ABSORPTION OF DRUGS FROM THE HUMAN ORAL CAVITY

The rate and extent of drug loss from the human oral cavity can be measured using several different methods. These include the buccal absorption test (Beckett and Triggs, 1967), disc methods (Kaaber, 1974; Schurr and Ziegler, 1983; Pimlott and Addy, 1985) and perfusion cells (Barsuhn et al., 1988; Rathbone, 1990). These methods have provided information on the mechanisms by which drugs are transported across oral cavity membranes and suggest that passive diffusion (Beckett and Triggs, 1967; Beckett and Moffat, 1968, 1969a,b) or carrier-mediated transport systems (Manning and Evered, 1976; Sadoogh-Abasian and Evered, 1979; Evered et al., 1980; Evered and Mallett, 1983; Hunjan and Evered, 1985) may be involved. An appropriate kinetic model to describe the transfer of drugs across oral cavity membranes is problematic (Beckett et al., 1968; Beckett and Moffat, 1970; Beckett and Pickup, 1975; Dearden and Tomlinson, 1971a; Schurmann and Turner, 1978). This is most likely due to the inherent disadvantages associated with the techniques used. Mathematical models describing drug loss from the oral cavity during a buccal absorption test appear equally successful (Ho et al., 1971; Lien et al., 1971; Vora et al., 1972; Wagner and Sedman, 1973). This is despite marked contrast in the underlying assumptions. The object of this review is to evaluate critically the methods available for studying drug loss from the human oral cavity. In addition we review studies which aimed to elucidate the mechanism of drug transfer across human oral cavity mucosa. The review considers literature that has been published since 1967 and highlights areas that appear worthy of further investigations.