Activity of local anesthetic agents in goldfish

The activity of procaine hydrochloride, lidocaine hydrochloride, tetracaine hydrochloride, and dibucaine hydrochloride in producing overturn in goldfish was measured in pH 8.0 buffer. Calculation of the apparent minimum effective concentration of local anesthetic necessary to result in overturn of the goldfish showed that the activity of these agents increased in the following order: procaine hydrochloride less than lidocaine hydrochloride less than tetracaine hydrochloride less than dibucaine hydrochloride. The effect of these agents on goldfish can be correlated with previous work on the minimum concentration necessary to block conduction in isolated nerve and muscle fibers. The activity of the local anesthetic agents could be explained, in part, by the relationship between the chloroform-pH 8 buffer partition coefficient and the minimum effective concentration in goldfish. Experimental results indicate that the unionized drug molecule is responsible for the observed effects.