AChE inhibitors increase the concentration of endogenous acetylcholine at cholinoceptors. There are three major groups:
- Quaternary alcohols including edrophonium
- Carbamate esters such as neostigmine and physostigmine
- Organophosphates such as echothiophate
Effects of inhibitors
In low concentrations cause diffuse activation on the electroencephalogram and a subjective alerting response. In higher concentrations, they cause generalized convulsions, which may be followed by coma and respiratory arrest.
In the heart, AChE inhibitors mimic the effects of vagal nerve activation on the heart. Negative chronotropic, dromotropic, and inotropic effects are produced, and cardiac output falls.
The net effect on the cardiovascular system is modest bradycardia, a fall in cardiac output, and no change or a modest fall in blood pressure. Large doses of these drugs cause more marked bradycardia (occasionally tachycardia) and hypotension.
Low (therapeutic) concentrations moderately prolong and intensify the actions of physiologically released acetylcholine. This increases strength of contraction, especially in muscles weakened by curare-like neuromuscular blocking agents or by myasthenia gravis. At higher concentrations, the accumulation of acetylcholine may result in fibrillation of muscle fibers. Antidromic firing of the motor neuron may also occur, resulting in fasciculations that involve an entire motor unit.
1. Katzung BG. Basic & clinical pharmacology. 10th ed. New York: McGraw-Hill Medical; 2007.