POTENTIATION OF LOCAL LIGNOCAINE-INDUCED SENSORY BLOCK BY CALCIUM-CHANNEL BLOCKERS IN RATS

We have studied the effects of three different types of calcium channe l blockers (verapamil, diltiazem, and nicardipine) on local lignocaine sensory block. The standardized tail flick test was used to measure t he duration and degree of lignocaine-induced conduction block in rats. After obtaining baseline tail flick latencies (mean 3.2 s), two 100-m u l doses of 0.3% lignocaine alone, a combination of verapamil 25, 100 or 200 mu g, diltiazem 25, 100 or 200 mu g, or nicardipine 0.5, 1.0 o r 2.0 mu g, and a large dose of calcium channel blockers (verapamil 20 0 mu g, diltiazem 200 mu g or nicardipine 2.0 mu g) were injected on o pposite sites of the tail base and the tail flick test was performed e very 5 min for 45 min. A large dose of the calcium channel blockers sh owed no prolongation of tail flick latencies. Administration of 0.3% l ignocaine alone produced a significant increase in tail flick threshol ds and the peak effect of the percentage maximum possible effect (%MPE ) was demonstrated at 5 min after drug injection (mean %MPE 28.8%; P < 0.01 vs baseline). Go-administration of 0.3% lignocaine and three dos es of verapamil produced significant increases in area under the curve (AUG) in a dose-dependent fashion. Mean AUC values for 0.3% lignocain e alone and a combination of verapamil 25, 100 or 200 mu g were 217.5, 502.5, 529.1 and 1600.3, respectively. Almost similar patterns of aug mentation in AUC values were demonstrated after addition of different doses of diltiazem or nicardipine to 0.3% lignocaine. We conclude that the use of mixtures of local anaesthetic and calcium channel blocker potentiated lignocaine sensory block at the level of the peripheral ne rves.