An anticholinergic agent is a substance that blocks the action of the neurotransmitter acetylcholine at synapses in the central and the peripheral nervous system. These agents 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, and many other parts of the body. Anticholinergics are divided into three categories in accordance with their specific targets in the central and peripheral nervous system: antimuscarinic agents, ganglionic blockers, and neuromuscular blockers.
Anticholinergic drugs are used to treat a variety of conditions:
- Dizziness (including vertigo and motion sickness-related symptoms)
- Extrapyramidal symptoms, a potential side-effect of antipsychotic medications.
- Gastrointestinal disorders (e.g., peptic ulcers, diarrhea, pylorospasm, diverticulitis, ulcerative colitis, nausea, and vomiting)
- Genitourinary disorders (e.g., cystitis, urethritis, and prostatitis)
- Insomnia, although usually only on a short-term basis
- Respiratory disorders (e.g., asthma, chronic bronchitis, and chronic obstructive pulmonary disease [COPD])
- Sinus bradycardia due to a hypersensitive vagus nerve
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.
Long-term use may increase the risk of both mental and physical decline. It is unclear whether they affect the risk of death generally. However, in older adults they do appear to increase the risk of death. Possible effects of anticholinergics include:
- Poor coordination
- Dementia, recent study
- Decreased mucus production in the nose and throat; consequent dry, sore throat
- Dry-mouth with possible acceleration of dental caries
- Cessation of sweating; consequent decreased epidermal thermal dissipation leading to warm, blotchy, or red skin
- Increased body temperature
- Pupil dilation; consequent sensitivity to bright light (photophobia)
- Loss of accommodation (loss of focusing ability, blurred vision – cycloplegia)
- Increased heart rate
- Tendency to be easily startled
- Urinary retention
- Urinary incontinence while sleeping
- Diminished bowel movement, sometimes ileus (decreases motility via the vagus nerve)
- Increased intraocular pressure; dangerous for people with narrow-angle glaucoma.
- Euphoria or dysphoria
- Respiratory depression
- Memory problems
- Inability to concentrate
- Wandering thoughts; inability to sustain a train of thought
- Incoherent speech
- Mental confusion (brain fog)
- Wakeful myoclonic jerking
- Unusual sensitivity to sudden sounds
- Illogical thinking
- Visual disturbances
- 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 (severe drop in systolic blood pressure when standing up suddenly) and significantly increased risk of falls in the elderly population.
Older patients are at a higher risk of experiencing CNS sideffects due to lower acetylcholine production.
A common mnemonic for the main features of anticholinergic syndrome is the following:
- Blind as a bat (dilated pupils)
- Red as a beet (vasodilation/flushing)
- Hot as a hare (hyperthermia)
- Dry as a bone (dry skin)
- Mad as a hatter (hallucinations/agitation)
- The Bowel and bladder lose their tone (or "Bloated as a toad"; ileus, "Full as a flask" urinary retention)
- And the heart runs alone (tachycardia)
Acute anticholinergic syndrome is reversible and subsides once all of the causative agent has been excreted. Reversible Acetylcholinesterase inhibitor agents such as physostigmine can be used as an antidote in life-threatening cases. Wider use is discouraged due to the significant side effects related to cholinergic excess including: seizures, muscle weakness, bradycardia, bronchoconstriction, lacrimation, salivation, bronchorrhea, vomiting, and diarrhea. Even in documented cases of anticholinergic toxicity, seizures have been reported after the rapid administration of physostigmine. Asystole has occurred after physostigmine administration for tricyclic antidepressant overdose, so a conduction delay (QRS > 0.10 second) or suggestion of tricyclic antidepressant ingestion is generally considered a contraindication to physostigmine administration.
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 of common anticholinergics:
- Antimuscarinic agents
- Antipsychotics (clozapine, quetiapine)
- Certain SSRIs (citalopram)
- Dicyclomine (Dicycloverine)
- Propantheline bromide
- Tricyclic antidepressants (28 compounds with numerous trade names)
- Antinicotinic agents
- Bupropion – Ganglion blocker
- Dextromethorphan - Cough suppressant and ganglion blocker
- Doxacurium – Nondepolarizing skeletal muscular relaxant
- Hexamethonium – Ganglion blocker
- Mecamylamine – Ganglion blocker and occasional smoking cessation aid
- Tubocurarine - Nondepolarizing skeletal muscular relaxant
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 (although an adenosine receptor antagonist) is able to counteract the anticholinergic symptoms by reducing sedation and increasing acetylcholine activity, thereby causing alertness and arousal.
