Pharmacokinetics of methylprednisolone acetate after intra-articular administration and its effect on endogenous hydrocortisone and cortisone secretion in horses.
OBJECTIVE
To determine the pharmacokinetics of methylprednisolone (MP) and develop a pharmacokinetic-pharmacodynamic model of the related changes in plasma concentrations of endogenous hydrocortisone (HYD) and cortisone (COR) following intra-articular administration of methylprednisolone acetate (MPA) in horses.


METHODS
6 Thoroughbreds.


METHODS
In each horse, 200 mg of MPA was injected intrasynovially into a carpal joint, and plasma MP, HYD, and COR concentrations were determined via liquid chromatography-mass spectrometry.


RESULTS
A 5-compartment pharmacokinetic-pharmacodynamic model was used to describe the concatenated changes in the plasma concentrations of MP, HYD, and COR and to estimate the instantaneous rate of endogenous HYD production. The median transfer half-life (t(1/2t)) of methylprednisolone from the joint to plasma and elimination half-life (t(1/2e)) from plasma were 1.7 and 19.2 hours, respectively. Maximum plasma concentration of methylprednisolone was 7.26 +/- 3.3 ng/mL at 8 hours, which decreased to 0.11 +/- 0.08 ng/mL at 144 hours after injection. At 3 hours after MPA administration, plasma COR and HYD concentrations were significantly decreased from baseline values (from 2.9 +/- 0.28 ng/mL to 2.10 +/- 1.0 ng/mL and from 61.1 +/- 18.9 ng/mL to 25.7 +/- 12.1 ng/mL, respectively).


CONCLUSIONS
The sensitivity of the analytic method used allowed complete description of the related kinetics of MP, HYD, and COR following intra-articular administration of MPA. A single intra-articular administration of MPA profoundly affected the secretion of HYD and COR in horses; secretion of endogenous corticosteroids remained suppressed for as long as 240 hours after injection.
New Bolton Center Campus, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348, USA.
Lawrence R
LR
Soma
Cornelius E
CE
Uboh
Yi
Y
Luo
Fuyu
F
Guan
Peter J
PJ
Moate
Ray C
RC
Boston
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D003348:Cortisone / Q000097:blood / Q000378:metabolism*; D006736:Horses / Q000097:blood*; D006854:Hydrocortisone / Q000097:blood / Q000378:metabolism*; D007270:Injections, Intra-Articular; D007700:Kinetics; D008775:Methylprednisolone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000077555:Methylprednisolone Acetate
D000893:Anti-Inflammatory Agents; D000077555:Methylprednisolone Acetate; D003348:Cortisone; D006854:Hydrocortisone; D008775:Methylprednisolone