Products
Parasympathomimetics are commercially available in the form of tablets, capsules, solutions, transdermal patches, injectable solutions, and eye drops, among others.
Structure and properties
Many parasympathomimetics are structurally related to the natural ligand acetylcholine.
Effects
Parasympathomimetics have cholinergic (parasympathomimetic) properties. They promote the effects of the parasympathetic nervous system, a portion of the autonomic nervous system. Direct parasympathomimetics bind as agonists to muscarinic and/or nicotinic acetylcholine receptors. Indirect parasympathomimetics (cholinesterase inhibitors) inhibit the breakdown of the natural neurotransmitter acetylcholine by inhibiting the enzyme acetylcholinesterase. This increases the local concentration of acetylcholine. Parasympathomimetics exert the following effects, among others:
- Pupil constriction
- Secretory stimulation: sweat, salivary, lacrimal glands, exocrine glands of the digestive tract, mucous cells of the respiratory tract
- Reduction of heart rate
- Stimulation of the smooth muscle of the intestinal tract.
- Tonus increase of the bronchial musculature
- Tonus and the motility increase of the urogenital tract, bile ducts and gallbladder.
- Promotion of urinary bladder emptying
Indications
Indications for use of parasympathomimetics (selection):
- Glaucoma.
- Myasthenia gravis
- Paralytic ileus (intestinal obstruction), motility disorders of the gastrointestinal tract, constipation.
- In anesthesia to antagonize non-depolarizing muscle relaxants.
- Bowel and bladder atony, bladder emptying disorders.
- Dry mouth
- Alzheimer’s disease
- Intoxication with nerve gas
Dosage
According to the SmPC. Parasympathomimetics are administered both systemically and topically.
Active ingredients
Direct parasympathomimetics (receptor agonists):
- Acetylcholine (miochol).
- Bethanechol chloride (myocholine-Glenwood)
- Carbachol (Miostat)
- Muscarine (not on the market)
- Pilocarpine (Spersacarpine, Salagen)
Indirect parasympathomimetics (cholinesterase inhibitors):
- Distigmine bromide (Ubretide, off label).
- Donepezil (Aricept, generic).
- Galantamine (Reminyl, generics)
- Neostigmine (Robinul-Neostigmine, with glycopyrronium bromide).
- Physostigmine (not commercially available)
- Pyridostigmine (Mestinon)
- Rivastigmine (Exelon, generic).
- Tacrine (out of commerce)
Contraindications
Full precautions can be found in the drug label.
Interactions
When parasympathomimetics are combined, adverse effects may be increased. Conversely, parasympatholytics may reduce the effects. The effects of muscle relaxants may be antagonized.
Adverse effects
Possible adverse effects include:
- Central disturbances, headache
- Bradycardia (slow heart rate), vasodilatation, drop in blood pressure.
- Bronchospasm and muscle spasms
- Diarrhea, abdominal cramps, gastrointestinal hyperactivity.
- Increased salivation, indigestion.
- Visual disturbances, pupil constriction.
- Sweating
- Urinary urgency, urinary incontinence