Assessing and addressing chronic pain is important for maintaining horses’ health and quality of life. Chronic pain is defined as pain that persists after a normal healing period and that persists or recurs for over 3–6 months.¹ Most horse owners and managers can tell when a horse is experiencing pain because they are usually familiar with a horse’s normal behavior. In some cases, it is easy to determine that a horse is experiencing pain, but not as easy in others. Like humans and other animals, horses differ in their individual tolerance of pain and in their demonstration of its outward signs. Additionally, chronic pain probably affects most, if not all, geriatric horses, yet it can go unrecognized by horse owners.²

Individual pain tolerance and how horses demonstrate pain may also vary based on factors like the horse’s age, previous experiences and environment. Some non-painful stimuli (e.g.,  anxiety, fear) can also give rise to similar signs, making recognition of pain in horses challenging. Common indicators of pain can include:

• Elevated heart rate
• Elevated respiratory rate
• Sweating 
• Dilated pupils
• Behavioral changes
• Ear position (Ears partially or fully back can be an indication of discomfort)
• Lameness, changes in movement
• Visceral signs (e.g., colic) – Pacing, rolling, pawing, or a horse kicking at its sides³

There are also a number of pain scales that are used to gauge the degree of pain in horses: 

• Verbal or numerical rating scales. In the verbal scales, the letters A to F are often used, where A indicates no lameness and F is the inability of the horse to move. The American Association of Equine Practitioners (AAEP) lameness grading system is a numerical rating scale from 0 (no lameness) to 5 (minimal weight bearing in motion or complete inability to move).
• The Obel grading system primarily rates the degrees of lameness associated with laminitis. This system ranges from Grade I (frequent shifting of weight between feet, no lameness at the walk, and bilateral lameness at the trot) to Grade IV (a horse will walk only if forced to do so).
• The modified composite pain score (MCPS) is also to evaluate laminitic horses. This numerical rating scale ranges from 1 (no pain) to 10 (moderate to severe pain, irritable, restless).²

Opioids (opiates) are frequently used for treating pain in horses that is chronic or idiopathic (pain of unknown cause). Butorphanol (Torbugesic) is the only opiate currently labeled for horses, but the cost and risk for abuse by humans make its long-term use controversial.⁴ There are, however, other opioids that can be safely used extra-label that are effective in the management of chronic pain in the horse. 

Tramadol for Equines

Tramadol is a synthetic codeine analogue that is widely used as an analgesic in human and veterinary medicine. It is used as an alternative or adjunct for the treatment of postoperative or chronic pain in many species. It may be most useful when used in combination with NSAIDs or other analgesic drugs.⁴

In horses, tramadol can be administered as an epidural, and is also useful as an analgesic. In donkeys, tramadol used with lidocaine as an epidural has a shorter onset and longer duration of action than when lidocaine is used alone.^4,5

“Tramadol has different pharmacokinetics in neonatal and weaned foals. After oral administration, higher bioavailability (53% vs 20%), shorter time to peak concentration (1 hour vs 1.25 hours), and peak levels occurred with neonatal (2 weeks of age) versus weaned (4 months of age) foals. Elimination half-life did not significantly differ (≈2 hours). The active metabolite (M1) remained above the reported therapeutic concentration for humans for 3 hours in neonatal foals and 8 hours in weaned foals. In another study, elimination half-life was ≈1.5 hours in foals up to 6 weeks of age.

“In adult horses, tramadol has relatively poor oral absorption and an elimination half-life of ≈1.5 to 2.5 hours after IV or IM administration and up to 10 hours when given orally. The M1 active metabolite half-life is ≈4 hours. Oral doses of 10 mg/kg yield concentrations of tramadol and M1 that are believed to be therapeutic, whereas lower doses (3-6 mg/kg) are inconsistent and transient.”⁵

Dosing suggestions for tramadol in horses are as follows (adapted from Plumb’s Veterinary Drugs):

• For analgesia: 10 mg/kg PO every 12 hours.
• Chronic laminitis pain: 10 mg/kg PO every 12 hours provided analgesia, whereas 5 mg/kg doses did not. Tramadol 5 mg/kg PO twice daily for 7 days—alone or with ketamine 0.6 mg/kg/hour IV CRI over 6 hours each day for the first 3 days of treatment—may also enhance pain relief.⁵

Where to buy Tramadol

Tramadol is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. TRAMADOL HCL 50 MG/ML, INJECTABLE SOLUTION 30ML by NexGen Pharmaceuticals is an excellent solution for the management of chronic pain in the horse.

This product carries numerous potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Merksey H., Bogduk N. Classification of Chronic Pain. 2nd ed. IASP Press; Seattle, WA, USA: 1994.

²thehorse.com.

³Lavand’homme P. The progression from acute to chronic pain. Curr. Opin. Anesthesiol. 2011;24:545–550.

⁴P. Cagnardi, C. Ferraresi, A. Zonca, A. Pecile, G. Ravasio, D.D. Zani & R. Villa (2014) Clinical pharmacokinetics of tramadol and main metabolites in horses undergoing orchiectomy, Veterinary Quarterly, 34:3, 143-1.

⁵Plumb’s Veterinary Drugs.