As a general rule hydrophylic preparations (phosphates) are short acting while
lipophylic molecules (acetates, acetonide) are long acting. As another rule, the
duration of symptomatic relief (months) far exceeds that of the intra-articular
half-lives of these preparations (days to weeks). It has recently been
suggested that long acting corticosteroids effect their duration of action by
binding to and persistently occupying intracellular receptors in the cytoplasm
of synoviocytes and chondrocytes long after intra-articular concentrations are
no longer detectable.
Even so, the choice of formulation, dose, and frequency of administration
remains somewhat empiric. Currently, the most commonly used formulations
are
triamcinolone
acetonide,
methyl-prednisolone
acetate,
and
betamethasone acetate. Less commonly used are isoflupredone acetate and
flumethasone. Doses vary depending on the type of joint (low- or highmotion), volume of synovial fluid in the joint, severity of inflammation, and the
number of other joints requiring treatment. This is an important consideration
in that a total body dosage of triamcinolone acetonide in excess of 18 mg has
been associated with induction of laminitis. At least one author however,
considers that a lack of good evidence exists linking laminitis to corticosteroid
injection. (McIlwraith 2010) although there have been anecdotal reports to the
contrary (Bathe. Doses are shown in the table. Post-injection rest results in a
lengthened response to corticosteroid injections in human joints. It is likely
that a period of restricted joint motion reduces clearance of the corticosteroid
preparation from the joint, enabling better penetration of intra-articular tissues.
It must be remembered that many racing and competition jurisdictions
consider intra-articular corticosteroids as banned substances in competition.
The situation is complicated as the drug detection time and drug withdrawal
time for corticosteroids (such as triamcinolone acetonide) are undoubtedly
variable and often longer than the commonly stated period of time of 10 days
historically used by veterinarians. Many racing jurisdictions are putting effort
into testing to identify medicated horses.
From Caron J (2005).
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
155