Low incidence of acute rejection within 6 months of kidney transplantation in HIV-infected recipients treated with raltegravir: the Agence Nationale de Recherche sur le Sida et les Hépatites Virales (ANRS) 153 TREVE trial.

OBJECTIVES: High rates of clinical acute rejection after kidney transplantation have been reported in people living with HIV (PLHIV), probably as a consequence of drug interactions. We therefore investigated the incidence of acute rejection within 6 months of transplantation in HIV-infected recipients treated with a protease-inhibitor-free raltegravir-based regimen. METHODS: The Agence Nationale de Recherche sur le Sida et les Hépatites Virales (ANRS) 153 TREVE (NCT01453192) study was a prospective multicentre single-arm trial in adult PLHIV awaiting kidney transplantation, with viral load < 50 HIV-1 RNA copies/mL, CD4 T-cell count > 200 cells/µL, and HIV-1 strains sensitive to raltegravir, aiming to demonstrate 6-month clinical acute rejection rates < 30%. Time to transplantation was compared with that for uninfected subjects matched for age, sex and registration date. RESULTS: In total, 61 participants were enrolled in the study, and 26 underwent kidney transplantation. Two participants experienced clinical acute rejection, corresponding to an estimated clinical acute rejection rate of 8% [95% confidence interval (CI) 2-24%] at 6 and 12 months post-transplantation. HIV infection remained under control in all but one participant, who temporarily stopped antiretroviral treatment. Median time to transplantation was longer in PLHIV than in controls (4.3 versus 2.8 years, respectively; P = 0.002) and was not influenced by blood group. CONCLUSIONS: Acute rejection rates were low after kidney transplantation in PLHIV treated with a raltegravir-based regimen. However, PLHIV have poorer access to transplantation than HIV-uninfected individuals after registration on the waiting list.

Worsening pneumonitis due to a pharmacokinetic drug-drug interaction between everolimus and voriconazole in a renal transplant patient.

WHAT IS KNOWN AND OBJECTIVE: Azole antifungals, prescribed prophylactically to avoid severe infections in immunosuppressed organ transplant recipients, can interact with drug substrates of CYP3A4. We report serious adverse effects due to interaction between orally administered voriconazole and everolimus in a renal transplant recipient. CASE DESCRIPTION: Despite reduction of the dose of everolimus by a third, the blood trough concentration of everolimus increased considerably in a kidney transplant recipient upon oral administration of voriconazole. Everolimus was then discontinued. Pneumonia secondary to pulmonary aspergillosis worsened, possibly due to the excessive immunosuppression. WHAT IS NEW AND CONCLUSION: Orally administered voriconazole inhibits intestinal and hepatic cytochrome P450-3A4 activity and thereby reduces everolimus metabolism. An 80% decrease in dose or discontinuation of everolimus is required when concomitant voriconazole is introduced. Daily blood monitoring of everolimus is warranted until a steady state of concentrations is reached.

Pharmacokinetics of rifampin and isoniazid in tuberculosis-HIV-coinfected patients receiving nevirapine- or efavirenz-based antiretroviral treatment.

