The effect of capsule size and density on transit through the proximal colon

Colonic transit of radiolabelled capsules has been monitored in 18 healthy subjects using gamma scintigraphy. The capsules ranged in volume from 0.3-1.8 cm3 and in density from 0.7-1.5 gcm-3. The capsules were administered after an overnight fast and entered the colon, on average, 5 h after dosing. Transit rates through the proximal colon were independent of capsule density. Any effect due to capsule volume was small when compared with intersubject variations in transit rates. Within 10 h of entering the colon 80% of the units had reached the splenic flexure. These findings have implications in the design of non-disintegrating, sustained release dosage forms.