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# Tenofovir Disoproxil Fumarate (TDF)
## Overview
Tenofovir disoproxil fumarate (TDF) is a nucleoside reverse transcriptase inhibitor (NRTI) used in the treatment of HIV infection and chronic Hepatitis B virus (HBV) infection.
## Primary Indications
* Treatment of Human Immunodeficiency Virus (HIV) 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 (6 weeks to less than 12 years and weighing 17 kg to less than 22 kg):** 10 mg/kg orally once daily.
* **HIV-1 Infection (6 years to less than 12 years and weighing 22 kg to less than 40 kg):** 15 mg/kg orally once daily.
* **HIV-1 Infection (12 years to less than 18 years and weighing less than 35 kg):** 10 mg/kg orally once daily.
* **HIV-1 Infection (12 years to less than 18 years and weighing 35 kg or more):** 300 mg orally once daily.
* **Chronic Hepatitis B:** Data is limited for pediatric use, consult specialist literature.
## Dose Adjustments
* **Renal Impairment (Adults):** Dosage adjustment is required based on creatinine clearance.
* CrCl 30-49 mL/min: 300 mg every 48 hours.
* CrCl < 30 mL/min (and not on hemodialysis): 300 mg every 72 hours.
* On hemodialysis: 300 mg every 7 days after a full weekly dose.
* **Pediatric Renal Impairment:** Dose adjustments based on renal function are not well-established. Exercise caution.
## Contraindications
* Hypersensitivity to tenofovir disoproxil fumarate or any of its components.
## Adverse Effects
* **Common:** Diarrhea, nausea, headache, rash, asthenia.
* **Serious:**
* **Nephrotoxicity:** Proximal tubulopathy, Fanconi syndrome, acute renal failure. Risk is increased with concomitant nephrotoxic agents.
* **Bone Mineral Density:** Decreased bone mineral density leading to osteomalacia and fractures.
* **Lactic Acidosis:** Potentially fatal, especially in women and obese patients.
* Hepatotoxicity (exacerbation of HBV).
## Key Drug Interactions
* **Nephrotoxic Agents:** Concomitant use with drugs that are potentially nephrotoxic (e.g., aminoglycosides, NSAIDs, certain antivirals like adefovir dipivoxil) increases the risk of renal adverse events. Avoid if possible.
* **Didanosine:** Increased risk of pancreatitis, peripheral neuropathy, and increased 2'-3'-dideoxyadenosine concentrations. TDF dose reduction may be necessary.
* **Protease Inhibitors:** Ritonavir and cobicistat can increase TDF concentrations, potentially increasing the risk of toxicity. TDF dose reduction may be required.
## Monitoring
* **Renal function:** Serum creatinine and urinalysis (including urine protein and glucose) at baseline and periodically during treatment.
* **Bone mineral density:** Particularly in patients with a history of fractures or other risk factors for osteoporosis.
* **Liver function tests:** Including HBV DNA levels for patients treated for chronic HBV.
* **Serum electrolytes and phosphate:** Especially in patients with renal impairment.
## Clinical Pearls
* TDF is associated with renal and bone toxicity. Consider tenofovir alafenamide (TAF) as an alternative in patients with pre-existing renal or bone disease, though TAF may have different drug interaction profiles.
* TDF should be taken with food to enhance absorption.
* Discontinuation of TDF in patients with HBV may lead to severe exacerbation of hepatitis.
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*This information is intended for healthcare professionals. Always verify current prescribing information with the official product labeling and consult relevant clinical guidelines.*
