FACTORS CONTROLLING THE BUOYANCY AND GASTRIC RETENTION CAPABILITIES OF FLOATING MATRIX CAPSULES - NEW DATA FOR RECONSIDERING THE CONTROVERSY

Optimized floating (F) and non-floating (NF) hydrophilic matrix capsul es have been characterized in vitro with regard to their buoyancy or n on-buoyancy capabilities and their diametral size evolution with time. The gastric residence times (GRTs) and transit behaviors of these F a nd NF forms prepared in small, medium, and large sizes were then compa ratively examined in fed volunteers remaining either upright or supine . The results show that all the optimized F forms do lastingly float u pon the gastric contents, whereas the NF forms sink rapidly after inge stion. In upright subjects, the F forms are consequently protected aga inst postprandial emptying. The GRTs of the NF forms are much more var iable and highly dependent on their size (mean GRT small < medium < la rge units, p < 0.05). The GRT prolongation obtained with the F forms w hen compared with the NF ones is hence significantly marked for the sm all and medium size dosage forms (p < 0.05) but not for the large ones (p greater than or equal to 0.05). In supine subjects, a size effect influences the GRT of both the F and NF forms (p < 0.05). The F forms are more often emptied before the NF ones but, size for size, the mean GRTs do not differ in the aggregate. These findings, together with li terature data, are used to explain why a number of former investigatio ns have come to contradictory conclusions about the effect of density of an undigestible form on GRT. Uncontrolled factors are hiding from d isclosure the GRT enhancement that should be observed when optimized F forms are used within defined conditions.