A boosted HIV protease inhibitor (a prodrug of amprenavir)
Fosamprenavir
A boosted HIV protease inhibitor used as part of combination therapy to control HIV.
What is Fosamprenavir?
Fosamprenavir is a specialist HIV medicine in the protease inhibitor group. It is a 'prodrug' of amprenavir, meaning the body converts it into the active medicine, and it is usually 'boosted' by another medicine to keep its levels up. It is taken as part of combination therapy alongside other HIV medicines. Common effects include rash (it is related to sulfonamide medicines), tummy upset such as diarrhoea, and raised blood fats. It controls HIV but does not cure it, so it must be taken consistently.
Education and reference only. This is a plain-language guide to Fosamprenavir — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Fosamprenavir is an HIV medicine belonging to a group called protease inhibitors. It is a prodrug, which means the body changes it into its active form (amprenavir) after it is taken. It is usually given 'boosted' with another medicine that raises and steadies its levels, and it is used as part of combination therapy, meaning together with other HIV medicines rather than alone. It is taken by mouth and is prescribed and supervised by a specialist HIV team. Like all current HIV treatment, it controls the virus but does not cure it.
How it works
HIV needs an enzyme called protease to make new, infectious copies of itself. After fosamprenavir is converted by the body into its active form, it blocks this enzyme so the virus cannot mature properly, and the amount of HIV in the body falls. It is usually combined with a booster medicine that slows its breakdown so enough stays in the body, and it is taken alongside other HIV medicines that attack the virus in different ways. Keeping the virus suppressed protects the immune system and lowers the chance of passing HIV on.
Company & origin
Originated / developed by: Specialist manufacturer.
A specialist HIV medicine used in the UK as part of combination therapy, usually boosted by another medicine.
Practical use
How to take Fosamprenavir
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth as prescribed, usually together with its booster medicine and your other HIV medicines.
- Take it consistently and do not skip doses, as missed doses can let the virus become resistant.
- Tell your team if you develop a rash, and seek urgent help for a severe rash with blisters, fever or feeling unwell.
- Mention any sulfonamide (sulfa) allergy before starting, as fosamprenavir is related to these medicines.
- Give your team a full list of your other medicines, as it interacts with several of them.
Weighing it up
Advantages & disadvantages of Fosamprenavir
Advantages
- An effective protease inhibitor option used as part of combination therapy to suppress HIV.
- Taken by mouth rather than by injection.
- Available as tablets and a liquid, which can suit different people.
Disadvantages
- Commonly causes rash, and is related to sulfonamide medicines.
- Can cause tummy upset such as diarrhoea and can raise blood fats over time.
- Usually needs a booster medicine and interacts with several other medicines.
Practical use
Good to know
A useful thing to know is that fosamprenavir is a prodrug, so the body has to turn it into its active form once you take it. It is related to sulfonamide medicines, and rash is a fairly common side effect, so tell your team if you have a sulfa allergy and report any rash, especially if it is severe or comes with blisters, fever or feeling unwell. It commonly causes tummy upset such as diarrhoea, and it can raise blood fats over time, which the team keeps an eye on. It is usually taken with a booster medicine and interacts with a number of other drugs, so keep an up-to-date medicines list. As with all HIV treatment, it works as part of combination therapy and must be taken consistently to keep the virus under control and avoid resistance.
Who should not take it / use with caution
- People who have had a serious allergic reaction to fosamprenavir or amprenavir should not take it.
- It is used with care in people with a sulfonamide (sulfa) allergy, as it is related to these medicines.
- It is used with care in people with liver problems and those on many other medicines, under specialist supervision.
Monitoring
- Checking the amount of HIV in the blood (viral load) and the immune cell count (CD4) to see how well it is working.
- Reviewing liver blood tests and blood fats over time.
- Watching for rash and other side effects, especially early in treatment.
Side effects
- Rash, which is fairly common and is usually mild but can occasionally be severe.
- Diarrhoea, nausea or other tummy upset.
- Raised blood fats (cholesterol and triglycerides) and changes in liver blood tests.
- Rarely but seriously, a severe skin reaction, which needs urgent medical attention.
Key interactions
- It is usually taken with a booster medicine, and other HIV medicines may need adjusting.
- It can be affected by, and affect, medicines such as some statins, certain sedatives and others, so check before adding anything.
- Herbal products such as St John's wort can lower its levels and should be avoided.
Available as: Tablets and an oral suspension taken by mouth.
Answers
Fosamprenavir: frequently asked questions
What is fosamprenavir used for?
It is an HIV protease inhibitor used, as part of combination therapy, to suppress HIV and protect the immune system.
What does 'prodrug' mean here?
It means fosamprenavir is converted by the body into its active form (amprenavir) after you take it, which is the part that acts against the virus.
Why might I get a rash?
Rash is a fairly common side effect, partly because fosamprenavir is related to sulfonamide medicines; tell your team about any rash, and seek urgent help if it is severe.
Why is it taken with another medicine?
It is usually 'boosted' with another medicine that raises and steadies its levels so enough stays in the body to work well.
Does it cure HIV?
No. Fosamprenavir controls HIV as part of combination therapy but does not cure it, so it must be taken consistently and continued long term.
The wider class
About HIV protease inhibitor (boosted)
Fosamprenavir belongs to the hiv protease inhibitor (boosted) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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