Pain Management: What the Research Says
Evidence from 19 peer-reviewed studies
What Professionals Should Know
- •CBD paste appears to be the preferred formulation for equine use given faster peak concentration achievement, though both oil and paste show similar overall bioavailability
- •Feeding status does not meaningfully affect CBD absorption in horses, so dosing can be flexible relative to meals
- •Current equine CBD supplementation lacks robust pharmacokinetic evidence—these baseline data support the need for further efficacy studies in painful conditions before widespread clinical recommendation
- •Oral morphine offers an effective analgesia option for horses without the neuroexcitation and GI side effects seen with IV dosing, making it potentially safer for field use and routine pain management
- •The anti-nociceptive effects of oral morphine are measurable and reproducible, supporting its use in clinical pain management protocols
- •Multiple dose regimens appear feasible, suggesting oral morphine could be incorporated into multimodal analgesia strategies for horses with acute or chronic pain
- •Oral codeine at 0.6 mg/kg may offer an alternative analgesic option for horses that avoids the neuroexcitation problems associated with morphine administration.
- •This pharmacokinetic profile suggests codeine could be useful for practitioners seeking safer opioid analgesia, though clinical efficacy data and safety monitoring protocols require further validation.
- •The conversion of codeine to morphine and its active metabolites in horses differs from morphine administration alone, potentially reducing undesirable behavioral and locomotor side effects.
- •Matrix fentanyl patches provide extended analgesia in horses without requiring venous catheterisation, with plasma concentrations maintained for up to 96 hours post-application
- •Application site (inguinal, metacarpal, or ventral tail base) does not significantly affect fentanyl pharmacokinetics, allowing flexibility in patch placement based on clinical preference
- •Further studies are needed to establish what plasma fentanyl concentration actually produces analgesia in horses before routine clinical use can be recommended
- •Epidural romifidine-morphine combination provides reliable moderate analgesia and sedation for equine procedures, with the higher dose (60 µg/kg romifidine) extending analgesia duration but requiring monitoring for hypotension
- •Expect significant blood pressure reduction with the 60 µg/kg romifidine dose between 75-120 minutes; the 30 µg/kg dose may be preferable for horses with cardiovascular compromise
- •This combination is suitable for moderate pain management in horses but monitor cardiopulmonary parameters closely, particularly arterial blood pressure and respiratory rate
- •Meperidine at 1 mg/kg is not effective for analgesia in horses via IM or subcutaneous routes and should not be relied upon for pain management in clinical practice
- •The rapid absorption but lack of observable pain relief suggests either insufficient dosing or that meperidine is unsuitable for equine analgesia at this dose
- •Consider alternative analgesic agents with proven efficacy in horses for perioperative or acute pain management
- •Tramadol and acetaminophen used individually as single-agent CRI do not appear to provide analgesic benefit in horses, but combination therapy may warrant further clinical investigation
- •If pursuing combination therapy, monitor cardiac rhythm closely as arrhythmias have been observed; discontinue if adverse effects develop
- •Clinical efficacy in pain conditions like laminitis remains unproven and requires further research before routine practice adoption
- •When using prolonged infusions of these drugs for severe pain, monitor gastrointestinal function closely as altered transit is a predictable side effect
- •Understand that lidocaine, ketamine, and butorphanol CRIs are effective for pain relief but require careful patient selection and monitoring in clinical cases
- •Consider the trade-offs between pain control efficacy and gastrointestinal complications when choosing between single agents and combinations
- •Systemic lidocaine may offer an alternative analgesic option for somatic pain in horses with fewer side effects than conventional agents (NSAIDs, opioids, alpha-2 agonists)
- •Lidocaine does not reliably address visceral pain, so other analgesic strategies remain necessary for colic and gastrointestinal conditions
- •Consider lidocaine as a complementary analgesic for musculoskeletal or superficial pain conditions, though further clinical trials are needed to establish optimal dosing and safety profiles
- •Acetaminophen CRI regimens appear safe in Andalusian horses and warrant clinical trials for perioperative pain management, with potential for both short high-dose infusions (3.33–10 mg/kg/h for 3 h) and longer lower-dose regimens (1.25–3.75 mg/kg/h for 8 h)
- •Sex-dependent pharmacokinetics means mares may require dose adjustment compared to stallions to achieve equivalent steady-state concentrations
- •High metabolite formation suggests monitoring liver function may be prudent in clinical applications, particularly with repeated dosing or in horses with hepatic compromise
- •High-dose morphine (0.5 mg/kg IV) is effective for pain management in donkeys with analgesic effects lasting 4-5 hours, making it suitable for acute pain relief in clinical settings
- •The shorter half-life in donkeys (51 minutes) compared to horses suggests donkeys may require more frequent dosing intervals for sustained analgesia
