Cytochrome P4503A does not mediate the interaction between methadone and ritonavir-lopinavir

Drug-drug interactions and clinical considerations with co-administration of antiretrovirals and psychotropic drugs

Psychotropic medications are frequently co-prescribed with antiretroviral therapy (ART), owing to a high prevalence of psychiatric illness within the population living with HIV, as well as a 7-fold increased risk of HIV infection among patients with psychiatric illness. While ART has been notoriously associated with a multitude of pharmacokinetic drug interactions involving the cytochrome P450 enzyme system, the magnitude and clinical impact of these interactions with psychotropics may range from negligible effects on plasma concentrations to life-threatening torsades de pointes or respiratory depression. This comprehensive review summarizes the currently available information regarding drug-drug interactions between antiretrovirals and pharmacologic agents utilized in the treatment of psychiatric disorders-antidepressants, stimulants, antipsychotics, anxiolytics, mood stabilizers, and treatments for opioid use disorder and alcohol use disorder-and provides recommendations for their management. Additionally, overlapping toxicities between antiretrovirals and the psychotropic classes are highlighted. Knowledge of the interaction and adverse effect potential of specific antiretrovirals and psychotropics will allow clinicians to make informed prescribing decisions to better promote the health and wellness of this high-risk population.

Effect of rilpivirine on the pharmacokinetics of methadone in HIV-Infected Chinese patients

Background: The combination of rilpivirine with methadone may result in complex interactions secondary to the induction of oxidative metabolism by rilpivirine. Research design and methods: TMC278IFD4007 was a single-center, prospective, open-label, multiple-dose study with 12 HIV-infected Chinese participants. The objective was to evaluate the potential effect of rilpivirine on the pharmacokinetics of methadone. The participants received a daily dose of 25 mg rilpivirine for 11 days with individualized methadone ranging from 25 to 100 mg. Pharmacokinetic studies of methadone were conducted on day 1 and 11. Opiate withdrawal symptoms were evaluated. Results: A large inter-subject variability was noted in methadone pharmacokinetics. Rilpivirine increased methadone minimum and maximum plasma concentrations (Cmin; Cmax) and area under the plasma concentration-time curve versus methadone alone (least-square mean ratio; 90% confidence interval) by 5% (1.05; 0.46, 2.39), 5% (1.05; 0.73, 1.52), and 6% (0.75; 0.74, 1.50) as measured in S-methadone, and 5% (1.05; 0.50, 2.22), 5% (1.05; 0.74, 1.50), and 5% (1.05; 0.76, 1.46) as measured in R-methadone, respectively. No opioid withdrawal symptoms or methadone dose adjustments were reported. Co-administration was well tolerated without serious adverse effects or discontinuations. Conclusion: Concomitant administration of rilpivirine was unlikely to have significant effects on the pharmacokinetics of methadone.

Drug-Drug Interaction Studies of Methadone and Antiviral Drugs: Lessons Learned

Different views appear in the literature on the extent of specific cytochrome P450 (CYP) involvement in methadone metabolism. The aim of this work is to leverage knowledge from drug-drug interaction (DDI) studies in new drug applications between methadone and antiviral medications to better understand methadone disposition and to inform design of future DDI studies with methadone. A database of DDI studies between all FDA-approved human immunodeficiency virus and hepatitis C virus medications and methadone was constructed. The database contains data from 29 DDI studies. Sixteen of the 29 studies had statistically significant changes in methadone area under the concentration-time curve. Methadone exposure was either decreased or unchanged when it was coadministered with weak to strong CYP3A inhibitors or a moderate CYP3A4 inducer. Methadone exposure was reduced when it was coadministered with CYP2B6 inducers. The role of other enzymes (CYP2C9, CYP2C19, and CYP2D6) cannot be fully elucidated from these studies. In conclusion, CYP2B6 plays a prominent role in methadone metabolism, although methadone exposure is not sensitive to CYP3A perturbation. In designing methadone DDI studies, (1) measuring R- and S-methadone is more informative than measuring total methadone, and (2) CYP2B6 genotyping of subjects enrolled in methadone DDI studies should be considered. Finally, there is a need for the development of predictive models to determine the influence of medications on methadone disposition.

