Incidence of allopurinol‐induced severe cutaneous adverse drug reaction in Malaysia

Aims Allopurinol is known to cause severe cutaneous adverse drug reactions (SCAR) in Malaysia. However, the incidence of allopurinol-induced SCAR is unknown. Therefore, we aimed to determine the incidence of allopurinol-induced SCAR in Malaysia over 5 years from 2015 to 2019. Methods This retrospective analysis was done in collaboration with the National Pharmaceutical Regulatory Agency (NPRA). All allopurinol-induced adverse drug reaction cases reported to NPRA from 2015 to 2019 were extracted. Allopurinol-induced SCAR cases were identified and the incidence over the 5 years was calculated. Results Incidence of allopurinol-induced SCAR averaged at 2.5 cases per 1000 new users over the 5-year period, with a reducing trend from 3.2 per 1000 new users in 2015 to 2.25 per 1000 in 2019; despite the increasing number of adverse drug reaction cases being reported over the years. Stevens-Johnson syndrome was the commonest form of allopurinol-induced SCAR reported, at 143 cases (46.8% of total SCAR reported). Among Malaysia's 3 main ethnicities, the Chinese had the highest percentages of allopurinol-induced SCAR when compared to the Bumiputera and Indians (3.18 x 10(-4)%). Conclusion The estimated incidence of allopurinol-induced SCAR in Malaysia from 2015 to 2019 was 2.5 cases per 1000 new users. This figure is consistent with the incidence reported in other Asian countries, namely Taiwan and Thailand.