An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine
in the central and the peripheral nervous system.
Anticholinergics inhibit parasympathetic nerve impulses by selectively blocking the binding
of the neurotransmitter acetylcholine to its receptor in nerve cells.
The nerve fibers of the parasympathetic system are responsible for the involuntary movement
of smooth muscles present in the gastrointestinal tract, urinary tract, lungs, etc.
Anticholinergics are divided into three categories in accordance with their specific targets
in the central and/or peripheral nervous system: antimuscarinic agents, ganglionic blockers,
and neuromuscular blockers.
Medical and recreational uses Anticholinergic drugs are used in treating
a variety of conditions: Gastrointestinal disorders
Genitourinary disorders Respiratory disorders
Sinus bradycardia due to a hypersensitive vagus nerve.
Insomnia, although usually only on a short-term basis.
Dizziness Anticholinergics generally have antisialagogue
effects, and most produce some level of sedation, both being advantageous in surgical procedures.
When a significant amount of an anticholinergic is taken into the body, a toxic reaction known
as acute anticholinergic syndrome may result.
This may happen accidentally or intentionally as a consequence of recreational drug use.
Anticholinergic drugs are usually considered the least enjoyable by many recreational drug
users, possibly due to the lack of euphoria caused by them.
In terms of recreational use, these drugs are commonly referred to as deliriants.
Because most users do not enjoy the experience, they do not use it again, or do so very rarely.
The risk of addiction is low in the anticholinergic class.
The effects are usually more pronounced in the elderly, due to natural reduction of acetylcholine
production associated with age.
Exceptions to the above include scopolamine, orphenadrine, dicycloverine/dicyclomine and
first-generation antihistamines with central nervous system penetration.
Side effects Possible effects of anticholinergics include:
Ataxia; loss of coordination Decreased mucus production in the nose and
throat; consequent dry, sore throat Xerostomia or dry-mouth with possible acceleration
of dental caries Cessation of perspiration; consequent decreased
epidermal thermal dissipation leading to warm, blotchy, or red skin
Increased body temperature Pupil dilation; consequent sensitivity to
bright light Loss of accommodation
Double-vision Increased heart rate
Tendency to be easily startled Urinary retention
Diminished bowel movement, sometimes ileus Increased intraocular pressure; dangerous
for people with narrow-angle glaucoma.
Possible effects in the central nervous system resemble those associated with delirium, and
may include: Confusion
Disorientation Agitation
Euphoria or dysphoria Respiratory depression
Memory problems Inability to concentrate
Wandering thoughts; inability to sustain a train of thought
Incoherent speech Irritability
Mental confusion Wakeful myoclonic jerking
Unusual sensitivity to sudden sounds Illogical thinking
Photophobia Visual disturbances
Periodic flashes of light Periodic changes in visual field
Visual snow Restricted or "tunnel vision"
Visual, auditory, or other sensory hallucinations Warping or waving of surfaces and edges
Textured surfaces "Dancing" lines; "spiders", insects; form
constants Lifelike objects indistinguishable from reality
Phantom smoking Hallucinated presence of people not actually
there
Rarely: seizures, coma, and death Orthostatic hypotension and significantly
increased risk of falls in the elderly population.
A common mnemonic for the main features of anticholinergic syndrome is the following:
Blind as a bat Red as a beet
Hot as a hare Dry as a bone
Mad as a hatter The bowel and bladder lose their tone
And the heart runs alone Remedies
Acute anticholinergic syndrome is completely reversible and subsides once all of the causative
agent has been excreted.
Reversible cholinergic agents such as physostigmine can be used in life-threatening cases.
Wider use is discouraged due to the significant side effects, such as rapid heart beat and
decreased blood pressure.
Piracetam, α-GPC and choline are known to activate the cholinergic system and alleviate
cognitive symptoms caused by extended use of anticholinergic drugs.
Pharmacology Anticholinergics are classified according
to the receptors that are affected: Antimuscarinic agents operate on the muscarinic
acetylcholine receptors.
The majority of anticholinergic drugs are antimuscarinics.
Antinicotinic agents operate on the nicotinic acetylcholine receptors.
The majority of these are non-depolarising skeletal muscle relaxants for surgical use
that are structurally related to curare.
Several are depolarizing agents.
Examples Examples of common anticholinergics:
Anti-Muscarinic agents Atropine
Benztropine Biperiden
Chlorpheniramine Dicyclomine
Dimenhydrinate Diphenhydramine
Doxylamine Glycopyrrolate
Ipratropium Orphenadrine
Oxitropium Oxybutynin
Tolterodine Tiotropium
Trihexyphenidyl Scopolamine
Solifenacin Tropicamide
Anti-Nicotinic agents Bupropion - Ganglion blocker
Dextromethorphan - Cough suppressant and ganglion blocker
Doxacurium - Nondeplorizing skeletal muscular relaxant
Hexamethonium - Ganglion blocker Mecamylamine - Ganglion blocker and occasional
smoking cessation aid Tubocurarine - Nondepolarizing skeletal muscular
relaxant
Plants of the Solanaceae family contain various anticholinergic tropane alkaloids, such as
scopolamine, atropine, and hyoscyamine.
Physostigmine is one of only a few drugs that can be used as an antidote for anticholinergic
poisoning.
Nicotine also counteracts anticholinergics by activating nicotinic acetylcholine receptors.
Caffeine is able to counteract the anticholinergic symptoms by reducing sedation and increasing
acetylcholine activity, thereby causing alertness and arousal.
Plant sources The most common plants containing anticholinergic
alkaloids are: Atropa belladonna, source of atropine
Brugmansia species Datura species
Hyoscyamus niger Mandragora officinarum
Use as a deterrent Certain preparations of some drugs, such as
hydrocodone, are mixed with an anticholinergic agent to deter intentional overdose.
References