneously measure the blood concentrations of four anti-tuberculosis drugs (isoniazid, rifampicin, pyrazinamide, and ethambutol) and two major metabolic ratios (acetylisoniazid/isoniazid and 25-desacetylrifampicin/rifampicin) using high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). A C18 reversed-phase column and gradients of methanol in 0.3% formic acid and water were used for HPLC separation. The drug concentrations were determined by multiple reaction monitoring in positive ion mode and the assay performance was evaluated. We determined peak concentration ranges for each drug and acetylisoniazid/isoniazid and 25-desacetylrifampicin/rifampicin ratios by analyzing 2-h post-dose samples in patients treated with standard dosing as a first-line treatment. The preparation of 20 samples including two steps of deproteinization with 50% and 100% methanol was performed within 20 min and chromatographic separation was achieved within 4 min/sample. Interassay calibration variability data obtained over concentrations of 0-8 microg/mL for isoniazid and ethambutol and 0-80 microg/mL for rifampicin and pyrazinamide showed a linear and reproducible curve. Within-run and between-run imprecision (CVs) were 1.9-5.5% and 3.5-10.5% and the lower limits of detection and quantification were 0.01-0.5 microg/mL and 0.05-1.0 microg/mL, respectively. The isoniazid concentration was found to be inversely correlated to the acetylisoniazid/isoniazid ratio (R=-0.739, P<0.001). The devised method allows for the simple, rapid, sensitive and reproducible quantification of isoniazid, rifampicin, pyrazinamide, ethambutol and their two metabolic ratios and should be helpful for therapeutic drug monitoring in tuberculosis patients.

Topics: Antitubercular Agents; Blood Chemical Analysis; Chromatography, High Pressure Liquid; Complex Mixtures; Humans; Isoniazid; Rifampin; Spectrometry, Mass, Electrospray Ionization

Few reports have addressed neonatal rifampicin plasma concentrations and data on neonatal rifampicin pharmacokinetics are completely lacking. Therefore, plasma concentrations of rifampicin and its main metabolite 25-O-desacetylrifampicin (DES) were measured in 123 surplus plasma samples from routine vancomycin monitoring in 21 neonates using reversed-phase HPLC. Rifampicin peak and trough plasma concentrations were 4.66 +/- 1.47 mg/L and 0.21 +/- 0.20 mg/L, respectively, after a dose of 8.5 +/- 2.1 (mean +/- SD) mg/kg per day. A significant linear relationship between rifampicin dose and peak plasma concentrations was found, but inter-patient variability was high. Pharmacokinetic parameters of rifampicin were calculated according to a one-compartment open model with iterative two-stage Bayesian fitting (MW\\PHARM 3.60, Mediware, The Netherlands). First-order elimination constant, volume of distribution corrected for weight, total body clearance corrected for weight (CL/W), and elimination half-life were 0.16 +/- 0.06 h(-1), 1.84 +/- 0.59 L/kg, 0.28 +/- 0.11 Lkg(-1) h(-1), and 4.9 +/- 1.7 h, respectively. A high Pearson correlation was found between CL/W rifampicin and the covariates plasma creatinine and CL/W gentamicin of a preceding gentamicin treatment course, r = 0.728 (n = 17) and r = 0.837 (n = 12), respectively. DES was detected in each plasma sample. Therefore, rifampicin seems to be eliminated by both renal and metabolic pathways in neonates. In 8 study patients, plasma concentrations of rifampicin and DES were measured again after two weeks of therapy. CL/W rifampicin was significantly higher (67 +/- 50%). The authors suggest maintaining the current dose regimen of 10 mg/kg once a day. Because of the large inter-patient variability in rifampicin plasma concentrations and CL/W increase during therapy, the authors suggest monitoring rifampicin peak and trough plasma concentrations to avoid low plasma concentrations. More research is needed to determine well-founded dosing guidelines.

