What is Tenofovir Disoproxil Fumarate (Viread)?
Tenofovir disoproxil fumarate (hereafter referred to as “tenofovir”) is a Nucleotide Reverse Transcriptase Inhibitor (NRTI) drug used for the treatment of HIV-1 infection as well as chronic Hepatitis B virus (HBV) infection, always in combination with other antiretroviral drugs. The drug works by binding to HIV-1 reverse transcriptase and HBV polymerase, disrupting viral replication. Tenofovir disoproxil fumarate should not be confused with the newer formulation “tenofovir alafenamide,” which differs in a various aspects.
Dosing & Administration
Tenofovir is indicated for the treatment of HIV infection and the treatment of chronic HBV infection in adults and children ages two and up and weighing at least 10 kg. It is also used off-label for HIV post-exposure prophylaxis following occupational or non-occupational exposure, including sexual assault, and for pre-exposure prophylaxis for heterosexual adults at high risk, and for IV drug users. This medication comes in oral tablet and oral powder formulations. It may be taken without food.
Tenofovir requires no dosage adjustments in patients with liver dysfunction, but should be used with caution due to risk of hepatotoxicity. Dosage adjustments are required for renal impairment, and has not been studied in children or adolescents with renal impairment. Dosage instructions and considerations are detailed in the product monograph.
Tenofovir is contraindicated in patients with hypersensitivity to the drug.
Tenofovir Side Effects
Tenofovir is associated with serious renal and bone-related side effects, as well as lactic acidosis and hepatomegaly (see precautions). A complete list of potential adverse effects is provided in the product monograph.
The drug may cause new or worsened renal failure, and Fanconi syndrome. Tenofovir may cause osteomalacia and should be used with caution in patients with or at risk for reduced bone mineral density. This medication has also been associated with lactic acidosis and hepatomegaly, including fatal cases. Recommendations for screening and monitoring are outlined in the product monograph.
All patients who test positive for HIV infection should be screened for comorbid Hepatitis B virus (HBV) and Hepatitis C virus (HCV) infection. Co-infected patients should be started on an antiretroviral regimen targeting co-infected viruses, regardless of CD4 counts or viral loads. Current HIV treatment guidelines outline drug regimens and prescribing considerations.
Tenofovir is associated with a large number of drug-drug interactions. These are listed in the product monograph.
Pregnancy & Lactation
Highly active retroviral combination treatment should be used in all pregnant women. Data from the Antiretroviral Pregnancy Registry do not suggest that tenofovir causes major birth defects above baseline. Current guidelines should be consulted when treating pregnant women. Tenofovir does not appear to be excreted in breast milk. The CDC recommends that all HIV positive women, treated or untreated, avoid breastfeeding to prevent vertical transmission of the virus.
There is no known antidote for tenofovir overdose, so standard supportive treatment should be used. The drug can be dialyzed.
Alternative Brand Names
Tenofovir is available under the brand name Viread, and as part of a combination product in Atripla, Cimduo, Complera, Stribild, and Truvada.
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