As fosamprenavir (Telzir) is converted into amprenavir (Agenerase) in the body, its side-effects are very similar to those of amprenavir. The commonest side-effects are headache, nausea, rash, diarrhoea, vomiting and fatigue. These are usually mild.

As a class, protease inhibitors have been associated with a syndrome of fat and metabolic irregularities. This syndrome includes fat redistribution, high blood fat levels, diabetes, increased levels of blood sugar and increased bleeding in haemophiliacs. The cause and long-term health implications of the syndrome are unknown at this stage. GlaxoSmithKline has presented test tube and animal studies that support its claim that amprenavir may not cause body fat changes, but further long-term data are required before this claim can be substantiated^[1][2].

Amprenavir is a sulfonamide drug, so people who have experienced adverse reactions to co-trimoxazole (Septrin) or other drugs of this type may experience reactions to fosamprenavir.

Less than 1% of people who have taken fosamprenavir have experienced severe and life-threatening skin reactions, including Stevens-Johnson syndrome.