rifampin and cholest-5-ene-3-4-diol

We conducted a clinical trial with 22 healthy volunteers to investigate the effects of pregnane X receptor (PXR) agonist rifampin on blood pressure (BP). The study was randomized, crossover, single-blind, and placebo-controlled. Rifampin 600 mg or placebo once daily was administered for a week and the 24-hour ambulatory BP was monitored at the end of each arm on the eighth day. Rifampin elevated the mean systolic and diastolic 24-hour BP (4.7 mmHg, P < 0.0001, and 3.0 mmHg, P < 0.001, respectively) as well as the mean heart rate (3.5 bpm, P = 0.038). The serum renin concentration and the plasma renin activity were increased. Although rifampin increased circulating 4β-hydroxycholesterol (4βHC) as expected, the plasma 4βHC concentration strongly negatively correlated with 24-hour BP, especially systolic, in both rifampin and placebo arms (rifampin systolic BP, r = -0.69, P < 0.001; placebo systolic BP, r = -0.70, P < 0.001). The 4βHC, an agonist for liver X receptor (LXR), induced renin expression modestly in LXR-α expressing Calu-6 cells but only at unphysiologically high 4βHC concentrations. In conclusion, rifampin stimulates renin activity and has a hypertensive effect. This finding should be considered when designing interaction studies involving rifampin or other PXR agonists. Furthermore, PXR may represent a putative therapeutic target for the treatment of hypertension.

Topics: Adult; Biomarkers; Blood Pressure; Cell Line, Tumor; Cross-Over Studies; Female; Finland; Healthy Volunteers; Heart Rate; Humans; Hydroxycholesterols; Liver X Receptors; Male; Pregnane X Receptor; Renin; Renin-Angiotensin System; Rifampin; Single-Blind Method; Time Factors; Young Adult

The objectives of this analysis were to establish the exposure-response relationship between plasma rifampicin and 4β-hydroxycholesterol (4βHC) concentration and to estimate the effect of weak, moderate, and potent CYP3A induction. Plasma rifampicin and 4βHC concentration-time data from a drug-drug interaction study with rifampicin 600 mg were used for model development. An indirect response model with an effect compartment described the relationship between rifampicin and 4βHC concentrations. The model predicted that the equilibration t

Topics: Adult; Cytochrome P-450 CYP3A Inducers; Drug Interactions; Female; Healthy Volunteers; Humans; Hydroxycholesterols; Male; Middle Aged; Models, Theoretical; Rifampin; Young Adult

This study aimed to assess changes in the plasma concentrationss of 4β-hydroxycholesterol (4βHC) against intravenous (i.v.) and oral midazolam (MDZ) pharmacokinetics (PK) after administration of a potent CYP3A inhibitor [ketoconazole (KETO)] and inducer [rifampicin (RIF)].. Thirty-two healthy subjects (HS) were allocated into three groups of 12 each in KETO and RIF and 10 in a placebo group (PLB). All HS were randomized to receive oral and i.v. MDZ on day 1 or 2 and on day 15 or 16 after receiving RIF (600 mg once daily), KETO (400 mg once daily) or PLB for 2 weeks. Subjects were followed until day 30. The effect of treatments on 4βHC was assessed by analyzing % change from baseline using a linear spline mixed effects model.. Compared with PLB, KETO decreased 4βHC mean values up to 13% (P = 0.003) and RIF increased 4βHC mean values up to 220% (P < 0.001). Within 14 days of stopping KETO and RIF, 4βHC had either returned to baseline (KETO) or was still returning to baseline (RIF). Compared with baseline, mean oral MDZ AUC increased by 11-fold (90% CI ranging from 9-fold to 13-fold increase) and decreased by 92% (90% CI ranging from 90% to 95% decrease) after KETO and RIF, respectively. Similar trends were observed for 6β-hydroxycortisol : cortisol (6βHCL : CL) urinary ratios.. Changes in plasma 4βHC can be utilized as a surrogate for MDZ PK after multiple doses of potent CYP3A inducers. There is a more limited dynamic range for 4βHC for assessment of potential CYP3A inhibitors. 4βHC is a valuable tool for the assessment of potential CYP3A inducers in early drug development.

