Anticholinergics

An anticholinergic agent is a member of a class of pharmaceutical compounds which serve to reduce the effects mediated by acetylcholine in the central nervous system and peripheral nervous system.

Anticholinergics are typically reversible competitive inhibitors of one of the two types of acetylcholine receptors, and are classified according to the receptors that are affected: antimuscarinic agents operate on the muscarinic acetylcholine receptors, and antinicotinic agents operate on the nicotinic acetylcholine receptors. The majority of anticholinergics are antimuscarinics.

Effects

When a significant amount of anticholinergic is taken into the body, a toxidrome known as acute anticholinergic syndrome may result. This may happen accidentally or intentionally as a form of recreational drug use. This class of drug is usually considered the least “fun” by experienced drug users, possibly due to the lack of euphoria caused by anticholinergics. Because most users do not enjoy the experience, they don’t use it again, or very rarely. Risk of addiction is low in the anticholinergic class. Effects are usually more pronounced in the elderly, due to the decrease of acetylcholine production associated with age.

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
  Cessation of perspiration; consequent increased thermal dissipation through the skin leading to hot, red skin
  Increased body temperature
  Pupil dilation (mydriasis); consequent sensitivity to bright light (photophobia)
  Loss of accommodation (loss of focusing ability, blurred vision — cycloplegia)
  Double vision (diplopia)
  Increased heart rate (tachycardia)
  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
• Respiratory depression
• Short-term memory loss
• Inability to concentrate
• Wandering thoughts; inability to sustain a train of thought
• Incoherent speech
• 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
  • Lifelike objects indistinguishable from reality
• Rarely: seizures, coma and death

Acute anticholinergic syndrome is completely reversible and subsides once all of the toxin has been excreted. Ordinarily, no specific treatment is indicated. However, in extreme cases, especially those that involves severe distortions of mental state, a reversible cholinergic agent such as physostigmine may be used.

Plant sources

The most common plants containing anticholinergic alkaloids are:

• Atropa belladonna (Deadly Nightshade)
  Mandragora officinarum (Mandrake)
  Hyoscamus niger (Henbane)
  Datura species (Datura)

Pharmaceuticals

• Unclassified
  • benztropine (Cogentin®)
• Muscarinic receptor antagonists
  • Belladonna alkaloids
    • Scopolamine (L-Hyoscine)
    • Atropine (D/L-Hyoscyamine)
  • Synthetic and Semisynthetic
    • Dicyclomine
      Flavoxate
      Ipratropium
      Oxybutynin
      Pirenzepine
      Tiotropium
      Tolterodine (Detrusitol®)
      Tropicamide
      Solifenacin (Vesicare®)
      Darifenacin (Enablex®)
• Nicotinic receptor antagonists
  • Ganglionic blocking agents
    • Trimethaphan
  • Nondepolarizing neuromuscular blocking agents
    • Atracurium
      Doxacurium
      Mivacurium
      Pancuronium
      Tubocurarine
      Vecuronium
  • Depolarizing neuromuscular blocking agents
    • Suxamethonium chloride

Many other drugs have anticholinergic properties, including cyclic antidepressants and the common allergy medications diphenhydramine (Benadryl) and its 8-chlorotheophylline salt dimenhydrinate (Dramamine), which are used medically for antihistaminergic and antiemetic purposes, and sometimes recreationally for their psychoactive effects. The common side effects of some SSRI antidepressants, such as Prozac (fluoxetine), often sweaty palms, are due to anticholinergic properties.

Some drugs, such as hydrocodone, are mixed with small amounts of an anticholinergic, such as Homatropine Methylbromide to discourage abuse.

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