A New Approach to Managing Ocular Pain in Veterinary Practice
Veterinary ocular pain can be challenging to manage, particularly in patients with corneal ulcers, abrasions, or contraindications to systemic analgesia. This downloadable clinical guide explores current pain management challenges, practical treatment considerations, and emerging approaches to corneal analgesia in veterinary medicine.
Inside the guide:
- Current challenges in ocular pain management
- Why corneal pain is difficult to control
- Understanding TRPV1 and corneal nociception
- Comparison of common analgesic approaches
- Practical in-clinic and take-home considerations
- Real veterinary case examples
- Safety and patient suitability considerations
Tramadol Ophthalmic Frequently asked questions
Topical ophthalmic tramadol is a compounded analgesic eye preparation that provides localised corneal pain relief through multiple pathways — including TRPV1 receptor agonism — without the ocular surface toxicity of repeated topical anaesthetics. It is intended to fill the gap between short-acting procedural anaesthesia and systemic analgesia for ongoing ocular pain in veterinary patients.
Mechanism of action
What is the proposed mechanism of action of topical ophthalmic tramadol?
Topical tramadol appears to exert analgesic effects through multiple pathways, including weak μ-opioid receptor activity, α2-adrenergic stimulation, inhibition of norepinephrine and serotonin reuptake, and agonism of TRPV1 receptors on corneal sensory neurons. Activation of TRPV1 is thought to induce subsequent desensitisation of corneal nociceptive fibres, reducing pain signalling.8,9,15
Why target TRPV1 receptors in corneal pain?
The cornea is densely innervated by small-diameter C-fibre sensory neurons expressing TRPV1 receptors. These nociceptive neurons are heavily involved in ocular pain signalling, making TRPV1 a relevant target for topical analgesia.1,9,14,15
Onset & duration
How rapidly does topical tramadol produce corneal analgesia?
In a published rat study, topical tramadol 5% achieved complete corneal anaesthesia (CTT = 0) within 1–5 minutes in 18 of 20 eyes.16
How long does the analgesic effect persist?
In the same corneal touch threshold (CTT) study, complete corneal anaesthesia persisted for 5–25 minutes, while CTT values remained significantly below baseline for up to 75 minutes post administration.16
Comparison with topical anaesthetics
How does topical tramadol compare with proparacaine?
Published CTT data showed topical tramadol produced substantial reductions in corneal sensitivity approaching those achieved with proparacaine — tramadol 5% reached complete corneal anaesthesia within 1–5 minutes in 18 of 20 eyes, with effects persisting below baseline for up to 75 minutes.16 The clinical distinction lies less in immediate potency and more in safety profile, duration, and suitability for therapeutic use.
Limitations of proparacaine
Proparacaine is intended primarily for short diagnostic or procedural use. Repeated or prolonged use is associated with significant ocular surface toxicity, including delayed epithelial healing, corneal epithelial degeneration, keratopathy, impaired corneal defence mechanisms, and worsening ulceration risk.3,4 It is therefore generally unsuitable as a take-home analgesic, and acts predominantly via sodium-channel blockade without multimodal or prolonged activity.2,3
Potential advantages of topical tramadol
- Multimodal analgesic activity via TRPV1, monoaminergic, adrenergic and opioid-related pathways.8,9
- Prolonged analgesic effect beyond immediate surface anaesthesia.16
- No demonstrated impairment of corneal wound healing in published studies.7
- Low systemic exposure following topical administration.
- Suitability for repeated dosing.
- Can be used on ulcerated or compromised corneas as it does not delay epithelial healing.7
- Applicability in geriatric or medically fragile patients where systemic analgesia may be undesirable.
Published and in-house data demonstrated that topical tramadol did not affect corneal reflexes, alter blink frequency, affect intraocular pressure, or impair corneal wound healing.7 Importantly, tramadol is not a replacement for procedural local anaesthetics during ophthalmic diagnostics or surgery; its value lies in filling the gap between short-acting topical anaesthesia and systemic analgesia for ongoing ocular pain management.1,4,7
Why are topical local anaesthetics unsuitable for chronic outpatient analgesia?
Traditional topical anaesthetics such as proparacaine are associated with ocular surface toxicity after repeated or prolonged administration, and are therefore unsuitable for long-term therapeutic pain management.3,4
Is there evidence that tramadol provides longer analgesia than conventional local anaesthetics?
Mechanistically, tramadol’s multimodal activity and TRPV1-mediated desensitisation may contribute to prolonged analgesic effects relative to traditional sodium-channel local anaesthetics.9,15
Safety & tolerability
Does topical tramadol impair corneal wound healing?
A published rat study using tramadol 5% twice daily for 7 days found no impairment of corneal wound healing, and no corneal damage was identified during the study period.7
Is topical tramadol safe on ulcerated or damaged corneas?
Current published and in-house data suggest topical tramadol does not adversely affect corneal reflexes, blink frequency, intraocular pressure, or epithelial healing — even on de-epithelialised corneas.7
What adverse effects have been reported with topical tramadol?
Transient irritation or a burning sensation may occur immediately after the first administration (less so with the 1% gel), typically lasting under 30 seconds — similar to local anaesthetics. This is hypothesised to result from initial TRPV1 activation before receptor desensitisation occurs.9,16
Does topical tramadol alter intraocular pressure?
