A single dose of methadone inhibits cytochrome P-4503A activity in healthy volunteers as assessed by the urinary cortisol ratio

Combined in vivo metabolic effects of quetiapine and methadone in brain and blood of rats

Changes in pharmacokinetics and endogenous metabolites may underlie additive biological effects of concomitant use of antipsychotics and opioids. In this study, we employed untargeted metabolomics analysis and targeted analysis to examine the changes in drug metabolites and endogenous metabolites in the prefrontal cortex (PFC), midbrain, and blood of rats following acute co-administration of quetiapine and methadone. Rats were divided into four groups and received cumulative increasing doses of quetiapine (QTP), methadone (MTD), quetiapine + methadone (QTP + MTD), or vehicle (control). All samples were analyzed using liquid chromatography-mass spectrometry (LC-MS). Our findings revealed increased levels of the quetiapine metabolites: Norquetiapine, O-dealkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide, in the blood and brain when methadone was present. Our study also demonstrated a decrease in methadone and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in the rat brain when quetiapine was present. Despite these findings, there were only small differences in the levels of 225-296 measured endogenous metabolites due to co-administration compared to single administrations. For example, N-methylglutamic acid, glutaric acid, p-hydroxyphenyllactic acid, and corticosterone levels were significantly decreased in the brain of rats treated with both compounds. Accumulation of serotonin in the midbrain was additionally observed in the MTD group, but not in the QTP + MTD group. In conclusion, this study in rats suggests a few but important additive metabolic effects when quetiapine and methadone are co-administered.

Validation of 4β-hydroxycholesterol and evaluation of other endogenous biomarkers for the assessment of CYP3A activity in healthy subjects

AIMS

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)].

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Interindividual and Intraindividual Variability of the Urinary 6β-Hydroxycortisol/Cortisol Ratio in Chinese Subjects: Implications of Its Use for Evaluating CYP3A Activity

The present study determined the interindividual and intrandividual variability of the urinary 6beta-hydroxycortisol/cortisol ratio, a useful marker for CYP3A induction and inhibition in Chinese subjects. The study consisted of 2 parts. In part I, 82 healthy male Chinese subjects underwent 3 study sessions, each separated by a 1-week interval. In part II, 20 subjects who initially completed part I underwent another 3 sessions over a period of 3 to 4 months. During each session, a first-morning urine specimen was collected from each subject for the quantification of urinary concentrations of cortisol and 6beta-hydroxycortisol. There were no significant differences in the mean 6beta-hydroxycortisol/cortisol ratios among the 3 sessions (P > .05, 1-way analysis of variance) for both part I and part II of the study. A normal distribution of the 6beta-hydroxycortisol/cortisol ratio was observed (P = .849, Kolmogorov-Smirnov test). This ratio varied 30-fold (range, 0.76-23.23) among the study subjects. The mean intraindividual variabilities during the short (3-week) and long (3- to 4-month) periods were 30.9% +/- 17.5% and 32.2% +/- 17.1%, respectively. The genetic fraction contributing to the observed variability in the 6beta-hydroxycortisol/cortisol ratio was estimated to be 0.91. The genetic component is likely to contribute significantly to the variability of the 6beta-hydroxycortisol/cortisol ratio, and such variability should be considered when the ratio is used to evaluate CYP3A induction or inhibition in a given ethnic population.

Study of urinary 6β-hydroxycortisol/cortisol ratio in spot urine sample as a biomarker of 3A4 enzyme activity in healthy and epileptic subjects of Egyptian population

The ratio of urinary 6 beta-hydroxycortisol/cortisol (6 beta-OHC/FC) in morning spot urine samples collected from 8:00 a.m. to 12:00 p.m. was studied using ELIZA kits (Stabiligen) in a group of healthy adult Egyptians (control group) of both sex (n=65, age range: 16-48 years). The frequency distribution of urinary 6 beta-OHC/FC ratio was widely distributed among subjects with higher values in males in comparison to females. No bimodality in either sex was observed. Another group of adult epileptic patients (n=16) was studied for the influence of chronic carbamazepine antiepileptic drug administration on urinary 6 beta-OHC/FC ratio in spot urine samples. The induction property of carbamazepine on CYP3A4 was observed through significant increase (p=0.01) in 6 beta-OHC/FC ratio among epileptic patients in comparison with control subjects. In conclusion, the frequency distribution of urinary 6 beta-OHC/FC ratio among Egyptians shows sexual dimorphism. Also, measurement of urinary 6 beta-OHC/FC ratio provides a simple non-invasive method to monitor CYP3A4 enzyme induction during administration of carbamazepine antiepileptic drug.