This is a substudy of the Agence Nationale de Recherches sur le Sida et les Hépatites Virales (ANRS) Comparison of Nevirapine and Efavirenz for the Treatment of HIV-TB Co-infected Patients (ANRS 12146-CARINEMO) trial, which assessed the pharmacokinetics of rifampin or isoniazid with or without the coadministration of nonnucleoside reverse transcriptase inhibitor-based HIV antiretroviral therapy in HIV-tuberculosis-coinfected patients in Mozambique. Thirty-eight patients on antituberculosis therapy based on rifampin and isoniazid participated in the substudy (57.9% males; median age, 33 years; median weight, 51.9 kg; median CD4(+) T cell count, 104 cells/µl; median HIV-1 RNA load, 5.5 log copies/ml). The daily doses of rifampin and isoniazid were 10 and 5 mg/kg of body weight, respectively. Twenty-one patients received 200 mg of nevirapine twice a day (b.i.d.), and 17 patients received 600 mg of efavirenz once a day (q.d.) in combination with lamivudine and stavudine from day 1 until the end of the study. Blood samples were collected at regular time-dosing intervals after morning administration of a fixed-dose combination of rifampin and isoniazid. When rifampin was administered alone, the median maximum concentration of drug in serum (Cmax) and the area under the concentration-time curve (AUC) at steady state were 6.59 mg/liter (range, 2.70 to 14.07 mg/liter) and 27.69 mg · h/liter (range, 11.41 to 109.75 mg · h/liter), respectively. Concentrations remained unchanged when rifampin was coadministered with nevirapine or efavirenz. When isoniazid was administered alone, the median isoniazid Cmax and AUC at steady state were 5.08 mg/liter (range, 1.26 to 11.51 mg/liter) and 20.92 mg · h/liter (range, 7.73 to 56.95 mg · h/liter), respectively. Concentrations remained unchanged when isoniazid was coadministered with nevirapine; however, a 29% decrease in the isoniazid AUC was observed when isoniazid was combined with efavirenz. The pharmacokinetic parameters of rifampin and isoniazid when coadministered with nevirapine or efavirenz were not altered to a clinically significant extent in these severely immunosuppressed HIV-infected patients. Patients experienced favorable clinical outcomes. (This study has been registered at ClinicalTrials.gov under registration no. NCT00495326.).

The ethics of a clinical trial when the protocol clashes with international guidelines.

Due to their nature and complexity, clinical trials often take some time to launch after the protocol has been designed and ethics approval obtained. During this time, there may be changes in international treatment guidelines and recommendations that result in a conflict between study protocol and recommended international best practice. Here, we describe the situation that arose in a pharmacokinetic study on the use of two different doses of rifabutin in patients with human immunodeficiency virus-associated tuberculosis who initiated antiretroviral therapy (ART) with a lopinavir-ritonavir-based regimen in South Africa and Viet Nam. The study protocol specified that ART should be started 10 weeks after the start of anti-tuberculosis treatment. The study in South Africa was approved in June 2008, went ahead as scheduled and was completed in August 2010. The study in Viet Nam was approved in October 2008 and was started in June 2010. A few weeks later, the World Health Organization released their 2010 guidelines for adult ART; one of its strong recommendations (with moderate quality of evidence) was that ART should be started 2-8 weeks after the start of anti-tuberculosis treatment. Emerging scientific evidence also supported this recommendation. The investigators felt that the Viet Nam study protocol was in conflict with recommended international best practice, and the trial was stopped in October 2010. An amended study protocol in which ART was started at 2 weeks was developed and implemented. The ethics issues around this decision and the need to change the study protocol are discussed in this article.

Du fait de la nature et de la complexité des études cliniques, leur mise en œuvre est souvent longue après l'élaboration du protocole et son approbation éthique. Pendant cette période, il peut y avoir un changement des lignes directrices internationales de traitement et des recommandations qui provoquent un conflit entre le protocole et les meilleures pratiques recommandées internationalement. Nous décrivons ici la situation apparue dans une étude pharmacocinétique portant sur l'utilisation de deux doses différentes de rifabutin chez des patients atteints de tuberculose (TB) associée au virus de l'immunodéficience humaine et commençant un traitement antirétroviral (ART) à base de lopinavir-ritonavir en Afrique du Sud et au Viet Nam. Le protocole de l'étude spécifiait de commencer l'ART 10 semaines après le début de la thérapie antituberculeuse. En Afrique du Sud, l'étude a été approuvée en juin 2008, s'est déroulée comme prévu et a été achevée en juin 2010. Au Viet Nam, l'étude a été approuvée en octobre 2008 et a démarré en juin 2010. Quelques semaines après, l'Organisation Mondiale de la Santé a publié ses lignes directrices de 2010 pour l'utilisation de l'ART chez les adultes, dont l'une des vives recommandations (basée sur des données de qualité modérée) était de commencer l'ART entre 2 et 8 semaines après le début du traitement de la TB. L'arrivée de nouvelles preuves scientifiques est aussi venue à l'appui de cette recommandation. Les investigateurs ont eu le sentiment que le protocole d'étude au Viet Nam était en conflit avec les meilleures pratiques internationales et l'étude a été arrêtée en octobre 2010. Un protocole d'étude amendé a été développé et mis en œuvre. Les problèmes éthiques entourant cette décision et la nécessité de changer le protocole sont discutés dans ce papier.

