Intratympanic versus intravenous delivery of dexamethasone and dexamethasone sodium phosphate to cochlear perilymph.

OBJECTIVE

To measure dexamethasone concentrations in the plasma and perilymph of the human ear after intravenous (IV) and intratympanic (IT) administration and to compare these with previous studies with methylprednisolone.

METHODS

Patients were administered dexamethasone by the IT or IV routes approximately 0.5 to 2 hours before cochlear implantation. The IT dose of 1.6 to 7.2 mg (0.4-1.8 ml of a 4 mg/ml solution) of dexamethasone sodium phosphate was administered by injection into the middle ear cavity through the external auditory canal via a 27-gauge needle passed through a small anterosuperior myringotomy. The IV dose of dexamethasone sodium phosphate was 0.17 mg/kg given as a single injection for 30 seconds. A sample of perilymph (approximately 20 μl) was collected using a needle passed through the round window, and blood was sampled simultaneously. Concentrations of free dexamethasone and dexamethasone sodium phosphate were measured using a validated liquid chromatography-tandem mass spectrometry method.

RESULTS

In the 22 patients studied, 22 perilymph samples and 19 plasma samples were available and suitable for measurement. The median perilymph concentration of dexamethasone after IV injection of 0.17 mg/kg was 0.016 mg/L (n = 9; range, 0.008-0.17), and 1.4 mg/L (n = 13; range, 0.1-16.3) after IT administration of approximately 4 mg. Perilymph concentrations were approximately 88-fold higher after IT compared with IV administration (p = 0.0004) or approximately 260 fold after correction for dosage. The median plasma concentration of dexamethasone after IV injection was 0.12 mg/L (n = 7; range, 0.07-0.14) and 0.003 mg/L (n = 12; range, <0.0005-0.005) after IT injection. Plasma concentrations were approximately 40-fold lower (p = 0.0005) or approximately 13-fold lower after dose correction. Concentrations of dexamethasone sodium phosphate were more variable and were even higher in perilymph and lower in plasma.

CONCLUSION

Administration of dexamethasone IT results in much higher perilymph concentrations and much lower plasma concentrations compared with IV administration.