Unlike acetylcholine and methacholine, carbachol contains a carbamino functional group instead of an acetyl group, which is not responsive to hydrolysis by cholinesterase. In vitro studies have shown that the rate of hydrolysis is at least twice as slow as that of acetyl-choline.
Carbachol is a powerful cholinic ester that stimulates both muscarinic and nicotinic receptors, as well as exhibits all of the pharmacological properties of acetylcholine while in addition resulting in vasodilation, a decrease in heart rate, an increase in tone and con-tractability of smooth muscle, stimulation of salivary, ocular, and sweat glands as well as autonomic ganglia and skeletal muscle. For this reason, use of carbachol, like acetyl-choline, is limited. The exception is that it is used in ophthalmological practice and post-operational intestines and bladder atony. Upon administration in the eye, the pupil constricts and the intraocular pressure is reduced. It is used for severe chronic glaucoma. Synonyms of this drug are doryl and miostat.
Betanechol: Betanechol, 2-carbamoyloxy-1-(N,N,N-trimethyl)propyl ammonium chloride (13.1.8), is made by either the subsequent reaction of 1-(N,N,N-trimethylammonium) propan-2-ol with phosgene, followed by ammonia, or by a completely analogous synthesis of carbachol by the reaction of 1-chloro-2-propanol with phosgene followed by consequent reactions with ammonia, and then with trimethylamine, giving betanechol (13.1.8) [14,15].
ch3 2 ch3 0
(CH3)3N —CH2—CH — 0-H Cl -^ (CH3)3N — CH2-CH— 0-C-NH2 Cl
CH3 2. NH3 CH3 0 (CH3)3N Cl-CH^C^0H -^ Cl—CH2-CH — 0-C-NH2 -»
Bentanechol is a drug, which has structurally unique qualities of both methacholine and carbachol, i.e. it contains both ^-methyl and carbamate functional groups, and quite logically exhibits pharmacological properties of both the drugs. It is resistant to hydrolysis by cholinesterases and has a very minor effect on nicotinic receptors of the autonomic ganglia and neuromuscular junctions. Betanechol has more of a selective action on muscarinic receptors of the gastrointestinal tract and the bladder than do other cholinic esters.
Therapeutic action of this drug is based on this action, and it is used for treating post-operational non-obstructive retention of urine and neurogenic bladder atony. Earlier, it was used for treating gastrointestinal illnesses and Alzheimer's disease. Synonyms of this drug are duvoid, miotonin, and urecholine.
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