Methadone Metabolism and Drug-Drug Interactions: In Vitro and In Vivo Literature Review

Methadone is utilized for the treatment of individuals with opiate dependence. Methadone undergoes N-demethylation by multiple cytochrome P450 (CYP) enzymes including CYP3A4, CYP2B6, CYP2C19, CYP2D6, CYP2C9, and CYP2C8. In vivo, polymorphism effects on methadone systemic exposure have been noted for CYP2B6, CYP3A4, and CYP2D6. Clinical drug interaction studies with antiviral drugs in methadone maintenance treatment patients yield varying results on methadone pharmacokinetics and pharmacodynamics. In general, CYP inhibitors altered methadone exposure with no adverse effects. CYP inducers generally decreased methadone exposure with some reports of withdrawal symptoms in the subjects. Interaction studies with antiviral drug combinations yielding differing results depend on the enzyme(s) affected. For certain antiviral medicines which are dual inhibitor(s) and inducer(s) for CYP enzymes, their effect on methadone pharmacokinetics can change with time since the effect of induction is usually delayed compared to the effect of inhibition.

Current Concepts in Methadone Metabolism and Transport

Methadone is a cornerstone therapy for opioid addiction and a public health strategy for HIV/AIDS and hepatitis C reduction. Methadone is also used for acute and chronic pain. As use for chronic pain has grown, so too have adverse events. Constitutive and acquired (drug interactions) inter- and intraindividual variability in methadone pharmacokinetics and pharmacodynamics confounds reliable clinical use. Identification of enzymes and transporters responsible for methadone disposition has been a long-sought ideal. Initial in vitro studies identified CYP3A4 as metabolizing methadone. Subsequently, by extrapolation, CYP3A4 was long assumed to be responsible for clinical methadone disposition. However, CYP2B6 is also a major catalyst of methadone metabolism in vitro. It has now been unequivocally established that CYP2B6, not CYP3A4, is the principal determinant of methadone metabolism, clearance, elimination, and plasma concentrations in humans. Methadone disposition is susceptible to inductive and inhibitory drug interactions. CYP2B6 genetics also influences methadone metabolism and clearance, which were diminished in CYP2B6*6 carriers and increased in CYP2B6*4 carriers. CYP2B6 genetics can explain, in part, interindividual variability in methadone metabolism and clearance. Thus, both constitutive variability due to CYP2B6 genetics, and CYP2B6-mediated drug interactions, can alter methadone disposition, clinical effect, and drug safety. Methadone is not a substrate for major influx or efflux transporters.

Pharmacokinetics and analgesic effects of methadone in children and adults with sickle cell disease

BACKGROUND

Vaso-occlusive episodes (VOEs) are a significant source of morbidity among children and adults with sickle cell disease (SCD). There is little information on methadone use for SCD pain. This investigation evaluated methadone pharmacokinetics in children and adults with SCD, with a secondary aim to assess pain relief and opioid consumption.

PROCEDURE

Participants included children (<18 years) and adults with a VOE requiring hospitalization. Patients were randomly assigned to receive standard care (opioid patient-controlled analgesia; control group) or one dose of intravenous methadone (0.1-0.125 mg/kg) in addition to standard care (methadone group). Venous methadone and metabolite concentrations were measured. Pain scores, pain relief scores, and opioid consumption were recorded.

RESULTS

Twenty-four children (12 methadone, 12 controls) and 23 adults (11 methadone, 12 controls) were studied. In children, the half-life of R- and S-methadone enantiomers was 34 ± 16 and 24 ± 9 hr, respectively. In adults, R- and S-methadone half-lives were 52 ± 17 and 38 ± 12 hr, respectively. Pain scores were lower (P = 0.002) and pain relief scores were higher (P = 0.0396) in children receiving methadone versus controls. There was no difference in pain scores and pain relief in adults receiving methadone versus controls. There was no difference in opioid consumption between methadone and control groups, in both adults and children.

