Studies of thyroid hormone and methimazole levels in patients with Graves' disease on a standardized anti-thyroid drug regimen.

The outcome of a standardized carbimazole (CMI) regimen was evaluated in fifty-four patients with Graves' disease. Triiodothyronine (T3) and thyroxine (T4) serum values were determined before and throughout the first 6-8 months of therapy. Before therapy, decreasing T4/T3 ratios were found with increasing T3 levels, reflecting a relative increase in T3 production compared with T4 in thyrotoxicosis. High pretreatment T3 values were comparatively common among patients in whom a fixed CMI dosage had a insufficient effect. T4 levels were less informative in this respect. Serum levels of methimazole (MMI), the active metabolite of CMI, were dose-dependent. A 50% reduction in dosage resulted in a similar decrease in the serum values. For a give dose, the MMI levels differed considerably among individuals. The variation was not related to thyroid hormone values. It appears that the response to the anti-thyroid drug is primarily dependent upon the severity of the disease, Which is clearly reflected in serum T3 levels, rather than individual differences in drug handling. A routine CMI regimen for the treatment of thyrotoxicosis is suggested.