Methadone Abacavir

Zidovudine had no effect on methadone levels in one study, but there is one report of a patient requiring a modest increase in methadone dose after starting zidovudine. Similarly case reports describe patients requiring a modest increase in methadone dose after starting abacavir. Methadone can increase zidovudine serum levels, and reduce levels of abacavir, stavudine, and didano-sine from the tablet formulation, but not the enteric-coated capsule preparation. Tenofovir, and a single dose of zidovu-dine/lamivudine had no effect on methadone pharmacokinetics. 

Drugs that might affect amprenavir include abacavir, aldesleukin, antacids, anticonvulsants, azole antifungals, clarithromycin, cyclosporine, dexamethasone, buffered didanosine, disulfiram, ethanol, indinavir, methadone, metronidazole, nelfinavir, nonnucleoside reverse transcriptase inhibitors, oral contraceptives, rifamycins, ritonavir, saquinavir, St. John s wort, tacrolimus, and zidovudine. 

Bart PA, Rizzardi PG, Gallant S, Golay KP, Baumann P, Pantaleo G, Eap CB. Methadone blood concentrations are decreased by the administration of abacavir plus amprena-vir. Ther Drug Monit 2001 23(5) 553-5. 

METHADONE NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS 1 efficacy of methadone when co-administered with abacavir Uncertain possibly enzyme induction Monitor for opioid withdrawal and consider increasing dose... 

Clinically important, potentially hazardous interactions with abacavir, atorvastatin, bepridil, bupropion, carbamazepine, clarithromycin, cyclosporine, dexamethasone, digoxin, felodipine, fluticasone propionate, fosamprenavir, itraconazole, ketoconazole, lovastatin, methadone, midazolam, nicardipine, nifedipine, phenobarbital, phenytoin, rifabutin, simvastatin, sirolimus, St John s wort, systemic lidocaine, tacrolimus, tenofovir, trazodone, vinblastine, vincristine, voriconazole, warfarin, zidovudine... 

The reduction in stavudine levels and the changes in abacavir peak levels with methadone are probably not clinically relevant, but again, further data are required. The reports with abacavir suggest that it would be prudent to monitor methadone dose requirements when this drug is started. Tenofovir does not appear to affect methadone levels. 

Sellers E, Lam R, McDowell J, Corrigan B, Hedayetullah N, Somer G, Kirby L, Kersey K, Yuen G. The pharmacokinetics of abacavir and methadone following coadministiaticn CNAA1012. InUrsci Conf Antimicrd) Agents Chemother 999) 39, 663. 

A study involving 16 opioid-dependent subjects found that amprenavir 1.2 g twice daily for 10 days decreased the AUCs for both f -methadone (active enantiomer) and 5-methadone (inactive enantiomer) by 13% and 40%, respectively. No clinically significant changes were noted in opioid effects and there was no evidence of opioid withdrawal. However, in another study methadone levels were reduced by 35% (range 28% to 87%) in 5 patients within 17 days of starting to take amprenavir 1.2 g twice daily and abacavir 600 mg twice daily. Two patients reported nausea before their daily methadone dose, which can be a sign of opiate withdrawal. Note that abacavir , (p.l75), may modestly reduce methadone levels, and could therefore have contributed to this effect. 

Cardiovascular A 57-year-old man with HIV infection taking abacavir, nevirapine, tenofovir, voriconazole, and methadone developed new-onset seizures [69 ]. An electrocardiogram showed sinus bradycardia and a prolonged QT interval of 690 msec. He had several episodes of torsade de pointes and ventricular tachycardia, which resolved spontaneously. They were accompanied by altered cognition and... 

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