Los ensayos clínicos, dadas sus características y su complejidad, suelen exigir mucho tiempo desde la elaboración del protocolo y la aprobación por parte del comité de ética hasta su realización. Durante este lapso, pueden surgir modificaciones en las recomendaciones y las directrices terapéuticas internacionales, lo cual genera un conflicto entre el protocolo del estudio y las prácticas óptimas recomendadas. A continuación se describe la situación que se presentó en Suráfrica y Viet Nam durante un estudio de farmacocinética sobre el uso de dos dosificaciones diferentes de rifabutina, en pacientes aquejados de tuberculosis (TB) asociada con la infección por el virus de la inmunodeficiencia humana (HIV), quienes habían comenzado el tratamiento antirretrovírico (ART) con un régimen basado en la asociación lopinavir y ritonavir. El protocolo del estudio precisaba que el ART se debía comenzar 10 semanas después de haber iniciado el tratamiento antituberculoso. En Suráfrica, el estudio recibió la aprobación en junio del 2008, comenzó en el tiempo previsto y se completó en agosto del 2010. En Viet Nam, se obtuvo la aprobación del estudio en octubre del 2008 y se comenzó en junio del 2010. A las pocas semanas, la Organización Mundial de Salud publicó sus directrices del ART en los adultos del 2010, una de cuyas recomendaciones más firmes consistía en que el ART se debía iniciar entre 2 y 8 semanas después de haber comenzado el tratamiento antituberculoso (con una calidad probatoria moderada). Algunos resultados científicos de aparición reciente respaldaban igualmente esta recomendación. Los investigadores consideraron que el protocolo del estudio en Viet Nam entraba en conflicto con las prácticas óptimas internacionales recomendadas e interrumpieron su realización en octubre del 2010. Se introdujeron modificaciones al protocolo, según las cuales el ART se comenzaría a las 2 semanas y se puso en práctica el estudio. En el presente artículo se analizan los aspectos éticos en torno a esta decisión y a la necesidad de modificar el protocolo del estudio.

Effect of adherence as measured by MEMS, ritonavir boosting, and CYP3A5 genotype on atazanavir pharmacokinetics in treatment-naive HIV-infected patients.

We investigated population pharmacokinetics and pharmacogenetics of ritonavir-boosted atazanavir (ATV), using drug intake times exactly recorded by the Medication Event Monitoring System. The ANRS 134-COPHAR 3 trial was conducted in 35 HIV-infected treatment-naive patients. ATV (300 mg), ritonavir (100 mg), and tenofovir (300 mg) + emtricitabine (200 mg), in bottles with MEMS caps, were taken once daily for 6 months. Six blood samples were collected at week 4 to measure drug concentrations, and trough levels were measured bimonthly. A model integrating ATV and ritonavir pharmacokinetics and pharmacogenetics used nonlinear mixed effects. Use of exact dosing data halved unexplained variability in ATV clearance. The ritonavir-ATV interaction model suggested that optimal boosting effect is achievable at lower ritonavir exposures. Patients with at least one copy of the CYP3A5*1 allele exhibited 28% higher oral clearance. We provide evidence that variability in ATV pharmacokinetics is defined by adherence, CYP3A5 genotype, and ritonavir exposure.

