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# Tenofovir Disoproxil Fumarate (TDF) - Also known as Tab 20 voihep
## Overview
Tenofovir disoproxil fumarate (TDF) is a nucleotide analog reverse transcriptase inhibitor (NtRTI) used in the treatment of HIV infection and chronic Hepatitis B virus (HBV) infection. It works by inhibiting viral reverse transcriptase, an enzyme essential for viral replication.
## Primary Indications
* Treatment of HIV-1 infection in combination with other antiretroviral agents.
* Treatment of chronic Hepatitis B virus (HBV) infection.
## Adult Dosing
* **HIV-1 Infection:** 300 mg orally once daily.
* **Chronic Hepatitis B:** 300 mg orally once daily.
## Pediatric Dosing
* **HIV-1 Infection:**
* 2 to <12 years: 10 mg/kg orally once daily, not to exceed 300 mg per dose.
* 12 years and older: 300 mg orally once daily.
* *Note: Dosing in children should be based on body weight and renal function. Specific product formulations may vary.*
## Dose Adjustments
* **Renal Impairment:** Dose adjustment is required for patients with a creatinine clearance (CrCl) < 50 mL/min.
* 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 after a full weekly dose, or approximately 300 mg after 4 hours of dialysis.
* *Dose adjustments may be guided by local protocol and serum creatinine monitoring.*
## Contraindications
* Hypersensitivity to tenofovir disoproxil fumarate or any of its components.
## Adverse Effects
* **Common:** Diarrhea, nausea, vomiting, abdominal pain, headache, dizziness, rash.
* **Serious:**
* **Nephrotoxicity:** Acute kidney injury, Fanconi syndrome, renal impairment. Monitor renal function regularly.
* **Bone Mineral Density Reduction:** Decreased bone mineral density (osteopenia, osteoporosis) and increased risk of fractures.
* **Lactic Acidosis:** Potentially fatal complication, particularly in patients with risk factors for liver disease.
* **Hepatotoxicity:** Exacerbations of HBV, hepatic decompensation (especially in patients with advanced liver disease or cirrhosis).
* **New Onset or Worsening Renal Impairment:** Can occur with concomitant use of other nephrotoxic drugs.
## Key Drug Interactions
* **Nephrotoxic Agents:** Concurrent use with other nephrotoxic drugs (e.g., aminoglycosides, NSAIDs, certain antiviral agents like adefovir dipivoxil, ciclosporin) increases the risk of renal toxicity. Separate administration or avoid if possible.
* **Didanosine:** TDF increases didanosine plasma concentrations, leading to increased risk of didanosine-related toxicities (pancreatitis, neuropathy). Use with caution or consider alternative.
* **Lopinavir/Ritonavir:** TDF increases lopinavir/ritonavir concentrations. Dose adjustment of lopinavir/ritonavir may be needed.
* **Atazanavir:** TDF may decrease atazanavir concentrations. Consider increasing atazanavir dose.
* **Anticoagulants (e.g., Warfarin):** Monitor INR closely.
## Monitoring
* **Renal Function:** Baseline and periodic serum creatinine and urinalysis (including urine protein and glucose).
* **Bone Mineral Density:** Baseline and periodic assessment, especially in patients with risk factors for osteoporosis.
* **Liver Function Tests:** Baseline and periodic liver function tests (ALT, AST, bilirubin), especially in patients with HBV.
* **Viral Load and CD4 Count:** For HIV treatment.
* **Hepatitis B Viral Load (HBV DNA):** For HBV treatment.
## Clinical Pearls
* TDF is associated with a higher risk of renal and bone toxicity compared to tenofovir alafenamide (TAF). Consider TAF for patients at increased risk of these toxicities.
* Administer TDF with food to improve absorption and reduce gastrointestinal upset.
* Discontinuation of TDF in patients with chronic HBV infection may lead to severe exacerbations of hepatitis. Monitor liver function closely after discontinuation.
* In patients with HIV and HBV co-infection, continued TDF therapy is recommended even if HIV treatment is stopped, to prevent HBV flares.
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*This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines before initiating or modifying drug therapy. Local protocols and institutional policies may also apply.*
