Tenofovir

Brand Names: Viread, Truvada (combination with emtricitabine), Descovy (combination with emtricitabine alafenamide)

Drug Class: Nucleotide Reverse Transcriptase Inhibitor (NRTI)

Overview

Tenofovir disoproxil fumarate is a nucleotide reverse transcriptase inhibitor used for the treatment of HIV-1 infection and chronic hepatitis B virus infection. It works by inhibiting viral replication through incorporation into viral DNA, leading to chain termination. The drug is also used in combination with emtricitabine for HIV-1 pre-exposure prophylaxis (PrEP) in at-risk individuals.

Mechanism of Action

Tenofovir disoproxil fumarate is a prodrug that is converted to tenofovir, which is then phosphorylated to tenofovir diphosphate. Tenofovir diphosphate inhibits HIV-1 reverse transcriptase and HBV polymerase by competing with the natural substrate deoxyadenosine 5'-triphosphate and, after incorporation into DNA, causes chain termination.

Indications

  • Treatment of HIV-1 infection in combination with other antiretroviral agents
  • Treatment of chronic hepatitis B virus infection
  • HIV-1 pre-exposure prophylaxis (PrEP) in combination with emtricitabine for at-risk individuals

Common Doses

  • 300 mg
  • 200 mg/300 mg (combination with emtricitabine)

Dosage

For HIV-1 treatment: 300 mg once daily. For chronic hepatitis B: 300 mg once daily. For HIV-1 PrEP (with emtricitabine): 200 mg/300 mg once daily. Dosage adjustments required for renal impairment.

Contraindications

  • Use in individuals with unknown or positive HIV-1 status when prescribed for HIV-1 PrEP
  • Severe renal impairment (creatinine clearance <30 mL/min) without dose adjustment

Side Effects

  • Nausea
  • Diarrhea
  • Headache
  • Fatigue
  • Renal impairment
  • Decreased bone mineral density
  • Lactic acidosis
  • Hepatomegaly with steatosis
  • Exacerbation of hepatitis B upon discontinuation

Interactions

  • Drugs that reduce renal function may increase tenofovir concentrations
  • Concomitant use with other nephrotoxic drugs increases risk of renal toxicity
  • Didanosine coadministration may increase didanosine concentrations

Counseling Points

  • Take exactly as prescribed, typically once daily with or without food
  • For HIV-1 PrEP, must have confirmed negative HIV-1 status before initiation and every 3 months during therapy
  • Report symptoms of lactic acidosis (nausea, vomiting, abdominal pain, weakness)
  • Monitor for signs of kidney problems (changes in urine output, swelling)
  • Do not stop medication without consulting healthcare provider, especially if HBV-infected
  • Use additional barrier protection methods for HIV prevention during PrEP therapy
  • Regular monitoring of renal function and bone density recommended