Topics: Adolescent; Adult; Biomarkers; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inducers; Cytochrome P-450 CYP3A Inhibitors; Dose-Response Relationship, Drug; Healthy Volunteers; Humans; Hydroxycholesterols; Injections, Intravenous; Ketoconazole; Limit of Detection; Midazolam; Middle Aged; Rifampin; Saliva; Substrate Specificity; Time Factors; Tissue Distribution; Young Adult

Midostaurin, a multitargeted tyrosine kinase inhibitor, is primarily metabolized by CYP3A4. This midostaurin drug-drug interaction study assessed the dynamic response and clinical usefulness of urinary 6β-hydroxycortisol to cortisol ratio (6βCR) and plasma 4β-hydroxycholesterol (4βHC) for monitoring CYP3A4 activity in the presence or absence of rifampicin, a strong CYP3A4 inducer.. Forty healthy adults were randomized into groups for either placebo or treatment with rifampicin 600 mg QD for 14 days. All participants received midostaurin 50 mg on day 9. Midostaurin plasma pharmacokinetic parameters were assessed. Urinary 6βCR and plasma 4βHC levels were measured on days 1, 9, 11, and 15.. Both markers remained stable over time in the control group and increased significantly in the rifampicin group. In the rifampicin group, the median increases (vs day 1) on days 9, 11, and 15 were 4.1-, 5.2-, and 4.7-fold, respectively, for 6βCR and 3.4-, 4.1-, and 4.7-fold, respectively, for 4βHC. Inter- and intrasubject variabilities in the control group were 45.6 % and 30.5 %, respectively, for 6βCR, and 33.8 % and 7.5 %, respectively, for 4βHC. Baseline midostaurin area under the concentration-time curve (AUC) correlated with 4βHC levels (ρ = -0.72; P = .003), but not with 6βCR (ρ = 0.0925; P = .6981).. Both 6βCR and 4βHC levels showed a good dynamic response range upon strong CYP3A4 induction with rifampicin. Because of lower inter- and intrasubject variability, 4βHC appeared more reliable and better predictive of CYP3A4 activity compared with 6βCR. The data from our study further support the clinical utility of these biomarkers.

Topics: Adult; Biomarkers; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inducers; Drug Interactions; Female; Humans; Hydrocortisone; Hydroxycholesterols; Male; Middle Aged; Protein Kinase Inhibitors; Rifampin; Staurosporine; Young Adult

CYP3A4, considered the most important enzyme in drug metabolism, is often involved in drug-drug interactions. When developing new drugs, appropriate markers for detecting CYP3A4 induction are needed. Our study compared endogenously formed 4β-hydroxycholesterol with the midazolam clearance in plasma and the 6β-hydroxycortisol/cortisol ratio in urine as markers for CYP3A4 induction. To this end, we performed a clinical trial in which 24 healthy subjects were randomized to 10, 20, or 100 mg daily doses of rifampicin for 14 days (n = 8 in each group) to achieve a low and moderate CYP3A4 induction. The CYP3A4 induction could be detected even at the lowest dose of rifampicin (10 mg) via the estimated midazolam clearance, the 4β-hydroxycholesterol ratio (both P < 0.01), and the 6β-hydroxycortisol ratio (P < 0.05). For the three dosing groups (10, 20, and 100 mg), the median fold induction from baseline was 2.0, 2.6, and 4.0 for the estimated midazolam clearance; 1.3, 1.6, and 2.5 for the 4β-hydroxycholesterol/cholesterol ratio; and 1.7, 2.9, and 3.1 for the 6β-hydroxycortisol/cortisol ratio. In conclusion, the 4β-hydroxycholesterol ratio is comparable to midazolam clearance as a marker of CYP3A4 induction, and each may be used to evaluate CYP3A4 induction in clinical trials evaluating drug-drug interactions for new drugs.

Topics: Adult; Biomarkers; Cholesterol; Cytochrome P-450 CYP3A; Drug Interactions; Enzyme Induction; Female; Humans; Hydrocortisone; Hydroxycholesterols; Male; Metabolic Clearance Rate; Midazolam; Rifampin

This study aimed to evaluate endogenous metabolic markers of hepatic cytochrome P450 (CYP)3A activity in healthy subjects using a metabolomics approach. Twenty-four subjects received the following medication during the following three study periods: 1 mg of i.v. midazolam alone (control phase), 1 mg of i.v. midazolam after 4 days of pretreatment with 400 mg of ketoconazole once daily (CYP3A-inhibited phase), and 2.5 mg of i.v. midazolam after 10 days of pretreatment with 600 mg of rifampicin once daily (CYP3A-induced phase). During each study period, 24 h before and after the administration of midazolam, urine samples were collected at 12-h intervals for metabolomic analyses. We derived an equation to predict midazolam clearance (CL) based on several of these markers. We demonstrated that a combination of the concentrations and ratios of several endogenous metabolites and the CYP3A5*3 genotype is a reliable predictive marker of hepatic CYP3A activity as assessed by i.v. administration of midazolam.

