Adverse effects of Abacavir 

In 3-9% of patients, a severe hypersensitivity reaction, usually with fever and sometimes with respiratory or gastrointestinal symptoms, malaise and rash, develops early in treatment (median of 11 days), but can occur at any time and may be fatal. Patients who experience a hypersensitivity reaction should not be rechallenged. It is controversial whether hypersensitivity reactions can occur when restarting abacavir after a hiatus in patients who previously tolerated the drug. When rash occurs without the systemic symptoms associated with hypersensitivity, the drug can sometimes be continued.