tropicamide

Tropicamide is a short-acting antimuscarinic agent used in ophthalmology to produce mydriasis (pupil dilation) and cycloplegia (loss of accommodation) for fundus examination and refractive assessment. It is typically administered as a topical ophthalmic solution, commonly 0.5% concentration, and may be used alone or in combination with phenylephrine to enhance dilation.

Mechanism and pharmacology: Tropicamide blocks muscarinic acetylcholine receptors on the iris sphincter and ciliary body, causing relaxation of the sphincter muscle and inhibition of accommodation. This leads to pupil dilation and impairment of accommodation. It is a tertiary amine with relatively rapid systemic absorption after ocular instillation, though systemic exposure is limited.

Pharmacokinetics: Onset of mydriasis is usually 15 to 30 minutes, with peak effect within 30 to 60 minutes. Duration of dilation is typically 4 to 6 hours, and cycloplegia can last around a similar timeframe.

Safety, contraindications, and precautions: Tropicamide is generally well tolerated, but adverse effects can include light sensitivity, blurred vision, conjunctival irritation, and dry mouth. Systemic anticholinergic effects such as tachycardia or confusion are uncommon but possible, especially in sensitive individuals. Contraindications include hypersensitivity to tropicamide or other ingredients; caution is advised in patients with narrow-angle or risk of angle-closure glaucoma, elderly patients with cognitive impairment, and young children.

Interactions and notes: It should be used with caution with other antimuscarinic drugs and certain sympathomimetics. Not intended for long-term therapy.