Equine Drugs

Equine NSAIDs and Analgesics

Remember, analgesics need to be given prior to the pain to prevent windup and hyperalgesia.

We don’t do preoperative medications well in most field surgeries (including castrations). Often we give our perioperative antibiotics after the procedure and we offer NSAIDs as a client option. If we give NSAIDs, it is often after recovery. And this makes no sense other than tradition.

  • Giving antibiotics preoperatively means they are on board to fight any contaminants. Giving them afterwards means the little buggers have had time to gain a foothold and even multiply.
  • Giving clients the option of NSAIDs means costs drives the discussion. Every horse deserves pain relief
  • Giving NSAIDs after the procedure is NOT cost effective. Your drugs are less useful due to windup and you have to give more to get to the same effect.
  • If cost is a concern, a preoperative dose is the most cost effective!

NSAIDs

NSAIDs are the most commonly used analgesic in horses. The most common non-steroidal agents used in horses are phenylbutazone (“Bute”), flunixin meglumine (“banamine”), and firocoxib (Equioxx), in that order. All three have similar side effects but to various degrees.

Phenylbutazone

“Bute” is the cheapest NSAID and is available in oral (tablet, powder, paste) and iv formulations. It is very irritating so should never be given intramuscularly. IV injections should be given carefully to avoid perivascular administration.

Standard doses for 1000# horses are 2-4 grams per day. The high end of the range (4 grams per day) should be given for as few days as possible. Phenylbutazone is generally used for musculoskeletal issues.

Bute does come in smaller sizes and can be compounded with flavoring. It has excellent bioavailability.  Higher doses increase duration vs increasing analgesia.

Phenylbutazone is the least safe in terms of side effects. It should be avoided in neonates as well as in animals with renal or GI disease. Bute should ideally  be minimized or avoided in pregnant mares. However, many performance mares are retired as broodmares due to musculoskeletal issues and have chronic pain. Many are on bute for the chronic pain. This can lead to birth defects and foals with bute toxicity.

Flunixin meglumine

Flunixin or “Banamine” is more expensive than “Bute” but is considered safer. It is generally used for gastrointestinal or other visceral pain. It comes in oral (paste) or iv formulations. While labeled for intramuscular use, it should never be given intramuscularly as it creates a significant risk of clostridial myositis.

Bioavailability is good at 80%. Higher doses increase duration vs increasing analgesia.

Banamine is commonly used for pain relief in colics. Avoid overdosing or “stacking” NSAIDs (using bute + banamine). Doubled up NSAIDS increase the likelihood of renal damage. Maintaining hydration is essential to minimize renal damage.

Firocoxib

Firocoxib or “Equiox” (LA version of Previcox) is much safer and the most expensive. It is used for long term therapy in horses that don’t tolerate phenylbutazone. Use of the small animal version is common but illegal.

A 3x initial dose is often used to more rapidly increase serum levels (FWIW).

Diclofenac sodium

Diclofenac or “Surpass” is a topical NSAID (cream) that is applied to inflamed areas. Side effects are minimized by restricting the dose to the affected site (minimal systemic absorption). It has been used rectally for postoperative pain.

General notes for NSAIDs

Increasing dose leads to increased duration of action rather than increased efficacy.  Two grams once a day has similar activity to one gram twice a day, and may be easier for owners to administer.

Blood levels are mostly irrelevant. NSAID levels at the site of action are necessary to determine appropriate dosing. Many articles publish blood levels! Be cognizant of their purpose in measuring blood levels. Many times blood levels are needed for regulatory purposes (e.g. did the horse show or perform while on NSAIDs?). This is not the same as effectiveness of the drug. And the discussion portion of the article often confuses the two.

Most common side effects are gastrointestinal (stomach ulcers, oral ulcers, right dorsal colitis) and urinary (kidney failure, hemorrhagic cystitis).  ***Lowered TPP (part of the PCV/TPP) is an early warning sign.*** Other symptoms include poor appetite and isosthenuric urine (due to renal damage).

Prostaglandins are important in most facets of physiology so NSAIDs have the potential to interfere with everything from bone healing to parturition.

Narcotics

Narcotics and other non-NSAID drugs are used when additional pain relief is needed or when the pain isn’t caused by inflammation.

Butorphanol

Schedule IV

Butorphanol is a narcotic analgesic. It acts as a narcotic but can reverse other narcotics (partial agonist-antagonist). It is commonly used in combination with sedatives such as xylazine or detomidine.

Typically, 0.5 -1 ml is given iv or 2 ml im (10 mg/ml). It is absorbed orally, as well.

More effective than morphine, it starts working in ~ 15 minutes and can last up to 4 hours.

Butorphanol is excitatory in healthy adult horses so should not be given alone. An excited horse can be a very dangerous horse. Butorphanol is more of a sedative in neonates and it tends to not cause excitement when given im to horses in pain (but use caution). Repeated doses can lead to poor motility and colic.

Butorphanol can reverse the effects of other narcotics so shouldn’t be given until those have worn off.