CONCLUSIONS

Intravenous methadone disposition in children and adults with SCD was comparable to that in subjects without SCD from prior studies. Methadone produced more pain relief than standard care in children with SCD. Higher methadone doses may be more effective and should be evaluated in both children and adults with SCD.

Pharmacokinetic Effects of Isavuconazole Coadministration With the Cytochrome P450 Enzyme Substrates Bupropion, Repaglinide, Caffeine, Dextromethorphan, and Methadone in Healthy Subjects

This report describes phase 1 clinical trials performed to assess interactions of oral isavuconazole at the clinically targeted dose (200 mg, administered as isavuconazonium sulfate 372 mg, 3 times a day for 2 days; 200 mg once daily [QD] thereafter) with single oral doses of the cytochrome P450 (CYP) substrates: bupropion hydrochloride (CYP2B6; 100 mg; n = 24), repaglinide (CYP2C8/CYP3A4; 0.5 mg; n = 24), caffeine (CYP1A2; 200 mg; n = 24), dextromethorphan hydrobromide (CYP2D6/CYP3A4; 30 mg; n = 24), and methadone (CYP2B6/CYP2C19/CYP3A4; 10 mg; n = 23). Compared with each drug alone, coadministration with isavuconazole changed the area under the concentration‐time curves (AUC_∞) and maximum concentrations (C_max) as follows: bupropion, AUC_∞ reduced 42%, C_max reduced 31%; repaglinide, AUC_∞ reduced 8%, C_max reduced 14%; caffeine, AUC_∞ increased 4%, C_max reduced 1%; dextromethorphan, AUC_∞ increased 18%, C_max increased 17%; R‐methadone, AUC_∞ reduced 10%, C_max increased 3%; S‐methadone, AUC_∞ reduced 35%, C_max increased 1%. In all studies, there were no deaths, 1 serious adverse event (dextromethorphan study; perioral numbness, numbness of right arm and leg), and adverse events leading to study discontinuation were rare. Thus, isavuconazole is a mild inducer of CYP2B6 but does not appear to affect CYP1A2‐, CYP2C8‐, or CYP2D6‐mediated metabolism.

Methadone dose in heroin-dependent patients: role of clinical factors, comedications, genetic polymorphisms and enzyme activity

AIMS

Methadone is characterized by wide intersubject variability regarding the dose needed to obtain full therapeutic response. We assessed the influence of sociodemographic, ethnic, clinical, metabolic and genotypic variables on methadone maintenance dose requirement in opioid-dependent responder patients.

METHODS

Eighty-one stable patients (60 men and 21 women, 43.7 ± 8.1 years old, 63.1 ± 50.9 mg day(-1) methadone), divided into quartiles with respect to the median daily dose, were enrolled and underwent clinical examination, treatment history and determination of liver/intestinal cytochrome P450 (CYP) 3A4 activity measured by the midazolam test, R,S-methadone trough concentration and clinically significant polymorphisms of the OPRM1, DRD2, COMT, ABCB1, CYP2B6, CYP3A5, CYP2C19 and CYP2D6 genes.

RESULTS

Methadone maintenance dose was correlated to the highest dose ever used (r(2) = 0.57, P < 0.0001). Fractioned methadone intake (odds ratio 4.87, 95% confidence interval 1.27-18.6, P = 0.02), bodyweight (odds ratio 1.57, 95% confidence interval 1.01-2.44, P = 0.04), history of cocaine dependence (80 vs. 44 mg day(-1) in never-addict patients, P = 0.005) and ethnicity (Asian > Caucasian > African, P = 0.04) were independently associated with high-dose methadone in multiple regression analysis. A modest correlation was observed between liver/intestinal CYP3A4 activity and methadone dose at steady state (Spearman rank correlation coefficient [rs ] = 0.21, P = 0.06) but not with highest dose ever used (rs = 0.15, P = 0.18) or dose-normalized R,S-methadone trough concentrations (rs = -0.05, P = 0.64). Concomitant CYP3A4 inhibitors only affected the relationship between methadone dose and R,S-methadone trough concentration. None of the genetic polymorphisms explored was predictive of the methadone maintenance dose.