Long-term efficacy of darunavir/ritonavir monotherapy in patients with HIV-1 viral suppression: week 96 results from the MONOI ANRS 136 study.

OBJECTIVES: Long-term results at week 96 are needed to evaluate the capacity of the darunavir/ritonavir monotherapy strategy to maintain a sustained control of the HIV-1 viral load. METHODS: MONOI is a prospective, open-label, non-inferiority, randomized, 96 week trial comparing darunavir/ritonavir monotherapy versus a darunavir/ritonavir triple-therapy strategy to maintain HIV-1 viral load suppression in HIV-1-infected patients. CLINICAL TRIAL REGISTRATION: NCT00412551. RESULTS: From 225 randomized patients, 219 patients reached the 48 week follow-up and 211 reached the 96 week follow-up (106 patients in the darunavir monotherapy arm and 105 in the darunavir triple-therapy arm). Baseline characteristics were well balanced between the two treatment groups. At week 96, in intent-to-treat analysis, 91/103 patients (88%, 95% CI 81-94) allocated to the darunavir/ritonavir monotherapy arm and 87/104 patients (84%, 95% CI 75-90) allocated to the darunavir triple-therapy arm achieved an HIV-1 viral load <50 copies/mL, with no statistical difference between the two groups. Throughout the 96 week follow-up, 66/112 patients (59%, 95% CI 49-68) and 79/113 patients (70%, 95% CI 61-78) consistently had HIV-1 RNA <50 copies/mL with darunavir/ritonavir monotherapy and darunavir/ritonavir triple therapy, respectively. CONCLUSIONS: The MONOI study establishes darunavir/ritonavir monotherapy as durable and efficacious for maintaining virological suppression in HIV-1 patients. Darunavir/ritonavir monotherapy should be considered as a (tailored) treatment option for standard triple-therapy patients who have had a substantial period of viral suppression.

Influence of alpha-1 glycoprotein acid concentrations and variants on atazanavir pharmacokinetics in HIV-infected patients included in the ANRS 107 trial.

Atazanavir is an HIV-1 protease inhibitor with high protein binding in human plasma. The objectives were first to determine the in vitro binding characteristics of atazanavir and second to evaluate whether plasma protein binding to albumin and alpha-1 glycoprotein acid (AAG) influences the pharmacokinetics of atazanavir in HIV-infected patients. For the in vitro study, atazanavir protein binding characteristics were determined in AAG- and albumin-containing purified solutions. Atazanavir was found to bind AAG on a high-affinity saturable site (association constant, 4.61x10(5) liters/mol) and albumin on a low-affinity nonsaturable site. For the in vivo study, blood samples from 51 patients included in trial ANRS 107--Puzzle 2 were drawn prior to drug intake at week 6. For 10 patients included in the pharmacokinetic substudy, five additional blood samples were collected during one dosing interval at week 6. Atazanavir concentrations were assayed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Albumin concentrations, AAG concentrations, and phenotypes were also measured in these patients. Concentrations of atazanavir were modeled using a population approach. A one-compartment model with first-order absorption and elimination best described atazanavir pharmacokinetics. Atazanavir pharmacokinetic parameters and their interindividual variabilities were as follows: absorption rate constant (ka), 0.73 h(-1) (139.3%); apparent clearance (CL/F), 13.3 liters/h (26.7%); and apparent volume of distribution (V/F), 79.7 liters (27.0%). Atazanavir CL/F decreased significantly when alanine aminotransferase and/or AAG levels increased (P<0.01). The ORM1*S phenotype also significantly increased atazanavir V/F (P<0.05). These in vivo results indicate that atazanavir pharmacokinetics is moderately influenced by its protein binding, especially to AAG, without expected clinical consequences.

High rate of virologic suppression with raltegravir plus etravirine and darunavir/ritonavir among treatment-experienced patients infected with multidrug-resistant HIV: results of the ANRS 139 TRIO trial.

