Immediate decrease by hydrocortisone of the plasma half-life of antipyrine.

Infusion of hydrocortisone in man caused an immediate shortening of the plasma half-life of antipyrine. There was no change in the 'apparent' volume of distribution of antipyrine and the plasma concentrations of hydrocortisone during the infusion remained within physiological limits. Similar changes in plasma half-lives of antipyrine were observed in the dog, but in vitro studies of drug oxidation with dog liver failed to show any difference between biopsy samples taken before and during steroid infusion.Many drugs and chemicals are known to stimulate rates of drug oxidation in both man and animals. Administration of these inducing agents results in an increase in the activity of enzymes catalyzing drug oxidation, most of which are located with-in the endoplasmic reticulum of liver cells. In man there is usually a delay of 4-8 days before an appreciable change in rates of drug metabolism is seen when such an agent is administered (Breckenridge, Orme, Thorgeirsson, Davies & Brooks, 1971); in rats, the administration of enzyme-inducing agents causes increased rates of drug metabolism only 24-48 h after their administration.We wish to report in this paper an immediate and hitherto undescribed effect of hydrocortisone on rates of antipyrine elimination in man.