Topics: Area Under Curve; Bayes Theorem; Chromatography, High Pressure Liquid; Drug Monitoring; Female; Humans; Infant, Newborn; Infusion Pumps; Infusions, Intravenous; Male; Metabolic Clearance Rate; Rifampin; Vancomycin

Topics: Antibiotics, Antitubercular; Chromatography, High Pressure Liquid; Humans; Reference Standards; Reproducibility of Results; Rifampin

The disposition of rifampin in six healthy mares after single intravenous (i.v.) and oral (p.o.) doses and after seven oral doses of 10 mg/kg administered twice a day was investigated using a high performance liquid chromatographic (HPLC) method. Pharmacokinetic variables for rifampin determined using the HPLC method were comparable to variables reported from earlier studies utilizing a microbiological assay. Desascetylrifampin, a major metabolite of the parent compound, could not be detected in the serum but was detected at low concentrations in urine. Mean trough concentrations of rifampin increased from the first to the second dose of the multiple dose oral study and then remained unchanged through 72 h. At 84 h after the first dose (i.e. 12 h after the final dose) the rifampin concentration was significantly decreased (P = 0.001). The harmonic mean of the half-life of rifampin decreased significantly from 13.3 h after a single oral dose of 7.99 h after the seventh oral dose. The mean serum protein binding of rifampin over the concentration range of 2-20 micrograms/ml was 78%. Mean trough serum concentrations of unbound rifampin after multiple oral doses ranged from 0.67 micrograms/ml at 24 h to 0.40 micrograms/ml at 72 h. The mean unbound serum rifampin concentration at 84 h (i.e., 12 h after the final dose) was 0.30 micrograms/ml. Trough concentrations and the 84-h sample concentration of unbound rifampin exceeded the minimum inhibitory concentration for most gram positive bacterial isolates from horses reported in this study. All organisms with minimum inhibitory concentrations less than 0.125 micrograms/ml were considered susceptible. Based on the pharmacokinetics of rifampin after p.o. administration, we concur with the current dosage recommendation of 10 mg/kg twice a day by mouth. At this dose, most streptococci, Rhodococcus equi, and coagulase-positive staphylococci would be considered susceptible to rifampin.

Topics: Administration, Oral; Animals; Bacteria; Female; Horses; Injections, Intravenous; Microbial Sensitivity Tests; Protein Binding; Rifampin

Topics: Aged; Antibiotics, Antitubercular; Antitubercular Agents; Chromogenic Compounds; Drug Interactions; Humans; Isoniazid; Male; Pyrazinamide; Rifampin; Tuberculosis, Pulmonary

A rapid liquid chromatographic method for simultaneous determination of isoniazid (INH), acetylisoniazid (AINH), rifampin (RIF), and deacetylrifampin (DARIF) in microsamples of deproteinized plasma is described. The compounds and internal standard (IS) (diphenylcarbazide) were separated on a 10-microns, 8 mm x 10-cm phenyl Radial Pak cartridge in conjunction with a binary linear gradient system at a flow rate of 3 ml/min. A dual electrochemical (+800 mV) and spectrophotometric (334 nm) detection system with a computerized data station was employed to measure the above compounds in the effluent. Prior to injection, the plasma sample was diluted (2:1) with a pH 3, 0.075 M phosphate buffer after adding the internal standard (6.67 micrograms/ml of plasma) and passed through an Amicon Centrifree-MS filter at 2000g. Under these conditions, no interference in the analysis was observed, and the retention times of AINH, INH, IS, DARIF, and RIF were 3.95, 4.89, 15.82, 17.25, and 19.34 min, respectively. The linearity of the assay for all four compounds was excellent (r greater than 0.9925), and the between- and within-day CV was not greater than 8% at any concentration. This method is currently being used for therapeutic monitoring and pharmacokinetic studies of INH, RIF, and their major metabolites in patients with tuberculosis.

Topics: Chromatography, Liquid; Electrochemistry; Isoniazid; Microchemistry; Rifampin; Spectrophotometry

Pharmacokinetics of rifampicin after its single intratracheal administration in the form of the liposome-encapsulated drug and its aqueous solution was studied on rats. It was shown that after the exposure to the liposome-incorporated rifampicin (10 mg/kg) the concentration-time curve in the blood and lungs was sigmoid with the retarded decrease in the blood drug concentration within 9 hours. The plateau segment of the curve provided at least a 4-fold longer maintenance of the rifampicin concentration in the blood and lungs at 3 to 4 micrograms/ml. The use of the liposome-incorporated antibiotic induced 2- and 1.5-fold increases in the AUC in regard to the lungs and blood, respectively.