BACKGROUND: The introduction of 2 or 3 fully active drugs in human immunodeficiency virus (HIV)-infected patients receiving failing antiretroviral therapy is a key determinant of subsequent treatment efficacy. The aim of this study was to assess the safety and efficacy of a regimen containing raltegravir, etravirine, and darunavir/ritonavir for treatment-experienced patients infected with multidrug-resistant HIV. METHODS: Patients enrolled in this phase II, noncomparative, multicenter trial were naive to the investigational drugs and had plasma HIV RNA levels >1000 copies/mL, a history of virologic failure while receiving nonnucleoside reverse-transcriptase inhibitors (NNRTI), > or =3 primary protease inhibitor and nucleoside reverse transcriptase inhibitor (NRTI) mutations, and < or =3 darunavir and NNRTI mutations. The primary end point was the proportion of patients with plasma HIV RNA levels <50 copies/mL at 24 weeks. RESULTS: A total of 103 patients enrolled in the study. At baseline, genotypic resistance profiles showed a median of 4 primary protease inhibitor mutations, 1 NNRTI mutation, and 6 NRTI mutations. In addition to the investigational drugs, 90 patients (87%) received optimized background therapy that included NRTIs (86 patients) or enfuvirtide (12 patients). At week 24, 90% of patients (95% confidence interval, 85%-96%) had an HIV RNA level <50 copies/mL. At week 48, 86% (95% confidence interval, 80%-93%) had an HIV RNA level <50 copies/mL. The median CD4 cell count increase was 108 cells/mm(3). Grade 3 or 4 clinical adverse events were reported in 15 patients (14.6%). Only 1 patient discontinued the investigational antiretroviral regimen, because of an adverse event. CONCLUSION: In patients infected with multidrug-resistant virus who have few remaining treatment options, the combination of raltegravir, etravirine, and darunavir/ritonavir is well tolerated and is associated with a rate of virologic suppression similar to that expected in treatment-naive patients.

Effect of coadministered HIV-protease inhibitors on tacrolimus and sirolimus blood concentrations in a kidney transplant recipient.

A patient with human immunodeficiency virus infection and end-stage renal disease received a renal transplant. At the time of surgery, the patient was on quadruple antiretroviral therapy (lamivudine, zidovudine, and amprenavir/ritonavir). Immunosuppression was initiated with basiliximab, corticosteroid, mycophenolate mofetil, and a single 0.5 mg dose of tacrolimus. In the following days, an increase in tacrolimus concentration was observed with a peak of 37 ng/mL. Tacrolimus half-life was 6.5 days and tacrolimus maintenance dose was 0.5 mg every 4 days. Eleven months later, the patient had developed Kaposi sarcoma. Tacrolimus was replaced by sirolimus (first dose 1 mg), and the patient was stabilized with 1.5 mg of sirolimus once a week. Increased tacrolimus half-life and increased dose interval of sirolimus and tacrolimus were due to CYP3A4/5 and/or P-glycoprotein inhibition by protease inhibitors. Close monitoring is required in the management of tacrolimus and sirolimus dosing regimens when combined with ritonavir boosted HIV-1 protease inhibitors.

Population pharmacokinetic analysis for nelfinavir and its metabolite M8 in virologically controlled HIV-infected patients on HAART.

