Anticholinergic

An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central and the peripheral nervous system. An example of an anticholinergic is dicyclomine. Generally speaking, it reduces the effects mediated by acetylcholine on acetylcholine receptors in neurons through competitive inhibition. The effect is therefore reversible.

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.

Effects

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 experienced recreational drug users, possibly due to the lack of euphoria caused by them. (For some of the recreational effects, see the article on 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 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 with possibly acceleration of caries
• Cessation of perspiration; consequent decreased 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)
• Easily startled
• Urinary retention
• Diminished bowel movement, sometimes ileus
• Increased intraocular pressure, dangerous for people with narrow-angle glaucoma
• Shaking

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 ^[1]
• 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^[1]
  • Warping or waving of surfaces and edges
  • Textured surfaces
  • "Dancing" lines; "spiders", insects
  • Lifelike objects indistinguishable from reality
  • Hallucinated presence of people not actually there
• 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)
• Brugmansia species (Brugmansia)
• Datura species (Datura)
• Hyoscamus niger (Henbane)
• Mandragora officinarum (Mandrake)

Use as a deterrent

Certain preparations of some drugs, such as Hydrocodone, are mixed with an anticholinergic agent to deter intentional overdose. ^[2]

References