Tenvir (Tenofovir Disoproxil Fumarate)

TDF and CHB

The World Health Organization (WHO) estimates that about 254 million people were living with chronic hepatitis B (CHB) in 2022. Chronic HBV infection can lead to long-term complications such as cirrhosis, liver failure, and a higher risk of hepatocellular carcinoma (HCC). Over the last decade, HBV management has improved, and effective antiviral treatment options include tenofovir disoproxil fumarate (TDF). In Canada, TDF is used in clinical practice as one of the established treatment options for suitable patients with chronic hepatitis B.

TDF is an oral prodrug of tenofovir, a nucleotide reverse transcriptase inhibitor that works against both hepatitis B virus (HBV) and HIV-1. For HIV-1, TDF is used only in combination with other antiretroviral agents. For chronic hepatitis B, TDF is used as an antiviral treatment option; patients should be tested for HIV-1 before starting TDF for HBV.

Clinical trial data show that TDF can help suppress HBV DNA in many patients during long-term treatment. In adult trials, ongoing follow-up included treatment for up to 384 weeks in extension phases. In chronic hepatitis B, the optimal length of treatment is unknown.

Important safety note: severe acute flare-ups of hepatitis B have been reported after stopping anti-hepatitis B treatment, including TDF. In clinical practice, liver function should be monitored with clinical and lab follow-up for at least several months after treatment is stopped; if appropriate, restarting treatment may be considered.

Indications

VIREAD (tenofovir disoproxil fumarate, TDF) is indicated for the treatment of chronic hepatitis B virus (HBV) in adults and pediatric patients 2 years of age and older weighing at least 10 kg.

Drug interactions

TDF is mainly eliminated by the kidneys. Taking it with drugs that are eliminated by active tubular secretion may increase levels of tenofovir and/or the other drug, and drugs that reduce kidney function may increase tenofovir levels. In the treatment of chronic hepatitis B, TDF should not be used together with adefovir dipivoxil.

• Coadministration decreases atazanavir concentrations. When coadministered with TDF, atazanavir should be given with ritonavir. Certain HIV-1 protease inhibitors, including lopinavir/ritonavir, and some HCV regimens can increase tenofovir concentrations; monitor for evidence of tenofovir toxicity, including renal adverse reactions.
• TDF increases didanosine concentrations. Dose reduction and close monitoring for didanosine toxicity are warranted.
• Examples of drugs eliminated by active tubular secretion include acyclovir, cidofovir, ganciclovir, valacyclovir, valganciclovir, aminoglycosides such as gentamicin, and high-dose or multiple NSAIDs. If coadministered, monitor renal function as clinically appropriate.

Possible side effects

Along with its intended effects, this medicine may also cause side effects. The side effect data in people with CHB and compensated liver disease are based on controlled clinical trials in 641 participants who received treatment during a 48-week double-blind period.

In these trials, the most common side effect of any severity was nausea (9%). Other treatment-emergent side effects reported in more than 5% of participants included abdominal pain, diarrhea, headache, dizziness, fatigue, nasopharyngitis, back pain, and skin rash.

It is important to note that stopping treatment can lead to a flare-up (worsening) of hepatitis B. Monitor liver function with clinical and lab parameters for at least several months during follow-up after discontinuation. If appropriate, restarting treatment may be considered.

Storage

Store TDF tablets at 25°C; excursions are permitted to 15°C to 30°C. Keep the bottle tightly closed and dispense only in the original container. Do not use if the seal over the bottle opening is broken or missing. Keep out of reach of children.