Bioequivalence study of stressed and nonstressed hard gelatin capsules using amoxicillin as a drug marker and gamma scintigraphy to confirm time and GI location of in vivo capsule rupture

Evaluate if crosslinked hard gelatin capsules (HGCs) having different in vitro dissolution profiles changed in vivo release times or altered bioavailability of a drug marker; assess if a two-tier dissolution test (with and without enzyme) predicted in vivo performance. Two classifications of stressed HGCs were artificially produced by exposure to formaldehyde (HCHO). HGCs were categorized as, a) pass/pass (p/p) which met in vitro dissolution criterion (75% drug dissolution at 45 min), b) moderately crosslinked fail/pass (f/p) which failed dissolution criterion in the absence of enzymes and passed in the presence of enzymes, and c) severely crosslinked fail/fail (f/f) which failed in vitro standards with or without enzymes. A six-way, single dose bioequivalence study (n = 10) administered the three HGCs under the fasted and fed condition. In vivo capsule rupture and GI transit were monitored via gamma scintigraphy, and blood samples were collected through six hours. Each crosslinked HGC was bioequivalent to the control p/p capsule when using AUC(0-infinity) and Cmax for comparison. Mean in vivo disintegration of the p/p capsule was 7 +/- 5 min for the fasted condition and 11 +/- 7 min for the fed condition. In vivo rupture for the f/p capsule was 22 +/- 12 min and 23 +/- 11 min for the fasted and fed studies, respectively, while the f/f HGC ruptured at 31 +/- 15 min and 71 +/- 19 min under the fasted and fed condition, respectively. Onset of amoxicillin absorption was dependent on in vivo HGC rupture and subsequent entry of the released radioactive marker into the small intestine. Consequently, fasted Tmax values were significantly later for the f/p HGC (1.62 +/- 0.53 hr) and f/f HGC (1.85 +/- 0.58 hr) as compared to the p/p HGC (1.17 +/- 0.30 hr). Fed Tmax values were statistically different only for the f/f capsule (2.55 +/- 0.44 hr) where Tmax values for the p/p and f/p HGCs under the fed condition were 1.50 +/- 0.47 hr and 1.60 +/- 0.46 hr, respectively. A two-tier dissolution procedure that retested a crosslinked hard gelatin capsule with addition of gastric or intestinal enzymes provided an adequate in vitro indicator of the formulation's in vivo performance. The observed delays in the onset of amoxicillin absorption and Tmax for the severely crosslinked f/f HGC was attributed to delayed in vivo capsule rupture, however, this delay did not adversely change AUC(0-infinity) nor Cmax.