Methadone Tenofovir

In a study in 13 healthy subjects receiving methadone, tenofovir 300 mg daily for 2 weeks did not alter the pharmacokinetics of methadone, and no symptoms of opioid toxicity or opioid withdrawal were detected. ... 

The buffer in didanosine tablets and powder interferes with absorption of indinavir, delavirdine, atazanavir, dapsone, itraconazole, and fluoroquinolone agents therefore, administration should be separated in time. Serum levels of didanosine are increased when -administered with tenofovir or ganciclovir, and are decreased by atazanavir, delavirdine, ritonavir, tipranavir, and methadone (Table 49-4). 

Allopurinol increases didanosine plasma concentrations and their coadministration is not recommended. Ganciclovir, tenofovir and disoproxil also increase didanosine plasma concentrations, and dose reduction is recommended. Conversely, methadone decreases didanosine plasma concentrations, and appropriate doses for the combination have not been established. Didanosine should not be administered with drugs that cause pancreatic or neurotoxicity. Ribavirin increases its risk of toxicity and should not be coadministered. 

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... 

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. 

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. 

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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