Investigation into the pharmacodynamics of ethanol as a nerve blocking agent

Abstract

Ethanol is a known nerve-blocking agent, yet its clinical use is minimal. This is partly due to unclear dosage levels and not enough knowledge of its pharmacodynamics and overwhelming dominance of its psychomotor properties. This research intended to investigate into the pharmacodynamics of ethanol as a nerve blocking agent, try and establish an effective dose that can be used clinically, as well as comparing its effects on various parts of the motor unit. A total of 105 sciatic nerve – gastrocnemius muscle specimens were isolated from frogs, Xenopus laevis. Ethanol at concentrations of 40%, 55% and 70%, each at doses of 1.5g/kg, 2.0g/kg and 2.5g/kg body weight (BW) was administered intraperitoneally, intramuscularly (into the gastrocnemius) and topically (onto the sciatic nerve). Using EPIC system to monitor muscle contractions, action potential and/or electromyogram the nerve block effects of each dose / concentration combination were assessed. The effects on the nerve, neuromuscular junction and muscle were assessed separately and compared, then as a single unit. Results showed that intraperitoneally administered ethanol had no effect on neuromuscular function. Intramuscular injections took 2.5 to 9.0 minutes to attain complete paralysis, and lasted for 29.5 to 61.0 minutes, depending on concentration and dose (>/= 55%; >/= 2.0g/kg BW). Topically applied ethanol took 15 to 30 seconds to block the nerve completely, depending on the concentration (>/= 40%). The blockade lasted for 5 to 10 minutes. Intramuscularly injected ethanol reduced the amplitude of indirectly elicited electromyography more than the directly evoked one. It was concluded that to achieve a complete and sustained ethanol nerve block, at least 55% concentration, 2.0g/kg BW dose and intramuscular route are required. The duration of blockade depends on concentration and dose administered. Ethanol affects both nerve and muscle. The effect is more pronounced and instant on the nerve than on muscle.