UNDER REVIEW (September 2016)
Mechanism of Action:
Muscarinic receptor antagonist (non-selective for the various subtypes). Muscarinic AChRs are seven-transmembrane G-protein-coupled receptors (7TM GPCRs) which are activated by the endogenous neurotransmitter, acetylcholine. They are generally associated with the parasympathetic nervous system, and also cholinergic transmission in the CNS. Actions of parasympathetic nerves include smooth muscle contraction, increased glandular secretion and pupil constriction. It is also important in accommodation for seeing near objects – by control of ciliary muscles, the contraction of which decreases the focal distance of the lens. Muscarinic antagonists (also known as parasympatholytics) block these actions.
Lecture and CAL materials:
Drug specifics
| Alternative drug name | not specified |
| Effects | Applied locally in drops to the eye to facilitate fundoscopic examination of the eye. It can also be used prior to or after surgery on the eye. Tropicamide causes mydriasis (pupil dilatation) and cycloplegia (loss of accommodation due to relaxation of ciliary muscles). |
| Adverse actions | Ocular side-effects of mydriatics and cycloplegics include transient local stinging and raised intra-ocular pressure (which is dangerous in patients with glaucoma. |
| Dose | Short-acting effect after single administration. |
| Interactions | d be exercised to avoid overdosage. Mydriasis may rarely precipitate acute angle-closure glaucoma in a very few patients, usually aged over 60 years and hypermetropic (long-sighted), who are predisposed to the condition because of a shallow anterior chamber. |
| Contraindications | not specified |
| Comments | Other muscarinic receptor antagonists include atropine and cyclopentolate which have similar actions but are more potent and longer-acting. It is inadvisable to drive for 1-2 hours after mydriasis due to increased sensitivity to bright light. Phenylephrine is a sympathomimetic that causes mydriasis. |
| Contributors |
eDrug by