BMA Concise Guide to Medicine & Drugs

Tenofovir

Brand name Viread

Used in the following combined preparations Atripla, Truvada

QUICK REFERENCE

Drug group Drug for HIV and immune deficiency and Antiviral drug

Overdose danger rating Medium

Dependence rating Low

Prescription needed Yes

Available as generic No

GENERAL INFORMATION

Tenofovir is an antiviral drug used to treat (but not cure) HIV and hepatitis B infection. It is a nucleotide reverse transcriptase inhibitor, which blocks the enzyme reverse transcriptase that viruses need to replicate. In treating HIV infection, tenofovir is usually used in combination with other anti-HIV drugs to reduce production of new viruses before the immune system is irreversibly damaged. This combined therapy is known as highly active antiretroviral therapy, or HAART. Tenofovir may also be used alone to treat some cases of chronic hepatitis B infection.

Although tenofovir reduces the viral load in people with HIV or hepatitis B, it does not completely rid the body of these viruses. They may still be transmitted to other people and so it is important to continue taking precautions to avoid infecting others.

INFORMATION FOR USERS

Your drug prescription is tailored for you. Do not alter dosage without checking with your doctor.

How taken/used Tablets.

Frequency and timing of doses Once daily, with food or liquid, at the same time every day. If you vomit within 1 hour of taking a tablet, take another one; if you vomit more than 1 hour after taking a tablet, do not take another one.

Adult dosage range 245mg daily (one tablet).

Onset of effect May take from many weeks to a year before the drug reduces virus levels significantly.

Duration of action Up to several days.

Diet advice None.

Storage Keep in original container at room temperature and out of the reach of children.

Missed dose Take the missed dose as soon as you remember unless your next dose is due within 12 hours, in which case omit the missed dose and take the next dose as scheduled.

Stopping the drug Do not stop the drug without consulting your doctor; your condition may worsen.

Exceeding the dose An occasional unintentional extra dose is unlikely to cause problems. However, a large overdose may cause serious side effects; notify your doctor immediately.

POSSIBLE ADVERSE EFFECTS

Gastrointestinal side effects are common with tenofovir. As part of combination therapy for HIV infection, it may also affect blood sugar and cholesterol levels and cause redistribution of body fat. Rarely, it may cause inflammation of the pancreas and bone problems. Common side effects include dizziness, headache, rash, muscle pain or weakness, tiredness, lethargy, altered distribution of body fat, and joint stiffness or pain. Discuss with your doctor if any of these are severe. Rarely, tenofovir may cause severe upper abdominal pain; if so, stop taking the drug and contact your doctor immediately.

INTERACTIONS

General note Various drugs that affect the kidneys may affect blood levels of tenofovir, necessitating an adjustment of its dose. Such drugs include antibacterials (e.g. aminoglycosides, pentamidine, and vancomycin); antifungals (e.g. amphotericin B); antivirals (e.g. foscarnet, ganciclovir, adefovir, and cidofovir); immunosuppressants (e.g. tacrolimus); and some anticancer drugs (e.g. interleukin-2).

Other anti-HIV drugs Tenofovir may interact with anti-HIV drugs containing didanosine to increase blood levels of didanosine and reduce CD4 white blood cell counts, which may result in severe inflammation of the pancreas and may sometimes be fatal.

SPECIAL PRECAUTIONS

Be sure to tell your doctor if:

· You have kidney or liver disease. You have diabetes.

· You have a high blood cholesterol level.

· You have lactose intolerance.

· You are pregnant or intend to become pregnant.

· You are taking other medicines, especially corticosteroids.

Pregnancy Safety not established. Discuss with your doctor.

Breast-feeding It is not known if this drug passes into breast milk. However, the HIV and hepatitis B viruses can be passed to the baby in breast milk so breast-feeding is not recommended.

Infants and children Not recommended.

Over 60 No known problems.

Driving and hazardous work Avoid such activities until you have learned how the drug affects you because it may cause dizziness.

Alcohol Avoid. Alcohol increases the risk of developing serious bone problems.

PROLONGED USE

Long-term use may cause loss of bone density and inflammation of the pancreas. In people with both HIV and hepatitis B or C, tenofovir may cause potentially fatal liver problems. HAART including tenofovir may cause redistribution of body fat and abnormal blood sugar and lipid levels.

Monitoring Liver function tests are routine and people being treated for HIV will have regular checks of blood cell counts (including CD4 counts), viral load, blood sugar and cholesterol levels, and response to treatment.