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Canadian Journal of Anesthesia, Vol 30, 242-247, Copyright © 1983 by Canadian Anesthesiologists' Society

Neuromuscular blocking action of verapamil in cats

B. J. KRAYNACK MD1, N. W. LAWSON MD1, and J. GINTAUTAS MD PHD1

1 Anesthesiology Research Laboratories, Texas Tech University Health Science Center, School of Medicine, Lubbock, Texas

Address Correspondence to: Dr. B.J. Kraynack, Richland Memorial Hospital, 3301 Harden Street; Columbia, S.C. 29203, USA.

The effects of the calcium (slow) channel blocker verapamil, on non-cardiac excitable membranes were examined in vivo. In barbiturate anaesthetized cats, the effect of intravenously administered verapamil (0.1, 0.2, and 0.4 mg·kg-1) on isometric twitch amplitude of the flexor carpi radialis muscle, elicited by indirect and direct electrical stimulation, was determined. At all doses tested, verapamil significantly reduced muscle twitch amplitude from control values. The effect of dosage on twitch reduction was far more pronounced for indirect than direct stimulation. Full recovery to control was observed by 90 minutes only with the lowest dose (0.1 mg·kg-1 IV). Reduction of twitch amplitude (direct and indirect) lasted the duration of the experiment (180 minutes) for the two higher doses of verapamil. No significant changes in blood pressure, cardiac rate or rhythm were observed. The specific site and mechanism of verapamil's neuromuscular blocking action remains unclear. In clinical situations where potent inhalation agents, adjuncts or neuromuscular blocking agents may be used, therapeutic doses of verapamil may interact to promote muscle weakness.

Key Words: IONS: calcium • MEMBRANES: muscle, nerve synapse • NEUROMUSCULAR TRANSMISSION: verapamil, neuromuscular junction, neuromuscular blocker • PHARMACOLOGY: verapamil






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Copyright © 1983 by the Canadian Anesthesiologists' Society.