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# Tab 20 voihep (Tenofovir Disoproxil Fumarate)
## Overview
Tenofovir disoproxil fumarate (TDF) is a nucleotide analog reverse transcriptase inhibitor (NtRTI) used in the treatment of chronic hepatitis B virus (HBV) infection and as part of combination antiretroviral therapy (ART) for the treatment of human immunodeficiency virus (HIV) infection.
## Primary Indications
* Chronic Hepatitis B Virus (HBV) Infection
* Human Immunodeficiency Virus (HIV) Infection (in combination ART)
## Adult Dosing
* **Chronic HBV:** 300 mg orally once daily.
* **HIV:** 300 mg orally once daily in combination with other antiretroviral agents.
## Pediatric Dosing
* **HIV (ages 2 to <12 years, weight 17 kg to <60 kg):** 11 mg/kg orally once daily, not to exceed 300 mg/day.
* **HIV (ages 2 to <12 years, weight ≥60 kg):** 300 mg orally once daily.
* **HIV (ages 12 to <18 years):** 300 mg orally once daily.
* **Chronic HBV:** Dosing in pediatric patients for HBV is not established.
## Dose Adjustments
No dose adjustment is necessary for patients with mild to moderate renal impairment. Dose reduction is recommended for severe renal impairment. Consult specific renal dosing guidelines.
## Contraindications
* Hypersensitivity to tenofovir disoproxil fumarate or any component of the formulation.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain, headache, dizziness, rash, asthenia.
* **Serious:**
* **Nephrotoxicity:** Acute kidney injury, proximal tubulopathy (Fanconi syndrome), renal failure.
* **Lactic Acidosis:** Potentially fatal complication, especially in women and obese patients.
* **Hepatotoxicity:** Exacerbation of hepatitis B upon discontinuation, liver decompensation.
* **Bone Mineral Density:** Decreased bone mineral density (osteopenia, osteoporosis) and increased risk of fractures.
* **Immune Reconstitution Inflammatory Syndrome (IRIS):** Can occur in patients with advanced HIV infection when ART is initiated.
## Key Drug Interactions
* **Nephrotoxic Agents:** Concurrent use with drugs that are renally toxic (e.g., certain NSAIDs, aminoglycosides, contrast media, cyclosporine) may increase the risk of renal adverse events.
* **Didanosine:** Increased risk of pancreatitis and mitochondrial toxicity. Concurrent use is generally not recommended.
* **HIV Protease Inhibitors (e.g., ritonavir, lopinavir):** May increase tenofovir concentrations. Monitor renal function.
## Monitoring
* **Renal Function:** Serum creatinine, BUN, and urinalysis at baseline and periodically throughout treatment.
* **Bone Mineral Density:** Consider baseline assessment and periodic monitoring, especially in patients with risk factors for bone disease.
* **Liver Function Tests:** ALT, AST, bilirubin, albumin, prothrombin time in patients with HBV.
* **Viral Load:** HBV DNA or HIV RNA.
* **Electrolytes:** Particularly phosphate.
## Clinical Pearls
* TDF is associated with renal toxicity and decreased bone mineral density. Consider alternative agents (e.g., tenofovir alafenamide) in patients with pre-existing renal or bone disease.
* Discontinuation of TDF in patients with chronic HBV may lead to severe hepatitis B exacerbation. Gradual withdrawal with close monitoring is recommended.
* Ensure adequate hydration to minimize the risk of renal toxicity.
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*This information is intended for clinical pharmacists and should not replace full prescribing information. Always consult the most current official product monograph and relevant clinical guidelines for complete and up-to-date information.*
