Lontophoretic administration of dexamethasone into the tarsocrural joint in horses.
OBJECTIVE
To determine whether iontophoretic administration of dexamethasone to horses results in detectable concentrations in synovial fluid, plasma, and urine.


METHODS
6 adult mares.


METHODS
Iontophoresis was used to administer dexamethasone. Treatments (4 mA for 20 minutes) were administered to a tarsocrural joint of each mare. The drug electrode contained 3 ml of dexamethasone sodium phosphate at a concentration of 4 or 10 mg/ml. Samples of synovial fluid, blood, and urine were obtained before and 0.5, 4, 8, and 24 hours after each treatment. All samples were tested for dexamethasone using an ELISA. Synovial fluid also was evaluated for dexamethasone, using high-performance liquid chromatography.


RESULTS
The lower and upper limits of detection for dexamethasone in synovial fluid with the ELISA were 0.21 and 1.5 ng/ml, respectively. Dexamethasone administered at a concentration of 10 mg/ml was detected by the ELISA in synovial fluid of 5 mares from 0.5 to 24 hours and in urine of 4 mares from 0.5 to 8 hours after each treatment, but it was not detected in plasma. Mean synovial fluid concentration of dexamethasone was 1.01 ng/ml. Dexamethasone administered at a concentration of 4 mg/ml was detected by the ELISA in urine of 2 mares at 0.5 and 4 hours after treatment, but it was not detected in synovial fluid or plasma.


CONCLUSIONS
Iontophoresis cannot be considered an effective method for delivery of dexamethasone to synovial fluid of horses, because drug concentrations achieved in this study were less than therapeutic concentrations.
Kaneps
Andris J
AJ
Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331-4402, USA.
Craig
A Morrie
AM
Walker
Karen C
KC
True
Jan E
JE
D000818:Animals; D003907:Dexamethasone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000652:urine; D004305:Dose-Response Relationship, Drug; D005260:Female; D006614:Hindlimb; D006736:Horses / Q000378:metabolism; D007478:Iontophoresis / Q000662:veterinary*; D007596:Joints / Q000187:drug effects*; D013582:Synovial Fluid / Q000737:chemistry
C004180:dexamethasone 21-phosphate; D003907:Dexamethasone