Carbachol, also known as carbamylcholine and sold under the brand name Miostat among others, is a
cholinomimeticdrug that binds and activates
acetylcholine receptors. Thus it is classified as a
cholinergic agonist. It is primarily used for various
ophthalmic purposes, such as for treating
glaucoma, or for use during ophthalmic surgery. It is generally administered as an ophthalmic solution (i.e.,
eye drops).
Carbachol produces effects comparable to those of
sarin if a massive overdose is administered (as may occur following industrial and shipping accidents) and therefore it is classified as an
extremely 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 a
cholinecarbamate and a positively charged quaternary ammonium compound.[3] It is not well absorbed in the
gastro-intestinal tract and does not cross the
blood–brain barrier. It is usually administered topical ocular or through intraocular injection.[3] Carbachol is not easily metabolized by
cholinesterase, 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 the
cat and
rat, carbachol is well known for its ability to induce
rapid eye movement (REM) sleep when microinjected into the
pontine reticular formation. Carbachol elicits this REM sleep-like state via activation of postsynaptic muscarinic
cholinergic receptors (
mAChRs).[3]
Carbachol is primarily used in the treatment of
glaucoma, 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 during
cataract surgery.
Topical ocular administration is used to decrease intraocular pressure in people with primary open-angle
glaucoma. 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 a
nerve 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.
^Moro C, Phelps C, Veer V, Clark J, Glasziou P, Tikkinen KA, Scott AM (January 2022). "The effectiveness of parasympathomimetics for treating underactive bladder: A systematic review and meta-analysis". Neurourology and Urodynamics. 41 (1): 127–139.
doi:
10.1002/nau.24839.
PMID34816481.
S2CID244530010.