Fosamprenavir is suitable for those both treatment-experienced and treatment-naive. It has proved to be as effective as other protease inhibitors, with or without ritonavir boosting, in patients who have not taken antiretroviral therapy before.

Fosamprenavir itself is not active in the body but it converts into amprenavir in the gut which is then active against HIV.

Basic info

Generic name fosamprenavir
Brand name Telzir
Also known as GW-433908
Drug class Protease Inhibitors
Pediatric dosing? Available in doses suitable for children and/or young people.
Availability in Australia Available on the Pharmaceutical Benefits Scheme (PBS) through S100 prescribers since
This drug may be available through clinical trials in Australia.
You may be able to import this drug from overseas for your personal use.
Formulation 700mg tablet

Taking it

Like most anti-HIV drugs, fosamprenavir must be taken in combination with other drugs to be completely effective. Commonly, fosamprenavir is combined with one other nucleoside (NRTI) drug and either a protease inhibitor or non-nucleoside, although other combinations are sometimes used. Your doctor will advise you on the right combination of drugs to suit your circumstances.


The normal daily dose is one 700mg tablet plus 100mg ritonavir twice a day

Regardless of what you read on this website or elsewhere, you should always take your medications according to your doctor's instructions. If you're unsure, speak to your doctor or pharmacist.

With or without food

fosamprenavir may be taken with or without food

Side effect

All drugs can produce side effects in some people. These may be mild, moderate or severe, so you should be aware of potential side effects before starting any drug, and speak to your doctor if you experience side effects that concern you.

  • Common side effects may include nausea (upset stomach, feeling sick to the stomach), diarrhoea, vomiting, headache, rash.
  • Less common side effects may include abdominal pain, numbness around the mouth, hyperlipidemia.
  • Rare side effects may include skin reactions, including Stevens-Johnson syndrome.
  • It's unlikely you will experience all of these side effects, and you may not experience any side effects at all. Before starting any new drug, ask your doctor about side effects you might experience and discuss strategies for dealing with side effects if they do occur. If you experience any significant side effect you should continue taking your medicine and see your doctor as soon as possible.

Interactions with other drugs

Drugs to watch out for include other antiretrovirals and drugs to treat tuberculosis, erectile dysfunction (such as Viagra), heart rhythm (antiarrhythmics) and migraine headaches. Interactions are also possible with several antihistamines, sedatives, drugs to lower cholesterol and anti-fungal drugs. Fosamprenavir should not be combined with Kaletra as levels of both lopinavir and fosamprenavir are reduced in the blood. If fosamprenavir is taken with ritonavir and efavirenz, the daily dosage of ritonavir may need to be increased. Some birth control pills may not work if you are taking fosamprenavir. Fosamprenavir causes major increases in blood levels of some antidepressants like Elavil and Tofranil. These drugs are sometimes used to treat peripheral neuropathy. However, fosamprenavir decreases blood levels of paroxetine, an antidepressant. A dose increase of paroxetine may be needed. Discuss use of antidepressants with your doctor. Fosamprenavir levels do not appear to be affected by use of antacids. Taking fosamprenavir with methadone can lower blood levels of both drugs. Check with your doctor if you use methadone. Watch for signs of excessive sedation with buprenorphine. The herb St. John's wort lowers the blood levels of some protease inhibitors. Do not take it while taking fosamprenavir. Fosamprenavir increases blood levels of several statin drugs used to lower cholesterol levels. Some statins should not be used. The dose of others should be reduced.