AIMS: To describe the pharmacokinetics of nelfinavir and its main metabolite M8 in HIV-infected patients with a sustained virological response, to characterize the effect of covariates and to estimate inter- and intra-individual variability in the pharmacokinetics. METHODS: Three hundred and twenty concentrations of both nelfinavir and M8 were measured in 46 patients enrolled in the COPHAR 1-ANRS 102 study. Blood samples were taken at a first visit (one sample before drug administration and four samples at fixed times after) and at a second visit 1 to 3 months later (one before and one 3 h after drug administration). The data from both visits on nelfinavir and M8 were modelled jointly in all patients using a population approach. RESULTS: A one-compartment model with first-order absorption and elimination best described nelfinavir data, with an additional compartment incorporating a first order rate-constant describing the metabolism of the drug to M8. For nelfinavir, the apparent volume of distribution (V/F ) (95% confidence interval for the mean), was 309 l (185, 516), the absorption rate constant (k(a)) was 0.4 h(-1) (0.2, 0.8), and the apparent clearance (CL/F ) was 37.3 l h(-1) (32, 44). For M8, V(m) /(Fk(m)) and CL(m)/(Fk(m)) were 866 l h(-1) (351, 2161) and 1670 l (965, 2894), respectively. The interindividual variabilities were 34.9%, 34.3% and 62.2% for V/F, CL/F and CL(m)/(Fk(m)), respectively. The interoccasion variability was 27.8% for CL/F. The mean half-lives were 05.38 h and 00.44 h for nelfinavir and M8, respectively. Significant but opposite effects of comedication with zidovudine were found on nelfinavir CL/F and M8 CL(m)/(Fk(m)), but they were not considered to be clinically relevant. CONCLUSIONS: A joint model was found to describe adequately nelfinavir and M8 concentrations and was used to estimate pharmacokinetic parameters for M8. The model can be used to build reference pharmacokinetic profiles for therapeutic drug monitoring of the drug.

Single-dose pharmacokinetics of amprenavir coadministered with grapefruit juice.

In this crossover study in 12 healthy volunteers, coadministration of amprenavir (1,200 mg; single dose) with grapefruit juice slightly reduced the maximum concentration of drug in serum (Cmax) compared to administration with water (7.11 versus 9.10 microg/ml), slightly increased the time to Cmax (1.13 versus 0.75 h), and did not affect the area under the concentration-time curve from 0 to 12 h (AUC(0-12)), the AUC(0-infinity), or the concentration at 12 h. Therefore, grapefruit juice does not clinically significantly affect amprenavir pharmacokinetics.

In vitro effects of tacrolimus on human cytochrome P450.

Tacrolimus, a potent immunosuppressive drug, is known to be metabolized predominantly in the liver by cytochrome P450 3A (CYP3A). In order to determine the potential of tacrolimus to inhibit the metabolism of other drugs, we have investigated its inhibitory effects on specific cytochrome reactions. Specific substrates for the seven cytochromes (CYPs) 1A2, 2A6, 2C9, 2C19, 2D6, 2E1 and 3A4/5 were incubated with human hepatic microsome preparations with or without specific inhibitors or tacrolimus and the metabolites were detected by high-pressure liquid chromatography (HPLC) or fluorimetric methods. All the specific inhibitors reduced or abolished the specific CYP activity. Tacrolimus had no effect on any CYP at concentrations below 1 microM, while at higher concentrations it had a mild inhibitory effect on CYP3A4 and 3A5. These observations suggest that tacrolimus is unlikely to potentiate the effect of coadministered drugs through inhibition of their metabolism in the liver.

[Drug interactions with antiretroviral agents]. / Interactions médicamenteuses avec les antirétroviraux.

Concomitant administration of three or more antiretroviral drugs is the standard treatment for HIV-infected patients. I.p. and NNRT are metabolized by cytochrome P450 and are inhibitors or inducers of CYP3A4. Therefore a number of drug-drug interactions are likely to occur. Ritonavir, a potent CYP3A4 inhibitor, is coadministered with saquinavir, indinavir and amprenavir to enhance their plasma concentrations and their virological efficacy. In contrast, nevirapine and efavirenz are CYP3A4 inducers, which warrant an increase in i.p. dosing. These properties lead to interactions with other drugs metabolized by CYP3A4 and a knowledge or the route of biotransformation is useful to avoid side-effects or decrease efficacy (as in the case of statine coadministration). Some important interactions can lead to contraindications such as coadministration of rifampicine, astemizole, ergot derivates or cizapride, as a large decrease or increase in concentration can lead to inefficacy or to major side-effects. Clinical trials and notification of side-effects are important to detect unpredictable interactions and to propose guidelines; such an example is therapeutic drug monitoring of methadone to avoid withdrawal syndrome when coadministered with ritonavir or nelfinavir.