Population pharmacokinetics of (R)-, (S)- and rac-methadone in methadone maintenance patients

AIM

To construct a population pharmacokinetic model for methadone enantiomers in the setting of methadone maintenance treatment for opioid dependence.

METHODS

A population pharmacokinetic model was developed using P-Pharm software for rac-, (R)- and (S)-methadone using data (8-13 plasma samples per subject) obtained from 59 methadone maintenance patients during one interdosing interval at steady state. The patients were randomly assigned to either a development (n = 38) or a validation dataset (n = 21). The model was refined by inclusion of all subjects to construct a final basic model, which was used to construct a covariate model.

RESULTS

A population-based two-compartment open model with first-order absorption and lag time was developed and validated for all analytes. The population geometric mean (coefficient of variation) of maximum a posteriori probability Bayesian estimated values for clearance, terminal half-life and volume of distribution at steady-state of the active (R)-enantiomer were 8.7 (42%) l h(-1), 51 (45%) h and 597 (45%) l, respectively. For all analytes, the volume of the central compartment was decreased with increasing plasma alpha(1)-acid glycoprotein concentration and was lower in females, while the delay in absorption was longer at higher doses. No covariates were identified for apparent oral clearance. The apparent oral clearance of (R)-methadone (geometric mean ratio; 95% confidence interval) was 105% (99, 110), that of (S)-methadone (P = 0.19), while (R)-methadone V(c)/F (154%; 151, 157), V(dss) /F (173%; 164, 183), t(1/2beta) (162%; 153, 172) and mean residence time (166%; 156, 176) were significantly greater (P < 0.0001) than for (S)-methadone. The population pharmacokinetic models were able to predict accurately oral clearance values from limited (one or two samples) blood sampling protocols.

CONCLUSIONS

The substantial stereoselectivity in methadone disposition reinforces the potential for misinterpretation of racemic methadone disposition data. The marked interindividual variability in (R)-methadone clearance, with no covariates identified, highlights the need for alternative methods to determine an individual's metabolic clearance. The ability to predict (R)-methadone clearance from one to two blood samples at steady state may prove clinically useful if a drug-drug interaction or poor adherence are suspected and guide the prescriber in deciding if a client's request for a dose increase is warranted or whether an alternative opioid would be more appropriate.

Effects of growth hormone deficiency and rhGH replacement therapy on the 6beta-hydroxycortisol/free cortisol ratio, a marker of CYP3A activity, in growth hormone-deficient children

OBJECTIVE

To determine the effect of both growth hormone deficiency (GHD) and rhGH replacement therapy on CYP3A activity as well as the potential influence of gender.

METHODS

The sample consisted of 35 GHD children (16 males and 19 females), aged 2.9-13.1 years, and a control group of 35 healthy children matched for age and sex. The urinary ratio 6beta-hydroxycortisol/free cortisol was used as a marker of CYP3A activity. In patients, urine samples were collected at two times, prior to starting rhGH replacement treatment and 30 days after beginning therapy.

RESULTS

A significantly higher metabolic activity in GHD children was observed in relation to controls ( P=0.0001) without sex differences. Paired comparisons demonstrated a sexually dimorphic effect of rhGH therapy on the CYP3A activity. While boys displayed a significant decrease ( P=0.003), girls showed no significantly different values of CYP3A marker ( P>0.05). Unpaired comparison between controls and GHD children after therapy demonstrated absence of significant differences in boys ( P>0.05) and a strikingly higher activity in girls ( P=0.0001).