CONCLUSIONS

Methadone maintenance dose was predicted by sociodemographic and clinical variables rather than genetic polymorphisms or liver/intestinal CYP3A4 activity in stable patients.

Ritonavir Use in Human Immunodeficiency Virus-Positive Surgical Patients Is Not Associated with an Increase in Postoperative Critical Respiratory Events

This study evaluated whether highly active antiretroviral therapy for human immunodeficiency virus (HIV) including ritonavir is independently associated with increased critical respiratory events after general anesthesia with opioid analgesia. The impact of ritonavir on hepatic microsomal enzymes was considered due to the effect of these enzymes on opioid metabolism. Medical records of over 1900 patients were reviewed, and those of 941 patients met inclusion criteria and were analyzed. Chronic treatment with ritonavir was not associated with critical respiratory events in HIV-positive patients.

Methadone Pharmacogenetics: CYP2B6 Polymorphisms Determine Plasma Concentrations, Clearance, and Metabolism

BACKGROUND

Interindividual variability in methadone disposition remains unexplained, and methadone accidental overdose in pain therapy is a significant public health problem. Cytochrome P4502B6 (CYP2B6) is the principle determinant of clinical methadone elimination. The CYP2B6 gene is highly polymorphic, with several variant alleles. CYP2B6.6, the protein encoded by the CYP2B6*6 polymorphism, deficiently catalyzes methadone metabolism in vitro. This investigation determined the influence of CYP2B6*6, and other allelic variants encountered, on methadone concentrations, clearance, and metabolism.

METHODS

Healthy volunteers in genotype cohorts CYP2B6*1/*1 (n = 21), CYP2B6*1/*6 (n = 20), and CYP2B6*6/*6 (n = 17), and also CYP2B6*1/*4 (n = 1), CYP2B6*4/*6 (n = 3), and CYP2B6*5/*5 (n = 2) subjects, received single doses of IV and oral methadone. Plasma and urine methadone and metabolite concentrations were determined by tandem mass spectrometry.

RESULTS

Average S-methadone apparent oral clearance was 35 and 45% lower in CYP2B6*1/*6 and CYP2B6*6/*6 genotypes, respectively, compared with CYP2B6*1/*1. R-methadone apparent oral clearance was 25 and 35% lower in CYP2B6*1/*6 and CYP2B6*6/*6 genotypes, respectively, compared with CYP2B6*1/*1. R- and S-methadone apparent oral clearance was threefold and fourfold greater in CYP2B6*4 carriers. IV and oral R- and S-methadone metabolism was significantly lower in CYP2B6*6 carriers compared with that of CYP2B6*1 homozygotes and greater in CYP2B6*4 carriers. Methadone metabolism and clearance were lower in African Americans in part because of the CYP2B6*6 genetic polymorphism.

CONCLUSIONS

CYP2B6 polymorphisms influence methadone plasma concentrations, because of altered methadone metabolism and thus clearance. Genetic influence is greater for oral than IV methadone and S- than R-methadone. CYP2B6 pharmacogenetics explains, in part, interindividual variability in methadone elimination. CYP2B6 genetic effects on methadone metabolism and clearance may identify subjects at risk for methadone toxicity and drug interactions.

Transporter-Mediated Disposition of Opioids: Implications for Clinical Drug Interactions

Opioid-related deaths, abuse, and drug interactions are growing epidemic problems that have medical, social, and economic implications. Drug transporters play a major role in the disposition of many drugs, including opioids; hence they can modulate their pharmacokinetics, pharmacodynamics and their associated drug-drug interactions (DDIs). Our understanding of the interaction of transporters with many therapeutic agents is improving; however, investigating such interactions with opioids is progressing relatively slowly despite the alarming number of opioids-mediated DDIs that may be related to transporters. This review presents a comprehensive report of the current literature relating to opioids and their drug transporter interactions. Additionally, it highlights the emergence of transporters that are yet to be fully identified but may play prominent roles in the disposition of opioids, the growing interest in transporter genomics for opioids, and the potential implications of opioid-drug transporter interactions for cancer treatments. A better understanding of drug transporters interactions with opioids will provide greater insight into potential clinical DDIs and could help improve opioids safety and efficacy.

