Methimazole Toxicity from High Doses

The toxic effects of high-dose methimazole therapy (120 mg/day) were studied in 25 consecutive patients receiving such therapy. Nine of the 25 patients had toxic reactions, 8 of which were severe. Rashes were most commonly seen, but two cases of agranulocytosis syndrome occurred. Although hyperthyroidism may be controlled more rapidly with high doses of this blocking agent, the observed morbidity suggests that such doses should not be used routinely.