(carbamylcholine) Carbachol [KAR-ba-kole] has both muscarinic as well as nicotinic actions (lacks a methyl group present in bethanechol; ( see Figure above ). Like bethanechol, carbachol is an ester of carbamic acid and a poor substrate for acetylcholinesterase . It is biotransformed by other esterases, but at a much slower rate. A single administration can last as long as 1 hour.
1. Actions: Carbachol has profound effects on both the cardiovascular system and the gastrointestinal system because of its ganglion-stimulating activity, and it may first stimulate and then depress these systems. It can cause release of epinephrine from the adrenal medulla by its nicotinic action. Locally instilled into the eye, it mimics the effects of acetylcholine, causing miosis and a spasm of accommodation in which the ciliary muscle of the eye remains in a constant state of contraction
2. Therapeutic uses: Because of its high potency, receptor nonselectivity, and relatively long duration of action, carbachol is rarely used therapeutically except in the eye as a miotic agent to treat glaucoma by causing pupillary contraction and a decrease in intraocular pressure.
3. Adverse effects: At doses used ophthalmologically, little or no side effects occur due to lack of systemic penetration (quaternary amine).