Differences in Methadone Metabolism by CYP2B6 Variants

Methadone is a long-acting opioid with considerable unexplained interindividual variability in clearance. Cytochrome P450 2B6 (CYP2B6) mediates clinical methadone clearance and metabolic inactivation via N-demethylation to 2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). Retrospective studies suggest that individuals with the CYP2B6*6 allelic variant have higher methadone plasma concentrations. Catalytic activities of CYP2B6 variants are highly substrate- and expression-system dependent. This investigation evaluated methadone N-demethylation by expressed human CYP2B6 allelic variants in an insect cell coexpression system containing P450 reductase. Additionally, the influence of coexpressing cytochrome b5, whose role in metabolism can be inhibitory or stimulatory depending on the P450 isoform and substrate, on methadone metabolism, was evaluated. EDDP formation from therapeutic (0.25-1 μM) R- and S-methadone concentrations was CYP2B6.4 ≥ CYP2B6.1 ≥ CYP2B6.5 >> CYP2B6.9 ≈ CYP2B6.6, and undetectable from CYP2B6.18. Coexpression of b5 had small and variant-specific effects at therapeutic methadone concentrations but at higher concentrations stimulated EDDP formation by CYP2B6.1, CYP2B6.4, CYP2B6.5, and CYP2B6.9 but not CYP2B6.6. In vitro intrinsic clearances were generally CYP2B6.4 ≥ CYP2B6.1 > CYP2B6.5 > CYP2B6.9 ≥ CYP2B6.6. Stereoselective methadone metabolism (S>R) was maintained with all CYP2B6 variants. These results show that methadone N-demethylation by CYP2B6.4 is greater compared with CYP2B6.1, whereas CYP2B6.9 and CYP2B6.6 (which both contain the 516G>T, Q172H polymorphism), are catalytically deficient. The presence or absence of b5 in expression systems may explain previously reported disparate catalytic activities of CYP2B6 variants for specific substrates. Differences in methadone metabolism by CYP2B6 allelic variants provide a mechanistic understanding of pharmacogenetic variability in clinical methadone metabolism and clearance.

Influence of HIV antiretrovirals on methadone N-demethylation and transport

Drug interactions involving methadone and/or HIV antiretrovirals can be problematic. Mechanisms whereby antiretrovirals induce clinical methadone clearance are poorly understood. Methadone is N-demethylated to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) by CYP2B6 and CYP3A4 in vitro, but by CYP2B6 in vivo. This investigation evaluated human hepatocytes as a model for methadone induction, and tested the hypothesis that methadone and EDDP are substrates for human drug transporters. Human hepatocyte induction by several antiretrovirals of methadone N-demethylation, and CYP2B6 and CYP3A4 transcription, protein expression and catalytic activity, and pregnane X receptor (PXR) activation were evaluated. Methadone and EDDP uptake and efflux by overexpressed transporters were also determined. Methadone N-demethylation was generally not significantly increased by the antiretrovirals. CYP2B6 mRNA and activity (bupropion N-demethylation) were induced by several antiretrovirals, as were CYP3A4 mRNA and protein expression, but only indinavir increased CYP3A activity (alfentanil dealkylation). CYP upregulation appeared related to PXR activation. Methadone was not a substrate for uptake (OCT1, OCT2, OCT3, OATP1A2, OATP1B1, OATP1B3, OATP2B1) or efflux (P-gp, BCRP) transporters. EDDP was a good substrate for P-gp, BCRP, OCT1, OCT3, OATP1A2, and OATP1B1. OATP1A2- and OCT3-mediated EDDP uptake, and BCRP-mediated EDDP efflux transport, was inhibited by several antiretrovirals. Results show that hepatocyte methadone N-demethylation resembles expressed and liver microsomal metabolism more than clinical metabolism. Compared with clinical studies, hepatocytes underreport induction of methadone metabolism by HIV drugs. Hepatocytes are not a good predictive model for clinical antiretroviral induction of methadone metabolism and not a substitute for clinical studies. EDDP is a transporter substrate, and is susceptible to transporter-mediated interactions.

