Cortisone, in its many different forms, is often used to reduce pain and inflammation in the horse.
But as with most effective pharmaceuticals, the cortisone family has a dark side. Read on to discover the upsides and downsides of this useful but potent family of drugs.
What is cortisone?
Cortisone is the generic term for a family of potent synthetic or artificial drugs that mimic the action of the natural glucocorticosteroids.
Natural glucocorticosteroids, such as cortisol and hydrocortisone, are secreted from the adrenal glands and play important roles in many functions throughout the horse's body including electrolyte and fluid balance, food metabolism and cardiovascular function.
Glucocorticosteroids also stop new tissue being developed as they are protein synthesis inhibitors.
Medically, glucocorticosteroid drugs are most often used for their anti-inflammatory action.
Cortisone molecules, as with all steroid drugs, work by binding to specific receptors on the surface of the cells that make up the tissues in the horse.
This changes protein synthesis in these cells by turning off or changing the expression of certain genes.
This change in the protein synthesis suppresses tissue inflammation through multiple actions including reducing bleeding and fluid accumulation and reducing inflammatory cell migration to the tissue injury site. Inhibiting the inflammatory process can also reduce pain but this can come at the cost of interfering with healing.
What are glucocorticosteroids used for?
Synthetic glucocorticosteroids are extensively used to treat conditions where a strong anti-inflammatory response and concurrent suppression of pain is desired. These conditions include arthritis, musculoskeletal disease, airway disease, allergic reactions, auto-immune disease and equine asthma.
Veterinarians do not prescribe glucocorticosteroids lightly as they are strong drugs with multiple side effects. These include suppression of the immune system (making the horse more vulnerable to infection) and disruption of the horse's own glucocorticosteroid system which has the potential to lead to serious metabolic issues.
Horses receiving a course of corticosteroids need to be weaned off the therapeutic dosage to allow the adrenal glands to recover.
Corticosteroids should not be used after surgery, when infection is present or in horses experiencing or prone to laminitis. Giving corticosteroids at the same time as non-steroidal anti-inflammatories such as "Bute" or meloxicam will increase the likelihood of a horse developing gastric ulcers and must be avoided.
Many preparations for treating eye conditions contain cortisone. Never use these treatments without having your veterinarian ensure that there is no damage to the cornea. Glucocorticosteroids inhibit corneal ulcer healing and can lead to catastrophic eye problems including blindness if used inappropriately.
Glucocorticosteroids and integrity
Glucocorticosteroids are very useful as they can limit the damage to tissues caused by the inflammatory process, but they do not assist in healing the underlying injury or tissue damage.
Glucocorticosteroids also interfere with healing and mask pain associated with injury.
To this end all glucocorticosteroids are prohibited substances in Standardbreds (See Australian Harness Racing Rule 188 A (b).
Please always consult with your veterinarian before using any form of glucocorticosteroid and be mindful of the withholding time before a horse treated with these drugs can race. For additional information on withholding times, click on this link Advice for trainers presenting horses free of therapeutic substances.
Types of glucocorticosteroids
Different glucocorticosteroids vary in their anti-inflammatory capabilities. The following is a summary of some of the types of glucocorticoids commonly used in horses:
Dexamethasone is a very potent and fast acting anti-inflammatory glucocorticosteroid. It is used in a wide range of inflammatory and immune mediated conditions in horses. It can be administered intravenously, intramuscularly, and orally. Bioavailability after oral administration varies markedly between horses. Dexamethasone formulations can be short or long acting. Long acting formulations will take longer to be excreted so extreme care must be taken to avoid penalties under Australian Harness Racing Rule 188 A (b).
Prednisolone is a moderately potent anti-inflammatory glucocorticosteroid. It is one of the few glucocorticoids that can be administered orally to horses and is commonly used to treat allergic and immune-mediated diseases. A single dose of prednisolone granules was found to be detectable for at least 48 hours1 but as the usual course is over 5 days trainers are advised to consult with their veterinarian on a suitable withhold period for horses that are racing.
This drug is administered via a metered dose inhaler to horses and is converted in the lungs to a very potent glucocorticoid. It is used to treat horses with equine asthma. This glucocorticoid has the same systemic effects as most other glucocorticoids and is subject to the same considerations regarding clearance from the horse's system prior to racing.
Fluticasone proprionate is also administered by a metered dose inhaler to treat inflammatory respiratory diseases. It does not seem to be absorbed systemically and can be used for longer periods with little or no reduction in the horse's overall immune functions. Again, trainers are advised to consult with their veterinarian about a suitable withholding period for horses that are racing.
Methylprednisolone has a moderate potency and is relatively long acting. It is used to reduce pain and inhibit inflammation in equine joints by joint injection. Research has shown that its use will damage joint cartilage and that this effect is worsened with higher doses and repeated administration. Other glucocorticosteroids are now more commonly used.
Betamethasone is another potent corticosteroid that is used in joint injections. It can be formulated as long acting, short acting, or a combination of both. It is often injected with hyaluronic acid to support joint health. The detrimental effects to joint cartilage are not as significant at lower doses.
Triamcinolone acetonide is also a potent glucocorticosteroids with an intermediate duration of action. Triamcinolone acetonide in high doses has been linked to the development of laminitis. Low doses are commonly administered directly into inflamed joints.
Glucocorticosteroids inhibit inflammation and reduce the pain associated with the inflammation caused by disease or injury. Some glucocorticosteroids reduce tissue damage caused by inflammation but the action of these drugs is to reduce protein synthesis. This means they will never heal underlying tissue damage. All synthetic glucocorticosteroids are banned in the horse that is presented to race or trial. Trainers are advised to work closely with their veterinarian to ensure that appropriate withholds are used for each of the different glucocorticoid formulations.
1RIRDC Detection Times for Equine Medications Pocket Guide November 2013 (click on this link for more information about detection times)