Topics: Adult; Biomarkers; Cortisone; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Enzyme Induction; Gas Chromatography-Mass Spectrometry; Humans; Hydrocortisone; Hydroxycholesterols; Ketoconazole; Liver; Male; Metabolomics; Midazolam; Pharmacogenetics; Rifampin; Young Adult

The Karolinska cocktail, comprising caffeine, losartan, omeprazole, and quinine, was given before and after administration of rifampicin (20, 100, or 500 mg daily) to measure induction of cytochrome P450 (P450) enzymes. Rifampicin was given for 14 days to eight healthy subjects (all of whom possessed at least one wild-type CYP2C9 and one wild-type CYP2C19 gene) in each dose group. 4beta-hydroxycholesterol was assessed as an endogenous marker of CYP3A4 induction. A fourfold induction of CYP3A4 was seen at the highest dose by both quinine:3'-hydroxyquinine and 4beta-hydroxycholesterol measurements (P < 0.001). CYP3A4 was also induced at the two lower doses of rifampicin when measured by these two markers (P < 0.01 or P < 0.001). CYP1A2, CYP2C9, and CYP2C19 were induced after 500 mg rifampicin daily (1.2-fold, P < 0.05; 1.4-fold, P < 0.05; and 4.2-fold, P < 0.01, respectively). In conclusion, we have shown that the Karolinska cocktail and 4beta-hydroxycholesterol can be used for an initial screening of the induction properties of a drug candidate.

Topics: Adult; Anti-Ulcer Agents; Antibiotics, Antitubercular; Antihypertensive Agents; Antimalarials; Caffeine; Central Nervous System Stimulants; Cytochrome P-450 Enzyme System; Drug Combinations; Enzyme Induction; Female; Humans; Hydroxycholesterols; Losartan; Male; Middle Aged; Omeprazole; Quinine; Rifampin

Preparations of plasma-derived small extracellular vesicles (sEVs) were deployed as liquid biopsy to study cytochrome P450 (CYP) 3A4 (CYP3A4) induction following modafinil 400 mg once daily × 14 days (young healthy volunteers, N = 10 subjects). Induction was confirmed using the 4β-hydroxycholesterol-to-cholesterol (4βHC/C) ratio, a plasma CYP3A4/5 biomarker, with a mean 2.1-fold increase (Day 15 vs. Day 1; 90% confidence interval (CI) = 1.8-2.3; P value = 0.0004). Proteomic analysis revealed the induction (mean Day 15 vs. Day 1 fold-increase (90% CI)) of both liver (1.3 (1.1-1.5), P value = 0.014) and nonliver (1.9 (1.6-2.2), P value = 0.04) sEV CYP3A4 protein expression. In CYP3A5 nonexpresser subjects, the baseline (pre-dose) 4βHC/C plasma ratio was more highly correlated with liver sEVs (r = 0.937, P value = 0.001) than nonliver sEVs (r = 0.619, P value = 0.101) CYP3A4 protein expression. When CYP3A5 expressers (CYP3A5*1/*3) were included, the correlation with liver sEVs (r = 0.761, P value = 0.011) and nonliver sEVs (r = 0.391, P value = 0.264) CYP3A4 protein was weaker. Although modafinil-induced changes in plasma 4βHC/C ratio did not correlate with sEVs CYP3A4 protein expression, the individual subject sEVs proteomic data were used successfully to predict victim drug (midazolam, triazolam, dextromethorphan, 17α-ethinylestradiol, and abemaciclib) area under the plasma concentration-time curve (AUC) ratios (AUCRs) following modafinil. Based on the AUCR values, modafinil was classified as a weak to moderate CYP3A4 inducer (vs. rifampicin). For the first time, it was possible to deploy plasma-derived sEVs to study CYP3A4 induction beyond rifampicin, a more potent CYP3A4 inducer.

