Cholinergic drugs: how do they work?

Cholinergic drugs have a wide selection of clinical indications. They are used to treat myasthenia gravis, dementia, open-angle glaucoma, and post-operative urinary retention, to call just a few. How exactly do these drugs work? Let’s take a more in-depth look.

Basic Overview (Britannica, n.d.)

Cholinergics are a category of medication that affect acetylcholine, one in every of the major neurotransmitters within the nervous system. To understand cholinergic agents, we must always first turn out to be conversant in the motion of acetylcholine in various parts of the nervous system. The nervous system is split into the central nervous system (CNS), which consists of the brain, cerebellum, and spinal cord, and the peripheral nervous system, which consists of the somatic nervous system and the autonomic nervous system. The somatic nervous system transmits signals from external stimuli and the CNS to skeletal muscles, and likewise mediates hearing, vision, and touch. The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems. The sympathetic nervous system stimulates the fight or flight response and prepares the body for stressful situations, while the parasympathetic nervous system helps the body conserve energy. The parasympathetic nervous system regulates certain organs and glandular functions at rest, including digestion, urination, bowel function, and secretion production.
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Acetylcholine, the major neurotransmitter of the parasympathetic nervous system (PNS), might be excitatory or inhibited, is stored on the terminals of cholinergic neurons and might act on muscarinic (M2, M2, M3, M4, M5) or nicotinic (Nm, Nn) receptors.

• In the central nervous system, acetylcholine plays a crucial role in memory and learning.
• In the peripheral nervous system, when a nerve impulse reaches the top of a motor neuron, acetylcholine is released into the neuromuscular junction. It then binds to a receptor molecule within the postsynaptic membrane of the muscle fiber. As nerve impulses accumulate, the muscle contracts.
• In the autonomic nervous system, acetylcholine not only acts as a vasodilator within the cardiovascular system, but additionally reduces heart rate and cardiac contraction. It affects the digestive system by increasing peristalsis, while within the urinary tract it reduces bladder capability and increases voluntary micturition pressure.

Action mechanism

There are two mechanisms of motion of cholinergic drugs: either by promoting the results of acetylcholine or by inhibiting the enzyme that breaks it down.

• or bind to and activate muscarinic receptors. When a neuron within the parasympathetic nervous system is stimulated, acetylcholine is released. Acetylcholine crosses the synapse and interacts with receptors within the neighboring neuron. Cholinergic agonists stimulate cholinergic receptors, mimicking the results of acetylcholine (Pakala, Brown, & Preuss, 2022).
• cholinergic agents or increase the supply of acetylcholine at cholinergic receptors. When acetylcholine stimulates the cholinergic receptor, it’s destroyed by the enzyme acetylcholinesterase. Anticholinesterase drugs inhibit acetylcholinesterase. As a result, acetylcholine is just not broken down and begins to build up, resulting in a chronic effect of acetylcholine.

Nursing Considerations (Pakala, Brown and Preuss, 2022)

Because cholinergic drugs act on muscarinic and nicotinic receptors, they might cause significant adversarial effects, including bradycardia, atrioventricular block, atrial fibrillation or flutter, hypotension, and even cardiac arrest. Additional unintended effects include abdominal cramps, intestinal evacuation, bladder emptying, bronchial asthma attack, salivation, sweating, lacrimation, gastric and tracheobronchial secretions. Pilocarpine may cause miosis and spasm of accommodation. Some anticholinergic drugs may cause depression.
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Anticholinergic drugs are contraindicated in pulmonary disease (COPD/bronchial asthma), arrhythmias, coronary artery disease, angle-closure glaucoma, hyperthyroidism, intestinal resection or anastomosis, urinary tract obstruction, orthostatic hypertension, and severe miosis.
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Full details might be present in each medicine’s package leaflet or within the Nursing2022 Medicines Manual + medicines updates.
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Britannica (n.d.). The chemical compound of acetylcholine. British. https://www.britannica.com/science/acetylcholine.
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Pakala, R. S., Brown, K. N. & Preuss, C. V. (2022, September 21). Cholinergic drugs. . https://www.ncbi.nlm.nih.gov/books/NBK538163/.

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