Tenofovir

Also written as Tenofovir disoproxil fumarate, Viread.

Tenofovir is a nucleotide reverse‑transcriptase inhibitor used for chronic hepatitis B and HIV. It blocks viral DNA synthesis, reducing viral load and disease progression.

Overview

Tenofovir is taken orally and converted in cells to an active diphosphate that mimics deoxyadenosine triphosphate, causing chain termination during viral DNA replication.

• Active against HIV‑1, HIV‑2, and hepatitis B virus (HBV).
• Low oral bioavailability; given as pro‑drug (TDF) to improve absorption.

Key concepts

Understanding tenofovir requires linking its mechanism to clinical outcomes and safety concerns, especially renal and bone effects.

• Renal tubular secretion can be impaired → proximal tubulopathy.
• Reduced bone mineral density due to phosphate wasting.

Clinical relevance

Tenofovir is a backbone of first‑line antiretroviral therapy (ART) and the preferred oral agent for chronic HBV in most guidelines.

• Serum creatinine & eGFR: Is renal function adequate for tenofovir? Normal or rising creatinine signals need to adjust or stop drug.
• Serum phosphate: Is there tubular phosphate loss? Low phosphate suggests Fanconi‑type toxicity.
• Bone mineral density (DXA) if available: Is there significant bone loss? Decline may prompt switching to tenofovir alafenamide or other agents.

• Used in combination with other ART drugs to prevent resistance.
• Preferred in patients co‑infected with HIV and HBV.

Exam pearls

Focus on mechanism, indications, and major toxicities; know how to monitor and what to do when labs are unavailable.

• Tenofovir → chain termination after incorporation into viral DNA.
• Key toxicity: proximal renal tubulopathy → monitor creatinine, phosphate.
• If eGFR <30 mL/min, avoid tenofovir; consider alternative regimen.

Common mistakes

Students often confuse tenofovir with other nucleoside analogues or overlook its renal safety monitoring.

• Mixing up tenofovir with lamivudine – different resistance profiles.
• Assuming normal creatinine rules out toxicity – need trend and urine analysis.
• Continuing tenofovir after severe acute kidney injury.

Questions an examiner may ask

• Explain how tenofovir inhibits viral replication and why resistance is rare when used in combination therapy.
• List the monitoring parameters for a patient started on tenofovir and interpret abnormal results.
• Describe the management steps when a patient on tenofovir develops proximal tubulopathy.

When to seek help

• Acute rise in serum creatinine >0.5 mg/dL within days
• New onset proteinuria or glucosuria with normal blood glucose
• Severe bone pain with fractures

Quick questions

Can tenofovir be used in pregnancy?

Yes, it is category B and recommended for HIV/HBV co‑infection when benefits outweigh risks.

What if renal testing is not available?

Use urine dipstick for protein/glucose and monitor blood pressure; if abnormalities appear, stop tenofovir and refer.

Why switch to tenofovir alafenamide (TAF)?

TAF delivers lower systemic exposure, reducing renal and bone toxicity while maintaining antiviral efficacy.