- Atropa belladonna (deadly nightshade)
- Brugmansia species
- Datura species
- Garrya species
- Hyoscyamus niger (henbane)
- Mandragora officinarum (mandrake)
Use as a deterrent
Several narcotic and opiate-containing drug preparations, such as those containing hydrocodone and codeine are combined with an anticholinergic agent to deter intentional misuse. Examples include Hydromet/Hycodan (hydrocodone/homatropine), Lomotil (diphenoxylate/atropine) and Tussionex (hydrocodone polistirex/chlorpheniramine). However, it is noted that opioid/antihistamine combinations are used clinically for their synergistic effect in the management of pain and maintenance of dissociative anesthesia (sedation) in such preparations as Meprozine (meperidine/promethazine) and Diconal (dipipanone/cyclizine), which act as strong anticholinergic agents.
- Clinical Pharmacology [database online]. Tampa, FL: Gold Standard, Inc.; 2009. Drugs with Anticholinergic Activity. Prescriber's Letter 2011; 18 (12):271233.
- Sharee A. Wiggins; Tomas Griebling. "Urinary Incontinence". Landon Center on Aging. Archived from the original on 2011-09-27.
- Page 592 in: Cahalan, Michael D.; Barash, Paul G.; Cullen, Bruce F.; Stoelting, Robert K. (2009). Clinical Anesthesia. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 978-0-7817-8763-5.
- Barash, Paul G. (2009). Clinical Anesthesia. ISBN 9780781787635. Archived from the original on 20 February 2017. Retrieved 8 December 2014.
- Bersani, F. S.; Corazza, O.; Simonato, P.; Mylokosta, A.; Levari, E.; Lovaste, R.; Schifano, F. (2013). "Drops of madness? Recreational misuse of tropicamide collyrium; early warning alerts from Russia and Italy". General Hospital Psychiatry. 35 (5): 571–3. doi:10.1016/j.genhosppsych.2013.04.013. PMID 23706777.
- Fox, C; Smith, T; Maidment, I; Chan, WY; Bua, N; Myint, PK; Boustani, M; Kwok, CS; Glover, M; Koopmans, I; Campbell, N (September 2014). "Effect of medications with anti-cholinergic properties on cognitive function, delirium, physical function and mortality: a systematic review". Age and Ageing. 43 (5): 604–15. doi:10.1093/ageing/afu096. PMID 25038833.
- "Here's More Evidence That Common Drugs May Cause Cognition Issues". Science Daily. 2016-04-19. Archived from the original on 2016-06-11. Retrieved 2016-05-09.
- "Popular drugs for colds, allergies, sleep linked to dementia". CBS News. 2016-04-21. Archived from the original on 2016-05-07. Retrieved 2016-05-09.
- "Common over-the-counter drugs can hurt your brain". CNN. 2016-04-18. Archived from the original on 2016-05-06. Retrieved 2016-05-09.
- "The Cold Medicine That's Linked to Cognitive Problems". Time. 2016-04-18. Archived from the original on 2016-05-10. Retrieved 2016-05-09.
- Risacher, Shannon L.; McDonald, Brenna C.; Tallman, Eileen F.; West, John D.; Farlow, Martin R.; Unverzagt, Fredrick W.; Gao, Sujuan; Boustani, Malaz; Crane, Paul K.; Petersen, Ronald C.; Jack, Clifford R.; Jagust, William J.; Aisen, Paul S.; Weiner, Michael W.; Saykin, Andrew J.; Alzheimer's Disease Neuroimaging Initiative (April 18, 2016). "Association Between Anticholinergic Medication Use and Cognition, Brain Metabolism, and Brain Atrophy in Cognitively Normal Older Adults". JAMA. 73 (6): 721–32. doi:10.1001/jamaneurol.2016.0580. PMC 5029278. PMID 27088965.
- Ruxton, K; Woodman, RJ; Mangoni, AA (2 March 2015). "Drugs with anticholinergic effects and cognitive impairment, falls and all-cause mortality in older adults: A systematic review and meta-analysis". British Journal of Clinical Pharmacology. 80 (2): 209–20. doi:10.1111/bcp.12617. PMC 4541969. PMID 25735839.
