ADL 08-0011 is an active metabolite of the u-opioid receptor antagonist alvimopan. It is produced from alvimopan via amide hydrolysis by gut microbiota. ADL 08-0011 is a u-opioid receptor antagonist (Ki = 0.25 nM). It is selective for u-opioid receptors over kappa- and delta-opioid receptors (Kis = 15.8 and 31.6 nM, respectively). ADL 08-0011 inhibits endomorphin 1-induced inhibition of electrically induced contraction of isolated guinea pig ileum (pA2 = 9.4). In vivo, ADL 08-0011 (0.03-1 mg/kg) reverses loperamide-induced delayed gastric emptying in a rat model of castor oil-induced diarrhea.