ABSTRACT
An alternative in vitro approach to drug screening has been the use of human cell cultures for antiviral agents and microbial cell cultures for the assessment of the carcinogenic potential of selected compounds. A number of protozoan species have been also used as drug screens for anti-protozoal agents. The ciliated protozoan Tetrahymena pyriformis species has been widely utilised as a drug screen for a variety of pharmacologically active agents. Accordingly, it was decided to investigate whether T. pyriformis could be used as a preliminary drug screen for evaluation of the local anaesthetic activity and duration of action of certain commercially available local anaesthetics. In this communication, the results of this new in vitro biological drug screen are reported. It is based on the complete protozoan cell immobilization by the anaesthetic solution. A positive inverse correlation was observed between the lowest concentration [minimum inhibitory concentration =MIC] that wholly inhibits the mobility of all cells of T. pyriformis and the duration of action of the test compounds. Generally, MIC was high for the short-acting anaesthetics and low for the long-acting ones. The results suggest the suitability of this new microbiological assay system for the evaluation of local anaesthetic activity and duration of action and possibly irritancy and toxicity of other local anaesthetics as well as potentially active therapeutic agents which possess surface activity