- •Donkeys show poor analgesia with low-dose morphine (0.1 mg/kg), so practitioners should use at least 0.5 mg/kg IV to achieve clinically meaningful pain relief
- •Tramadol achieves plasma concentrations in horses that exceed those needed for analgesia in humans, but analgesic efficacy in horses remains unproven and requires further clinical investigation
- •Higher tramadol doses (≥1.5 mg/kg IV) produce neuromuscular side effects (fasciculations and tremors) that warrant monitoring during clinical use
- •The relatively short half-life (2–3 hours) suggests frequent dosing intervals may be needed if tramadol is used for pain management in equine practice
- •Gabapentin can be safely dosed at 120 mg/kg q12h in horses without causing detectable toxicity or serum chemistry changes over 14 days of treatment
- •Plasma drug accumulation occurs with repeated dosing, particularly at higher doses, which may improve analgesic efficacy but requires further clinical validation
- •High-dose gabapentin protocols appear well-tolerated and warrant investigation as part of multimodal pain management strategies in equine practice
- •Topical capsaicin products are prohibited in competition horses under FEI rules; even when used as directed, systemic absorption occurs and can be detected in testing
- •If using capsaicin-containing products for therapeutic purposes, allow sufficient clearance time before competitions or understand doping test implications
- •Serum sampling is the preferred diagnostic material for detecting capsaicin residues in anti-doping compliance testing
- •Recognize that occupational injury in horseracing staff carries high risk of anxiety and depression; implement supportive workplace practices and encourage professional mental health support following injury
- •Perceived employer support is strongly associated with mental health outcomes; transparent communication about job security and assistance during recovery may help reduce anxiety and depression
- •Monitor for problematic pain management and substance use coping mechanisms in injured staff, as these may indicate underlying anxiety or depression requiring intervention
- •PEMF therapy is widely used in the equine industry with high perceived efficacy, but you should be aware this is based on user perception rather than rigorous scientific evidence
- •Current practice shows considerable variation in application sites and session length; standardized protocols based on clinical evidence are lacking and needed
- •If considering PEMF for your clients, set realistic expectations about timing of effects and recognize the need for controlled studies to validate claims about performance enhancement and stress reduction
- •Firocoxib dosing in horses is 0.1 mg/kg; oral paste formulations can be used for up to 14 days, while tablets maintain effective concentrations for 7-14 days—knowing these parameters helps avoid overdosing and unnecessary prolonged treatment
- •COX-2 selectivity of firocoxib reduces gastrointestinal and renal side effects compared to traditional NSAIDs, making it safer for chronic pain management when dosing guidelines are followed
- •Never extrapolate dosing or pharmacokinetics between species; firocoxib dosing for horses differs significantly from dogs, so always use species-specific protocols to prevent adverse effects
- •Understanding current drug usage patterns among peer equine practitioners can inform your own anaesthetic protocol selection and best practice standards
- •The survey identifies which sedative, analgesic and anaesthetic combinations are most commonly used in the profession, helping you benchmark your own practice
- •Provides evidence-based information to guide discussions with clients about anaesthetic options and their prevalence in equine veterinary medicine
- •If using nimesulide in horses, dose at 1.5 mg/kg every 12-24 hours depending on inflammation severity, but recognize this is extra-label use without strong safety evidence
- •Be aware that nimesulide loses its COX-2 selectivity at clinical doses in horses, potentially increasing risk of gastrointestinal side effects compared to labeled use in other species
- •Consider administering oral doses with or without food consistently, as feeding status affects drug bioavailability and could impact efficacy
Key Research Findings
CBD paste achieved peak concentration (Cmax) in a shorter timeframe compared to CBD oil formulation in horses
No statistically significant differences in pharmacokinetics between fed and fasted states following oral CBD administration at 1 mg/kg
No statistically significant differences in overall pharmacokinetic parameters (AUC) between CBD oil and paste formulations
Cannabinoid receptors present in equine dorsal root ganglia, blood vessels, and synoviocytes can be modulated by inflammatory conditions
Oral morphine administration in horses produces comparable morphine-6-glucuronide (M6G) concentrations to IV administration without neuroexcitation or gastrointestinal adverse effects
Single and multiple oral doses of morphine demonstrated thermal anti-nociceptive effects in horses
Oral morphine provides a viable alternative to IV administration for equine analgesia with improved tolerability
Oral codeine at 0.6 mg/kg produced morphine and M6G concentrations comparable to clinically effective IV morphine doses without morphine's neuroexcitatory adverse effects in horses.
Codeine demonstrated dose-dependent pharmacokinetics with measurable morphine and M6G metabolites at all three doses tested (0.3, 0.6, 1.2 mg/kg).
Thermal nociceptive thresholds and behavioral responses were evaluated to assess analgesic efficacy and safety compared to IV morphine control.
