[Pharmacokinetics of phenazone in patients with fast and slow euthyroidism after methimazole treatment]

Hyperthyroidic patients treated with methimazole were retrospectively divided into two groups, depending on the period of time required for euthyreosis: these attaining euthyreosis up to 28 days of therapy (A) and these in whom thyroid gland functioning is normalized after a 35-day therapy with full dose of methimazole (B). The study aimed at investigating whether clinical euthyreosis is related to the activity of microsomal enzymes in the liver using phenazone elimination test for this purpose. Phenazone elimination test was performed just before the treatment and after 8 weeks of methimazole administration. A decrease in kel and Clt as well as an increase in AUC were noted. These changes were more pronounced in patients of group A than those of group B. It might be concluded that phenazone pharmacokinetics is different in patients quickly attaining euthyreosis. The difference is probably due to the difference in biotransformation of methimazole in the liver in which microsomal enzymes play some role.