Interaction of ethinyloestradiol with ascorbic acid in man

Abstract

Ethinyloestradiol is the oestrogen most often present in combined oral contraceptive steroid preparations. We have shown that this steroid has a mean bioavailability of only 40%1owing to extensive first-pass metabolism. A large proportion of this first-pass metabolism occurs in the gut wall during absorption with the formation of a sulphate conjugate.2 Sulphate conjugation of other drugs such as paracetamol is inhibited by ascorbic acid,3 a drug that also undergoes sulphate conjugation in the gut wall. In a preliminary study four out of six women showed an increase in plasma ethinyloestradiol concentrations when a single dose of ethinyloestradiol was administered with ascorbic acid.4 We therefore studied the effect of ascorbic acid in women receiving long-term treatment with oral contraceptive steroids. © 1981, British Medical Journal Publishing Group. All rights reserved.