Matrix fentanyl patches showed rapid absorption with time to maximum plasma concentration of 10±3.79, 14.3±5.13, and 10±3.79 hours for inguinal, metacarpal, and tail base applications respectively
No significant difference in pharmacokinetic parameters (Cmax, AUC, Tmax) among the three anatomical application sites
Fentanyl persisted in plasma for up to 96 hours with area under curve of 46.6±9.3, 44.6±6.0, and 46.2±7.68 ng·hours/mL for the three sites
No adverse effects observed on heart rate, respiratory rate, or rectal temperature across all treatments
Both romifidine doses (30 and 60 µg/kg) combined with morphine produced significant sedation with no statistically significant difference between treatments
Evidence Base
Pharmacokinetics of a single oral administration of two cannabidiol formulations in fed and fasted horses.
Di Salvo Alessandra, Bazzano Marilena, Rocca Giorgia Della et al. (2025) — Frontiers in veterinary science
Pharmacokinetics and thermal anti-nociceptive effects of oral morphine in horses.
Knych Heather K, Steinmetz Stacy J, Traynham Megan L et al. (2024) — Frontiers in veterinary science
Pharmacokinetics, adverse effects and effects on thermal nociception following administration of three doses of codeine to horses.
Knych Heather K, Stucker Kristen, Gretler Sophie R et al. (2022) — BMC veterinary research
The pharmacokinetics of a fentanyl matrix patch applied at three different anatomical locations in horses.
Skrzypczak Heather, Reed Rachel, Brainard Benjamin et al. (2022) — Equine veterinary journal
Analgesic and Cardiopulmonary Effects of Epidural Romifidine and Morphine Combination in Horses.
Natalini Claudio C, Paes Simone Dla, Polydoro Alexandre da S (2021) — Journal of equine veterinary science
Pharmacokinetics and pharmacodynamics of meperidine after intramuscular and subcutaneous administration in horses.
Hanafi Amanda L, Reed Rachel A, Trenholme Heather N et al. (2021) — Veterinary surgery : VS
Comparison of Analgesic Effects of a Constant Rate Infusion of Both Tramadol and Acetaminophen Versus those of Infusions of Each Individual Drug in Horses.
Tavanaeimanesh Hamid, Azarnoosh Afrooz, Ashar Fereidoon Saberi et al. (2018) — Journal of equine veterinary science
Systemic and anti-nociceptive effects of prolonged lidocaine, ketamine, and butorphanol infusions alone and in combination in healthy horses.
Elfenbein Johanna R, Robertson Sheilah A, MacKay Robert J et al. (2014) — BMC veterinary research
Effect of systemic lidocaine on visceral and somatic nociception in conscious horses.
Robertson S A, Sanchez L C, Merritt A M et al. (2005) — Equine veterinary journal
Population pharmacokinetics and clinical evaluation of intravenous acetaminophen and its metabolites in Andalusian horses.
Granados M M, Medina-Bautista F, Navarrete-Calvo R et al. (2025) — Veterinary journal (London, England : 1997)
Morphine in donkeys: Antinociceptive effect and preliminary pharmacokinetics.
Maney Jill K, Dzikiti Brighton T, Escobar Andre et al. (2023) — Equine veterinary journal
Pharmacokinetics and selected pharmacodynamic effects of tramadol following intravenous administration to the horse.
Knych H K, Corado C R, McKemie D S et al. (2013) — Equine veterinary journal
Pharmacokinetics and pharmacodynamics of repeat dosing of gabapentin in adult horses.
Gold Jenifer R, Grubb Tamara L, Cox Sherry et al. (2022) — Journal of veterinary internal medicine
The detection of capsaicin and dihydrocapsaicin in horse serum following long-term local administration.
Zak A, Siwinska N, Slowikowska M et al. (2018) — BMC veterinary research
Anxiety and Depression in British Horseracing Stud and Stable Staff Following Occupational Injury.
Davies Emma, Liddiard Sophie, McConn-Palfreyman Will J et al. (2023) — Animals : an open access journal from MDPI
24 Prevalence, Usage, and Perceptions of Pulsed Electromagnetic Field Therapy (PEMF) in the Equine Industry
Rostad Delaney R, Ivey Jennie L (2022) — Journal of Animal Science
Pharmacological Regulation in the USA and Pharmacokinetics Parameters of Firocoxib, a Highly Selective Cox-2, by Pain Management in Horses.
Rangel-Nava Ana, Ramírez-Uribe José Manuel, Recillas-Morales Sergio et al. (2019) — Journal of equine veterinary science
The use of sedatives, analgesic and anaesthetic drugs in the horse: an electronic survey of members of the American Association of Equine Practitioners (AAEP).
Hubbell J A E, Saville W J A, Bednarski R M (2010) — Equine veterinary journal
Oral and intravenous administration of nimesulide in the horse: rational dosage regimen from pharmacokinetic and pharmacodynamic data.
Villa R, Cagnardi P, Belloli C et al. (2007) — Equine veterinary journal