MYDRIACYL 1% OPHTHALMIC PREPARATION

Indications

• Mydriasis for ocular fundus examination
• Cycloplegia in diagnostic and therapeutic procedures
• Adjunct in the management of anterior uveitis

Dosage

Adults: For adults, the typical dosage is to instill one to two drops of tropicamide 1% eye drops into the conjunctival sac 15 to 30 minutes before the

Mechanism of action

Tropicamide binds to muscarinic acetylcholine receptors, particularly the M3 subtype, which are involved in controlling smooth muscle function in the eye. By inhibiting these receptors, tropicamide relaxes the sphincter pupillae muscle leading to pupil dilation (mydriasis) and prevents the ciliary muscle from contracting, thus inhibiting accommodation. This action diminishes the parasympathetic influence, allowing sympathetic responses to prevail.

Pharmacodynamics

As an anticholinergic drug, tropicamide works by blocking muscarinic receptors to induce mydriasis and cycloplegia. Mydriasis typically occurs within 10 to 15 minutes after administration, with optimal effects observed at around 25 to 30 minutes. The duration of mydriasis is generally four to eight hours but can extend up to 24 hours in some individuals. The cycloplegic effect is also noted within 20 minutes, lasting four to 10 hours. Tropicamide may elevate intraocular pressure, although serious systemic adverse effects are rare with its ophthalmic use.

Pharmacokinetics

Tropicamide is administered topically as eye drops, allowing rapid absorption through the ocular surface. The drug undergoes minimal systemic absorption, which limits systemic side effects. It has a relatively short half-life and is primarily eliminated through the liver metabolism and renal excretion of its metabolites. The pharmacokinetic profile supports its use as a short-acting mydriatic agent.

Contra-indications

• Hypersensitivity to tropicamide or any excipients
• Concomitant use of ocular formulations containing mercury-based preservatives
• Preterm neonates

Adverse effects

• Eye erythema
• Eye irritation (especially with prolonged administration)
• Eye pain
• Headache
• Hypotension
• Nausea
• Syncope
• Blurred vision
• Punctate keratitis
• Cytotoxicity
• Eye discolouration

Interactions

• Clozapine: Unknown additive effect
• Second-generation antipsychotics: Unknown additive effect

Precautions

• Caution in patients with hypersensitivity to other anticholinergics
• Use with caution in patients with narrow-angle glaucoma
• Monitor for elevation of intraocular pressure

Pregnancy

Manufacturer advises caution due to limited data on safety during pregnancy.

Breast-feeding

Manufacturer advises avoiding use unless no suitable alternative is available due to limited information.

Storage

Store below 25°C. Protect from light. Do not freeze.

Formulations

• Tropicamide 1% eye drops (Mydriacyl, Alcon Eye Care UK Ltd)
• Tropicamide 1% unit dose eye drops (Minims, 0.5ml)

Mechanism of action

Muscarinic acetylcholine receptors are involved in numerous ocular functions. The M₃ subtype is predominantly expressed by smooth muscle cells of the sphincter pupillae, which is a circular muscle of the iris, and ciliary muscles. In response to light or binding of acetylcholine, M₃ receptor signalling leads to contraction of the sphincter pupillae and pupil constriction. Contraction of the ciliary muscle via M₃ receptor signalling also leads to accommodation, adjusting the lens for near vision. The eye is also innervated by parasympathetic nerves: ciliary ganglion neurons project to the ciliary body and the sphincter pupillae muscle of the iris to control ocular accommodation and pupil constriction. Tropicamide is a non-selective muscarinic antagonist that binds to all subtypes of muscarinic receptors. By binding to muscarinic receptors, tropicamide relaxes the pupillary sphincter muscle and causes pupil dilation. By blocking the muscarinic receptors of the ciliary body, tropicamide also prevents accommodation. Like other muscarinic antagonists, tropicamide inhibits the parasympathetic drive, allowing the sympathetic nervous system responses to dominate. Tropicamide is thought to ameliorate sialorrhea by blocking M₄ receptors expressed on salivary glands and reducing hypersalivation.

Pharmacodynamics

Tropicamide is an anticholinergic drug and that works by non‐selectively blocking muscarinic receptors to cause mydriasis and cycloplegia. It relaxes the pupillary sphincter to dilate the pupil. The onset of tropicamide‐induced mydriasis is about 10 to 15 minutes, with optimal effect occurring 25 to 30 minutes post-administration. Mydriasis caused by tropicamide wears off within four to eight hours, but it was seen up to 24 hours in some individuals. Tropicamide hinders accommodation by causing the contraction of the ciliary muscle. The cycloplegic effect occurs within 20 to minutes following administration, with a duration of action of four to 10 hours. Tropicamide can elevate intraocular pressure. The ophthalmic use of tropicamide is not typically associated with serious systemic adverse events. One randomized pilot study showed that oral tropicamide alleviated perceived symptoms of sialorrhea in patients with Parkinson's Disease: anticholinergics are believed to restore the dopaminergic to cholinergic activity imbalance in neurodegenerative diseases. Similarly in one case report, tropicamide administered via ophthalmic solution relieved clozapine-induced sialorrhea. Interestingly, in rodent models, tropicamide suppressed drug-induced tremulous jaw movements which are often used as a model of parkinsonian tremor: the significance of this finding requires further investigations.