Peribulbar corticosteroid injection: vitreal and serum concentrations after dexamethasone disodium phosphate injection

PURPOSE: To study the dexamethasone level reached in human vitreous after a peribulbar injection of 5 mg of dexamethasone disodium phosphate and to assess its systemic uptake.

METHODS: In a prospective study, 61 eyes of 61 patients scheduled for vitrectomy received a single peribulbar injection of 5 mg of dexamethasone disodium phosphate at varied intervals before surgery. At the start of vitrectomy, an undiluted vitreous sample was taken. In 22 patients, multiple serum samples were collected. Dexamethasone concentrations were measured by radioimmunoassay. The physiologic cortisol concentration was determined in the vitreous of 12 eyes of 12 patients who did not receive dexamethasone.

RESULTS: An average dexamethasone peak concentration of approximately 13 ng/ml was reached in vitreous 6 to 7 hours after peribulbar injection. In serum the average peak concentration was approximately 60 ng/ml 20 to 30 minutes after peribulbar injection. The average physiologic cortisol concentration in vitreous was 5.1 ng/ml.

CONCLUSIONS: After a peribulbar injection of 5 mg of dexamethasone disodium phosphate, an average intravitreal dexamethasone concentration is reached with a 75 times greater anti-inflammatory potency than physiologically present cortisol. Dexamethasone concentration in serum, however, is several times higher. Peribulbar injection is not just a local treatment but results in serum levels comparable to those achieved by a high oral dose.