A horse will likely need medication at some point – to battle illness, for first aid, or for sedation for uncomfortable procedures such as teeth floating or sheath cleaning. Many drugs used today have existed for more than a century, while others are taking equine veterinary medicine in new and exciting directions.

As a partner in Calgary, Alberta’s Moore Equine Veterinary Centre since 1972 and a large animal veterinarian for 47 years, Dr. Dennis Rach has administered and prescribed a multitude of equine medication over the years. But there are a few he reaches for almost daily. Dr. Rach offers Horse Canada a look at some of the drugs he has in his figurative “little black bag.”

ANTI-INFLAMMATORIES

Non-steroidal anti-inflammatories (NSAIDs) are at the top of Dr. Rach’s most-used medication list. They reduce production of prostaglandins, chemicals that induce pain, inflammation and fever where there’s tissue damage or infection.

“They’re all in the same class as Aspirin® and ibuprofen,” he said.

NSAIDs are safe, but misuse or overuse of this type of medication can lead to serious problems. Combining different NSAIDs together or with other drugs, particularly corticosteroids, may intensify each drugs’ response and increase the likelihood of complications and adverse reactions. NSAIDs mask lameness, so shouldn’t be used before a soundness exam. Horses may also exacerbate an existing injury or cause re-injury.

Phenylbutazone, bute (various brand names)
Bute, probably the most prescribed equine medication, is inexpensive. “Its maximum effectiveness is in place within two to four hours,” said Dr. Rach. “It works quickly and is quite effective.”

Administration
Bute is usually given as a paste, gel, powder or tablet, once or twice a day usually for no longer than three days. Not recommended for long-term use, oral bute should be fed with grain or beet pulp to reduce the possibility of gastrointestinal irritation. It’s also available as an intravenous (IV) injection.

Side Effects

  • Oral or gastric ulcers
  • Kidney function decline
  • Allergic reaction
  • Lowered blood protein levels

Contraindications (factors or conditions that make giving the drug inadvisable)

  • Allergy to bute
  • Ulcers or other gastrointestinal problems
  • Kidney disease
  • Unknown effect in pregnant, lactating mares
  • Toxicity risk in debilitated or older horses, ponies and foals

Flunixin meglumine (brand name Banamine®)
More expensive and about four times stronger than bute, flunixin meglumine, usually referred to by the brand name Banamine®, is a “fairly potent pain killer,” said Dr. Rach. The go-to drug for colic is also used for musculoskeletal disorders, toxic shock and tying-up.

Administration
Banamine® is usually given by IV injection, especially for quick pain relief. For colic, it should only be re-administered once. For other conditions, treatment can last up to five days. It’s also available in granule and paste form. Serious risks are associated with intramuscular (IM) injection.

Side Effects

  • Ulcers
  • Kidney damage (especially in dehydrated horses)
  • Toxicity
  • Allergic reaction
  • Clotting or blood disorder
  • Not recommended for IM injection – possibility of abscesses, irreversible muscle damage, fatal infections
  • Accidental injection into an artery can trigger seizures, collapse, death

Contraindications

  • Similar to bute

Firocoxib (brand name Previcox®)
Firocoxib is a newer subclass of NSAID that is generally easier on gastrointestinal system.

“It doesn’t kill as much pain as bute, but for low-level pain, it’s really great for some old horses with chronic arthritis where you just want to make them happier,” said Dr. Rach.

Administration
Only licensed for dogs in Canada, firocoxib, used off-label in horses, comes in 337-mg tablets. “A horse dose on maintenance is a quarter of a tablet, so they handle it completely differently than a dog,” explained Dr. Rach. “They just need a fraction per pound. At that dose, it gets pretty inexpensive to treat a horse that’s got low-level chronic inflammatory problems.”

In the U.S., firocoxib tablets, IV and paste called Equioxx® are specifically approved for equine arthritis.

