A muscarinic receptor antagonist (MRA) is a type of anticholinergic agent that blocks the activity of the muscarinic acetylcholine receptor.
Anticholinergic agents are is a group of substances that blocks the action of the neurotransmitter acetylcholine (ACh) at synapses in the central and the peripheral nervous system, and, in broad terms, neuromuscular junction.
Such 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.
The parasympathetic cholinergic process enhances ACh function.
Anticholinergics are divided into two categories in accordance with their specific targets in the central, peripheral nervous system and neuromuscular junction: antimuscarinic agents, and antinicotinic agents which are ganglionic blockers, neuromuscular blockers).
Anticholinergic drugs are used to treat a variety of conditions:
Dizziness-vertigo and motion sickness-related symptoms
Gastrointestinal disorders-peptic ulcers, diarrhea, pylorospasm, diverticulitis, ulcerative colitis, nausea, and vomiting?
Genitourinary disorders-cystitis, urethritis, and prostatitis.
Respiratory disorders-asthma, chronic bronchitis, and chronic obstructive pulmonary disease [COPD])
Sinus bradycardia due to a hypersensitive vagus nerve.
Anticholinergics generally decrease saliva production, and most produce some level of sedation, both being advantageous for surgery procedures.
Physiological effects include:
ocular symptoms–mydriasis, pupil dilation, and acute angle-closure glaucoma in those with shallow anterior chamber.
anhidrosis/dry mouth/dry skin
The most significant feature is delirium.
Long-term use may increase the risk of both cognitive and physical decline.
Older adults hav an increased risk of death.
Possible effects of anticholinergics include:
Decreased mucus production in the nose and throat.
Dry, sore throat.
Dry-mouth with possible acceleration of dental caries.
Cessation of sweating.
Decreased epidermal thermal dissipation.
Increased body temperature
Loss of accommodation
Loss of focusing ability, blurred vision.
Increased heart rate
Tendency to be easily startled
Urinary incontinence while sleeping
Diminished bowel movements, decreasing motility via the vagus nerve.
Increased intraocular pressure;
Possible effects in the central nervous system resemble those associated with delirium, and may include:
Euphoria or dysphoria
Inability to concentrate
Wandering thoughts; inability to sustain a train of thought
Wakeful myoclonic jerking
Visual, auditory, or other sensory hallucinations
Warping or waving of surfaces and edges
“Dancing” lines; “spiders”, insects; forts.
Contraindications to antimuscarinic medication include: narrow angle glaucoma, impaired gastric emptying, and in patients with oral forms of potassium chloride.
Relative contraindications include post void residual excess, and impaired or decline in cognitive function.