Direct-acting muscarinic agonists

They bind to muscarinic acetylcholine receptors and switch them on, copying the parasympathetic nervous system. Glands then secrete more saliva, sweat and tears, the bladder's detrusor and the gut wall contract, the pupil narrows and the heart can slow. Bethanechol, a choline ester, is not broken down by cholinesterase, so it acts for longer than acetylcholine.

• PilocarpineA plant alkaloid rather than a choline ester like bethanechol, and used both as eye drops and as tablets.
• BethanecholResists cholinesterase, unlike acetylcholine, so its effect lasts; atropine is the specific antidote when too much is given.

• Glaucoma and raised pressure in the eye
• Dry mouth after radiotherapy or in Sjögren's syndrome
• Urinary retention without a blockage

• Heavy sweatingKnown for
• Excess salivaKnown for
• Watery eyes
• Passing urine often or urgently
• Diarrhea
• Abdominal cramps
• Nausea and vomiting
• Slow heart rateSerious
• Narrowing of the airways (bronchospasm)Serious
• Blurred or dim vision

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Asthma and COPD: they tighten the airways and add bronchial secretions; bethanechol is contraindicated in asthma.
• Bladder or bowel obstruction: making the muscle contract against a blockage can do harm.
• Heart disease, slow heart rate or low blood pressure: they can lower pressure and disturb the rhythm.
• Atropine, a muscarinic blocker, reverses an overdose.

Written for biofideX in plain words, after checking these references:

• Bethanechol chloride tablets: label (DailyMed)
• Pilocarpine hydrochloride tablets: label (DailyMed)
• Pilocarpine (NCI Thesaurus)
• Bethanechol chloride (NCI Thesaurus)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.