THE TOXICITY OF SOME LOCAL ANESTHETICS AFTER APPLICATION ON DIFFERENT MUCOUS MEMBRANES AND ITS RELATION TO ANESTHETIC ACTION ON THE NASAL MUCOSA OF THE RABBIT

¹ Research Laboratories of AB ASTRA, Södertälje, Sweden

The toxicities of tetracaine, cocaine, lidocaine and -n-propylamino-2-methylpropionanilide (L 67 Astra) have been compared in rabbits after intravenous, intratracheal, intranasal and intravesical application. The efficiency of these compounds as topical anesthetics has also been estimated on the nasal mucosa of rabbits.

The very rapid rate of absorption of tetracaine is illustrated by the LD50 being nearly equal for the i.v. and intratracheal routes of administration. Lidocaine and L 67 in the concentrations used were only about one-fourth to one-fifth as toxic by the intratracheal as compared to the intravenous route. Cocaine toxicity occupied a place between tetracaine and lidocaine when applied on the mucous membranes.

A comparison of the topical anesthetic effects of the different compounds showed that tetracaine is about 10 times (cocaine about 2 to 3 times) as efficient as lidocaine and L 67 if the EC50's are compared. However, if duration of anesthesia is taken into account 1% solutions of tetracaine and cocaine are comparable to 2% lidocaine and L 67. By comparing the toxicities and anesthetic efficiencies by the nasal route the relative safety of the different compounds has been discussed.