Published safety studies demonstrated no significant effect on intraocular pressure following topical administration.7
Does topical tramadol affect corneal reflexes or blink rate?
Published safety data demonstrated no clinically significant effects on corneal reflexes or blink frequency.7
Has any mouthing, hypersalivation or foaming been reported in response to residual taste?
No. In post-administration observations from veterinary cases, no such responses were reported.
Pharmacokinetics & systemic exposure
Does repeated administration result in systemic accumulation?
In-house pharmacokinetic studies demonstrated minimal plasma accumulation following repeated topical administration over 28 days, with plasma concentrations remaining low throughout the dosing period.
What systemic exposure occurs following topical administration?
Systemic exposure appears minimal. Plasma concentrations declined rapidly within 12 hours post-dose and remained substantially below those associated with oral tramadol administration.
Does corneal integrity alter systemic absorption?
In-house pharmacokinetic studies reported no significant impact of corneal integrity on plasma tramadol concentrations following topical administration.
Why might a gel formulation be preferred over a solution?
In-house pharmacokinetic data demonstrated increased exposure of the conjunctiva, cornea and aqueous humour with the gel formulation compared with solution formulations of equivalent strength, supporting improved local tissue residence time.
Clinical use
What clinical indications are most appropriate for topical tramadol?
Potential indications include:
- Corneal ulceration
- Corneal abrasions
- Post-operative ocular pain
- Cases where corticosteroids are contraindicated
- Patients unsuitable for systemic NSAIDs or opioids
- Geriatric or medically compromised animals4,7
Can topical tramadol be used alongside systemic analgesics?
Clinical case reports describe concurrent use with systemic meloxicam and topical antibiotics without reported adverse effects.
Has topical tramadol been evaluated clinically in veterinary ophthalmology cases?
Clinical case reports describe use in corneal ulceration, corneal degeneration, conjunctival graft procedures, post-corneal surgery analgesia, and patients unsuitable for systemic medications. Reported outcomes included rapid eye opening, improved comfort scores, and no apparent delay in healing.
Why may topical tramadol be advantageous in geriatric or comorbid patients?
Because systemic exposure appears low after topical administration, tramadol ophthalmic may provide localised analgesia while reducing reliance on systemic NSAIDs or opioids in patients with concurrent disease.
Patent
What is the patent on the tramadol ophthalmic product?
Aqueous compositions suitable for topical administration to the human or animal eye contain at least one water-soluble polymeric ophthalmic lubricant — such as hyaluronate, carbomer gel or hypromellose — together with a water-soluble analgesic. The analgesic may be an opioid, particularly one with affinity for 5-HT receptors, such as tramadol.
Patent number: WO2012136969 — Ophthalmic Treatments. Full details: patentscope.wipo.int/search/en/WO2012136969
References
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- Bryant JS, Busbee BG, Reichel E. Overview of ocular anesthesia: past and present. Curr Opin Ophthalmol 2011;22:180–184.
- Proparacaine Ophthalmic. 2026. Retrieved 24 March 2026.
- Tuli SS, Schultz GS, Downer DM. Science and strategy for preventing and managing corneal ulceration. Ocul Surf 2007;5:23–39.
- Sauve F. Use of topical glucocorticoids in veterinary dermatology. Can Vet J 2019;60:785–788.
- Wilhelmus KR. Indecision about corticosteroids for bacterial keratitis: an evidence-based update. Ophthalmology 2002;109:835–842.
- Cuvas Apan O, Ozer MA, Takir S, Apan A, Sengul D. Effect of topical administration of tramadol on corneal wound healing in rats. Int Ophthalmol 2016;36:675–680.
- Lewis KS, Han NH. Tramadol: a new centrally acting analgesic. Am J Health Syst Pharm 1997;54:643–652.
- Marincsak R, Toth BI, Czifra G et al. The analgesic drug, tramadol, acts as an agonist of the transient receptor potential vanilloid-1. Anesth Analg 2008;106:1890–1896.
- Knotkova H, Pappagallo M, Szallasi A. Capsaicin (TRPV1 Agonist) therapy for pain relief: farewell or revival? Clin J Pain 2008;24:142–154.
- Bianchi M, Rossoni G, Sacerdote P, Panerai AE. Effects of tramadol on experimental inflammation. Fundam Clin Pharmacol 1999;13:220–225.
- Tsai YC, Chang PJ, Jou IM. Direct tramadol application on sciatic nerve inhibits spinal somatosensory evoked potentials in rats. Anesth Analg 2001;92:1547–1551.
- Sousa AM, Ashmawi HA, Costa LS, Posso IP, Slullitel A. Percutaneous sciatic nerve block with tramadol induces analgesia and motor blockade in two animal pain models. Braz J Med Biol Res 2012;45:147–152.
- Evans HE, de Lahunta A. Miller’s Anatomy of the Dog. 4th edn. Elsevier, St. Louis, 2013:746–786.
- Bates BD, Mitchell K, Keller JM et al. Prolonged analgesic response of cornea to topical resiniferatoxin, a potent TRPV1 agonist. Pain 2010;149:522–528.
- Lelescu CA, Dumitras DA, Iurian S, Staffieri F, Muresan C. Effects of topical application of tramadol with/without dexmedetomidine and proparacaine on corneal sensitivity in rats. Int Ophthalmol 2021;41:465–473.
