Dexamethasone and dexamethasone phosphate detected by 1H and 19F NMR spectroscopy in the aqueous humour.

To apply nuclear magnetic resonance (NMR) spectroscopy to study the penetration of dexamethasone phosphate into the aqueous humour from rabbit following topical administration. After topical administration of 0.1%, 1.0% and 10% dexamethasone phosphate solutions, respectively, samples of aqueous humour were aspirated, freeze-dried, redissolved in deuterium oxide and analyzed by high resolution 1H and 19F NMR spectroscopy. In order to study the lipophilic and hydrophilic metabolites of the drug, samples obtained after application of 1% dexamethasone phosphate were extracted with methanol/chloroform, and then extracted with perchloric acid. In all samples obtained from eyes denuded of the corneal epithelium prior to administration of dexamethasone, signals corresponding to the chemical shifts of the drug were identified in 19F NMR spectra. In the experiments performed with 1% dexamethasone phosphate, both dexamethasone and dexamethasone phosphate were detected in the aqueous humour. Using 10% dexamethasone phosphate solutions, signals from the drug were detected in 1H NMR spectra simultaneously with signals from about twenty other substances present in the aqueous humour. NMR spectroscopy appears to be a valuable method for studying dexamethasone metabolism and penetration into ocular tissues. It provides simultaneous detection of both the drug metabolites and other substances in the sample and might offer a complementary approach to other analytical methods. Copyright 1998 Academic Press Limited.