Anticholinergic Drugs; Types, Indications/Uses, Side Effects, Drug Interactions

Anticholinergic Drugs
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Anticholinergic drugs agent is a substance that blocks the neurotransmitter acetylcholine 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

Types Anticholinergic Drugs

Antimuscarinic agents

  • Atropine
  • Benztropine
  • Biperiden
  • Chlorpheniramine
  • Dicyclomine (Dicycloverine)
  • Dimenhydrinate
  • Diphenhydramine
  • Doxepin
  • Doxylamine
  • Glycopyrrolate
  • Glycopyrronium
  • Ipratropium
  • Orphenadrine
  • Oxitropium
  • Oxybutynin
  • Propantheline bromide
  • Tolterodine
  • Tiotropium
  • Tricyclic antidepressants
  • Trihexyphenidyl
  • Scopolamine
  • Solifenacin
  • Tropicamide

Antinicotinic agents

  • Bupropion (Zyban, Wellbutrin) – 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

Mechanism of action of Anticholinergic Drugs

Anticholinergic blocks muscarinic cholinergic receptors, without specificity for subtypes, resulting in a decrease in the formation of cyclic guanosine monophosphate (cGMP). Most likely due to actions of cGMP on intracellular calcium, this results in decreased contractility of smooth muscle.

or

Anticholinergic is a synthetic derivative of the alkaloid atropine with anticholinergic properties. Anticholinergic antagonizes the actions of acetylcholine at parasympathetic postganglionic effector cell junctions. When inhaled, anticholinergic binds competitively to cholinergic receptors in the bronchial smooth muscle thereby blocking the bronchoconstrictor actions of the acetylcholine (Ach) mediated vagal impulses. Inhibition of the vagal tone leads to dilation of the large central airways resulting in bronchodilation.

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Indications/uses of Anticholinergic Drugs

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
  • Sinus bradycardia due to a hypersensitive vagus nerve

Anticholinergics generally have antisialagogue effects (decreasing saliva production), and most produce some level of sedation, both being advantageous in surgical procedures.

Side effects of Anticholinergic Drugs

  • Poor coordination
  • Dementia
  • Decreased mucus production in the nose and throat; consequent dry, sore throat
  • Dry-mouth with possible acceleration of dental caries
  • Stopping 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)
  • Double-vision
  • 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.

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 (brain fog)
  • 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 (severe drop in systolic blood pressure when standing up suddenly) and significantly increased risk of falls in the elderly population
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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)
  • Bloated as a toad (ileus, urinary retention)
  • And the heart runs alone (tachycardia)

Drug Interactions

An anticholinergic may interact with the following drugs, supplements & may change the efficacy of drugs

References

  1. https://www.fda.gov/ForIndustry/DataStandards/SubstanceRegistrationSystem-UniqueIngredientIdentifierUNII/

  2. PubChem

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