Side Effects

  • Clinical trials indicate fewer gastric side effects than other NSAIDs, but horses are still at risk
  • Oral and facial sores and ulcers

Contraindications

  • Similar to other NSAIDS

ANTIBIOTICS

Antibiotics are powerful drugs that combat bacterial infections and diseases.

Trimethoprim sulfa, TMS
TMS is broad-spectrum (kills a wide variety of bacteria) antibiotic for routine ailments like wounds and mild infection and upper respiratory infections.

Administration
Available as tablets (brand name Sulfatrim™), powder and granules (Uniprim®), an IV or IM injectable (Tribrissen®) and, according to Dr. Rach, can also be compounded into an oral liquid.

“It is widely used now because you don’t have to inject it. That becomes a problem for some horse owners – trying to give a needle,” he said.

Although treatment duration is usually once or twice daily for five to 10 days, Dr. Rach added, “Some horses with chronic internal infections could be on it for six weeks or more at a time. It’s pretty safe. They really tolerate it well.”

Side Effects

  • Dr. Rach said hydration is “about the only thing to worry about.” Sulfa crystals can create kidney problems in dehydrated horses. “You really want to make sure they’re drinking water.”
  • Other possible, but rare, side effects include: anemia, fatigue and allergic reactions, ranging from swelling to coma.

Contraindications

  • Known TMS, sulfa allergy
  • Liver and blood diseases, kidney stones
  • Undetermined effects on unborn foals

Ceftiofur sodium (brand name Excenel®)
A broad-spectrum antibiotic mainly used to treat bacterial respiratory infections, especially streptococcus equi (strangles) and pneumonia, ceftiofur also treats what Dr. Rach calls “serious conditions” such as Lyme disease.

Administration
The IM injection is usually given once a day for up to 10 days.

Side Effects

  • Pain, swelling at injection site
  • High doses cause severe diarrhea, colic, appetite loss
  • Allergic reactions

Contraindications

  • Horses under extreme stress can develop serious, possibly fatal diarrhea
  • Unestablished safety in breeding animals and foals under six months

Penicillin (many brand names)
Produced from a mould, penicillin was discovered in the 1920s and is still one of the most widely used antibiotics.

Administration
Best administered by IV or IM injection; it isn’t well absorbed orally. A normal course of treatment is once or twice daily for up to a week.

Side Effects

  • Allergic reactions – mainly hives, respiratory distress
  • Injection-site irritation
  • Nerve damage from improper injection

Contraindications

  • Known penicillin allergy

TRANQUILIZERS & SEDATIVES

These drugs are used to facilitate veterinary and some grooming procedures and even to calm horses for training. Tranquilizers ease anxiety and aggressiveness, but don’t usually cause excessive drowsiness or pain relief. Sedatives cause sleepiness and, said Dr. Rach, “in some cases, are used to control pain.”

“When you’re working on a horse in terms of veterinary medicine, you’re often doing something the horse doesn’t like,” said Dr. Rach. “If you’re trying to inject a joint or even if you’re trying to clip them to, say, examine them with an ultrasound machine or something, lots of times you don’t have patient compliance, so you need to use sedation.”

Xylazine (Rompun™)
A sedative that reduces brain activity, which relaxes muscles and decreases excitement.

Administration
Xylazine is the shortest acting sedative, offering 15 to 20 minutes before having to redose, explained Dr. Rach. Romifidine (SediVet®) gives 30 to 35 minutes of sedation, while detomidine (Dormosedan®) offers 40 minutes. IV injection is fast, most effective and requires less medication than IM. A newer oral Dormosedan® gel for syringe application under the tongue is also available.

Side Effects

  • “Since they’re out of the system so quickly, they’re quite safe,” said Dr. Rach.
  • Small risk of colic
  • Choke if the horse eats before fully out of sedation

Contraindications

  • Known allergy to the respective medications

Butorphanol tartrate (Torbugesic®)
Butorphanol is a synthetic opiate largely used for colic pain. Its sedative effect also renders horses easier and safer to handle. Dr. Rach often uses it as an add-on to other sedatives.

