Toxicity drug-induced psychosis

CNS toxicity occurs because isoniazid has structural similarities to pyridoxine (vitamin Be) and can inhibit its actions. This toxicity is dose-related and more common in slow acetylators. Manifestations include peripheral neuropathy, optic neuritis, ataxia, psychosis and seizures. The administration of pyridoxine to patients receiving INH does not interfere with the tuberculostatic action of INH but it prevents and can even reverse neuritis. Hematological effects include anaemia which is also responsive to pyridoxine. In some 20% of patients antinuclear antibodies can be detected but only in a minority of these patients drug-induced lupus erythematosus becomes manifest. 

Secondly, it is generally agreed that of all the psychotomimetic drugs, the toxic effects of amphetamine most closely resemble pathological psychosis in man. The possibility cannot be excluded, therefore, that the effects of amphetamine demonstrated here are related to the psychotomimetic action of the drug and may provide some clue to the cause of drug-induced and pathological psychosis in man. 

Agranulocytosis (and systemic lupus erythematosus) are autoimmune syndromes that can be drug-induced. They are type II reactions involving IgM and IgG antibodies that bind to circulating blood cells. The patient was probably treated with clozapine for his psychosis (see clozapine toxicity. Chapter 29). The answer is (D). 

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