The pharmacokinetics of oral and intramuscular administration of dexamethasone in late pregnancy

Background. To compare the pharmacokinetics of orally administered dexamethasone with intramuscular administration in antenatal patients at risk of preterm delivery. Method. Ten antenatal patients at risk for preterm delivery were given two intramuscular and then one oral dose of dexamethasone. Plasma which was collected at set intervals following the first intramuscular dose and the oral dose was assayed for dexamenthasone. The results were analyzed using pharmacokinetic data-fitting software and pharmacokinetic parameters calculated. Results. After oral administration of dexamethasone the mean maximum plasma concentration obtained was 65% that of the intramuscular dose and the bioavailability of the oral route was calculated as 72% of the intramuscular route. The terminal half-lives of dexamethasone were similar for both routes. Conclusions. These limited data would suggest that if dexamethasone is to be administered orally, which would be both preferable to patients and more economic, then a proportionately increased dose of oral dexamethasone would be required to provide similar maternal plasma pharmacokinetics to the intramuscular dose in current use. Further, larger studies are now required to confirm this. (C) Acta Obstet Gynecol Scand 1996