Toxicity and drug interactions of levamisole.

Clinical signs and lesions of levamisole toxicosis include: nausea, vomiting, increased salivation, frequent urination and defecation, colic, dizziness, headache, muscle tremors, ataxia, anxiety, hyperesthesia with irritability, clonic convulsions, depression, rapid respiration, dyspnea, prostration, collapse, hemorrhages in the subepicardium and thalamus, enteritis, hepatic degeneration and necrosis, and splenic congestion. Most of these signs and lesions are similar to those observed in nicotine poisoning. Levamisole causes vasopressor and panting effects which are blocked by ganglionic blocking agents hexamethonium and mecamylamine but are not blocked by atropine. The vasopressor effect of levamisole is blocked by alpha-adrenergic antagonists phentolamine and dibenamine; however, the respiratory effect of levamisole is not affected by these alpha-adrenergic antagonists. Repeated IV injections of levamisole cause a tachyphylactic response. With levamisole-induced tachyphylaxis, the effects of other ganglionic stimulants dimethylpiperazinium and nicotine are also abolished. Levamisole causes an electroencephalographic arousal which is antagonized by atropine sulfate and mecamylamine. There is also a structural similarity of levamisole to nicotine. These studies suggest that levamisole is a nicotine-like compound. Possible treatment of levamisole poisoning is discussed. Drug interactions of levamisole with organophosphates and anthelmintics, eg, pyrantel, methyridine, and diethylcarbamazine, are also discussed.