Tenofovir disoproxil fumarate-emtricitabine coformulation for once-daily dual NRTI backbone

Truvada is the coformulation of tenofovir disoproxil fumarate (TDF; 300 mg) and emtricitabine (FTC; 200 mg) in a single tablet, providing the nucleotide backbone for once-daily dosing, as a component of highly active antiretroviral therapy (HAART). TDF (the bioavailable prodrug of tenofovir) is hydrolyzed to tenofovir intracellularly and phosphorylated to the active metabolite, tenofovir diphosphate. Tenofovir is a nucleotide analog of deoxyadenosine monophosphate, with activity against HIV-1, -2 and hepatitis B virus. FTC, the fluorinated derivative of lamivudine, is an analog of deoxycitidine, active against HIV-1, -2 and hepatitis B virus. Their long half-lives in plasma and in peripheral blood mononuclear cells allow once-daily dosing. Both are eliminated renally. Resistance mutation K65R is selected for by tenofovir and confers a two- to fourfold reduced susceptibility to this drug. The incidence of K65R is low (3%) and has not been observed in clinical trials with the concomitant use of tenofovir and FTC. FTC selects for M184V mutation less frequently than lamivudine. Tenofovir drug interactions include increased exposure to didanosine and inferior immune recovery that preclude their concomitant use. Boosted protease inhibitors increase exposure to tenofovir without dose adjustment required. FTC has no significant drug interactions. They are not metabolized by cytochrome P450, which confers little potential for interactions with drugs metabolized by these enzymes. As tenofovir and FTC are renally eliminated, drugs eliminated by tubular secretion must be avoided. Both antiretrovirals, as individual agents and in coadministration have evidenced antiviral potency in clinical trials. Pivotal study 934 evidenced superior efficacy of the combination TDF/FTC/efavirenz (EFV) versus zidovudine/FTC/EFV. The toxicity profile of tenofovir and FTC has been extensively studied. Lipid profile is more favorable with tenofovir than thymidine analog. Tenofovir requires surveillance of glomerular filtration rate and dosing interval adjustment when creatinine clearance is less than 50 ml/min and avoidance less than 30 ml/min. Fat loss is less likely with tenofovir than with thymidine analog. Clinical trials have assessed the performance of the coformulation of TDF and FTC.