Tenofovir

What is Tenofovir?

Tenofovir is an antiviral medication belonging to a class of drugs called nucleotide reverse transcriptase inhibitors. It is primarily used to treat HIV infection and chronic hepatitis B virus (HBV) infection. The drug works by interfering with viral replication, helping to control these chronic viral conditions.

Uses

• HIV treatment: Used as part of combination therapy to treat HIV-1 infection in adults and adolescents, helping to reduce viral load and maintain immune function
• HIV prevention (PrEP): Prescribed for pre-exposure prophylaxis in high-risk individuals to prevent HIV acquisition when used consistently
• Chronic hepatitis B: Treats chronic hepatitis B virus infection in adults with evidence of active viral replication and persistent liver inflammation
• Post-exposure prophylaxis: Used as part of emergency treatment regimens following potential HIV exposure in healthcare or other high-risk settings
• HIV treatment in pregnancy: Helps prevent mother-to-child transmission of HIV when used as part of antiretroviral therapy during pregnancy

How it works

Tenofovir is converted inside cells into tenofovir diphosphate, which mimics one of the natural building blocks of viral DNA. When HIV or hepatitis B viruses attempt to replicate their genetic material, they incorporate this drug instead of the natural component, causing the viral DNA chain to terminate prematurely. This process effectively stops the virus from reproducing and spreading to new cells.

Side effects

Common side effects:

• Nausea and vomiting
• Diarrhea
• Headache
• Dizziness
• Fatigue
• Abdominal pain
• Flatulence
• Rash

Serious side effects to watch for:

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• Kidney problems including decreased kidney function
• Bone density loss and increased fracture risk
• Lactic acidosis (buildup of lactic acid in blood)
• Severe liver problems with hepatomegaly
• Immune reconstitution syndrome in HIV patients

Warnings and precautions

• Kidney monitoring required: Regular kidney function tests are essential as tenofovir can cause kidney damage, particularly in patients with pre-existing kidney disease or those taking other nephrotoxic medications
• Bone health surveillance: Long-term use may decrease bone mineral density, requiring monitoring and potential supplementation with calcium and vitamin D
• Hepatitis B flare risk: Patients with hepatitis B may experience severe liver problems if tenofovir is discontinued abruptly, requiring careful monitoring
• Pregnancy considerations: While generally considered safe during pregnancy for HIV treatment, benefits and risks should be carefully evaluated with healthcare providers
• Drug resistance concerns: Should only be used as part of combination therapy for HIV to prevent development of resistant viral strains

Interactions

• Nephrotoxic drugs: Aminoglycosides, amphotericin B, and high-dose NSAIDs may increase kidney toxicity risk when combined with tenofovir
• Didanosine: Concurrent use increases didanosine levels significantly, requiring dose reduction and careful monitoring for toxicity
• Atazanavir: This HIV protease inhibitor can increase tenofovir concentrations, potentially enhancing both efficacy and side effects
• Lopinavir/ritonavir: May increase tenofovir levels by approximately 30%, requiring monitoring for enhanced toxicity
• Hepatitis C direct-acting antivirals: Some combinations may require dose adjustments due to altered drug concentrations
• Probenecid: Can increase tenofovir levels by reducing kidney elimination of the drug
• Ledipasvir/sofosbuvir: May increase tenofovir concentrations when used together for HIV/hepatitis C coinfection
• Supplemental interactions: High-dose vitamin C may theoretically affect drug absorption, though clinical significance is unclear

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Dosage

For HIV treatment in adults, the typical dose is 300 mg once daily taken with food, always in combination with other antiretroviral medications. For chronic hepatitis B, the standard dose is also 300 mg once daily. Pre-exposure prophylaxis for HIV prevention typically uses the same 300 mg daily dose, often combined with emtricitabine in a single tablet. Kidney function must be assessed before starting treatment, and doses may need adjustment in patients with reduced kidney function. All dosing decisions should be made by a qualified healthcare provider based on individual patient factors, kidney function, and specific treatment goals.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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