Chem. Pharm. Bull. 54(8) 1155—1161 (2006)

ions and is widely used to determine the activity and concentration of hydrogen ions. Metal ion-selective electrodes, such as potassium ions and calcium ions, are also commercially available. Drug ion selective electrodes are prepared and are used to determine the concentrations of drug ions. Other applications of drug ion electrodes include studies of protein binding of drug ions, mechanisms of drug action, and estimation of bitter taste of a drug. Recently, biosensors of taste and smell are commercially available. For instance, Toko et al. have developed a multi-channel taste sensor whose transducer is composed of several kinds of lipid/polymer membranes with different characteristics. This sensor is used to taste foods and medicines objectively, instead of human sensory evaluation. The majority of the orally administrated drugs tastes very bitter. Such drugs are usually administrated as tablets. However, because some of the small children and aged people cannot swallow intact tablets, crushed tablets or liquid formulations are administered to them. In these cases an appropriate masking agent would be added to reduce or eliminate the bitter taste. A number of masking agents of the bitter taste are known. As well known, a concentrated solution of sucrose masks the bitter taste of drugs by its intense sweetness. Cyclodextrins (CyDs) can reduce the bitter taste of drugs by complex formation: The complexed drug is not bitter, whereas the uncomplexed drug is bitter. This masking mechanism was established quantitatively. Lipoprotein that is composed of phosphatidic acid, b-lactoglobulin, bovine serum albumin, and other substances is a good masking agent. Some polysaccharides, synthetic polymer, and jellies can mask the bitter taste of drugs. It is suggested that complex formation of a drug with the lipoprotein and polymers reduces the concentration of the drug in the free state. Most bitter compounds are hydrophobic and some of them are positively charged. Propantheline bromide (PB) and oxyphenonium bromide (OB), shown in Fig. 1, are bitter anticholinergic drugs. As already reported, suppression of the bitter taste of PB by native CyDs (a-, b-, and g-CyDs) can be predicted from the observed surface tensions of mixed solutions of PB and one of the CyDs. Furthermore, masking of the bitter taste of OB by the native CyDs and several modified CyDs has been investigated with the OB ion selective electrode. The ion selective electrode method will be applicable to more masking agents than the surface tension method, because the latter method is inapplicable to surface active masking agents. In this work, we aimed to find better masking agents with August 2006 1155