Three Counties Equine Hospital
Three Counties Equine Hospital LLP
 Registered in England & Wales OC 346516
spacer Tel: (01684) 592099  |  Fax: (01684) 592181  |  Accounts: (01684) 591260   
About TCEH
Special Veterinary Procedures
Conditions of Current Interest
Recent Articles
  Tendon Injuries
  Lifting the lid on Laminitis
Could your horse be
a victim?
How to choose
and buy a horse
Care of mares and foals in hospital
Continuing Education Programme
Contact TCEH
Job Vacancies and Extra-Mural Studies
Useful Links

Don't be a Dope!

The abuse of drugs in sport has been recognised for centuries. The earliest reference to the use of performance enhancing drugs dates back to 8BC when Greek Olympians were reported to have eaten sheep’s testicles now known to be a source of testosterone (a naturally occurring anabolic steroid). The vast majority of illicit drugs used in sport enhance performance by increasing muscular mass and strength such as anabolic steroids or human growth hormones. Arguably the most notorious case involving the use of anabolic steroids in sport was that of the Canadian sprinter Ben Johnson, who was stripped of his gold medal after testing positive to Stanozolol, during the 1988 Olympics. Other drug abuse includes the use of stimulants, such as amphetamines or caffeine. Amphetamine abuse was implicated in the death of the cyclist Tom Simpson, who collapsed and subsequently died during his ascent of Mont Ventoux in the 1967 Tour de France. He allegedly requested, “…put me back on my bike, I’m fine…”.

Similarly, prohibited substances are sometimes used in equine sport to enhance performance by increasing muscle mass (anabolics) or to mask pain (analgesics). In spite of rigorous testing on the racecourse, positive cases are regularly identified.

Behaviour Modifying Drugs

Behaviour Modifying drugs have also been used in equine sport and Showing is no exception. It is common knowledge that they are often used in excitable, fractious individuals to help calm them in the Show Ring.

There are several sedative drugs licensed for use in horses in the United Kingdom. One frequently used in the show ring to calm horses is acetylpromazine, commonly known as ACP. The only oral form of the drug licensed for use in horses is Sedalin Gel or Sedazine Paste, as ACP tablets are not licensed. ACP is classified in the veterinary literature as an anxiolytic (i.e. it reduces anxiety in patients) and is closely related to chlorpromazine (Largactil) used in humans as an anti-pyschotic drug. It has a dis-inhibitory effect on the part of the central nervous system (CNS) known as the pyramidal system, resulting in inhibition of normal behaviour, which in some individuals may result in aggressive behaviour, not previously experienced.

The onset of action of the drug is more rapid if given intra-muscularly or intravenously, compared with oral administration. The effective dose of the drug is extremely variable, with some horses being relative refractory to its effects. However, in those cases in which it is effective, its effects are readily recognisable. A calming effect may be particularly obvious following previous unruly behaviour in an earlier class. There may be lowering of the head, drooping of the eyelids and in males’ priapism i.e. relaxation of the penis.

The untoward side effects of ACP include tripping and stumbling, dulling of reflexes and slowing of avoidance responses (which could endanger the pony, the handler, the rider, or all three). Other side effects include prolonged hypotension, which can result in irreversible renal damage especially in dehydrated individuals. Furthermore, the penile relaxation previously described, may be permanent.

We are aware of several other drugs used in horses, which are only licensed for use in humans. The most commonly used are Modecate (fluphenazine) and Rakelin (reserpine).

Fluphenazine is from the same family of drugs as ACP (phenothiazines) but is an oil-based, long-acting injectable form. It is available in this form as it is reported that approximately 40% of human schizophrenics do not take prescribed tablets and therefore long-acting preparations are required for maintenance therapy. Its main effect is mediated through the pyramidal system in the CNS as previously described for ACP. However, nowadays it is prescribed far less for humans and has been superseded by more refined drugs due to its extra-pyramidal side-effects. These include Parkinsonian symptoms (including tremor); abnormal face and body movements (dystonia); restlessness (akathisia); rhythmic, involuntary movements of the tongue face and jaw (tardive dyskinesia). Most of these side effects, also recognised in horses, resolve after drug withdrawal; however tardive dyskinesia is of particular concern as it may be irreversible.

Reserpine, occurring naturally as a plant extract, has been used in medicine for centuries for the treatment of insanity but is now obsolete in psychiatry. However, due to its profound effect on reducing blood pressure it retains a clinical use in the treatment of hypertension. At higher doses it causes mental depression and clinical signs similar to Parkinson’s disease.

Drug Detection and Elimination Times

The majority of drugs, both therapeutic and prohibited, are metabolised (broken down) in the liver and excreted in the urine or they may simply be excreted in the urine unaltered. Detection of drugs therefore relies upon the identification of the drug or its metabolites (break-down products) in either blood or urine samples. Urine, which is obviously more easily retrieved than blood, usually has higher concentrations of any drug or its metabolites and is therefore more useful for drug detection.

There is data for many drugs which outlines the number of days which must elapse before the drug is no longer detectable (Withdrawal Time). However, this data should be used as a guide only, as there is huge variation between individuals. Factors such as age, sex, concurrent illness and disease, stress, sub-clinical liver disease and many others can prolong elimination of any drug and result in a positive test after the recommended Withdrawal Time has been observed. Furthermore, elimination of drugs is not fully understood and it is well recognised that a patient (horse or human), after the full withdrawal time has been observed, can have a negative “dope- test” followed by a positive test a few days or weeks later, even though no further drug has been administered. It is this phenomenon which has lead to “positive-tests” in many human athletes.

Furthermore, the public outcry against doping and the creation of the World Anti-Doping Agency in 1999 has lead to huge advances in laboratory techniques for dope testing. These advances have lead to a markedly increased sensitivity of the tests, meaning that the drug can now be detected at far lower concentrations in blood or urine. Inevitably, this means that drugs can be detected for far longer after their last administration. It is also possible to detect sedative drugs at levels which are a fraction of their therapeutic range i.e. the blood concentration at which they have an effect. Furthermore, long-acting, depot preparations such as Modecate inevitably have longer elimination times and are therefore readily detectable for many weeks after their last administration.

There is an extensive list of prohibited substances for competition and as indicated these can be readily identified by collection and testing of a urine sample, the practice of which is becoming more widespread at NPS shows. In addition, notwithstanding the abhorrence of using prohibited substances to gain an unfair advantage, the use of prohibited substances puts the health and safety of your horse and the safety of others at significant risk. Although I have only described the side-effects of a handful of drugs, all drugs have untoward side-effects. Don’t be a dope…don’t do it!

Andrew Harrison BVSc CertEP CertVA MRCVS

(Published 2007 in the NPS Magazine)