Introduction
Tropicamide is an alkaloid atropine‐derived anticholinergic drug and a non‐selective antagonist of muscarinic acetylcholine (mACh) receptors. Usually available in ophthalmic formulations, tropicamide is used to cause mydriasis and cycloplegia for eye exams or ocular procedures. It is also used in combination with hydroxyamphetamine for the same indication. Oral tropicamide has been investigated as a potential drug to relieve sialorrhea in patients with Parkinson's Disease.
Uses
Tropicamide is a muscarinic receptor antagonist used to induce mydriasis and cycloplegia for diagnostic procedures.
Tropicamide is indicated to induce mydriasis (dilation of the pupil) and cycloplegia (paralysis of the ciliary muscle of the eye) in diagnostic procedures. It is used in combination with hydroxyamphetamine for the same indication.
Associated Conditions
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 causes accommodation by causing 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.
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.
Absorption
Following ocular administration of 40 μL drops of 0.5% tropicamide in female subjects, tropicamide reached its mean peak concentration in plasma of 2.8 ± 1.7 ng/mL (mean ± SD) at five minutes.
Volume of Distribution
No information can be found.
Protein Binding
The extent of protein binding has not been established. Tropicamide binds to albumin.[A230168]
Route of Elimination
No information can be found.
Half Life
Tropicamide has a plasma half-life of 30 minutes.
Clearance
No information can be found.
Toxicity
Oral LD50 is 865 mg/kg in rats and 565 mg/kg in mice. Intraperitoneal LD50 is 1210 mg/kg in rats and 695 mg/kg in mice. Subcutaneous LD50 is 872 mg/kg in rats and 665 mg/kg in mice.
There is limited information on tropicamide overdose. Systemic adverse effects, such as tachycardia, central nervous system disturbances, and muscle rigidity have been reported with the use of tropicamide. Psychotic reactions, behavioral disturbances, and vasomotor or cardio-respiratory collapse have been reported with the use of anticholinergic in children.
Food Interactions
No interactions found.
Dosage
For examination of the fundus: instill 1 drop 15 to 20 minutes prior to examination.
