Tenofovir alafenamide (TAF) is a novel prodrug of tenofovir, a nucleotide reverse transcriptase inhibitor (NRTI). It is designed to deliver the active metabolite, tenofovir diphosphate, more efficiently to target cells (lymphocytes and macrophages) while minimizing systemic exposure. This results in potent antiviral activity against HIV-1 and HBV at a significantly lower dose (25mg) compared to the older prodrug tenofovir disoproxil fumarate (TDF, 300mg), leading to an improved renal and bone safety profile. It is a cornerstone of modern antiretroviral therapy (ART) and hepatitis B treatment in India.
Adult: HIV-1 Treatment: One tablet containing TAF 25mg once daily with food, as part of a complete ART regimen (e.g., TAF 25mg + Emtricitabine 200mg). HBV Treatment: One tablet containing TAF 25mg once daily with food. Note: Dosage is based on the FDC; TAF 25mg is rarely available as a standalone tablet.
Note: Must be taken orally with food to enhance bioavailability. Swallow whole; do not crush, split, or chew. Maintain strict adherence to the prescribed schedule. If a dose is missed, take it as soon as remembered unless it is almost time for the next dose. Do not double the dose.
TAF is a phosphonamidate prodrug of tenofovir. It is more stable in plasma than TDF, leading to lower circulating tenofovir levels. It enters target cells (CD4+ cells, hepatocytes) efficiently via passive diffusion and potentially specific transporters. Intracellularly, it is cleaved by cathepsin A to release tenofovir, which is then phosphorylated by cellular kinases to its active form, tenofovir diphosphate (TFV-DP). TFV-DP acts as a competitive inhibitor of viral reverse transcriptase (HIV) and DNA polymerase (HBV). It is incorporated into the growing viral DNA chain, causing chain termination due to the lack of a 3'-OH group, thereby inhibiting viral replication.
Pregnancy: Pregnancy Category B. Animal studies show no risk, but adequate human studies are lacking. TAF crosses the placenta. It is recommended as a preferred NRTI component in ART regimens for pregnant women living with HIV due to its efficacy and improved safety profile. The benefit of treating HIV/HBV outweighs potential risks. Use under specialist supervision.
Driving: Dizziness and fatigue have been reported. Patients should be cautioned about operating machinery or driving if they experience these effects.
| Rifabutin, Rifampicin, Rifapentine (strong CYP inducers) | Significantly decrease TAF plasma concentrations, leading to loss of virological response and possible resistance. | Major - Contraindicated or requires alternative agent. |
| Carbamazepine, Phenytoin, Phenobarbital (anticonvulsants) | May decrease TAF levels. Use alternative anticonvulsant or monitor virological response closely. | Major |
| St. John's Wort (Hypericum perforatum) | Decreases TAF plasma concentration. Contraindicated. | Major |
| Nephrotoxic drugs (e.g., Aminoglycosides, Amphotericin B, Ganciclovir, NSAIDs like Ibuprofen, Diclofenac) | May increase risk of renal impairment. Monitor renal function. | Moderate |
| Drugs that inhibit renal transporters (e.g., Cidofovir, High-dose or multiple NSAIDs) | May increase tenofovir concentrations. Monitor for renal effects. | Moderate |
| Antacids containing Aluminium/Magnesium Hydroxide | May be taken simultaneously with TAF if taken with food. No significant interaction when administered with food. | Minor |