Do antidiarrhoeal opiates accumulate in the rat intestinal lumen?

The opiate antidiarrhoeal drugs loperamide (0.6 mg kg-1, i.p.) or difenoxin (0.77 mg kg-1, s.c.), were administered in an anaesthetic mixture (pentobarbitone 60 mg kg-1) to rats. A length of jejunum (approx. 30 cm) was cannulated, washed and then perfused with iso-osmotic saline for 20 min. The perfusion commenced 50 min after drug administration and continued for 20 min. The perfusates were collected for analysis of fluid transport rates and antidiarrhoeal drug content. These doses of the antidiarrhoeals caused marked inhibition of intestinal fluid secretion induced by intra-arterial infusion of vasoactive intestinal peptide. However, neither of the antidiarrhoeal drugs were detected in the intestinal perfusates (< 0.5 ng by HPLC). The results indicate that loperamide and difenoxin have a different pharmacokinetic profile compared with that previously found for morphine under the same conditions.