Effect of four potassium channel agonists on bupivacaine-induced toxicity in mice

Kinetics of bupivacaine after levcromakalim treatment in mice

Previous workers have reported that 0.01 mg kg-1 of levcromakalim injected intraperitoneally did not modify bupivacaine-induced neurotoxicity but increased the duration of action of bupivacaine. This study was designed to document possible changes in the pharmacokinetic behaviour of bupivacaine and its main metabolite, N-desbutylbupivacaine in mice after a single 0.01 mg kg-1 intraperitoneal injection of levcromakalim. The kinetic parameters of bupivacaine were determined after a single 20 mg kg-1 intraperitoneal injection of bupivacaine in controls and in levcromakalim-treated mice. It was found that levcromakalim did not change any kinetic parameters of bupivacaine or of its main metabolite, N-desbutylbupivacaine. The previously reported findings of the influence of the low dose (0.01 mg kg-1) of levcromakalim on bupivacaine-induced toxicity agree well with the lack of influence of 0.01 mg kg-1 of levcromakalim on bupivacaine and N-desbutylbupivacaine pharmacokinetics, although the reported increase in the duration of action of bupivacaine after levcromakalim treatment can hardly be explained by the pharmacokinetics of bupivacaine when associated with levcromakalim. We suggest that levcromakalim might interfere directly with ion-channel block caused by bupivacaine by altering conduction properties or indirectly by enhancing bupivacaine-induced voltage and time-dependent sodium-channel block.

Potassium channel agonists modify the local anaesthetic activity of bupivacaine in mice

PURPOSE

The mechanisms of action of local anaesthetics and potassium channel agonists (PCAs) may interfere by acting in a direct or indirect manner on the same ion channels. In a previously reported study, the bupivacaine-induced mortality was shown to be modified in different ways by four PCAs tested (diazoxide (D), levcromakalim (L), nicorandil (N) and pinacidil (P)) since bupivacaine-induced mortality was increased by high doses of P and L, decreased by N and stayed unchanged by D. The present study was designed to document the changes in bupivacaine (B) local anaesthetic activity in mice after a single injection of one of the four PCAs (D, L, N and P).

METHODS

Each PCA was tested at three different dosages. Controls received saline. The local anaesthetic activity was evaluated using sciatic nerve blockade. After injection of bupivacaine in the region of the sciatic nerve, the local anaesthetic activity was estimated as the loss of motor control of the injected limb.

RESULTS

PCA treatment increased (P = 0.0001) the time needed for recovery from bupivacaine-induced local anaesthesia. The area under the effect vs time curve, assessing the total anaesthetic effect, was greater for N (P = 0.0016) and P (P = 0.038) but not for L (P = 0.11). Compared with controls, the maximal effect (Emax) was less for D (P = 0.009) and N (P = 0.038) but not for L (P = 0.185) or P (P = 0.45) treated groups. The injection of the PCA in the region of the sciatic nerve of the right hindlimb did not induce any alteration of the motor activity of the injected limb.

CONCLUSION

The four PCAs decreased the maximal local anaesthetic effect and increased the duration of action of bupivacaine.

Kinetics of bupivacaine after nicorandil treatment in mice

Previous studies have reported interactions between potassium-channel agonists and bupivacaine. This study was designed to document possible changes in the pharmacokinetic behaviour of bupivacaine and its main metabolite, N-desbutylbupivacaine, in mice after a single 1 mg kg-1 intraperitoneal injection of nicorandil. The kinetic variables of bupivacaine were determined after a single 20 mg kg-1 intraperitoneal dose of bupivacaine in controls (group 1) and in nicorandil-treated mice (group 2). The maximal concentration in the serum (Cmax 0.618 +/- 0.051 vs 0.408 +/- 0.041 microgram mL-1 for group 1 vs 2, P = 0.01) and the area under the concentration curve (AUC 1.039 +/- 0.051 vs 0.758 +/- 0.072 microgram mL-1 h for group 1 vs 2, P = 0.013) of bupivacaine were significantly lower in nicorandil-treated mice, while CL (0.579 +/- 0.025 vs 0.815 +/- 0.079 for group 1 vs 2, P = 0.022) and Vd (0.506 +/- 0.054 vs 0.981 +/- 0.117 for group 1 vs 2, P = 0.1006) were increased in nicorandil-treated animals. The ratio of AUC for N-desbutylbupivacaine to AUC for bupivacaine, which may partially indicate the rate of metabolism, was higher in the presence of nicorandil (1.142 +/- 0.017 compared with 0.877 +/- 0.013, P = 0.0001). Our data may indicate an increased metabolism of bupivacaine in nicorandil-treated mice. These results do not explain the previously reported enhanced anaesthetic activity of bupivacaine in the presence of nicorandil, but may participate, at least in part, in the relative protective effect of nicorandil against the previously reported bupivacaine-induced toxicity.