- "Study suggests link between long-term use of anticholinergics and dementia risk". Alzheimer's Society. 2015-01-26. Archived from the original on 2015-11-12. Retrieved 2015-02-17.
- Talan, Jamie (July–August 2008). "Common Drugs May Cause Cognitive Problems". Neurology Now. 4 (4): 10–11. doi:10.1097/01.NNN.0000333835.93556.d1. Archived from the original on 2019-06-26. Retrieved 26 June 2019.
- "Lifeline Learning Center". Lifeline.theonlinelearningcenter.com. Archived from the original on 12 July 2012. Retrieved 8 December 2014.
- "Anticholinergic Toxidrome". Life in the Fast Lane. Archived from the original on 2015-05-10. Retrieved 2015-06-08.
- Rosen, Peter, John A. Marx, Robert S. Hockberger, and Ron M. Walls. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Mosby Elsevier, 2014.
- " How well do you know your anticholinergic (antimuscarinic) drugs? | Therapeutics Initiative". Therapeutics Initiative. 10 September 2018. Retrieved 20 September 2018.
- Carroll FI, Blough BE, Mascarella SW, Navarro HA, Lukas RJ, Damaj MI (2014). Bupropion and bupropion analogs as treatments for CNS disorders. Adv. Pharmacol. Advances in Pharmacology. 69. pp. 177–216. doi:10.1016/B978-0-12-420118-7.00005-6. ISBN 9780124201187. PMID 24484978.
- Dwoskin, Linda P. (29 January 2014). Emerging Targets & Therapeutics in the Treatment of Psychostimulant Abuse. Elsevier Science. pp. 177–216. ISBN 978-0-12-420177-4. Archived from the original on 20 March 2017.
- Tasman, Allan, Kay, Jerald, Lieberman, Jeffrey A., First, Michael B., Maj, Mario (11 October 2011). Psychiatry. John Wiley & Sons. ISBN 978-1-119-96540-4. Archived from the original on 20 March 2017.
- Damaj, M. I.; Flood, P; Ho, K. K.; May, E. L.; Martin, B. R. (2004). "Effect of Dextrometorphan and Dextrorphan on Nicotine and Neuronal Nicotinic Receptors: In Vitro and in Vivo Selectivity". Journal of Pharmacology and Experimental Therapeutics. 312 (2): 780–5. doi:10.1124/jpet.104.075093. PMID 15356218.
- Lee, Jun-Ho; Shin, Eun-Joo; Jeong, Sang Min; Kim, Jong-Hoon; Lee, Byung-Hwan; Yoon, In-Soo; Lee, Joon-Hee; Choi, Sun-Hye; Lee, Sang-Mok; Lee, Phil Ho; Kim, Hyoung-Chun; Nah, Seung-Yeol (2006). "Effects of dextrorotatory morphinans on α3β4 nicotinic acetylcholine receptors expressed in Xenopus oocytes". European Journal of Pharmacology. 536 (1–2): 85–92. doi:10.1016/j.ejphar.2006.02.034. PMID 16563374.
- Hernandez, S. C.; Bertolino, M; Xiao, Y; Pringle, K. E.; Caruso, F. S.; Kellar, K. J. (2000). "Dextromethorphan and Its Metabolite Dextrorphan Block α3β4 Neuronal Nicotinic Receptors". The Journal of Pharmacology and Experimental Therapeutics. 293 (3): 962–7. PMID 10869398.
- Shytle, RD; Penny, E; Silver, AA; Goldman, J; Sanberg, PR (Jul 2002). "Mecamylamine (Inversine): an old antihypertensive with new research directions". Journal of Human Hypertension. 16 (7): 453–7. doi:10.1038/sj.jhh.1001416. PMID 12080428.
- "NIH DailyMed – Hydromet Syrup". Dailymed.nlm.nih.gov. Archived from the original on 2011-05-23. Retrieved 2008-08-17.
- Zacny, James P. (2003). "Characterizing the subjective, psychomotor, and physiological effects of a hydrocodone combination product (Hycodan) in non-drug-abusing volunteers". Psychopharmacology. 165 (2): 146–156. doi:10.1007/s00213-002-1245-5. PMID 12404072.