Altered plasma half‐lives of antipyrine, propylthiouracil, and methimazole in thyroid dysfunction

Abstract

In normal, nonmedicated volunteers and in patients with thyroid disorders the plasma half-lives of antipyrine, propylthiouracil, and methimazole were determined after single oral doses. The plasma half-lives ± S.D. of antipyrine, propylthiouracil, and methimazole were 11.9 ± 1.4 hr, 6.7 ± 1.0 hr, and 9.3 ± 1.4 hr, respectively, in normal volunteers, but were shortened to 7.7 ± 1.2 hr, 4.3 ± 0.7 hr, and 6.9 ± 0.6 hr, respectively, in hyperthyroid patients. In hypothyroid patients the plasma half-lives of these drugs were prolonged to 26.4 ± 4.0 hr, 24.7 ± 34.5 hr, and 13.6 ± 4.8 hr, respectively. Return to the euthyroid state restored plasma half-lives to or toward normal. Alterations in plasma drug half-lives during thyroid dysfunction appear to result mainly from accelerated hepatic microsomal drug metabolism in hyperthyroidism and retarded drug biotransformation during hypothyroidism.