Efficacy of oral and intravenous dexamethasone in horses with recurrent airway obstruction.
BACKGROUND
Although the efficacy of dexamethasone for the treatment of recurrent airway obstruction (RAO) has been documented, the speed of onset of effect and duration of action are unknown, as is the efficacy of orally administered dexamethasone with or without fasting.


OBJECTIVE
To document the time of onset of effect and duration of action of a dexamethasone solution i.v. or orally with and without fasting.


METHODS
Protocol 1 used 8 RAO-affected horses with airway obstruction in a crossover design experiment that compared the effect of i.v. saline and dexamethasone (0.1 mg/kg bwt) on pulmonary function over 4 h. Protocol 2 used 6 similar horses to compare, in a crossover design, the effects of dexamethasone i.v. (0.1 mg/kg bwt), dexamethasone per os (0.164 mg/kg bwt) with and without prior fasting, and dexamethasone per os (0.082 mg/kg) with fasting.


RESULTS
Dexamethasone i.v. caused significant improvement in lung function within 2 h with a peak effect at 4-6 h. Dexamethasone per os was effective within 6 h with peak effect at 24 h at a dose of 0.164 mg/kg bwt prior to feeding. The duration of effect was, for all dexamethasone treatments, statistically significant for 30 h when compared to saline and tended to have a longer duration of effect when used orally. Dexamethasone per os at a dose of 0.164 mg/kg bwt to fed horses had mean effects comparable to dexamethasone at a dose of 0.082 mg/kg bwt per os given to fasted horses, indicating that feeding decreases bioavailability.


CONCLUSIONS
Dexamethasone administered i.v. has a rapid onset of action in RAO-affected horses. Oral administration of a bioequivalent dose of the same solution to fasted horses is as effective as i.v. administration and tends to have longer duration of action. Fasting horses before oral administration of dexamethasone improves the efficacy of treatment.


CONCLUSIONS
Oral administration to fasted horses of a dexamethasone solution intended for i.v. use provides an effective treatment for RAO-affected animals.
Cornelisse
C J
CJ
Pulmonary Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824-1314, USA.
Robinson
N E
NE
Berney
C E A
CE
Kobe
C A
CA
Boruta
D T
DT
Derksen
F J
FJ
D000284:Administration, Oral; D000402:Airway Obstruction / Q000188:drug therapy / Q000662:veterinary*; D000818:Animals; D001682:Biological Availability; D018592:Cross-Over Studies; D003907:Dexamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D005215:Fasting / Q000502:physiology; D005260:Female; D006734:Horse Diseases / Q000188:drug therapy*; D006736:Horses; D007275:Injections, Intravenous / Q000662:veterinary; D008297:Male; D011897:Random Allocation; D012008:Recurrence; D016896:Treatment Outcome
D003907:Dexamethasone