Dexamethasone concentration in vitreous and serum after oral administration.

PURPOSE: To determine the dexamethasone concentration in vitreous and serum of patients after oral administration of dexamethasone and to compare the results with the concentrations in vitreous and serum found in a previous study with peribulbar injection of 5 mg dexamethasone disodiumphosphate.
METHODS: In a prospective study, 54 patients who were scheduled for vitrectomy received 7.5 mg dexamethasone orally at varied time intervals before surgery. A vitreous sample was taken from each patient and serum samples were collected at multiple time points from 32 out of 54 patients. Dexamethasone concentrations were measured by radioimmunoassay.
RESULTS: Dexamethasone concentrations in serum ranged from 2.5 to 98.1 ng/ml (median, 61.6 ng/ml) between 1 and 3 hours after oral administration of 7.5 mg dexamethasone. Serum concentrations after peribulbar injection of 5 mg dexamethasone disodiumphosphate (containing 3.75 mg dexamethasone) were lower by a factor of 1.5. Concentrations in vitreous ranged from 1.7 to 23.4 ng/ml (median, 5.2 ng/ml) between 4 and 10 hours after oral administration. After peribulbar injection of 5 mg dexamethasone disodiumphosphate, the intravitreal concentrations were 3.9 times higher.
CONCLUSIONS: An oral dose of 7.5 mg dexamethasone resulted in an intravitreal corticosteroid concentration with an anti-inflammatory potency that is clearly above physiological level. This concentration, however, is several times lower than is the intravitreal concentration after a peribulbar injection of 5 mg dexamethasone disodiumphosphate, although the two routes of administration resulted in nearly equal dexamethasone concentrations in serum. The higher intravitreal concentration after peribulbar injection is probably caused by diffusion from the serum and additional transscleral diffusion.