Bimatoprost — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	Topical ophthalmic	1 drop of 0.03% solution	q24h (once daily)	Duration: Chronic (lifelong for glaucoma) Notes: Administer in the affected eye(s). Can be used in combination with other glaucoma medications. Monitor IOP regularly.
Cat	Topical ophthalmic	1 drop of 0.03% solution	q24h (once daily)	Duration: Chronic Notes: Use with caution; may cause local irritation. Monitor for signs of uveitis.
Horse	Topical ophthalmic	1 drop of 0.03% solution	q24h (once daily)	Duration: Chronic Notes: Off-label use. Ensure proper placement in the conjunctival sac.

Clinical Indications & Species Uses

General Indications

Reduction of intraocular pressure in animals with glaucoma

Dog (Canine)

Treatment of glaucoma (primary and secondary)
Ocular hypertension
Adjunct to other glaucoma therapies

Cat (Feline)

Treatment of glaucoma (less common)
Ocular hypertension

Horse (Equine)

Treatment of equine recurrent uveitis-associated glaucoma (off-label)

Rabbit & Small Mammals

Experimental use for glaucoma research

Pharmacology & Mechanism of Action

Drug Class: Prostaglandin Analog | Pharmacological Group: Ophthalmic Hypotensive Agent

Mechanism of Action: Bimatoprost is a synthetic prostamide analog that mimics the actions of endogenous prostamides. It reduces intraocular pressure (IOP) by increasing the outflow of aqueous humor through both the trabecular meshwork and the uveoscleral pathway. The exact mechanism is not fully understood but involves binding to prostaglandin F (FP) receptors and possibly other prostamide receptors, leading to remodeling of the extracellular matrix in the ciliary muscle and increased fluid drainage.

Pharmacodynamics: Bimatoprost effectively lowers IOP in normotensive and glaucomatous eyes. It also promotes eyelash growth (hypertrichosis) and can cause iris pigmentation changes. In veterinary medicine, it is primarily used to treat glaucoma and ocular hypertension. The onset of IOP reduction occurs within 4 hours, with peak effect at 8-12 hours after topical administration.

⚡ Pharmacokinetics Summary

Absorption: After topical ocular administration, bimatoprost is absorbed through the cornea. Systemic absorption is minimal but measurable. Peak plasma concentrations are reached within 10-20 minutes in humans; similar kinetics are expected in animals.

Distribution: Bimatoprost distributes into ocular tissues, particularly the iris, ciliary body, and retina. It has a volume of distribution of approximately 0.3 L/kg in humans. Systemic distribution is limited due to low plasma concentrations.

Metabolism: Bimatoprost is metabolized in the liver and ocular tissues via oxidation, N-deethylation, and glucuronidation. The major metabolite is the acid form, which is also pharmacologically active.

Excretion: Bimatoprost and its metabolites are excreted primarily in the urine (67%) and feces (25%) after systemic absorption. In ocular use, most of the drug is eliminated via aqueous humor turnover and nasolacrimal drainage.

Half-Life: The plasma half-life in humans is approximately 45 minutes after intravenous administration, but the ocular hypotensive effect lasts over 24 hours. In dogs, the half-life is not well-defined but is expected to be similar.

Bioavailability: Systemic bioavailability after ocular administration is very low (<10%) due to minimal corneal penetration and rapid metabolism.

Protein Binding: Approximately 88% bound to plasma proteins in humans.

Available Formulations & Strengths

Ophthalmic Solution 0.03% (0.3 mg/mL) (Topical ocular)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to bimatoprost or any component of the formulation
Use in patients with active intraocular inflammation (e.g., uveitis) unless benefits outweigh risks
Use in patients with compromised corneal integrity (e.g., corneal ulcers) due to potential for exacerbation

Warnings & Clinical Precautions:

May cause changes in iris pigmentation (darkening) and eyelash growth; these are usually reversible but may be permanent.
Use with caution in patients with a history of ocular inflammation, macular edema, or aphakia/pseudophakia with torn posterior lens capsule.
May cause temporary blurred vision; advise caution when driving or operating machinery.
Do not touch the dropper tip to the eye or surrounding tissues to avoid contamination.
Systemic absorption is minimal but possible; use with caution in patients with hepatic or renal impairment.
In food animals, not approved for use; extra-label use requires a valid veterinary-client-patient relationship and withdrawal times must be observed.

Adverse Effects & Reactions

Common:

Conjunctival hyperemia (redness)
Ocular irritation (burning, stinging)
Foreign body sensation
Pruritus
Increased lacrimation
Eyelash growth (hypertrichosis)
Periocular skin darkening

Serious / Severe:

Iritis/uveitis
Cystoid macular edema (rare)
Retinal detachment (rare)
Corneal edema
Systemic hypotension (very rare)

Rare:

Allergic reactions
Bronchospasm (in predisposed individuals)
Headache (in humans; not reported in animals)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Other prostaglandin analogs (e.g., latanoprost, travoprost)	Additive IOP-lowering effect; may increase risk of ocular side effects.	Moderate
Cholinergic agonists (e.g., pilocarpine)	Additive IOP reduction; may require dose adjustment.	Mild
Beta-blockers (e.g., timolol)	Additive IOP reduction; may be used in combination.	Mild
Carbonic anhydrase inhibitors (e.g., dorzolamide)	Additive IOP reduction; may be used in combination.	Mild
Corticosteroids (topical or systemic)	May increase IOP, counteracting the effect of bimatoprost.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Ocular irritation
Conjunctival hyperemia
Systemic effects are unlikely due to low absorption, but may include hypotension, bradycardia, and gastrointestinal upset if ingested.

Emergency Treatment Protocol: If accidental ingestion occurs, induce vomiting if recent and monitor for systemic signs. For ocular overdose, flush the eye with saline or water. No specific antidote; supportive care is recommended.

Food Animal Withdrawal Times

Not approved for use in food animals. If used extra-label, a withdrawal time of at least 7 days for meat and 7 days for milk is recommended, but consult with a veterinary pharmacologist.

Storage, Handling & Regulatory Information

Storage Temperature: Store at 15-25°C (59-77°F). Protect from freezing.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Keep the bottle tightly closed when not in use. Do not use if the solution is discolored or contains particulate matter.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use (Lumigan).

Extra-Label (Off-Label) Use: In the US, bimatoprost is FDA-approved for humans (Lumigan) and is used extra-label in animals under the Animal Medicinal Drug Use Clarification Act (AMDUCA). It must be used by or on the order of a licensed veterinarian within a valid VCPR. For food animals, extra-label use is prohibited if an approved animal drug exists that is effective and available.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Bimatoprost is a potent ocular hypotensive agent used primarily in dogs for the management of glaucoma. It is often used when other medications (e.g., beta-blockers, carbonic anhydrase inhibitors) are insufficient. It is administered once daily, preferably in the evening. Regular monitoring of IOP is essential to assess efficacy and adjust therapy. Adverse effects are generally mild and local, but iris color changes and eyelash growth may be cosmetically undesirable. In cats, use is limited due to potential for uveitis; however, it may be used in refractory cases. In horses, it is used off-label for glaucoma secondary to uveitis, but caution is advised due to the inflammatory component. Always consider the cost and availability of the drug. For food animals, avoid use unless absolutely necessary and adhere to withdrawal times.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)