Carbachol, also known ascarbamylcholine and sold under the brand nameMiostat among others, is acholinomimeticdrug that binds and activatesacetylcholine receptors. Thus it is classified as acholinergic agonist. It is primarily used for variousophthalmic purposes, such as for treatingglaucoma, or for use during ophthalmic surgery. It is generally administered as an ophthalmic solution (i.e.,eye drops).
Carbachol produces effects comparable to those ofsarin if a massive overdose is administered (as may occur following industrial and shipping accidents) and therefore it is classified as anextremely hazardous substance in the United States as defined in Section 302 of the U.S.Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.[1]
Carbachol is acholinecarbamate and a positively charged quaternary ammonium compound.[3] It is not well absorbed in thegastro-intestinal tract and does not cross theblood–brain barrier. It is usually administered topical ocular or through intraocular injection.[3] Carbachol is not easily metabolized bycholinesterase, it has a 2 to 5 minute onset of action and its duration of action is 4 to 8 hours with topical administration and 24 hours for intraocular administration. Since carbachol is poorly absorbed through topical administration,benzalkonium chloride is mixed in to promote absorption.[3]
In thecat andrat, carbachol is well known for its ability to inducerapid eye movement (REM) sleep when microinjected into thepontine reticular formation. Carbachol elicits this REM sleep-like state via activation of postsynaptic muscariniccholinergic receptors (mAChRs).[3]
Carbachol is primarily used in the treatment ofglaucoma, but it is also used during ophthalmic surgery.[3] Carbachol eyedrops are used to decrease the pressure in the eye for people with glaucoma. It is sometimes used to constrict the pupils duringcataract surgery.
Topical ocular administration is used to decrease intraocular pressure in people with primary open-angleglaucoma. Intraocular administration is used to produce miosis after lens implantation during cataract surgery. Carbachol can also be used to stimulate bladder emptying to treat the condition of underactive bladder.[5]
In most countries carbachol is only available by prescription. Outside the United States, it is also indicated for urinary retention as an oral (2 mg) tablet.[3][6]
The effects of a systemic overdose will probably be similar to the effects of anerve agent (they both act on the cholinergic system, increasing cholinergic transmission), but its toxicity is much weaker and it is easier to antagonize in overdose. When administered ocularly there is little risk of such effects, since the doses are much smaller (see topical versus systemic administration).[7]
^World Health Organization (2021).World Health Organization model list of essential medicines: 22nd list (2021). Geneva: World Health Organization.hdl:10665/345533. WHO/MHP/HPS/EML/2021.02.