Topics: Biomarkers; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inducers; Drug Administration Schedule; Drug Interactions; Enzyme Induction; Extracellular Vesicles; Healthy Volunteers; Humans; Hydroxycholesterols; Liquid Biopsy; Liver; Modafinil; Models, Biological; Plasma; Proteomics; Rifampin; Time Factors

Organic anion-transporting polypeptide (OATP) 1B induction is an evolving mechanism of drug disposition and interaction. However, there are contradictory reports describing OATP1B expression in hepatocytes and liver biopsies after administration of an inducer. This study investigated the in vivo effects of the common inducer rifampin (RIF) on the activity and expression of cynomolgus monkey OATP1B1 and OATP1B3 transporters, which are structurally and functionally similar their human OATP1B counterparts. Multiple doses of oral RIF (15 mg/kg) resulted in a steady 3.9-fold increase of CYP3A biomarker, 4

Topics: Animals; Biomarkers; Coproporphyrins; Female; Gene Expression; Hydroxycholesterols; Intestine, Small; Kidney; Liver; Macaca fascicularis; Male; Rifampin; Solute Carrier Organic Anion Transporter Family Member 1B3

CYP3A probe drugs such as midazolam and endogenous markers, and plasma 4β-hydroxycholesterol (4β-OHC) and urinary 6β-hydroxycortisol-to-cortisol ratios (6β-OHC/C) have been used as markers of CYP3A induction in cynomolgus monkeys, as with humans. However, there is limited information on their sensitivity and ability to detect CYP3A induction, as most studies were evaluated only at a high dose of the inducer, rifampicin (RIF; 20 mg/kg). In the present study, the CYP3A induction by RIF over a range doses of 0.2, 2 and 20 mg/kg (n = 4) was examined using CYP3A probe drugs (midazolam, triazolam and alprazolam) and the plasma and urinary endogenous CYP3A markers (4β-OHC and 6β-OHC/C). The sensitivity and relationship for detecting CYP3A induction was compared among the markers. Four days repeated oral administration of rifampicin to cynomolgus monkeys reduced the area under the plasma concentration-time curve of all CYP3A probe drugs in a rifampicin dose-dependent manner. Although the endogenous CYP3A markers (4β-OHC and 6β-OHC/C) were also changed for the middle (2 mg/kg) and high (20 mg/kg) doses of rifampicin, the fold-changes were relatively small, and CYP3A induction could not be detected at the lowest dose of rifampicin (0.2 mg/kg). In conclusion, CYP3A probe drugs are more sensitive for detecting CYP3A induction than endogenous CYP3A markers in cynomolgus monkeys, even for a short experimental period.

Topics: Alprazolam; Animals; Area Under Curve; Biomarkers; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inducers; Dose-Response Relationship, Drug; Drug Interactions; Hydrocortisone; Hydroxycholesterols; Macaca fascicularis; Male; Midazolam; Rifampin; Triazolam

Midostaurin (PKC412) is being investigated for the treatment of acute myeloid leukemia (AML) and advanced systemic mastocytosis (advSM). It is extensively metabolized by CYP3A4 to form two major active metabolites, CGP52421 and CGP62221. In vitro and clinical drug-drug interaction (DDI) studies indicated that midostaurin and its metabolites are substrates, reversible and time-dependent inhibitors, and inducers of CYP3A4. A simultaneous pharmacokinetic model of parent and active metabolites was initially developed by incorporating data from in vitro, preclinical, and clinical pharmacokinetic studies in healthy volunteers and in patients with AML or advSM. The model reasonably predicted changes in midostaurin exposure after single-dose administration with ketoconazole (a 5.8-fold predicted versus 6.1-fold observed increase) and rifampicin (90% predicted versus 94% observed reduction) as well as changes in midazolam exposure (1.0 predicted versus 1.2 observed ratio) after daily dosing of midostaurin for 4 days. The qualified model was then applied to predict the DDI effect with other CYP3A4 inhibitors or inducers and the DDI potential with midazolam under steady-state conditions. The simulated midazolam area under the curve ratio of 0.54 and an accompanying observed 1.9-fold increase in the CYP3A4 activity of biomarker 4

Topics: Adult; Biomarkers; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inducers; Cytochrome P-450 CYP3A Inhibitors; Drug Interactions; Female; Humans; Hydroxycholesterols; Ketoconazole; Male; Midazolam; Middle Aged; Models, Biological; Rifampin; Staurosporine; Young Adult

