Drug recovery following buccal absorption of propranolol.

1 Buccal absorption of propranolol in two volunteers was followed by repeated rinsing of the mouth with buffer solutions for twelve 2 min periods. Values for absorption, recovery and asymptotic recovery were calculated. 2 Large amounts of propranolol were recoverable from the buccal mucosa; recovery was biexponential and the amount recovered depended on the time allowed for absorption and on the pH of buffers used for recovery. 3 In the case of the drug studied, the buccal absorption test was not an adequate model of passive drug transfer through lipid membranes, and more clearly reflected partitioning into the buccal mucosa. 4 It does not follow from disappearance of drug from the buccal cavity that it has entered the circulation. Unabsorbed drug clearly cannot enter the circulation, but other conclusions about systemic absorption cannot be drawn with certainty from the buccal absorption model. 5 Partitioning back into the saliva after absorption also needs to be taken into account for a true model of systemic absorption of orally administered drugs, and a revised schematic representation of the kinetics of oral drug absorption is presented.