CONCLUSIONS

The data suggests that: (a) GHD in children increases CYP3A activity in a non-sex-dependent manner, (b) rhGH treatment for 30 days to GHD children results in a sexually dimorphic effect on CYP3A activity, with a significant decrease in males toward normalization in relation to controls and non-significant changes in females. The results of this study may have important clinical implications for GHD children, since changes in CYP3A activity importantly affect the metabolism of both steroid hormones and CYP3A substrate drugs.

The variability of liver graft function and urinary 6beta-hydroxycortisol to cortisol ratio during liver regeneration in liver transplant recipients

The urinary ratio of 6beta-hydroxycortisol to cortisol (6beta-OHF/F) is considered to be the simplest and most practical method for estimation of hepatic cytochrome P450 3A4 (CYP3A4) activity as a non-invasive marker of human in vivo CYP3A4 activity. However, the inter- and intra-individual variability of the urinary 6beta-OHF/F ratio during liver regeneration and the effect of variability on optimal dose of tacrolimus have not yet been clarified. The objective of this study was to clarify the change in the urinary 6beta-OHF/F ratio during liver regeneration and to determine the effect of the liver graft function on the optimal tacrolimus dose in liver transplant recipients. Two liver transplant recipients (one male and one female) and eight healthy volunteers (five males and three females) were enrolled in this study. Urine samples were collected from the recipients from 08.00 hours for 24 h on post-transplant period, 1-10 and 21-30 days postoperatively. In the healthy volunteers, morning spot urine samples were collected at 08.00 hours. The mean urinary 6beta-OHF/F ratio in the immediate postoperative period was significantly low (p < 0.05). However, a marked difference in the regulation of CYP3A4 activity during liver regeneration was found in the two recipients. A significant correlation was found between the urinary 6beta-OHF/F ratio and the C/D ratio of tacrolimus (R = 0.658, p < 0.05). The urinary 6beta-OHF/F ratio is a useful probe for estimating the variability of CYP3A4 activity in liver transplant recipients in early postoperative phase. Future studies should evaluate the clinical usefulness of the urinary 6beta-OHF/F ratio as a predictor of tacrolimus pharmacokinetics in liver transplantation.

Interindividual variability of the clinical pharmacokinetics of methadone: implications for the treatment of opioid dependence

Methadone is widely used for the treatment of opioid dependence. Although in most countries the drug is administered as a racemic mixture of (R)- and (S)- methadone, (R)-methadone accounts for most, if not all, of the opioid effects. Methadone can be detected in the blood 15-45 minutes after oral administration, with peak plasma concentration at 2.5-4 hours. Methadone has a mean bioavailability of around 75% (range 36-100%). Methadone is highly bound to plasma proteins, in particular to alpha(1)-acid glycoprotein. Its mean free fraction is around 13%, with a 4-fold interindividual variation. Its volume of distribution is about 4 L/kg (range 2-13 L/kg). The elimination of methadone is mediated by biotransformation, followed by renal and faecal excretion. Total body clearance is about 0.095 L/min, with wide interindividual variation (range 0.02-2 L/min). Plasma concentrations of methadone decrease in a biexponential manner, with a mean value of around 22 hours (range 5-130 hours) for elimination half-life. For the active (R)-enantiomer, mean values of around 40 hours have been determined. Cytochrome P450 (CYP) 3A4 and to a lesser extent 2D6 are probably the main isoforms involved in methadone metabolism. Rifampicin (rifampin), phenobarbital, phenytoin, carbamazepine, nevirapine, and efavirenz decrease methadone blood concentrations, probably by induction of CYP3A4 activity, which can result in severe withdrawal symptoms. Inhibitors of CYP3A4, such as fluconazole, and of CYP2D6, such as paroxetine, increase methadone blood concentrations. There is an up to 17-fold interindividual variation of methadone blood concentration for a given dosage, and interindividual variability of CYP enzymes accounts for a large part of this variation. Since methadone probably also displays large interindividual variability in its pharmacodynamics, methadone treatment must be individually adapted to each patient. Because of the high morbidity and mortality associated with opioid dependence, it is of major importance that methadone is used at an effective dosage in maintenance treatment: at least 60 mg/day, but typically 80-100 mg/day. Recent studies also show that a subset of patients might benefit from methadone dosages larger than 100 mg/day, many of them because of high clearance. In clinical management, medical evaluation of objective signs and subjective symptoms is sufficient for dosage titration in most patients. However, therapeutic drug monitoring can be useful in particular situations. In the case of non-response trough plasma concentrations of 400 microg/L for (R,S)-methadone or 250 microg/L for (R)-methadone might be used as target values.

