Tenofovir: Medication Information and Guidelines

Medication Information and Guidelines

Tenofovir is a nucleotide reverse transcriptase inhibitor (NRTI) used in the treatment of HIV infection and chronic hepatitis B virus (HBV) infection. It is available in various formulations, including oral tablets, oral powder, and intravenous injection. Tenofovir is a key component of combination antiretroviral therapy (ART) regimens for the management of HIV/AIDS and is also used as monotherapy or in combination with other antiviral agents for the treatment of chronic HBV infection.

Recommended Dose and Dosage Regimen

The recommended dose of tenofovir varies depending on the indication, patient age, weight, renal function, and concomitant medications. For the treatment of HIV infection in adults and adolescents weighing ≥35 kg, the typical dose of tenofovir disoproxil fumarate (TDF) is 300 mg orally once daily, administered as part of a combination ART regimen. For the treatment of chronic HBV infection in adults, the recommended dose of TDF is 300 mg orally once daily, with or without food. Tenofovir alafenamide (TAF), a prodrug of tenofovir, is also available and has a lower dose due to improved pharmacokinetic properties and reduced renal and bone toxicity.

Frequency of Administration

Tenofovir is administered orally as a once-daily regimen for the treatment of HIV infection and chronic HBV infection. It should be taken consistently at the same time each day to maintain therapeutic drug levels in the body. Tenofovir can be taken with or without food, depending on the specific formulation used. For individuals unable to tolerate oral administration, intravenous formulations of tenofovir are available for use in clinical settings under medical supervision.

Route of Administration

Tenofovir is administered orally in tablet or powder form, with the option for intravenous administration in select clinical situations. Oral tablets should be swallowed whole with a full glass of water and can be taken with or without food. Tenofovir is absorbed from the gastrointestinal tract and undergoes intracellular phosphorylation to form tenofovir diphosphate, the active metabolite responsible for inhibiting viral replication. Intravenous formulations of tenofovir are reserved for individuals unable to tolerate oral medications or in situations requiring rapid initiation of therapy.

Mechanism of Action (MOA)

Tenofovir exerts its antiviral effects by inhibiting the activity of HIV reverse transcriptase, an enzyme essential for viral replication. As a nucleotide analog, tenofovir competitively binds to the active site of HIV reverse transcriptase and incorporates into the growing viral DNA chain, leading to chain termination and inhibition of viral replication. Tenofovir also exhibits activity against HBV by interfering with viral DNA synthesis and polymerase activity. Its potent antiviral effects contribute to the suppression of HIV replication and HBV viral load, leading to improved clinical outcomes and disease management.

Pharmacokinetics (PK)

Following oral administration, tenofovir is rapidly absorbed from the gastrointestinal tract, with peak plasma concentrations reached within 1 to 2 hours. Tenofovir is primarily eliminated unchanged in the urine via glomerular filtration and active tubular secretion. Tenofovir undergoes minimal hepatic metabolism, and dose adjustments are necessary in patients with renal impairment to prevent drug accumulation and toxicity. Tenofovir alafenamide (TAF) has improved pharmacokinetic properties compared to tenofovir disoproxil fumarate (TDF), resulting in lower systemic exposure and reduced renal and bone toxicity.

Pharmacodynamics (PD)

Tenofovir’s pharmacodynamic effects result from its potent inhibition of HIV reverse transcriptase and HBV polymerase activity. By blocking viral replication and DNA synthesis, tenofovir suppresses HIV viral load and HBV viral replication, leading to reduced plasma viral RNA levels and improved markers of liver function. Tenofovir’s high barrier to resistance and long half-life allow for once-daily dosing and sustained virologic suppression in patients with HIV/AIDS or chronic HBV infection.

Primary Indications

Tenofovir is indicated for the treatment of HIV infection in combination with other antiretroviral agents in adults and adolescents, as well as for the treatment of chronic HBV infection in adults. It is prescribed for individuals with confirmed HIV or HBV infection who require antiviral therapy to suppress viral replication, improve immune function, and reduce the risk of disease progression, opportunistic infections, and transmission to others.