Topics: Animals; Catheterization, Peripheral; Drug Carriers; Liposomes; Liver; Lung; Models, Biological; Rats; Rifampin; Time Factors; Trachea

A procedure for determination of rifampicin and 25-desacetylrifampicin in plasma by HPLC was developed. The plasma proteins are precipitated by acetonitrile and the supernatant layer (50 microliters) is used for the assay under isocratic conditions on an analytical column 250 x 4.6 mm in size containing the reversed phase sorbent (C18). The size of the precolumn is 50 x 4.6 mm. An UV detector (at lambda 335 nm) is used. For preparing the mobile phase 630 ml of methanol and 370 ml of 0.058 M sodium nitrite solution are mixed. The flow rate of the mobile phase is 40.7 ml/min. The assay duration is about 10 min. The retention time is 9.6 min for rifampicin and 6.5 min for 25-desacetylrifampicin. The minimum detectable amount of the antibiotic and its metabolite is 0.10 micrograms/ml. The standard curves of rifampicin and 25-desacetylrifampicin are linear within the concentration ranges of 0.5-100 and 0.5-10 micrograms/ml respectively. The procedure is useful in studies on pharmacokinetics of rifampicin and 25-desacetylrifampicin.

Topics: Chromatography, High Pressure Liquid; Humans; Rifampin

Topics: Adult; Chromatography, High Pressure Liquid; Humans; Male; Papaverine; Rifampin; Rifamycins; Tuberculosis

Topics: Animals; Chromatography, High Pressure Liquid; Rabbits; Rifampin

Pharmacokinetics of rifampicin studied in 15 patients after its intravenous administration in a dose of 10 mg/kg was described by a two-compartment model. The drug levels in serum and urine were determined with a chemical method. At the moment of the infusion discontinuation the maximum drug levels in serum averaged to 14.05 micrograms/ml. The mean values of the total clearance, distribution of the kinetic volume and half-lives were 93.2 ml/(h X kg), 1016.1 ml/kg and 8.1 h respectively. Cumulative excretion of the total rifampicin within 24 hours amounted to 19.4 per cent of the administered dose, the proportions of the main metabolite (25-O-desacetyl rifampicin) and intact rifampicin being equal to 29 and 71 per cent respectively. The renal and nonrenal clearance of rifampicin amounted to 14.2 and 79 ml/(h X kg) respectively.

Topics: Adult; Humans; Infusions, Intravenous; Kinetics; Male; Rifampin; Time Factors; Tuberculosis, Pulmonary

Topics: Chromatography, High Pressure Liquid; Electrochemistry; Humans; Rifampin; Spectrophotometry, Ultraviolet

After oral administration of rifampicin and 25-desacetylrifampicin, which is a major metabolite of rifampicin in man but not in rat, to male Wister rats for 7 days, hepatic microsomal cytochrome P450, cytochrome b5, and activities of aniline hydroxylase, aminopyrine demethylase, bilirubin-conjugating enzymes and supernatant glutathione S-transferase were measured. Rifampicin induced bilirubin UDP-glucuronyltransferase, bilirubin UDP-glucosyltransferase, bilirubin UDP-xylosyltransferase and glutathione S-transferase activities, but did not induce mixed function oxidase activities. No inductive effect of desacetylrifampicin on any enzymes was observed. Serum bilirubin increased till the third day, and decreased after 7 days of rifampicin treatment. Plasma clearances of indocyanine green and sulfobromophthalein showed a marked delay after 1 day and 7 days of rifampicin treatment. Induction of bilirubin-conjugating enzymes and glutathione S-transferase by rifampicin in rats was different from that in humans, in which selective induction of mixed function oxidase is reported to occur. This species difference does not seem to be derived from the species difference of rifampicin metabolism, because no effect of desacetylrifampicin was observed. These results suggested that in rats rifampicin directly inhibits the hepatic excretion of bilirubin, whereas it enhances bilirubin conjugation due to enzyme induction.