The exposure of G2917 decreased by four-fold at oral doses of 100 mg/kg twice daily for seven days in cynomolgus monkeys. Additional investigative work was conducted to understand: (1) the causes for the significant reduction in G2917 exposure in monkeys; (2) the extrapolation of in vitro induction data to in vivo findings in monkeys, and (3) the relevance of this pre-clinical finding to humans at the projected human efficacious dose.. Pharmacokinetic and induction potency (in vitro and in vivo) of G2917 in monkeys, and the in vitro human induction potency were studied. The hepatic CYP3A biomarkers 4β-hydroxycholesterol (4β-HC) and 6β-hydroxycortisol/cortisol ratio (6β-OHC/C) were monitored in in vivo studies. The static mechanistic model was used to quantitatively understand the in vitro-in vivo extrapolation (IVIVE) on the magnitude of induction retrospectively. Physiologically based pharmacokinetic (PBPK) modeling was used to predict the human pharmacokinetics and induction-based drug-drug interactions (DDI).. All in vitro and in vivo data indicate that the significant reduction in exposure of G2917 in monkeys is caused by auto-induction of CYP3A. The mechanistic understanding of IVIVE of G2917 induction in monkey provides higher confidence in the induction risk prediction in human using the PBPK modeling. PBPK model analysis predicted minimum auto-induction and DDI liability in humans at the predicted efficacious dose.. The learning of this example provided a strategy to address the human CYP3A induction risk prospectively when there is an auto-induction finding in preclinical toxicology study.

Topics: Administration, Oral; Animals; Computer Simulation; Cytochrome P-450 CYP3A; Drug Discovery; Drug Interactions; Enzyme Induction; Humans; Hydrocortisone; Hydroxycholesterols; Liver; Macaca fascicularis; Midazolam; Models, Biological; Pharmacokinetics; Rifampin; RNA, Messenger

Cytochrome P450 3A (CYP) enzymes are involved in the elimination of many drugs and are known to be regulated by several environmental factors. Thus, it was the aim of this study to develop and validate an analytical method allowing estimation of the hepatic CYP3A enzyme activity using the 4-hydroxycholesterol to cholesterol ratio as an endogenous biomarker in serum. Both compounds were isolated from the biological matrix by liquid-liquid extraction using n-hexane after saponification with ethanolic sodium methoxide solution (2M) to cleave the steroids from their esterified forms without any kind of further derivatization. Chromatographic separation was achieved on a reversed-phase column (SupelcoAcsentis(®), C8) within 7min using an isocratic elution with ammonium acetate 5mM (pH=3.8, 10%) and acetonitrile (90%) at a flow rate of 300μl/min. d6-cholesterol and d7-4β-hydroxycholesterol were used as internal standards. Detection was done on a triple quadrupole mass spectrometer using the following mass transitions: 369.3/161.5, 369.3/147.1 and 369.3/95.2 for cholesterol; 385.2/367.4, 385.2/109.1 for 4-hydroxycholesterol; 374.4/152.7 and 392.2/108.9 for d6-cholesterol and d7-4-hydroxycholesterol, respectively as the internal standards. The method was validated according to current bioanalytical guidelines considering selectivity, linearity, accuracy, precision, recovery, stability. The analytical range was 5-250 and 50-1000ng/ml, for 4-hydroxycholesterol and cholesterol, respectively. The method was shown to be selective for both compounds with good linearity over the selected range (r>0.99) as well as good within- and between day accuracy (error: -1.2-3.7% for 4-hydroxycholesterol and -7.7-9.5% for cholesterol) and within- and between day precision (2.1-14.6% for 4-hydroxycholesterol and 1.1-14.9% for cholesterol). Recovery was found to be over 80% for both analytes while significant stability issues could not be observed. Finally, the validated assay was applied to measure 4-hydroxycholesterol and cholesterol in serum samples of clinical studies in humans and foals that could verify induction of hepatic CYP3A4 (human) and CYP3A89 (foals) after premedication with the known enzyme inducer rifampicin.

