K. Sako et al., INFLUENCE OF PHYSICAL FACTORS IN GASTROINTESTINAL-TRACT ON ACETAMINOPHEN RELEASE FROM CONTROLLED-RELEASE TABLETS IN FASTED DOGS, International journal of pharmaceutics, 137(2), 1996, pp. 225-232
Four types of controlled-release (CR) acetaminophen (AAP) tablets, nam
ely A, B, C and D, were prepared to investigate the influence of physi
cal factors in the gastrointestinal (GI) tract on AAP release in faste
d dogs. CR-A was designed as a completely resistant formulation to mec
hanical destructive force but to show an agitation speed-dependent dis
solution rate. CR-B, CR-C and CR-D were designed to have different wet
strengths but to show similar dissolution rates. The absorption profi
les of the four CR forms in dogs showed biphasic patterns, with phase
change about 2 h after oral dosing. The first phase of the absorption
profile of CR-A and in vivo release directly observed were close to it
s in vitro profiles at a speed of 25-50 revs./min, indicating that agi
tation intensity in the dog GI tract may be relatively low. The first
phase of the absorption profiles of the CR-B, CR-C and CR-D differed f
rom each other, despite the fact that dissolution rates in vitro were
similar. The tablet with low wet strength showed a faster absorption r
ate, indicating that it would be destructed by GI mechanical forces. F
urthermore, absorption during the second phase was extremely low for a
ll CR tablets. We confirmed on necroscopy that the suppression of drug
absorption in the second phase was caused by the termination of AAP r
elease from the tablets in the colon. These results will be useful in
evaluating the in vivo performance of CR tablets in fasted dogs.