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# Tab Voihep (Tenofovir Disoproxil Fumarate) ## Overview Tenofovir disoproxil fumarate (TDF) is a nucleoside reverse transcriptase inhibitor (NRTI) used in the treatment of chronic hepatitis B virus (HBV) infection and as part of combination antiretroviral therapy (cART) for human immunodeficiency virus (HIV) infection. ## Primary Indications * Treatment of chronic hepatitis B virus (HBV) infection in adults and pediatric patients. * Treatment of HIV infection in adults and pediatric patients as part of combination therapy. ## Adult Dosing * **Chronic Hepatitis B:** 300 mg orally once daily. * **HIV Infection:** 300 mg orally once daily, typically in combination with other antiretroviral agents. ## Pediatric Dosing * **Chronic Hepatitis B:** * Ages 12 to <18 years: 300 mg orally once daily. * Ages 2 to <12 years: Dosing depends on weight. Refer to specific pediatric guidelines or product labeling for weight-based dosing (e.g., 8 mg/kg/dose orally once daily, not to exceed 300 mg/day). * **HIV Infection:** * Ages 2 to <12 years: Dosing depends on weight. Refer to specific pediatric guidelines or product labeling for weight-based dosing. * Ages 6 months to <2 years: Dosing depends on weight and formulation. Refer to specific pediatric guidelines or product labeling. ## Dose Adjustments * **Renal Impairment:** Dose adjustment is required based on creatinine clearance (CrCl). * CrCl 50-80 mL/min: 300 mg every 24 hours. * CrCl 30-49 mL/min: 300 mg every 48 hours. * CrCl 10-29 mL/min: 300 mg every 72 hours. * CrCl <10 mL/min or patients on hemodialysis: 300 mg every 7 days or after 4 hours of hemodialysis. * Dosing frequency should be adjusted based on CrCl. * **Hepatic Impairment:** No dose adjustment is generally required. ## Contraindications * Hypersensitivity to tenofovir disoproxil fumarate or any component of the formulation. ## Adverse Effects * **Common:** Nausea, diarrhea, vomiting, abdominal pain, headache, dizziness, rash. * **Serious:** Renal toxicity (Fanconi syndrome, acute kidney injury), bone mineral density loss (osteomalacia, decreased bone mineral density), lactic acidosis, hepatomegaly with steatosis, exacerbations of hepatitis B upon discontinuation. ## Key Drug Interactions * **Nephrotoxic Agents:** Concomitant use with drugs that are potentially nephrotoxic (e.g., NSAIDs, certain diuretics, aminoglycosides) may increase the risk of renal adverse events. * **Didanosine:** Coadministration with didanosine can increase didanosine plasma concentrations, potentially leading to increased adverse events. A dose reduction of didanosine is recommended. * **Lamiuvdine:** Generally well-tolerated together. * **Emtricitabine:** Generally well-tolerated together. ## Monitoring * **Renal Function:** Serum creatinine and estimated glomerular filtration rate (eGFR) regularly, especially in patients with pre-existing renal impairment or those taking other nephrotoxic drugs. Monitor urine glucose and protein. * **Bone Mineral Density:** Consider monitoring bone mineral density, particularly in patients with a history of fractures or other risk factors for osteoporosis. * **Liver Function:** Liver function tests (ALT, AST, bilirubin) regularly. * **HBV DNA Levels:** Monitor viral load to assess treatment efficacy. * **Viral Resistance:** Consider resistance testing if treatment failure occurs. ## Clinical Pearls * TDF should be taken with food to improve absorption. * Discontinuation of TDF in patients with chronic HBV may lead to severe, acute exacerbations of hepatitis B. Consider monitoring and follow-up for at least several months after stopping treatment. * Patients with HIV should not use TDF alone for treatment. * Consider tenofovir alafenamide (TAF) as an alternative to TDF for patients at higher risk of renal or bone toxicity, as TAF has a better renal and bone safety profile. *** *Disclaimer: This information is intended for clinical use and does not substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions.*