What Is Amprenavir?

Amprenavir is a drug used as part of antiretroviral therapy (ART). It is also called Agenerase^®. It was manufactured by GlaxoSmithKline.

Manufacture of amprenavir was discontinued in October 2007. It is being replaced by fosamprenavir (see Fact Sheet 448). Fosamprenavir is a pro-drug of amprenavir. This means that when fosamprenavir is taken, it is broken down to produce amprenavir.

Who Should Take It?

Amprenavir was approved in 1999 as an antiretroviral drug (ARV) for people with HIV infection. It has been studied in adults and children over 4 years old.

There are no absolute rules about when to start ART. You and your health care provider should consider your CD4 cell count, your viral load, any symptoms you are having, and your attitude about taking ARVs. Fact Sheet 404 has more information about guidelines for the use of ART.

If you take amprenavir with other ARVs, you can reduce your viral load to extremely low levels, and increase your CD4 cell counts. This should mean staying healthier longer.

What About Drug 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 ARV. When this happens, the drug will stop working. This is called "developing resistance" to the drug. See Fact Sheet 126 for more information on resistance.

Sometimes, if your virus develops resistance to one drug, it will also have resistance to other ARVs. This is called "cross-resistance." Amprenavir might not be cross-resistant with other protease inhibitors.

Resistance can develop quickly. It is very important to take ARVs according to instructions, on schedule, and not to skip or reduce doses.

How Is It Taken?

Amprenavir is taken by mouth as a capsule. The normal adult dose was 1200 milligrams (mg) two times a day. This was based on 150 mg capsules which are no longer available. Instead, people can use fosamprenavir (Lexiva, see Fact Sheet 448). The dose is lower, based on body weight, for children and people who weigh less than 50 kilograms (110 pounds). Amprenavir is available in 50 mg capsules and as oral solution.

Amprenavir was also approved in two combinations with the protease inhibitor ritonavir:

• 600 mg (4 capsules) of amprenavir plus 100 mg (one capsule) of ritonavir, taken twice a day, or
• 1200 mg (8 capsules) of amprenavir plus 200 mg (2 capsules) of ritonavir, taken just once a day.

Different doses are used in some combinations. Be sure you know how much amprenavir your health care provider has prescribed for you, and when and how to take each dose. If you have liver problems, you may need to take a lower dose of amprenavir.

Amprenavir is available as gelatin capsules and as a liquid. The gelatin capsules should be kept at room temperature. If they get too warm, they can melt. People taking the liquid form should not drink alcoholic beverages.

It can be taken with or without food, but high-fat meals should be avoided. Do not take antacids within one hour of taking amprenavir.

Vitamin E

Amprenavir capsules contain vitamin E. The vitamin E improves how the drug is absorbed and how it works. Each 50 mg capsule contains approximately 36 International Units (IU) of vitamin E. This information can help you decide what vitamin supplements to take.

What Are the Side Effects?

The most common side effects are nausea, diarrhea, vomiting, rash, numbness around the mouth, and abdominal pain. About 1% of people get serious skin reactions, including Stevens-Johnson syndrome. No other side effects seem to be very serious. The diarrhea in most cases can be controlled with over-the-counter medications.

Amprenavir might not cause problems with high cholesterol levels the way that other protease inhibitors do.

Amprenavir is a sulfa drug. If you are allergic to sulfa drugs, be sure to tell your health care provider.

The liquid version contains an ingredient called propylene glycol. It can cause problems, and should not be used by the following patients:

• infants or children under 4 years old
• pregnant women
• people with liver or kidney failure
• people taking certain medications (check with your health care provider)

How Does It React With Other Drugs?

Amprenavir can interact with other drugs or supplements that you are taking. These interactions can change the amount of each drug in your bloodstream and cause an under- or overdose. New interactions are being identified all the time. Make sure that your health care provider knows about ALL drugs and supplements you are taking.

Drugs to watch out for include other ARVs, drugs to treat tuberculosis (see Fact Sheet 518), for erectile dysfunction (such as Viagra), for heart rhythm (antiarrhythmics), and for migraine headaches. Interactions are also possible with several antihistamines (allergy medications), sedatives, drugs to lower cholesterol, and anti-fungal drugs.

Amprenavir works better if it is taken with the reverse transcriptase inhibitor abacavir.

Ritonavir increases blood levels of amprenavir. Ritonavir-boosted amprenavir has been approved by the FDA.

If you are taking amprenavir and ddI, take them one hour apart. You should also take amprenavir one hour apart from antacids.

Some birth control pills may not work if you are taking amprenavir. Talk to your health care provider about how to prevent an unwanted pregnancy.

Taking amprenavir with methadone can lower blood levels of both drugs. Watch for signs of excessive sedation if you take amprenavir with buprenorphine.

The herb St. John's Wort (see Fact Sheet 729) lowers the blood levels of some protease inhibitors. Do not take it with amprenavir.-->