Administration
“Just a little bit of Torbugesic® is enough to really put them over,” said Dr. Rach. “If you’re doing a joint injection, it’s nine times as potent as morphine. They don’t feel the needle go in, so they don’t jump. You don’t want a horse jumping when you’re trying to put a needle in the joint. And for doing dentals, I use it in every case because it keeps all four feet on the floor instead of in my face.”

IV injection starts to ease pain within 15 minutes and can be effective for up to four hours.

Side Effects

  • Allergic reaction
  • Loss of coordination, staggering
  • Loss of appetite, nausea, diarrhea
  • Over-excitement (a rare paradoxical effect)

Contraindications

  • Known allergy to butorphanol
  • Effect isn’t known in breeding horses, weanlings and foals
  • Effects may be increased when combined with other sedatives or analgesics.

Acepromazine maleate (various brand names)
ACE, as it’s commonly called, is a tranquilizer that depresses the central nervous system. Dr. Rach calls it a “true tranquilizer.”

Administration
It’s available in IV or IM injection or granules. Effects can last from one to eight hours. Combined with other drugs, ACE can boost pain relief and sedation duration. Dr. Rach explained when he’s set to do dental procedures on several horses, he will give them all ACE about 20 minutes prior to starting, to minimize Rompun™ doses. Plus, he added, “ACE also relaxes the tongue because it’s a skeletal muscle relaxant.”

Side Effects

  • Allergic reaction
  • Reduced blood pressure
  • Sweating, increased temperature
  • Trembling
  • Excitement, restlessness, increased heart, respiratory rates
  • Unsteadiness at high doses
  • Pink, reddish urine
  • Inability to retract the penis, while rare, can lead to serious complications
  • Accidental injection into artery can cause seizures even death
  • Choke

Contraindications

  • Known allergies to ACE
  • Breeding stallions
  • Horses that are debilitated, aged, in shock, pregnant/lactating, with liver or heart disease

CORTICOSTEROIDS

Corticosteroids decrease inflammation and immune system activity. They are used in a wide variety of first aid and treatment scenarios. They slow progression of degenerative joint diseases, help manage shock, trauma, spinal cord injuries and anaphylactic reactions, and resolve allergic reactions, skin infections and eye ailments such as conjunctivitis and uveitis.

Triamcinolone, betamethasone and methylprednithoze
Commonly used in the treatment of joint pain.

Administration
All are administered by direct injection into the joint space (intra-articularly). Providing relief for several months, this procedure is often cost-effective compared to other treatments. Corticosteroids are frequently combined with hyaluronic acid (HA), an injectable also used for joint health and improved lubrication.

Other applications: Depending on the condition being treated, corticosteroids such as hydrocortisone, prednisolone and dexamethasone can be administered via IM and IV injection, oral powders and topical creams and sprays. (Read Respiratory Drugs, on page 48 to discover how “dex” also helps horses breathe better.)

Side Effects

  • Risk of side effects heightens with increasing dosages and duration of treatment or when corticosteroids are administered with other medications
  • Development or worsening of gastrointestinal ulcers (especially with concurrent NSAID use)
  • Lethargy
  • Laminitis (especially ponies)
  • Excessive drinking, urination
  • Muscle wasting with long-term use
  • Cushing’s and Addison’s disease due to overuse or rapid withdrawal
  • Immune response suppression, causing increased susceptibility to infection
  • Intra-articular treatments: risk of joint infections; post-injection pain, heat, swelling

Contraindications

  • Known allergy to corticosteroid
  • Pregnant/lactating mares, young foals
  • Pituitary gland issues
  • Ulcers
  • Post-surgical use
  • Systemic bacterial or fungal infections

RESPIRATORY DRUGS

Chronic, non-infectious lower airway disease – best known as heaves – is what Dr. Rach calls “an allergic phenomenon.” Because corticosteroids suppress immune response and reduce inflammation, they’re particularly useful in managing this condition.

