The absorption site of cyclosporin in the human gastrointestinal tract.

1. An emulsion preparation of cyclosporin was administered locally to different parts of the small and large intestine by gavage: to the duodenum (opposite to the papilla of Vater), jejunum (150 cm distal to the teeth), ileum (300 cm distal to the teeth), and to the colon descendens (30 cm proximal to the anus). 2. The bioavailability of cyclosporin after these instillations was compared with that after oral administration of a hard gelatine capsule formulation. 3. Cyclosporin was found to be absorbed predominantly in the small intestine. This may have implications for dosage in patients with reduced absorptive surface area.