Conversion from cyclosporin A to tacrolimus in pediatric liver transplantation.

The dosing regimen for conversion from cyclosporin A (CsA) to tacrolimus immunosuppression was studied in 12 pediatric liver allograft recipients. Patients were stratified according to their age. Tacrolimus was started orally at a dosage of 0.05 mg/kg b.i.d., 12 h after stopping CsA administration and increased thereafter if needed. Tacrolimus and CsA concentrations were assayed by immunoassay using, respectively, an IMx and a TDx autoanalyzer (Abbott-France). Mean CsA concentration was in the therapeutic range 12 h prior to and at the time of introduction of tacrolimus. After 72 h of tacrolimus therapy, CsA concentrations were undetectable whereas mean tacrolimus concentration was 10.4 ng/mL with a mean dose of 0.09 mg/ kg b.i.d. The decline of CsA concentration was clearly biphasic. A slower decline in CsA concentration was detected after initiation of tacrolimus therapy, suggesting an inhibition of CsA metabolism by tacrolimus. No nephrotoxicity was observed. This dosage regimen allowed effective immunosuppression while avoiding additive nephrotoxicity.

Simultaneous high-performance liquid chromatographic determination of the antiretroviral agents amprenavir, nelfinavir, ritonavir, saquinavir, delavirdine and efavirenz in human plasma.

This article describes a method for the simultaneous determination of four licensed HIV protease inhibitors (amprenavir, nelfinavir, saquinavir and ritonavir) and two novel non-nucleoside reverse transcriptase inhibitors (efavirenz and delavirdine) in human plasma in a single run. Plasma samples (500 microl) were treated by liquid-liquid extraction with methyl tert.-butyl ether. The compounds were separated by reversed-phase liquid chromatography on a C(18) column with spectrophotometric detection at 260 nm. The method is linear over the specific ranges investigated, accurate (inaccuracy <11.7%) and showed intra-day and inter-day precision within the ranges of 0.9-7.0 and 1.9-8.8%, respectively. The six compounds were stable in plasma after 6 months of storage at -20 degrees C and after five freeze-thaw cycles.

In vitro effects of racemates, separate enantiomers and major metabolites of mefloquine and halofantrine on metoprolol biotransformation by rat liver microsomes.

1. The effects of the anti-malarial drugs mefloquine and halofantrine and of their major metabolites on metoprolol metabolism by rat liver microsomes have been investigated. 2. The observed Km and Vmax, and the formation kinetics of alpha-hydroxymetoprolol and O-demethylmetoprolol, two major metoprolol metabolites, were in keeping with published data. 3. In vitro, mefloquine competitively inhibited metoprolol biotransformation, whereas halofantrine did so in a mixed fashion. The mefloquine Ki of metoprolol alpha-hydroxylation and O-demethylation were 3.4 and 5.8 microM respectively, whereas those of halofantrine were 0.15 and 0.32 microM respectively. 4. The main metabolites, N-debutylhalofantrine and carboxymefloquine, were 4-10-fold less inhibitory than the parent drugs. The difference in inhibitory potency of parent drugs and metabolites was higher for halofantrine than for mefloquine. The potency order for metoprolol metabolism inhibition was halofantrine >> mefloquine = N-debutylhalofantrine > carboxymefloquine. 5. A preliminary study with anti-malarial enantiomers showed a weak difference, in metoprolol metabolism inhibition between the enantiomers of halofantrine or mefloquine. 6. It is concluded that halofantrine is a potent inhibitor of metoprolol metabolism and that halofantrine metabolites or its enantiomers may have a different inhibitor potency than the parent drug: (1) the inhibition potency of these compounds should be studied in vitro and (2) their in vivo elimination half-life and plasma concentrations should be taken into be account to extrapolate this experimental results to in vivo.