Allopurinol is a drug used primarily to treat hyperuricemia (excess uric acid in blood plasma) and its complications, including chronic gout. First approved by FDA under the trade name Zyloprim in 1966, it is now a generic drug sold under a variety of brand names, including Allohexal, Allosig, Milurit, Alloril, Progout, Zyloprim, Zyloric, Zyrik, and Aluron.Wikipedia
Allopurinol is contraindicated in individuals with a HLA-B*5801 variant allele due to significantly increased risk of severe cutaneous adverse reactions (SCAR), which includes drug hypersensitivity syndrome, Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN).
Gout flares are associated with serum urate concentrations above 0.42 mmol/L (7 mg/dL). Urate-lowering therapy (ULT) that reduces urate to below 0.36 mmol/L is considered effective. Clinical trials indicate that allopurinol at daily doses of 100 to 300 mg decreases serum urate adequately in only about 40% of gout patients while febuxostat at 80 mg daily reduces serum urate adequately in approximately 70% of gout patients. The response to allopurinol may vary depending on variants in the ABCG2 gene, most notably rs2231142.[PMID 29931553]