Allopurinol EP Impurity A ;

Allopurinol USP RC A ;

5-Amino-1H-pyrazole-4-carboxamide hemisulfate ;

CAS # 27511-79-1 (free base) ;

C4H6N4O (free base) ; MW 126.12 ;

C4H6N4O . ½ H2SO4 ; MW: 175.16 ;