Allopurinol Hypersensitivity

Allopurinol hypersensitivity is strongly associated with the presence of the HLA-B*58:01 allele, most commonly found in patients of Asian and African ancestry.  Because allopurinol hypersensitivity can cause such severe reactions, Clinical Pharmacogenomics Implementation Consortium guidelines recommend testing for the presence of the HLA-B*58:01 allele prior to initiating allopurinol therapy.  If the HLA-B*58:01 allele is detected, use of allopurinol is contraindicated, and an alternative therapy should be considered. Note that the absence of the HLA-B*58:01 allele does not exclude a patient from possessing sensitivity to allopurinol, especially since less severe rashes can occur in 2 to 3% of patients and are not associated with the HLA-B*58:01 allele.  In these cases, FDA guidelines recommend discontinuing allopurinol treatment, even if the patient is negative for the HLA-B*58:01 allele.