A COMPARISON OF THE BIOAVAILABILITY OF ORAL AND INTRAMUSCULAR DEXAMETHASONE IN WOMEN IN LATE PREGNANCY

Objective: To compare the bioavailability of oral and intramuscular (I M) dexamethasone in third-trimester pregnant women. Methods: Oral and IM dexamethasone levels were compared in a randomized, parallel, cross over bioavailability study involving 11 gravid women in the third trim ester of pregnancy. Subjects were randomized to receive either 6 mg of IM or 8 mg of oral dexamethasone. The following week, the alternative regimen was administered. Serial blood samples were obtained after dr ug administration. Dexamethasone concentrations were measured by radio immunoassay. Total area under the curve was compared for the oral and IM groups using a paired t test. Results: Eight of the 11 women comple ted the study through 12 hours; all 11 women completed the study throu gh 6 hours. Among the 11 women, peak levels of dexamethasone occurred 30 minutes after IM injection (mean +/- standard deviation, 101.7 +/- 19.2 ng/mL) and 120 minutes after oral administration (65.9 +/- 20.5 n g/mL). Area under the curve did not differ significantly between those receiving IM dexamethasone (258.3 +/- 50.0 ng/minute/mL) and those re ceiving oral dexamethasone (251.8 +/- 59.7 ng/minute/mL) when measured 6 hours after administration of the drug. Terminal half-lives were si milar in the IM and oral groups. Similar findings were noted among the eight women who were studied through 12 hours. This study had a power of 87% to detect a 20% difference in area under the curve between the two groups. Conclusion: The bioavailability of 8 mg of oral dexametha sone is similar to that of a 6-mg IM dose, as determined by the area u nder the curve. Copyright (C) 1997 by The American College of Obstetri cians and Gynecologists.