Cytosolic ADH alpha dimer catalyzes the reaction of abacavir and NAD to form abacavir 5'-carboxylate and NADH + H+. Abacavir 5'-carboxylate is one of the major forms in which abacavir is excreted from the body. Studies with purified enzymes in vitro indicate that only the alpha isoform of ADH has this activity. These studies also suggest that the reaction proceeds in two steps via an unstable aldehyde intermediate (Walsh et al. 2002). Whether conversion of the aldehyde to the carboxylate is spontaneous or also catalyzed by ADH has not been established.