Introduction
Tenofovir disoproxil is an antiretroviral medication primarily used for the treatment of HIV and chronic hepatitis B infections. It is a prodrug of tenofovir, a nucleotide reverse transcriptase inhibitor (NRTI), which helps reduce viral load in the body. This drug is often prescribed in combination with other antiretrovirals for HIV management and as monotherapy or combination therapy for hepatitis B.
Uses
Tenofovir disoproxil is used for:
- Treatment of HIV-1 infection in adults and children aged 2 years and older, in combination with other antiretroviral agents.
- Treatment of chronic hepatitis B infection in adults and pediatric patients aged 12 years and older.
- Off-label use for pre-exposure prophylaxis (PrEP) to prevent HIV infection in high-risk individuals.
| Brand Name | Retrovir |
|---|---|
| Type | Tablet |
| Weight | 300 mg |
| Generic | Tenofovir Disoproxil |
| Manufacturer | Pharmasia Limited |
| Available in | English বাংলা |
Mechanism of Action
Tenofovir disoproxil is converted into its active form, tenofovir diphosphate, inside the body. Tenofovir diphosphate works by inhibiting reverse transcriptase, an enzyme critical for the replication of HIV and hepatitis B viruses. It integrates into the viral DNA, causing premature chain termination and thus preventing further viral replication.
How Long Does It Take to Work?
The antiviral effects of tenofovir disoproxil can be seen within a few weeks of therapy, but complete suppression of the virus may take several months, especially in chronic hepatitis B treatment.
Absorption
Tenofovir disoproxil is rapidly absorbed after oral administration and has a bioavailability of about 25%. Taking the drug with food increases its bioavailability and absorption efficiency.
Route of Elimination
Tenofovir is primarily eliminated by the kidneys through glomerular filtration and active tubular secretion. A small amount is excreted unchanged in the urine.
Dosage
The size and frequency of the dosage must be adjusted to the needs of the individual patient. Tenofovir disoproxil 245 mg oral tablets should be administered once daily orally, without regard to food.Recommended Dose in Adults: For the treatment of HIV-1 or chronic hepatitis B: The dose is 245 mg Tenofovir tablet once daily taken orally, without regard to food. In the treatment of chronic hepatitis B, the optimal duration of treatment is unknown.
Recommended Dose in Pediatric Patients (12 years of age and older and greater than or equal to 35 kg): For the treatment of HIV-1 in pediatric patients 12 years of age and older with body weight greater than or equal to 35 kg: The dose is one 245 mg Tenofovir tablet once daily taken orally, without regard to food.
For HIV-1 infection:
- Adults: 300 mg orally once daily, in combination with other antiretroviral agents.
- Pediatrics (2 years and older, weighing at least 17 kg): Dosage is based on body weight.
- Adults: 300 mg orally once daily.
- Pediatrics (12 years and older): Dosage is the same as adults.
- Adults: 300 mg orally once daily, in combination with emtricitabine.
Administration
Tenofovir disoproxil is administered orally, with or without food, although taking it with food enhances absorption. It is available in tablet form.
Side Effects
Common side effects include:
- Nausea
- Diarrhea
- Headache
- Dizziness
- Fatigue
Serious side effects include lactic acidosis, liver toxicity, kidney problems, and reduced bone mineral density.
Toxicity
High doses of tenofovir can result in toxicity, particularly affecting the kidneys (renal toxicity) and bone (osteomalacia or decreased bone mineral density). Signs of overdose may include fatigue, muscle pain, and kidney dysfunction.
Precautions
Patients with pre-existing kidney disease, bone disease, or liver problems should use tenofovir with caution. Regular monitoring of renal function is recommended during long-term therapy. Dosage adjustments may be necessary in individuals with renal impairment.
Interaction
Drug Interactions
Tenofovir disoproxil may interact with other nephrotoxic drugs, increasing the risk of kidney damage. It also interacts with certain antiretrovirals, particularly protease inhibitors, which may increase the concentration of tenofovir in the bloodstream. Concomitant use with adefovir is not recommended.
Food Interactions
Taking tenofovir disoproxil with food increases its absorption, leading to higher concentrations in the blood.
Disease Interactions
Patients with liver disease, especially those with chronic hepatitis B or cirrhosis, should be monitored closely due to the potential for liver toxicity.
Pregnancy Use
Tenofovir disoproxil is classified as pregnancy category B, indicating that animal studies have not demonstrated a risk to the fetus, but there are no well-controlled studies in pregnant women. It is commonly used in pregnant women with HIV to prevent mother-to-child transmission of the virus.
Lactation Use
Tenofovir is excreted in breast milk, but its effect on a nursing infant is not well understood. HIV-infected mothers are generally advised not to breastfeed to prevent the transmission of the virus to the infant.
Acute Overdose
In the case of an overdose, supportive measures should be taken. Hemodialysis can effectively remove tenofovir from the bloodstream due to its relatively high clearance rate during dialysis.
Contraindication
Tenofovir disoproxil is contraindicated in patients with a known hypersensitivity to tenofovir or any of its components. It should also be avoided in those with severe renal impairment (creatinine clearance <30 mL/min) unless dosage adjustments are possible.
Use Direction
Patients should follow the prescribed dosage and timing of tenofovir disoproxil strictly. Missing doses can lead to drug resistance, particularly in the treatment of HIV. Patients should also avoid sharing the medication with others.
Storage Conditions
Store tenofovir disoproxil tablets at room temperature (20°C to 25°C) in a tightly sealed container. Protect from moisture and keep out of reach of children.
Volume of Distribution
The volume of distribution of tenofovir is approximately 1.3 liters per kilogram.
Half-Life
The half-life of tenofovir disoproxil is approximately 17 hours in plasma. This allows for once-daily dosing.
Clearance
The renal clearance of tenofovir is around 210 mL/min, with the drug being eliminated largely unchanged by the kidneys.
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