Dexamethasone, dex (various brand names)
One of the most commonly used corticosteroids for heaves is dexamethasone. “Dex is a great drug,” said Dr. Rach. “It’s cheap and it’s been around for more than half a century. It’s a potent form of cortisone.”

Administration
For quick and systemic results, dex is administered by IV injection, but it also comes in IM injections and oral powder. It is particularly effective and can provide dramatic improvement within three days.

Dr. Rach said for more severe cases, aerosolized dex and other corticosteroids such as fluticasone and beclomethasone, offer inhaled, targeted doses at high levels. “We’ll put the horse in a mask – or a puffer – and let them breathe that in, just like with people,” said Dr. Rach.

This provides relief from coughing and difficulty breathing within two hours, as the medication reduces airway spasms, inflammation, mucus, and dilate airways with fewer systemic (body-wide) effects than oral or injected forms. Anti-inflammatories, antibiotics and bronchodilators are also prescribed for inhalation therapy and are given concurrently with corticosteroids.

Side Effects

  • Laminitis (“A fat pony on dex could run the risk of laminitis,” said Dr. Rach. “But for regular horses, it doesn’t seem to be as much risk for a three-week treatment.”)
  • Ulcers
  • Susceptibility to infections
  • Increased urination and water consumption, loss of muscle mass after extended use. “Long-term use would have effects on the whole body,” said Dr. Rach. “But somewhere between two and three weeks, we’d be trying to figure out another strategy to treat this horse anyway.”

Contraindications

  • Ulcers
  • Currently on on NSAIDs
  • Pregnant/lactating mares

Clenbuterol (Ventipulmin®)
“As far as helping the horse breathe more easily, there’s a drug called clenbuterol,” said Dr. Rach. A bronchodilator, it opens constricted airways and decreases mucus thickness. It also can reduce how much corticosteroid is required.

Administration
A syrup that’s top-dressed on food twice a day, it takes effect within an hour and lasts about eight hours after a single dose, 12 hours on repeated doses twice a day. Dr. Rach said horses usually eventually become immune to its effects. “You have to take them off for a week or so if you’re going to put them back on it,” he said.

Side Effects

  • Sweating
  • Muscle tremors
  • Restlessness
  • Hives
  • Increased heart rate

Contraindications

  • Known allergy to clenbuterol
    Currently on corticosteroids
    Cardiovascular issues
    Discontinue when a pregnant horse is expected to deliver – contractions may be suppressed
    Undetermined effect on stallion and broodmare fertility

The Pros and Cons of Compounding

Compounding – changing a medication from the original, Health Canada-approved form – is done for several reasons:

1. To offer alternate ways of administering a drug. For example, as Dr. Dennis Rach explained, the antibiotic Trimethoprim sulfa, usually available as tablets, powder, granules IV or IM injections, can be compounded into an oral liquid to use as a drench or mixed with feed.

2. Adding flavouring to encourage a horse to
eat or accept medication.

3. Mixing drugs for ease of administration or enhanced effect.

4. To accommodate individual dosing requirements.

5. Providing an alternative to a commercially unavailable drug.

The process of altering a medication can modify or quash the drug’s action, leaving a horse at risk.

Owners might be tempted to save a buck by using compounded drugs (often sold online), but these formulations are often created in large batches with ingredients of unknown quality. Compounding should only ever be carried out for individual cases by a veterinarian or a registered compounding pharmacy working from a veterinarian’s prescription.

Take-Home Observations

All medication, and medications, is dangerous when misused. It’s imperative you consult a veterinarian before administering any drugs to your horse. They consider manufacturer’s directions, but a host of other factors that could play into effective, safe dosing, such as setting and facilities, environment (i.e. busy versus quiet barn), horse’s temperament, size and age, even breed. They also are more equipped than lay people to assess benefits of giving a drug versus potential risks.

Follow dosage instructions and course of treatment as stipulated by your veterinarian. That means never skipping doses or stop giving the medication. And always tell them about other medications, supplements, natural remedies your horse is receiving to avoid negative interactions.