Changes in drug metabolism in children with thyroid disorders.

The rate of disappearance of antipyrine from the plasma is a useful indicator for the in vivo capacity of mixed function oxidation. The half-life of antipyrine was measured before and after treatment in three hypothyroid and three hyperthyroid children, aged three months to 14 years, in order to examine the effect on drug metabolism of thyroid disorders in children. The half-life of antipyrine decreased in all three hypothyroid subjects and increased in all three hyperthyroid subjects after treatment. The mean half-life decreased from 34.5 h to 8.6 h after treatment of the hypothyroid subjects and increased from 6.1 to 10.1 h after treatment of the hyperthyroid subjects. The mean metabolic clearance rate of antipyrine increased from 11.7 to 25 ml/h in the hyothyroid patients while in the hyperthyroid children there was a decrease from 43 to 25 ml/h. The apparent volume of distribution did not change significantly in the treatment, thus changes in the half-life of antipyrine were most likely attributable to alterations in the metabolic clearance rate of antipyrine.