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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 phosphorylated intracellularly to its active diphosphate form, tenofovir diphosphate. This active metabolite competes with deoxyadenosine triphosphate for incorporation into viral DNA by viral reverse transcriptase, leading to DNA chain termination. ## 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 * **HIV-1 Infection:** * Ages 2 to <12 years or weighing 17 kg to <22 kg: 10 mg/kg orally once daily (maximum 300 mg). * Ages 2 to <12 years or weighing 22 kg to <40 kg: 5 mg/kg orally once daily (maximum 300 mg). * Ages 2 to <12 years or weighing ≥40 kg: 300 mg orally once daily. * Ages 6 months to <2 years: Dosing depends on specific weight bands and may require further consultation of the prescribing information or local protocol. * **Chronic Hepatitis B:** * Pediatric patients 12 years and older weighing at least 35 kg: 300 mg orally once daily. * Use in pediatric patients younger than 12 years for HBV is not generally recommended. ## Dose Adjustments * **Renal Impairment:** Dose adjustment is required based on creatinine clearance (CrCl). * CrCl 50 to 80 mL/min: 300 mg every 24 hours. * CrCl 30 to <50 mL/min: 300 mg every 48 hours. * CrCl 10 to <30 mL/min: 300 mg every 72 hours. * CrCl <10 mL/min or on hemodialysis: 300 mg every 7 days after hemodialysis. * Consult prescribing information for specific adjustments for patients with CrCl < 10 mL/min not on hemodialysis. ## Contraindications * Hypersensitivity to tenofovir disoproxil fumarate or any of its components. ## Adverse Effects * **Common:** Diarrhea, nausea, vomiting, abdominal pain, headache, dizziness, rash. * **Serious:** * **Renal Impairment:** Acute kidney injury, Fanconi syndrome, proximal tubulopathy. Risk is increased with concomitant nephrotoxic agents. * **Bone Abnormalities:** Decreased bone mineral density (osteomalacia, osteoporosis) leading to fractures. * **Lactic Acidosis:** Potentially fatal, especially in combination with other NRTIs. * **Hepatotoxicity:** Exacerbation of hepatitis B, hepatic decompensation. * **Immune Reconstitution Inflammatory Syndrome (IRIS):** May occur in HIV-infected patients treated with combination antiretroviral therapy. ## Key Drug Interactions * **Nephrotoxic Agents:** Increased risk of renal toxicity when co-administered with drugs that can impair renal function (e.g., NSAIDs, certain antibiotics like aminoglycosides, certain antivirals like adefovir, cidofovir). * **Didanosine:** Increased risk of pancreatitis and peripheral neuropathy. Avoid co-administration. If co-administration is necessary, consider reducing the didanosine dose. * **Lopinavir/Ritonavir:** No dose adjustment of TDF is generally required, but patients should be monitored for renal toxicity. ## Monitoring * **Baseline and periodic renal function tests:** Serum creatinine, BUN, urinalysis (proteinuria, glucosuria), and CrCl. * **Baseline and periodic serum phosphate.** * **Bone mineral density:** Particularly in patients with risk factors for bone disease. * **Liver function tests:** In patients with chronic hepatitis B, monitor for signs of hepatic decompensation. * **HIV viral load and CD4 count:** For HIV treatment. * **HBV DNA levels:** For chronic hepatitis B treatment. ## Clinical Pearls * TDF can be taken with or without food. * Ensure adequate hydration to minimize the risk of renal toxicity. * Consider tenofovir alafenamide (TAF) as an alternative for patients at higher risk for renal or bone toxicity, as TAF has a different pharmacokinetic profile with lower plasma concentrations of tenofovir. * Discontinuation in HBV patients may lead to severe hepatitis B exacerbation; monitor liver function closely after discontinuation. *** **Disclaimer:** This information is intended for educational purposes only and does not constitute medical advice. Always consult the most current prescribing information and your healthcare provider for any medical decisions or before making any changes to your medication regimen.