• There is a risk of precipitating acute attacks of gout for approximately 12 months after starting allopurinol [Jordan et al, 2007]. People who experience acute attacks of gout after initiation of treatment with allopurinol, or during established treatment, should not stop taking the allopurinol.
• Pruritic maculopapular skin rashes may occur in up to 10% of people who take allopurinol — a rash can be the first sign of a rare hypersensitivity reaction, so advise them to immediately stop the allopurinol if this occurs and to seek medical advice promptly [DynaMed, 2007].
• If the rash was mild and subsequently resolves, gradually reintroduce the allopurinol. If the rash recurs, immediately discontinue the allopurinol.
• When starting on allopurinol, people should be cautious about driving or using machinery until they are reasonably certain that it does not adversely affect performance, as somnolence, vertigo, and ataxia have been reported.
• Since allopurinol and its metabolites are excreted by the kidney, impaired renal function may lead to retention of the drug and/or its metabolites, with consequent prolongation of plasma half-life.
• Overall, adverse effects are rare but their incidence (particularly rashes) is higher in the presence of renal impairment [Jordan et al, 2007].

[ABPI Medicines Compendium, 2006]