Ocular penetration of oral doxycycline in the horse.
OBJECTIVE
To investigate intraocular penetration of orally administered doxycycline in the normal equine eye and to compare intraocular and serum doxycycline concentrations. Procedures Six mares were administered doxycycline at 10 mg/kg every 12 h by nasogastric tube for 5 days. Blood, aqueous, and vitreous samples were collected on days 1 and 5. All samples were assayed for doxycycline concentrations. Aqueous and vitreous samples were also assayed for protein quantitation.


RESULTS
Doxycycline was rapidly absorbed after the first dose (T(max) value of 1.42 +/- 1.28 h); and elimination of doxycycline occurred slowly (median t(1/2) = 10.88 h). Doxycycline could not be detected in the aqueous on days 1 and 5, nor could it be detected in the vitreous on day 1. On day 5, the mean vitreous doxycycline concentration was 0.17 +/- 0.04 microg/mL at 2 h after drug administration.


CONCLUSIONS
Repeated oral administration of doxycycline in the horse resulted in steady state serum concentrations of < 1 microg/mL; however, it did not result in appreciable concentrations of drug in the aqueous and vitreous in normal eyes.
Gilmour
Margi A
MA
Veterinary Clinical Sciences, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK, USA. gmargi@cvm.okstate.edu
Clarke
Cyril R
CR
Macallister
Charles G
CG
Dedeo
Jacqueline M
JM
Caudell
David L
DL
Morton
Rebecca J
RJ
Pugh
Martin
M
D000284:Administration, Oral; D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis / Q000097:blood / Q000493:pharmacokinetics*; D001082:Aqueous Humor / Q000737:chemistry / Q000378:metabolism*; D019540:Area Under Curve; D001682:Biological Availability; D004318:Doxycycline / Q000032:analysis / Q000097:blood / Q000493:pharmacokinetics*; D005260:Female; D006734:Horse Diseases / Q000188:drug therapy; D006736:Horses / Q000378:metabolism*; D014605:Uveitis / Q000188:drug therapy / Q000662:veterinary; D014822:Vitreous Body / Q000737:chemistry / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D004318:Doxycycline