Topics: Adult; Animals; Biomarkers; Cholesterol; Chromatography, Liquid; Cytochrome P-450 CYP3A; Horses; Humans; Hydroxycholesterols; Male; Reference Standards; Reproducibility of Results; Rifampin; Tandem Mass Spectrometry; Young Adult

It has been proposed that in humans 4β-hydroxycholesterol is formed mainly by CYP3A-catalyzed metabolism of cholesterol and thus may serve as an endogenous marker for CYP3A activity. The cynomolgus monkey is widely used as one of the nonrodent preclinical safety species in pharmaceutical research. In the current study, the potential application of 4β-hydroxycholesterol as an endogenous biomarker of CYP3A in response to drug treatment was evaluated in cynomolgus monkeys. Following multiple oral administration of rifampicin (a known CYP3A inducer) at 15 mg/kg/d in cynomolgus monkeys, the mean serum 4β-hydroxycholesterol levels increased 4-fold from the baseline of 55.3 ± 21.7 to 221 ± 53.4 ng/ml. The mean concentration ratios of 4β-hydroxycholesterol to cholesterol increased 5-fold. The data suggest that 4β-hydroxycholesterol formation from cholesterol metabolism was induced by rifampicin treatment in monkeys. This observation correlated with the metabolism of midazolam (a probe substrate of CYP3A activity) monitored in the same study. The serum exposure (area under the curve) of midazolam was markedly decreased by ∼95%, confirming the induction of CYP3A catalytic activity by rifampicin treatment in monkeys. The formation of 4β-hydroxycholesterol from cholesterol was specifically mediated by recombinant cynomolgus CYP3A8 and CYP3A5. The Km values of CYP3A8 and CYP3A5 for 4β-hydroxycholesterol formation from cholesterol were 204 and 104 μM, respectively, and Vmax values were 0.600 and 0.310 pg/pmol/min, respectively. The results suggest that 4β-hydroxycholesterol can be used as an endogenous biomarker to identify strong CYP3A inducers in cynomolgus monkeys, which may help to evaluate drug-drug interaction potential of drug candidates in preclinical settings.

Topics: Administration, Oral; Animals; Biomarkers; Biotransformation; Cholesterol; Chromatography, High Pressure Liquid; Cytochrome P-450 CYP3A; Drug Evaluation, Preclinical; Enzyme Induction; Female; Hydroxycholesterols; Macaca fascicularis; Male; Midazolam; Rifampin; Substrate Specificity; Tandem Mass Spectrometry

To assess the effect of the major efavirenz metabolizing enzyme (CYP2B6) genotype and the effects of rifampicin co-treatment on induction of CYP3A by efavirenz.. Two study arms (arm 1, n = 41 and arm 2, n = 21) were recruited into this study. In arm 1, cholesterol and 4β-hydroxycholesterol were measured in HIV treatment-naive patients at baseline and then at 4 and 16 weeks after initiation of efavirenz-based antiretroviral therapy. In arm 2, cholesterol and 4β-hydroxycholesterol were measured among patients taking efavirenz during rifampicin-based tuberculosis (TB) treatment (efavirenz/rifampicin) just before completion of TB treatment and then serially following completion of TB treatment (efavirenz alone). Non-linear mixed-effect modelling was performed.. A one-compartment, enzyme turnover model described 4β-hydroxycholesterol kinetics adequately. Efavirenz treatment in arm 1 resulted in 1.74 (relative standard error = 15%), 3.3 (relative standard error = 33.1%) and 4.0 (relative standard error = 37.1%) average fold induction of CYP3A for extensive (CYP2B6*1/*1), intermediate (CYP2B6*1/*6) and slow (CYP2B6*6/*6) efavirenz metabolizers, respectively. The rate constant of 4β-hydroxycholesterol formation [mean (95% CI)] just before completion of TB treatment [efavirenz/rifampicin co-treatment, 7.40 × 10(-7) h(-1) (5.5 × 10(-7)-1.0 × 10(-6))] was significantly higher than that calculated 8 weeks after completion [efavirenz alone, 4.50 × 10(-7) h(-1) (4.40 × 10(-7)-4.52 × 10(-7))]. The CYP3A induction dropped to 62% of its maximum by week 8 of completion.. Our results indicate that efavirenz induction of CYP3A is influenced by CYP2B6 genetic polymorphisms and that efavirenz/rifampicin co-treatment results in higher induction than efavirenz alone.