Reversal: naloxone

https://equimed.com/drugs-and-medications/reference/butorphanol

Buprenorphine

Buprenorphine (5-10 ug/kg bwt iv) is a narcotic that has been found to be superior to butorphanol in managing equine surgical pain. As a narcotic, it should typically be given with sedation.  The recommended dose is 7.5 ug/kg iv to avoid excitement. The antinociceptive effect lasts 6-12 hours.

Buprenorphine can be administered sublingually in foals.

It was not found to be associated with any increased risk of colic.

Reversal: naloxone.

A multicentre, prospective, randomised, blinded clinical trial to compare some perioperative effects of buprenorphine or butorphanol premedication before equine elective general anaesthesia and surgery. Equine veterinary journal, 2016-07, Vol.48 (4), p.442-450

Morphine

Schedule II

Morphine is a narcotic with similar effects to butorphanol but with lower level analgesia and longer duration. GI motility disturbances are more noticeable (constipation and colic). Systemic morphine causes hyperphagia but also caused gastric distension and decreased intestinal activity. This could lead to significant issues, particularly gastric rupture or impaction.

Dose 0.1–0.3 mg/kg (0.045–0.15 mg/lb) IM q4-hr; often preferred as a CRI:

  • Morphine loading dose: 0.16 mg/kg (0.07 mg/lb) IV
  • Morphine CRI: 0.1 mg/kg/hr (0.045 mg/lb/hr) IV

Reversal: naloxone

Tessier C. Systemic morphine administration causes gastric distention and hyperphagia in healthy horses. Equine Veterinary Journal 51 (2019) 653–657

Fentanyl (patch)

Schedule II

Fentanyl patches are useful for pain relief in patients when NSAIDs are contradicted or not sufficient. Patches should be applied to an area with minimal hair covering and secured in place (upper forelimb).

One 10-mg patch per 150 kg of body weight is recommended. Patches can take 4 hours to provide analgesia and last 36-48 hours. There is great variability between horses in how much fentanyl is absorbed; this variability is increased in sick horses.

Humans can absorb the fentanyl from the patch so careful monitoring, handling and removal is indicated.

https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/duragesic

Gabapentin

Gabapentin is an anti-epileptic drug that has been used to treat neuropathic pain and prevent windup. It’s mechanism of action is unclear but is thought to involve inhibition of neurotransmitter release.

It has been shown to be absorbed in horses when given iv but has poor oral bioavailability (16%). Studies on its efficacy are limited but it is being used to treat laminitic pain.

Check the literature for the latest recommendations.

https://onlinelibrary-wiley-com.ezp1.lib.umn.edu/doi/full/10.1111/j.1365-2885.2010.01161.x

Future drugs

NMDA antagonists – Ketamine and magnesium block the development of hyperalgesia and are being investigated in multiple species for pain control.

Other drugs with potential include grapiprant, epoxide hydrolase inhibitor, and antibodies against nerve growth factor.

Non-pharmacological pain control

Acupuncture, extracorporeal shock wave therapy, chiropractic and massage may help with pain.

Local anesthesia (epidurals, local blocks, neurectomy, etc) also have a role in selected cases.

Resources

Pain management in horses, by our own Dr. Guedes; VCNA 2017-04, Vol.33 (1), p.181-211

BEVA primary care clinical guidelines: Analgesia;  EVJ l 52 (2020) 13–27- systematic review of the research, focusing on field practice

Excerpt: Key guidelines produced by the panel included recommendations that horses undergoing routine castration should receive intratesticular local anaesthesia irrespective of methods adopted and that horses should receive NSAIDs prior to surgery (overall certainty levels high). Butorphanol and buprenorphine should not be considered appropriate as sole analgesic for such procedures
(high certainty). The panel recommend the continuation of analgesia for 3 days following castration (moderate certainty) and conclude that phenylbutazone provided superior analgesia to meloxicam and firocoxib for hoof pain/laminitis (moderate certainty), but that enhanced efficacy has not been demonstrated for joint pain. In horses with colic, flunixin and firocoxib are considered to provide more effective analgesia than meloxicam or phenylbutazone (moderate certainty)

Perioperative pain management in horses, Equine Veterinary Education, July 2019, Vol.31(7), pp.374-383-review article with guidelines on what to use and when

Therapeutic developments in equine pain management, The Veterinary Journal, May 2019, Vol.247, pp.50-56- review article with more thoughts on future drugs-  and case examples

Nonsteroidal Anti-inflammatory Drug Use in Horses, Veterinary Clinics of North America: Equine Practice, April 2017, Vol.33(1), pp.1-15- the entire volume is dedicated to NSAIDS; this is a nice review of actions, contraindications, side effects, etc.

Study break it isn’t all about horses

License

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Large Animal Surgery - Supplemental Notes by Erin Malone, DVM, PhD; Elaine Norton, DVM PhD; Erica Dobbs, DVM; and Ashley Ezzo, DVM is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.