Contraindications

Contraindications to tenofovir use include hypersensitivity to tenofovir or any component of the formulation and concurrent use of medications that may interact with tenofovir or increase the risk of adverse effects. Tenofovir should be used with caution in patients with preexisting renal impairment, bone disorders, or hepatitis B-related liver cirrhosis. It is not recommended for use during pregnancy unless the potential benefits outweigh the risks to the fetus, and alternative treatment options are not suitable.

Purpose of Taking Medication

The purpose of tenofovir therapy is to suppress HIV replication and HBV viral load, thereby improving clinical outcomes, reducing the risk of disease progression, and prolonging survival in individuals with HIV/AIDS or chronic HBV infection. Tenofovir-based regimens are effective in achieving and maintaining virologic suppression, preserving immune function, and preventing the development of drug resistance, allowing patients to lead healthier and more productive lives.

Usage Instructions

Tenofovir should be taken orally as directed by a healthcare provider, typically once daily with or without food. The dosage and duration of treatment depend on the specific indication, patient characteristics, and response to therapy. Patients should adhere to the prescribed dosing schedule and avoid missing doses to maintain therapeutic drug levels and optimize treatment outcomes. Regular monitoring of viral load, CD4 cell count, renal function, and bone density may be required during tenofovir therapy to assess treatment efficacy and safety.

Precautions and Care

Patients receiving tenofovir therapy should be monitored regularly for signs of renal dysfunction, including changes in serum creatinine, estimated glomerular filtration rate (eGFR), and urinary protein excretion. Tenofovir may cause renal toxicity, including proximal tubular dysfunction and acute kidney injury, particularly in patients with preexisting renal impairment or risk factors for kidney disease. Bone mineral density should also be assessed periodically, especially in individuals at risk for osteoporosis or bone fractures.

Dietary Considerations

There are no specific dietary restrictions associated with tenofovir therapy. However, patients should maintain a balanced diet and adequate hydration to support overall health and minimize the risk of renal toxicity or electrolyte imbalances. Patients should be counseled on the importance of avoiding excessive alcohol consumption, smoking, and illicit drug use, as these may exacerbate liver or kidney dysfunction and interfere with treatment outcomes.

Possible Side Effects

Common side effects of tenofovir may include gastrointestinal disturbances (e.g., nausea, diarrhea, abdominal pain), headache, fatigue, dizziness, insomnia, rash, and elevated liver enzymes. These side effects are usually mild to moderate in severity and resolve with continued use or dose adjustment. Less common but more serious adverse effects may include renal impairment, bone mineral density loss, lactic acidosis, hepatotoxicity, and immune reconstitution syndrome. Patients should be advised to seek medical attention if they experience severe or persistent side effects while taking tenofovir.

Storage and Disposal

Tenofovir tablets or oral solutions should be stored at room temperature away from heat, light, and moisture, and kept out of reach of children and pets. Unused or expired medication should be discarded properly according to local regulations or guidelines for pharmaceutical waste disposal. Injectable formulations of tenofovir should be stored as directed by the manufacturer and used within the specified expiration date.

Overdose or Emergency

In case of tenofovir overdose or emergency, seek immediate medical attention or contact a poison control center. Overdose may lead to excessive drug concentrations, renal toxicity, metabolic disturbances, or other adverse effects. Treatment of tenofovir overdose may involve supportive care, symptomatic management of adverse effects, and monitoring of renal function and electrolyte balance. Patients should be educated on the signs of overdose and instructed to seek help immediately if an overdose is suspected.

Important Note: Always consult with a healthcare professional for personalized medical advice and guidance regarding the use of given drug, especially regarding dosing, administration, and potential side effects. Your healthcare provider can provide tailored recommendations based on your individual medical history, current medications, and specific treatment needs. Never self-adjust your given drug regimen or discontinue treatment without first consulting your healthcare provider. If you have any questions or concerns about given drug or its use, talk to your doctor or pharmacist for further information and assistance.