Topics: Animals; Bilirubin; Enzyme Induction; Glucosyltransferases; Glucuronosyltransferase; Glutathione Transferase; Liver; Male; Microsomes, Liver; Mixed Function Oxygenases; Pentosyltransferases; Rats; Rats, Inbred Strains; Rifampin

The absorption and metabolism of streptomycin, isoniazid, rifampicin, and pyrazinamide were evaluated after administration of each drug alone and in combination. In the combination sessions, isoniazid, rifampicin, and pyrazinamide were administered orally, either individually or in a single fixed-ratio triple preparation. The results have shown that the pattern of absorption and metabolism (acetyl-isoniazid, desacetyl-rifampicin, and pyrazinoic acid) found after administration of each drug alone did not differ from that found after administration of the drugs in free and fixed combination. The 3 orally administered drugs given in a fixed combination resulted in a reduction of the order of 50% of the total number of tablets to be ingested.

Topics: Absorption; Antitubercular Agents; Humans; Isoniazid; Kinetics; Male; Pyrazinamide; Rifampin; Streptomycin

Topics: Enzyme Induction; Humans; Rifampin

Four rates of rifampicin infusion ranging from 3.3 to 15 mg/min in 12 tuberculous patients were studied. Blood samples (n = 10) were drawn during infusion and 8 h later. Urine samples were collected in six fractions during a 24-h period. Rifampicin and desacetylrifampicin were measured by high-pressure liquid chromatography. Results show that the maximum plasma concentrations increase linearly for each dose with the rate of infusion, and that the amounts excreted in the urines are highly dependent on the administered dose. Simulation of plasma concentrations after different dosage regimens shows that a double rate of infusion--20 mg min-1 during 1 h and then 200 mg h-1--allows plasma concentrations to be quickly reached and maintained at a 20 mg L-1 level, far higher than the minimum inhibitory concentrations of most germs.

Topics: Adult; Aged; Female; Half-Life; Humans; Infusions, Parenteral; Kinetics; Male; Middle Aged; Rifampin; Tuberculosis, Pulmonary

The pharmacokinetics of rifampicin (RMP) and its principal active metabolite desacetylrifampicin (DA-RMP) were studied in six subjects, ranging in age from 78 to 95 years, after single oral doses of 10 mg/kg RMP. The maximal plasma concentrations (Cmax) and the elimination half-lives (t 1/2 beta) of RMP are 8.83 +/- 1.72 mg L-1 and 4.09 +/- 2.59 h, respectively. They are comparable to those reported in young adults. The same applies to the Cmax value (1.93 +/- 0.53 mg L-1) and t 1/2 beta value (4.65 +/- 2.61 h) of DA-RMP. However, the renal clearance of RMP (0.0075 +/- 0.0036 L h-1) and the amounts of RMP (20.7 +/- 9.9 mg) and DA-RMP (13.3 +/- 5.6 mg) excreted in the urine during a 24-h period are lower than those reported in young adults. The renal excretion of RMP and DA-RMP, therefore, is reduced in the elderly. But since the drug is also excreted through the liver to such an extent that serum levels are the same as in young adults, for therapeutic purposes the metabolism of RMP may be globally considered as unaltered in elderly patients.

Topics: Aged; Female; Half-Life; Humans; Kinetics; Male; Rifampin

A method for the determination of rifampicin, desacetylrifampicin, isoniazid, and acetylisoniazid by high-performance liquid chromatography and using the same extract of the same sample is reported. After protein precipitation and extraction of these antituberculous drugs, two reversed-phase chromatographies were necessary. The technique was applied to serum extracts, polymorphonucleocytes and alveolar macrophages from patients treated for tuberculosis.

Topics: Chromatography, High Pressure Liquid; Humans; Isoniazid; Macrophages; Neutrophils; Rifampin; Tuberculosis, Pulmonary

Topics: Chromatography, High Pressure Liquid; Humans; Rifampin