Dexamethasone Administration Routes in Horses Compared

Researchers recently evaluated and compared the absorption rate of the common equine anti-inflammatory and immune-suppressing corticosteroid drug dexamethasone (DXM), finding the drug behaves similarly regardless of how enters the equine body.

Dexamethasone is prescribed to treat a variety of equine conditions, including arthritis, allergic reactions, and heaves. The drug is commonly administered orally (PO), intravenously (IV), or intramuscularly (IM), and its absorption rates via these methods has been studied. However, less was known about the absorption rate of DXM when it is administered intra-articularly (into the joint).

A team of researchers led by Lawrence Soma, VMD, Dipl. ACVA, professor of anesthesia and veterinary medicine at University of Pennsylvania School of Veterinary Medicine, recently performed a study, aiming to learn how DXM is absorbed by the body and how it affected naturally-produced hydrocortisone (HYD) production when administered through IA routes.

DXM and other corticosteroids suppress the body's natural production of hydrocortisone, a hormone with many important regulatory functions within the body. "Continuous administration of corticosteroids will eventually shut off the secretion of endogenous HYD," relayed Soma. "They should only be given for seven to 10 days at a time."

Using a two-week study cycle with a two-week washout period, researchers administered dexamethasone sodium phosphate (DSP, a more soluble formulation of DXM), to six Thoroughbred horses (ages 6-10). Joints injected included the knee, fetlock, and stifle.

For comparison purposes, horses also received the drug through IV, IM, and PO routes for a total of six drug administrations per horse. To analyze DXM and HYD levels, blood samples were collected before and continuously after each drug administration for up to five days.

Key findings from the study included:

  • DXM levels in blood plasma differed among the three injected joints up until 15 minutes after DSP administration. Beyond 15 minutes, no significant differences were observed;
  • No significant differences in DXM bioavailability (degree to which drug becomes available to target tissue) in the three different joints were observed; and
  • Among the six methods of drug administration, no significant differences in suppression of HYD levels were observed.

"The specific duration of the anti-inflammatory effects of IA administration of corticosteroids has not been studied in the horse," the team relayed, adding that further studies are needed in this area.

The study, "Pharmacokinetics of dexamethasone following intra-articular, intravenous, intramuscular, and oral administration in horses and its effects on endogenous hydrocortisone," appeared in Journal of Veterinary Pharmacology and Therapeutics in May 2012. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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