Interactions between recreational drugs and antiretroviral agents

OBJECTIVE

To summarize existing data regarding potential interactions between recreational drugs and drugs commonly used in the management of HIV-positive patients.

DATA SOURCES

Information was obtained via a MEDLINE search (1966-August 2002) using the MeSH headings human immunodeficiency virus, drug interactions, cytochrome P450, medication names commonly prescribed for the management of HIV and related opportunistic infections, and names of commonly used recreational drugs. Abstracts of national and international conferences, review articles, textbooks, and references of all articles were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

Literature on pharmacokinetic interactions was considered for inclusion. Pertinent information was selected and summarized for discussion. In the absence of specific data, prediction of potential clinically significant interactions was based on pharmacokinetic and pharmacodynamic properties.

RESULTS

All protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors are substrates and potent inhibitors or inducers of the cytochrome P450 system. Many classes of recreational drugs, including benzodiazepines, amphetamines, and opioids, are also metabolized by the liver and can potentially interact with antiretrovirals. Controlled interaction studies are often not available, but clinically significant interactions have been observed in a number of case reports. Overdoses secondary to interactions between the "rave" drugs methylenedioxymethamphetamine (MDMA) or gamma-hydroxybutyrate (GHB) and PIs have been reported. PIs, particularly ritonavir, may also inhibit metabolism of amphetamines, ketamine, lysergic acid diethylmide (LSD), and phencyclidine (PCP). Case series and pharmacokinetic studies suggest that nevirapine and efavirenz induce methadone metabolism, which may lead to symptoms of opiate withdrawal. A similar interaction may exist between methadone and the PIs ritonavir and nelfinavir, although the data are less consistent. Opiate metabolism can be inhibited or induced by concomitant PIs, and patients should be monitored for signs of toxicity and/or loss of analgesia. PIs should not be coadministered with midazolam and triazolam, since prolonged sedation may occur.

CONCLUSIONS

Interactions between agents commonly prescribed for patients with HIV and recreational drugs can occur, and may be associated with serious clinical consequences. Clinicians should encourage open dialog with their patients on this topic, to avoid compromising antiretroviral efficacy and increasing the risk of drug toxicity.

Gas chromatography-mass spectrometry measurement of 6beta-OH-cortisol/cortisol ratio in human urine: a specific marker of enzymatic induction

The urinary 6beta-OH-cortisol/cortisol ratio is a specific, non-invasive marker for evaluating inductive or inhibitory effects on cytochrome P450 3A activity. We propose a new quantitative gas chromatography-mass spectrometry with isotope dilution (GC-ID-MS) method for the simultaneous determination of urinary free cortisol (UFC) and 6beta-OH-cortisol (6beta-OHC). The method utilizes the following: (a) addition of internal standard (2H2 cortisol) to 1 ml of urine; (b) loading on to an Extrelut column and elution with dichloromethane; (c) derivatization to dimethoxime tri-(trimethyl-silyl)ether (MOX-TMS); (d) separation and identification by GC-ID-MS. The detection limit for cortisol was 22 pg injected (signal-to-noise ratio 10:1) and for 6beta-OH-cortisol 123 pg injected (signal-to-noise ratio 10:1). The intra-assay and the inter-assay imprecision were 4.69% and 7.4% for 6beta-OHC and 2.44% and 3.53% for cortisol, respectively. We used this method to analyze 57 morning urine samples of healthy volunteers and patients under different conditions. We found that chronic alcoholics had a significantly higher ratio of 6beta-OHC/UFC compared to controls (p<0.0001), whereas adults undergoing methadone therapy and patients with acute alcohol intoxication exhibited a significantly lower urinary 6beta-OHC/UFC ratio (p<0.05 and p<0.01, respectively). The proposed method allows a rapid and accurate assessment of the 6beta-OHC/UFC ratio.