Fact Sheet Number 428
- WHAT IS TENOFOVIR?
- WHO SHOULD TAKE TENOFOVIR?
- WHAT ABOUT DRUG RESISTANCE?
- HOW IS TENOFOVIR TAKEN?
- WHAT ARE THE SIDE EFFECTS?
- HOW DOES TENOFOVIR REACT WITH OTHER
DRUGS?
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PrintTenofovir (Viread®), also called bis-POC PMPA, is a drug used
for antiviral therapy. It is manufactured by Gilead Sciences.
The FDA approved tenofovir for use against HIV in October 2001.
Tenofovir is a nucleotide analog reverse transcriptase inhibitor,
or nuke. These drugs stop HIV from multiplying by preventing the
reverse transcriptase enzyme from working. This enzyme changes
HIV’s genetic material (RNA) into the form of DNA. This has to
occur before HIV’s genetic code gets inserted into an infected
cell’s genetic codes.
In addition to fighting HIV, tenofovir helps control Hepatitis
B.
TENOFOVIR?
Tenofovir was approved as an antiviral drug for people with HIV
infection. There are no absolute rules about when to start antiviral
drugs. You and your doctor should consider your T-cell
count, your viral load,
any symptoms you are having, and your attitude about taking HIV
medications. Fact Sheet 411
has more information about guidelines
for the use of antiviral medications.
Be sure to let your doctor know if you have any kidney problems.
This might interfere with using tenofovir.
If you take tenofovir with other antiviral drugs, you can reduce
your viral load to extremely low levels, and increase your T-cell
counts. This should mean staying healthier longer.
Tenofovir is also being studied as a possible way to prevent
HIV infection with only one pill a day.
RESISTANCE?
Many new copies of HIV are mutations. They are slightly different
from the original virus. Some mutations can keep multiplying even
when you are taking an antiviral drug. When this happens, the
drug will stop working. This is called “developing resistance”
to the drug. See Fact Sheet 414
for more information on resistance.
Sometimes, if your virus develops resistance to one drug, it
will also have resistance to other antiviral drugs. This is called
“cross-resistance”. However, tenofovir seems to have
very little cross resistance with other antiviral drugs.
Resistance can develop quickly. It is very important to take
antiviral medications according to instructions, on schedule,
and not to skip or reduce doses.
A benefit of tenofovir is that it works against several strains
of HIV that are already resistant to AZT, ddC, or ddI.
TAKEN?
The normal adult dose of tenofovir is 300 milligrams (mg) taken
as one pill, once a day, with a meal. People who are taking both
tenofovir and ddI (didanosine, Videx) should take tenofovir 2
hours before, or one hour after didanosine.
EFFECTS?
With the start of any antiviral treatment there may be temporary
side effects such as headaches, high blood pressure, or a general
sense of feeling ill. These side effects are likely to get better
or even disappear over time.
The most common side effects of tenofovir are nausea, vomiting
and loss of appetite. In some people, tenofovir can increase creatine
and transaminases. These are enzymes related to the kidneys and
liver. High levels can indicate damage to these organs.
REACT WITH OTHER DRUGS?
Tenofovir increases blood levels of didanosine
(Videx.) A recent study showed that taking 250 mg of the “enteric
coated” version of ddI (Videx EC) with tenofovir results
in blood levels as high as taking 400 mg of Videx EC by itself.
If you are taking both drugs, check with your doctor about the
correct dosing of Videx. Another study showed that tenofovir does
not affect blood levels of methadone.
Tenofovir is eliminated by the kidneys. It is not metabolized
in the liver, so it is not expected to interact with many other
drugs. However, antiviral drugs with names that end in “-ovir,”
such as acyclovir and ganciclovir, may interact with tenofovir.
Be sure your doctor knows about all medications you are taking.
Tenofovir should be used as part of combination antiviral therapy
against HIV. It is normally used along with a nucleoside analog
reverse transcriptase inhibitor (nuke) plus a non-nucleoside reverse
transcriptase inhibitor (NNRTI) or a protease inhibitor.
Revised November 8, 2002
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New Mexico AIDS Education and Training Center
and the New Mexico Department of Health