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# Tenofovir Disoproxil Fumarate (TDF) ## Overview Tenofovir disoproxil fumarate (TDF) is a nucleoside reverse transcriptase inhibitor (NRTI) used in the treatment of HIV-1 infection and chronic hepatitis B virus (HBV) infection. It is a prodrug of tenofovir, which is then phosphorylated intracellularly to its active diphosphate form. ## Primary Indications * Treatment of HIV-1 infection in combination with other antiretroviral agents. * Treatment of chronic hepatitis B virus (HBV) infection. ## Adult Dosing * **HIV-1 Infection:** 300 mg orally once daily. * **Chronic Hepatitis B:** 300 mg orally once daily. ## Pediatric Dosing Dosing in pediatric patients varies by age and weight. Consult specific pediatric guidelines or product labeling for detailed dosing. For example, a common regimen for HIV-1 in children aged 2 to 12 years and weighing less than 17 kg is 8 mg/kg orally once daily. For children weighing 17 kg to <22 kg, it is 6 mg/kg orally once daily. For children weighing 22 kg to <28 kg, it is 5 mg/kg orally once daily. For children weighing 28 kg to <35 kg, it is 4 mg/kg orally once daily. For children weighing 35 kg or more, the adult dose of 300 mg orally once daily is recommended. ## Dose Adjustments * **Renal Impairment:** Dose adjustment is required for patients with impaired renal function. * CrCl 30-49 mL/min: 300 mg every 48 hours. * CrCl <30 mL/min: Not recommended unless benefit outweighs risk and no alternative is available. If used, consult specific guidelines for dose and frequency. * Hemodialysis: 300 mg every 7 days after a full weekly dose, or 300 mg every 48 hours with 120 minutes of dialysis. ## Contraindications * Hypersensitivity to tenofovir disoproxil fumarate or any of its components. ## Adverse Effects * **Common:** Diarrhea, nausea, headache, rash, abdominal pain. * **Serious:** Renal toxicity (including acute kidney injury and Fanconi syndrome), bone mineral density reduction (osteomalacia, osteoporosis), lactic acidosis, hepatotoxicity (particularly with HBV treatment, can lead to exacerbations). ## Key Drug Interactions * **Nephrotoxic agents (e.g., NSAIDs, aminoglycosides, certain antivirals like cidofovir):** Increased risk of renal toxicity. * **Didanosine:** Increased risk of pancreatitis, elevated didanosine concentrations, and neuropathy. Coadministration with TDF and didanosine is generally not recommended. * **Lopinavir/Ritonavir:** TDF can increase lopinavir concentrations. Dose adjustment of lopinavir/ritonavir may be needed. * **Atazanavir:** Concurrent use with TDF may increase the risk of hyperbilirubinemia and renal toxicity. Consider dose adjustment of atazanavir or alternative agents. ## Monitoring * **Renal Function:** Serum creatinine, estimated creatinine clearance (CrCl), and urinalysis (for proteinuria and glucosuria) at baseline and regularly during treatment. * **Bone Mineral Density:** Consider assessment at baseline and periodically in patients with risk factors for bone disease. * **Liver Function Tests:** AST, ALT, bilirubin in patients with HBV. * **Viral Load and CD4 Count:** For HIV-1. * **Hepatitis B Viral Load (HBV DNA):** For chronic HBV. ## Clinical Pearls * TDF is associated with renal and bone toxicity. Careful monitoring of renal function and bone density is crucial. * Consider switching to tenofovir alafenamide (TAF) in patients with pre-existing renal impairment or high risk for renal events, as TAF has a more favorable renal and bone safety profile. * Discontinue treatment in patients who develop Fanconi syndrome. * Hepatitis B can be exacerbated upon discontinuation of TDF; monitor liver function closely after stopping therapy. *** **Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making therapeutic decisions.