Figure 11-14 Metabolic pathway of remifentanil. De-esterification by nonspecific plasma and tissue esterases to form a carboxylic acid metabolite (GI90291) that has only 1/300 to 1/1,000 the potency of the parent compound is the primary metabolic pathway. N-dealkylation of remifentanil to GI94219 is a minor metabolic pathway. (From Egan TD, Lemmens HJ, Fiset P, et al: The pharmacokinetics of the new short-acting opioid remifentanil [GI87084B] in healthy adult male volunteers. Anesthesiology 79:881–892, 1993.)