For orally administered drugs, first=pass metabolism by the liver is a formidable barrier to efficient delivery. Extensive first-pass metabolism, in addition to decreasing the percentage of dose reaching its intended site of action, often leads to significant variability in bioavailability, necessitating careful monitoring of patient blood levels. While first-pass metabolism can be avoided by selecting alternate routes of administration (i.v., transdermal, rectal, etc.), the oral route is generally preferred. Rational approaches for minimizing first-pass metabolism would therefore be quite valuable. Propranolol, used extensively in the treatment of angina pectoris, hypertension, and cardiac arrhythmia, has been shown to undergo extensive presystemic metabolism after oral administration leading to reduced bioavailabihty (Paterson et al., 1970; Shand et al., 1970; Lo et al., 1982) and significant inter-subject variability in blood levels (Kornhauser et al., 1978). Garceau et al. (1978) have shown that the hemisuccinate ester of propranolol, when administered orally to beagle dogs, yields propranolol levels 8 times higher than after an equivalent dose of propranolol hydrochloride.