An intradermal study of the local anaesthetic and vascular effects of the isomers of mepivacaine.

The duration of action and vascular effects of L(+) and D(-) and racemic mepivacaine were investigated in a double-blind study in 23 fit volunteers. Isosmolar 0.1-ml intradermal injections of a range of concentrations of each agent from 0.011% to 2.7%, and physiological saline were given in duplicate to at least 14 subjects. Local colour changes were observed 5-10 min after injection, and analgesia to pinprick was tested at 5-min intervals thereafter until full recovery. Both isomers were vasoconstrictor at concentrations of 0.3% and less; at greater concentration the L isomer produced more vasodilation and haemorrhagic change. The duration of action of both isomers increased with concentration between 0.05 and 0.9%, but the L isomer was significantly longer acting than the D at 0.3% and more. The log dose-duration curve could be interpreted as linear between 0.1 and 0.9% with the slope of L isomer being twice as steep as the D. The findings for racemic mepivacaine were between those of the two isomers. The longer duration of analgesia of L-mepivacaine was not associated with superior vasoconstrictor power.