Injectable dexamethasone sodium phosphate administered orally? A pharmacokinetic analysis of a common emergency department practice

Background: The injectable formulation of dexamethasone has been administered orally, for the treatment of pediatric asthma and croup. The practice is followed in emergency departments around the country, but pharmacokinetic data supporting this practice are lacking.

Objectives: This study evaluated the relative bioavailability and pharmacokinetics of dexamethasone sodium phosphate for injection (DSPI) administered orally compared to dexamethasone oral concentrate (DOC) in healthy adults.

Methods: This was an open label, crossover study of 11 healthy adults 18 to 45 years of age. All subjects received 8 mg of dexamethasone oral concentrate initially. After a 1-week wash-out period, subjects received 8 mg of DSPI administered orally. Dexamethasone levels were measured by liquid chromatography in tandem mass spectrometry. Cmax and area under the curve (AUC (0-t) and AUC (0-∞)) were calculated and compared between groups using the paired t test.

Results: The mean ± SD AUC(0-t) for dexamethasone oral concentrate and DSPI were 5497.23 ± 1649 and 4807.82 ± 1971) ng/dL/hr, respectively; 90% confidence interval (CI) was 78.8%-96.9%. The mean ± SD AUC(0-∞) for dexamethasone oral concentrate and DSPI were 6136.43 ± 2577 and 5591.48 ± 3075 ng/dL/hr, respectively; 90% CI was 79.0% -105.2%. Mean Cmax ± SD for DOC and DSPI were 942.94 ± 151 and 790.92 ± 229 ng/dL, respectively; 90% CI 76.8%-91.7%. The relative bioavailability of DSPI administered orally was 87.4% when using AUC(0-t) and 91.1% when using AUC(0-∞). The calculated absolute bioavailability was 75.9%.

Conclusions: DSPI is not bioequivalent to dexamethasone oral concentrate when administered orally. The existing literature supports the efficacy of DSPI despite this. Dosing adjustments may be considered.