This preparation contains the sodium phosphate ester of dexamethasone, a fluoro-methyl derivative of prednisolone, which is a potent glucocorticoid with minimal mineralocorticoid activity. Dexamethasone has ten to twenty times the anti-inflammatory activity of prednisolone.

Following intramuscular injection this soluble ester of dexamethasone is rapidly absorbed and hydrolysed to the parent alcohol giving a prompt response which is maintained for approximately 48 hours.

Dexadreson is a short acting dexamethasone preparation with a rapid onset of activity. It contains the disodium phosphate ester of dexamethasone. After extravascular (intramuscular, subcutaneous, intra-articular) administration, the ester is rapidly resorbed from the injection site followed by immediate hydrolysation into the parent compound, dexamethasone. Absorption of dexamethasone is rapid. The time to reach maximum plasma concentrations (Cmax) of dexamethasone in cattle, horse, pig and dog is within 20 min after intramuscular administration. Bioavailability following i.m. administration (compared to i.v. administration) is high in all species. Elimination half-life after intravenous administration in horses is 3.5 h. After intramuscular administration, apparent elimination half-life has been shown to range between 1 and 20 hours according to the species.