Tropicamide
Tropicamide is a synthetic, short-acting **anticholinergic** agent primarily used for **mydriasis** (pupil dilation) and **cycloplegia** (paralysis of the ciliary muscle). It is considered the mydriatic of choice for intraocular examinations due to its rapid onset of action (20-30 minutes) and relatively short duration. > **Clinical Pearl:** Tropicamide is more effective as a mydriatic than as a cycloplegic. Therefore, it is less effective than atropine in relieving ciliary body muscle spasms associated with uveitis.
Mechanism: Tropicamide acts as a competitive antagonist of acetylcholine at muscarinic receptors. **Acetylcholine inhibition** at the iris sphincter muscle → relaxation of the sphincter → **mydriasis** (pupil dilation). **Acetylcholine inhibition** at the ciliary body muscles → paralysis of accommodation → **cycloplegia**.
Dosing by species
- Mydriasis and cycloplegia for intraocular examination · 1 drop per eye · topical · repeat after 20-30 min if necessary · Duration of action is 2-12 hours.
- Mydriasis and cycloplegia for intraocular examination · 1 drop per eye · topical · repeat after 20-30 min if necessary · Duration of action is 4-9 hours. May cause salivation.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Glaucoma (may increase intraocular pressure)
Adverse effects
- Salivation (particularly in cats, though less marked than with atropine)
- Transient stinging upon application
- Photophobia (due to pupil dilation)
Monitoring
- Intraocular pressure (IOP)
- Pupillary light reflex
- Resolution of mydriasis
Overdose
Systemic toxicity is rare with standard topical ophthalmic use. However, excessive administration or ingestion could theoretically lead to systemic anticholinergic signs such as **tachycardia**, **dry mucous membranes**, **ileus**, and **urinary retention**. Treatment is generally supportive.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.