Topics: Adult; Alkynes; Anti-HIV Agents; Antitubercular Agents; Benzoxazines; Cyclopropanes; Cytochrome P-450 CYP2B6; Cytochrome P-450 CYP3A; Female; Genotype; HIV Infections; Humans; Hydroxycholesterols; Male; Middle Aged; Rifampin; Tuberculosis

To compare plasma 4β-hydroxycholesterol : cholesterol with urinary 6β-hydroxycortisol : cortisol as markers of cytochrome P4503A4 activity before and after treatment with rifampicin for 2 weeks.. 6β-hydroxycortisol and cortisol were determined by liquid chromatography tandem mass spectrometry and 4β-hydroxycholesterol was determined by gas chromatography-mass spectrometry in three groups of healthy volunteers.. Induction ratios for 6β-hydroxycortisol : cortisol were 1.8, 3.9 and 4.5 for 20 mg day(-1) , 100 mg day(-1) or 500 mg day(-1) of rifampicin, respectively. The corresponding ratios for 4β-hydroxycholesterol : cholesterol were 1.5, 2.4 and 3.8.. Plasma 4β-hydroxycholesterol : cholesterol gave similar induction ratios to urinary 6β-hydroxycortisol : cortisol.

Topics: Antibiotics, Antitubercular; Biomarkers; Cholesterol; Chromatography, Liquid; Cytochrome P-450 CYP3A; Female; Gas Chromatography-Mass Spectrometry; Humans; Hydrocortisone; Hydroxycholesterols; Male; Rifampin

The delivery of clarithromycin (CRL) to its site of action in bronchial/alveolar epithelial cells (EC), bronchial epithelial lining fluid (ELF), and bronchoalveolar lavage cells (BALC) may be influenced by CYP3A4 and the drug transporters, ATP-binding cassette (ABC) B1 and ABCC2 and organic anion-transporting polypeptides (OATPs), which can be modulated and/or up-regulated via the nuclear pregnane X receptor (PXR) by rifampicin (RIF). Therefore, we evaluated the disposition and pulmonary distribution of CLR (7.5 mg/kg b.i.d., 21 days) and expression of ABCB1, ABCC2, OATP1A2, and OATP2B1 in EC and BALC before and after comedication of RIF (10 mg/kg b.i.d., 11 days) in nine healthy foals (41-61 days, 115-159 kg) in which the genetic homology of drug transporters is close to that of their human analogs. After RIF comedication, relative bioavailability of CLR decreased by more than 90%. Concentrations in plasma (29.8 ± 26.3 versus 462 ± 368 ng/ml), ELF (0.69 ± 0.66 versus 9.49 ± 6.12 μg/ml), and BALC (10.2 ± 10.2 μg/ml 264 ± 375 μg/ml; all P < 0.05) were lowered drastically, whereas levels of the metabolite 14-hydroxyclarithromycin were not elevated despite higher 4β-hydroxycholesterol/cholesterol plasma concentration ratio, a surrogate for CYP3A4 induction. In the presence of CLR, ABCC2 and PXR mRNA contents were significantly and coordinately (r(2) = 0.664, P < 0.001) reduced in BALC after RIF. In EC, mRNA expression of OATP1A2 increased but that of OATP2B1 decreased (both P < 0.05). RIF interrupts oral absorption and decreases CRL plasma levels below the minimal inhibitory concentration for eradication of Rhodococcus equi. Evidence that RIF influences the cellular uptake of CLR in bronchial cells and the PXR expression in BALC in the presence of high CLR concentrations exists.

Topics: Absorption; Animals; ATP-Binding Cassette Transporters; Bronchi; Cholesterol; Clarithromycin; Drug Interactions; Epithelial Cells; Horses; Hydroxycholesterols; Lung; Mouth Mucosa; Multidrug Resistance-Associated Protein 2; Organic Anion Transporters; Pregnane X Receptor; Receptors, Steroid; Rifampin; RNA, Messenger

Plasma 4β-hydroxycholesterol (4βHC) has been proposed as an endogenous marker of cytochrome P450 3A (CYP3A). To assess its utility as a CYP3A metric, a pharmacokinetic model, assuming no alteration in cholesterol plasma concentrations, was developed to simulate the effect of CYP3A induction and inhibition on 4βHC plasma levels under different treatment durations. By incorporating the long plasma half-life of 4βHC (~17 days) into the model, the inductive effect of 2 known inducers (carbamazepine and rifampicin) reported in the literature was adequately described. Furthermore, the simulations showed that it was possible to resolve none, weak, moderate, and potent inducers within 2 weeks of dosing. On the other hand, simulations indicated that at least 2 weeks of dosing would be needed to detect the potent inhibition of CYP3A (maximal ~40% decrease in 4βHC plasma levels). Greater differentiation of weak, moderate, and potent CYP3A inhibitors would require a longer duration of dosing (≥1 month). When considering 4βHC as a metric, one should take into account assay precision, the anticipated magnitude of the effect, and the feasibility of dosing beyond 2 weeks. In addition, the 4βHC metric needs to be normalized with the corresponding cholesterol plasma level in the same subject.