Cyclosporine-inhibitable cerebral drug transport does not influence clinical methadone pharmacodynamics

BACKGROUND

Interindividual variability and drug interaction studies suggest that blood-brain barrier drug transporters mediate human methadone brain biodistribution. In vitro and animal studies suggest that methadone is a substrate for the efflux transporter P-glycoprotein, and that P-glycoprotein-mediated transport influences brain access and pharmacologic effect. This investigation tested whether methadone is a transporter substrate in humans [corrected].

METHODS

Healthy volunteers received oral (N=16) or IV (N=12) methadone in different crossover protocols after nothing (control) or the validated P-glycoprotein inhibitor cyclosporine (4.5 mg/kg orally twice daily for 4 days, or 5 mg/kg IV over 2 h). Plasma and urine methadone and metabolite concentrations were measured by mass spectrometry. Methadone effects were measured by miosis and thermal analgesia (maximally tolerated temperature and verbal analog scale rating of discreet temperatures).

RESULTS

Cyclosporine marginally but significantly decreased methadone plasma concentrations and apparent oral clearance, but had no effect on methadone renal clearance or on hepatic N-demethylation. Cyclosporine had no effect on miosis or on R-methadone concentration-miosis relationships after either oral or IV methadone. Peak miosis was similar in controls and cyclosporine-treated subjects after oral methadone (1.4±0.4 and 1.3±0.5 mm/mg, respectively) and IV methadone (3.1±1.0 and 3.2±0.8 mm, respectively). Methadone increased maximally tolerated temperature, but analgesia testing was confounded by cyclosporine-related pain.

CONCLUSIONS

Cyclosporine did not affect methadone pharmacodynamics. This result does not support a role for cyclosporine-inhibitable transporters mediating methadone brain access and biodistribution.

Phase I safety, pharmacokinetics, and pharmacogenetics study of the antituberculosis drug PA-824 with concomitant lopinavir-ritonavir, efavirenz, or rifampin

There is an urgent need for new antituberculosis (anti-TB) drugs, including agents that are safe and effective with concomitant antiretrovirals (ARV) and first-line TB drugs. PA-824 is a novel antituberculosis nitroimidazole in late-phase clinical development. Cytochrome P450 (CYP) 3A, which can be induced or inhibited by ARV and antituberculosis drugs, is a minor (∼20%) metabolic pathway for PA-824. In a phase I clinical trial, we characterized interactions between PA-824 and efavirenz (arm 1), lopinavir/ritonavir (arm 2), and rifampin (arm 3) in healthy, HIV-uninfected volunteers without TB disease. Participants in arms 1 and 2 were randomized to receive drugs via sequence 1 (PA-824 alone, washout, ARV, and ARV plus PA-824) or sequence 2 (ARV, ARV with PA-824, washout, and PA-824 alone). In arm 3, participants received PA-824 and then rifampin and then both. Pharmacokinetic sampling occurred at the end of each dosing period. Fifty-two individuals participated. Compared to PA-824 alone, plasma PA-824 values (based on geometric mean ratios) for maximum concentration (Cmax), area under the concentration-time curve from 0 to 24 h (AUC0-24), and trough concentration (Cmin) were reduced 28%, 35%, and 46% with efavirenz, 13%, 17%, and 21% with lopinavir-ritonavir (lopinavir/r) and 53%, 66%, and 85% with rifampin, respectively. Medications were well tolerated. In conclusion, lopinavir/r had minimal effect on PA-824 exposures, supporting PA-824 use with lopinavir/r without dose adjustment. PA-824 exposures, though, were reduced more than expected when given with efavirenz or rifampin. The clinical implications of these reductions will depend upon data from current clinical trials defining PA-824 concentration-effect relationships. (This study has been registered at ClinicalTrials.gov under registration no. NCT01571414.).