Most of us are familiar with the little sachets of white powder sometimes sprinkled into a feed bowl. They contain bute, which is short for phenylbutazone, the chemical name of the active ingredient.

Different manufacturers try to give their product a distinctive trade name, but all versions contain the same basic drug. Bute is classed as a non-steroidal anti-inflammatory drug. Other drugs in the same chemical family include aspirin and ibuprofen.

Bute is versatile and powerful. It is used both in the short term, to reduce immediate pain and swelling after an injury, and also in the longer term, for example, to treat stiffness and discomfort caused by arthritis. Bute reduces localised infection, perhaps around a cut or an embedded thorn, which in turn helps the antibiotic to reach the site. The drug may also be given for a more generalised bacterial or viral infection, lowering the horse’s temperature and reducing the severity of symptoms.

Bute was first synthesised in 1949, and was originally used as a painkiller for people with arthritis. It proved to be effective, but unfortunately it also materialised that, in rare cases, it could cause potentially fatal changes to the patient’s blood cells and bone marrow. Its use was banned in human medicine, but it proved to be an equally good painkiller in animals without causing bone marrow suppression.

No drug is without side-effects, however, and bute is no exception. The important question is how significant these effects are compared to the drug’s treatment value. Bute is comparatively safe when used at the correct dose and can be given daily for weeks or even months at a time with little adverse effect. It has a relatively low safety margin, however, and just two or three times the normal dose can cause severe side-effects in as little as a few days.

For this reason, never increase the amount of bute you give without checking with your vet first. The standard dose for a 500kg horse is usually one sachet twice daily. An initial dose of up to two sachets twice a day can be given for the first couple of days, but the dose should then be reduced.

Bute is a prescription-only drug and must be supplied or prescribed by your vet. If your horse is receiving bute long-term, the vet is required to examine him regularly — typically every three to six months — to ensure the medication is appropriate. Owners sometimes complain about such checks, but please remember they are a regulatory requirement and not simply a case of the vet trying to increase your bill.

A bitter pill

Bute works by inhibiting enzymes that are released from damaged cells. These enzymes trigger pain and inflammation, but they also have low-level protective effects on the gut lining and are needed for normal kidney function. This explains why the side-effects of bute can include stomach and intestinal ulcers, kidney problems and liver damage.

Young and sick horses are more susceptible to these unwanted effects and require careful monitoring. This can include giving them anti-ulcer drugs and taking blood tests to check liver function.
One part of the body that bute does not affect is the brain. It is not a mind-altering substance and has no ability to make horses either excessively sleepy or, as is more commonly claimed, alarmingly hyperactive. If a horse does become more of a handful, it is probably because he is relieved at being pain-free.

Other medicines from the same family as bute have slightly milder side effects. Meloxicam, for example, has less effect on the stomach and intestines because it blocks fewer of the beneficial actions of the inflammatory enzymes. When painkilling power and price are compared, however, bute is often the cheapest and most effective treatment to use.

Bute has a bitter taste, so some horses won’t touch it in their food. It is available as an injection, but this can only be given intravenously by vets, while an oral paste form is much more expensive.

As a result, owners have come up with a variety of ingenious ways of getting their horse to take his medicine — sprinkled on a honey sandwich is one favourite, but mashing up bute with a banana or mixing it into a jelly has also been used with success.

Bute does not dissolve well in water, but can be mixed with yoghurt or ready-made custard and then syringed into the horse’s mouth like a wormer. Apple-flavoured bute sachets are now available, but we lag behind the US, where a whole range of different flavours is available.

Suxibuzone, sold under the tradename Danilon, is marketed as a more palatable alternative to bute. The taste is supposedly less bitter, but, because the drug is converted to phenylbutazone in the liver, its action and side-effects are similar.

Welfare concerns

Horses are not allowed to compete in affiliated competition while on bute because of the potential to be performance-enhancing. The drug can be detected in a horse’s system for up to seven days, so even though any beneficial effect from the drug would be negligible after 48hrs, treatment must be stopped more than a week before competition.

Governing bodies, such as the FEI and the British Horseracing Authority, have a zero-tolerance policy, which means that any trace of bute detected will result in a doping charge. The aim is to ensure a level playing field, but there is more to it than that.

Human athletes are allowed to take painkillers, even when they are competing at an elite level such as the Olympics, so why not horses? The answer comes down to welfare; humans can choose to compete even if they are injured, but horses cannot. It is vital that they are protected from being asked to compete when they are carrying an injury that could be made worse by competition.

Ref Horse & Hound; 18 January 2018