Sedatives and Sedation in Horses

It’s important to remember that all sedatives temporarily alter the way the horse’s brain and body works, and have a serious impact on the heart and circulatory system. As a result, they’re all prescription-only medicines, and your vet will want to satisfy themselves that the patient doesn’t have any underlying heart problems etc before using them. Overdose of a sedative is rarely fatal in a healthy horse, but it can still be dangerous, especially if there is any underlying illness that makes them less good at maintaining their blood pressure. Its also vitally important to tell your vet the horse’s whole medical history if you’re asking them to give a sedative – there have been cases of horses who were being treated with a (very safe) antibiotic (TMPS); the owner forgot to tell a vet this, and the combination of sedative and this antibiotic has resulted in a heart attack (technically, a fatal arrhythmia).

By syringe or in feed.
This is the slowest, least powerful and least reliable way to sedate a horse, but it has two advantages – you don’t need a vet to come and do it, and you don’t need to get so close to the horse to give it.
The drug most commonly used is ACP, sold as Sedalin or Relaquin paste. Occasionally ACP tablets are used, although there are strict restrictions on when a vet is allowed to prescribe tablets instead of paste. There is a newer drug now available as a syringe, detomidine (sold as Domosedan gel), which is absorbed across the membranes in the mouth so shouldn’t usually be given with food, but does work faster and give better sedation than ACP.

2) By injection into the muscle.
Many injectable sedatives can be given into the muscle – this injection is more reliable than by mouth, but requires much higher doses than if given into the vein (in my experience, you need 4-5 times as much, and it takes about twice as long to work). It’s only usually needed if the horse is too wild or dangerous to get a vein, but it’s quite useful to “take the edge off”, and then I can top up with intravenous sedatives if needed. The other situation where I’ve occasionally used it is when a severely colicing horse has to take a long ride in a box to get to a surgical centre. In these cases, I have sometimes given the driver a preloaded syringe so that if he horse freaks out or goes crazy in transit, they can give it something to calm it down and relieve the pain until they arrive.

3) By intravenous injection.
Intravenous sedation is by far the best option if possible – it works fast (usually 5-10 minutes), you need lower doses, and you get much better sedation than by any other route. This is what I’ll be concentrating on below.