Abacavir 5'-4-Chloro-6-methylpyrimidine-2,5-diamine (Abacavir EP Impurity B) is a degradation product of Abacavir Sulfate (A105000). Abacavir is a carbocyclic 2'-deoxyguanosine nucleoside reverse transcriptase inhibitor and an anti-HIV drug used to treat HIV infection (1). Intracellular enzymes convert Abacavir to its active form, carbovir-triphosphate (CBV-TP), which then selectively inhibits HIV reverse transcriptase by incorporating into viral DNA (2). Abacavir is metabolized in the liver by uridine diphosphate glucuronyltransferase and alcohol dehydrogenase resulting in inactive glucuronide and carboxylate metabolites, respectively. Molecular Formula: C18H21ClN10O Molecular Weight: 428.88