Original Article

Antidotal effect of 4-aminopyridine on acute poisoning induced by magnesium sulfate

Wei ZHANG, Yuan-pei ZHANG, Rui-ying FANG


In anesthetized cats, the toxic effects, such as hypotension, respiratory failure and depression of anterior tibialis muscle twitches, induced by MgSO4 were promptly antagonized by iv 4-aminopyridine 0.6-1.3 mg/kg. In mice, 4-AP (3.0 mg/kg, ip) increased the LD50 of sc MgSO4 from 645 to 1062 mg/kg. Concurrent injections of 4-AP and CaCl2 in suitable dose levels showed a synergistic antidotal effect. 4-AP (1.5-2.0 mg/kg iv in divided doses) protected the conscious rabbits, which had been given lethal dose (650 mg/kg, im) of MgSO4, from death. Experiments on phrenic nerve discharge in anesthetized rabbits and rat phrenic nervediaphragm praparations revealed that the occurrence of respiratory failure during Mg2+ intoxication was due to neuromuscular blockade, not due to respiratory center depression, and the respiratory recovering effect of 4-AP chiefly resulted from its neuromuscular transmission facilitating effect.

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