Topics: Biomarkers; Carbamazepine; Computer Simulation; Cytochrome P-450 CYP3A; Enzyme Induction; Enzyme Inhibitors; Half-Life; Humans; Hydroxycholesterols; Models, Biological; Rifampin; Time Factors

The oxysterol 4beta-hydroxycholesterol has been suggested as a marker for CYP3A4/5 activity. We have previously shown that plasma 4beta-hydroxycholesterol continues to increase for several weeks after maximal induction of CYP3A4/5 by carbamazepine at the dose given. In the present study we aimed to determine the time course of the decrease in plasma 4beta-hydroxycholesterol after termination of induction of CYP3A4/5 by rifampicin. An additional aim was to determine the variation in plasma level of 4beta-hydroxycholesterol with time in 12 untreated healthy volunteers.. Twenty-four healthy subjects were allocated into three study groups of equal sizes. The volunteers were treated with rifampicin (either 20 mg day(-1), 100 mg day(-1) or 500 mg day(-1)) for 2 weeks. Blood samples were taken before, during and after rifampicin treatment. In another group of 12 untreated volunteers blood samples were collected at different time points in order to determine the intraindividual variations in plasma 4beta-hydroxycholesterol concentrations. Plasma levels of 4beta-hydroxycholesterol were determined by isotope-dilution gas chromatography-mass spectrometry.. Rifampicin treatment increased plasma 4beta-hydroxycholesterol levels. After termination of rifampicin treatment plasma levels of 4beta-hydroxycholesterol decreased slowly with an apparent half-life of 17 days. The intraindividual variation in plasma levels of 4beta-hydroxycholesterol in untreated subjects was low, with coefficients of variation of between 4.8 and 13.2% over a period of 3 months.. After termination of induction of CYP3A4/5, plasma 4beta-hydroxycholesterol levels decreased slowly during 8 weeks. The half-life of elimination (17 days) resembled that of cholesterol rather than other oxysterols. The long half-life results in stable plasma concentrations with time.

Topics: Biomarkers; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Enzyme Inhibitors; Gas Chromatography-Mass Spectrometry; Half-Life; Humans; Hydroxycholesterols; Rifampin

Rifampicin (rifampin) is a potent inducer of cytochrome P450 (CYP) 3A4. It was recently identified as a substrate of the polymorphic organic anion transporting polypeptide 1B1 (OATP1B1) expressed on the sinusoidal membrane of human hepatocytes. The present study aimed to investigate the possible association of single nucleotide polymorphisms (SNP) in the SLCO1B1 gene encoding for OATP1B1 with the inducing effect of rifampicin on hepatic CYP3A4. A total of 38 healthy volunteers who had participated in drug interaction studies with rifampicin were genotyped for the g. - 11187G > A and c.521T > C SNPs in SLCO1B1, c.3435C > T SNP in ABCB1 and g.6986A > G SNP in CYP3A5. The plasma concentration of 4beta-hydroxycholesterol, an endogenous marker of CYP3A4 activity, was measured before and after administration of 600 mg rifampicin once daily for 9-11 days. Treatment with rifampicin significantly increased the mean +/- SD plasma concentration of 4beta-hydroxycholesterol from 55.2 +/- 17.9 ng/ml to 120.9 +/- 32.0 ng/ml (P < 0.001). A large intersubject variability existed in the induction of CYP3A4 by rifampicin, but no associations were observed between the variability in induction and any of the polymorphisms studied. These data suggest that SLCO1B1 polymorphism does not affect the extent of induction of hepatic CYP3A4 by rifampicin, probably because other uptake transporters, such as OATP1B3, can compensate for reduced uptake of rifampicin by OATP1B1. However, the present study had sufficient power to detect only a considerably smaller rifampicin-induced increase in 4beta-hydroxycholesterol in carriers of the SLCO1B1 c.521C allele compared to subjects with the reference genotype.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Enzyme Induction; Genotype; Humans; Hydroxycholesterols; Liver; Liver-Specific Organic Anion Transporter 1; Organic Anion Transporters; Polymorphism, Genetic; Rifampin