Can diastereoisomerism of alkoxyphenylcarbamates influence their local anesthetic activity?

The surface local anesthetic activity (LAA) in the homologous series of rac emic (+/-)-cis- and (+/-)-trans-N,N-dimethyl-2-(2-alkoxyphenylcarbamoyloxy) cyclopentylmethylamonium chlorides was evaluated. The potency was expressed in rabbits as efficiency indices (EI) in comparison to the standard drug c ocaine. All tested racemic mixtures of the phenylcarbamates were local anes thetically active and their potency increased with the size of alkoxysubsti tution from the propyloxy- to the hexyloxyderivative and then decreased abr uptly (cut-off effect). When different mixtures of both dia stereoisomers w ere applied the synergistic effect - i.e. increase of the LAA of one diaste reomer when adding the other was observed. It seems that an optimal racemic ratio of the compounds could increase their local anesthetic efficiency.