Cholinergic therapy - Overview: Nursing pharmacology

Cholinergic therapy uses medications that affect the parasympathetic nervous system, which is often nicknamed the “rest and digest” or “feed and breed” system of the autonomic nervous system. When activated, the parasympathetic nervous system promotes activities such as digestion, elimination, and sexual arousal, and it helps the body calm down after periods of stress or danger. Commonly used cholinergic medications include bethanechol, a direct-acting cholinergic agonist, and atropine, a cholinergic antagonist.

Now, bethanechol is referred to as a parasympathomimetic because it works by mimicking the parasympathetic neurotransmitter, acetylcholine. By stimulating the muscarinic receptors in the bladder, it stimulates the contraction of the bladder’s detrusor muscle and relaxes the external urinary sphincter, promoting urination in non-obstructive urinary retention. By stimulating muscarinic receptors in the gastrointestinal tract, it promotes bowel motility.

In contrast, atropine is referred to as a parasympatholytic, because it binds to acetylcholine receptors, blocking its effects. This leads to inhibition of the parasympathetic nervous system which results in increased heart rate and cardiac output and other antimuscarinic effects. It’s used to treat conditions like overactive bladder and bradycardia. It can also be used to promote pupillary dilation during eye exams and can be given preoperatively to reduce excessive respiratory secretions.

Alright, cholinergic medications have several side effects which are related to their actions on the parasympathetic nervous system. By promoting parasympathetic effects in the heart and lungs, bethanechol can cause hypotension, bradycardia, and bronchoconstriction. It also promotes exocrine gland activity, causing sweating and increased salivation.

In addition, increased gastrointestinal activity can cause cramping and diarrhea. Other effects include blurred vision due to miosis, or pupillary constriction, as well as urinary urgency.

On the other hand, atropine inhibits parasympathetic effects, so in the heart, it can cause tachycardia and palpitations. It reduces secretions throughout the body, causing decreased salivation and dry mouth, thickening of bronchial secretions, as well as anhidrosis or decreased sweating, resulting in dry, flushed skin, and an increased temperature.

Gastrointestinal activity slows down, which causes nausea, abdominal distension, and constipation. Other effects include mydriasis, or pupillary dilation, resulting in blurred vision, photophobia, and increased intraocular pressure.

Atropine can also cross the blood brain barrier, and could result in agitation, hallucinations, or paranoid behavior. Lastly, urinary retention may occur.