Are you having a hard time understanding the difference between cholinergic and anticholinergic drugs?
At first, it may be a confusing topic, but as long as you understand the basics, and understand them by heart, there should be no problem.
This study guide will help you get to know the sympathetic and parasympathetic nervous system more, in turn, helping you better understand cholinergic and anticholinergic drugs.
So let’s get into it.
How does the Nervous System Work?
You must know how the nervous system works to understand cholinergic and anticholinergic drugs fully.
The Nervous System has two major subdivisions:
- Central Nervous System (CNS) – It comprises the brain and the spinal cord.
- Peripheral Nervous System (PNS) – It is responsible for the body’s nerves, and it connects the brain and spinal cord to the organs, muscles, and other senses in the periphery of the body.
The Peripheral Nervous System consists of:
- Somatic Nervous System (SNS) – It relays motor and sensory information back and forth to the CNS.
- Autonomic Nervous System (ANS) – It controls the glands and internal organs.
In this topic, we will focus more on the Autonomic Nervous System that is subdivided into:
- Sympathetic
- Parasympathetic
To understand more of the Parasympathetic and Sympathetic Nervous system, here is a summarized and easy-to-understand guide on their functions in the body. Just remember that these two basically have opposite functions.
| Parasympathetic | Sympathetic |
|
– Constrict: Pupil & Bronchi – Stimulates: Salivation, Digestion & Bladder – Decreased: Heart Rate & Blood Pressure – Study Tip: The Parasympathetic nervous system is responsible for the stimulation of “Rest and Digest” or “Feed and Breed” activities |
– Dilate: Pupil and Bronchi – Inhibit: Salivation, Digestion, Bladder – Increased: Heart Rate & Blood Pressure – Study Tip: It stimulates the “Fight or Flight” response of the body |
Cholinergic vs. Anticholinergic Drugs
Now that we have recapped what the nervous system does and its bodily functions, it would be easier for us to understand the mechanism of action of cholinergic and anticholinergic drugs.
The role of acetylcholine now comes in. It is the primary neurotransmitter in the Parasympathetic Nervous System that is responsible for stimulating muscle cells and secretion of glands.
Cholinergic Drugs
- Works as the substitute for acetylcholine, in short, it supplies acetylcholine.
- Cholinergic drugs make sure that the parasympathetic nervous system works properly.
- It also makes sure that it blocks acetylcholinesterase (an enzyme that breaks up acetylcholine).
- It stimulates the parasympathetic nervous system.
- Antidote: The anticholinergic drug Atropine
- There are two types of cholinergic drugs: (1) Direct-Acting (2) Indirect-Acting
| Direct-Acting Cholinergic Drugs | Indirect-Acting Cholinergic Drugs |
|
– It binds to cholinergic receptors – It stimulates organs the same way acetylcholine does. – It has a widespread system effect including the smooth muscle, cardiac muscle, exocrine glands and the eye. |
– It inhibits the acetylcholinesterase enzyme. – It has an added cholinergic effect to improve skeletal muscle strength and tone. – Used for Alzheimer’s Disease. |
The Effects of Cholinergic Drugs
Remember that cholinergic drugs mimic the functions of the parasympathetic system. Remember that having too much cholinergic drugs may result in the overstimulation of the parasympathetic nervous system and may lead to unwanted side effects.
| Body System / Organ | Effect on Body | Used For: |
|---|---|---|
| CNS |
– enhanced cognitive functions – memory encoding, arousal and attention |
– treatment for dementia and Alzheimer’s Disease |
| Eye | Pupil constriction | Glaucoma (treatment and surgery) |
| GI | Stimulates the smooth muscle | Paralytic ileus and postoperative abdominal distention |
| GU | Stimulates the urinary bladder | Urinary retention |
| Musculoskeletal | Improves strength and muscle tone | Treatment of myasthenia gravis |
The adverse effects of cholinergic drugs (also known as Muscarinic effects or Cholinergic Syndrome) can be easily remembered with the acronym SLUDGE-M.
- Secretions (in excess) especially salivation
- Lacrimation
- Urination
- Defecation
- Gastric Cramping
- Emesis
- Miosis and Blurred Vision
If you noticed, it’s just its exact opposite – the SYMPATHETIC effect. Other adverse effects are: decreased heart rate and blood pressure, dizziness, convulsions, headache, increased bronchial secretions and bronchospasms.
Examples of Generic Names of Cholinergic Drugs:
- Direct-acting: Bethanechol & Pilocarpine
- Indirect-acting: Neostigmine & Donepezil
Contraindications – CHAP acronym:
- Coronary Artery Disease
- Hyperthyroidism
- Asthma
- Peptic Ulcer
Anticholinergic Drugs
- It blocks the action of acetylcholine of the parasympathetic nervous system.
- It interacts with muscarinic cholinergic receptors of the secretory glands, brain and heart.
- Anticholinergic Toxicity: Physostigmine
The Effects of Anticholinergic Drugs:
| Body System / Organ: | Effects on the Body | Used For: |
|---|---|---|
| CNS | Muscle tremors and decreased muscle rigidity | Parkinson’s disease |
| Eye | Pupil Dilation | For diagnostic and surgery purposes |
| Salivary & Lacrimal Glands | Decreased secretion | Respiratory conditions with secretions |
| Heart | Increased heart rate | |
| Respiratory | Decreased bronchial secretions, decreased airway resistance, and decreased bronchial secretions | Indicated for asthma and COPD |
| GI | – Relaxes the smooth muscle
– Decreased: Gastric and Intestinal secretions, peristalsis and motility |
Indicated for Irritable Bowel Syndrome and Peptic Ulcer Disease |
The Adverse Effects of Anticholinergic Drugs:
- CNS stimulation
- Tachycardia
- Constipation
- Dry mouth
- Urinary retention
- Decreased sweating (hot & dry skin)
- Blurred vision
- Dilation of the pupil
Examples of Anticholinergic Drugs
- Atropine
- Ipratropium
- Scopolamine
- Benztropine
- Oxybutynin
- Solifenacin succinate (VESIcare)
Contraindications to Using Anticholinergic Drugs
- Myasthenia gravis
- Glaucoma
- Myocardial Infarction
Simply put it this way…
Remember the 3S when understanding cholinergic and anticholinergic drugs: SEE, SPIT, SHIT (Excretion)
Cholinergic drugs make you SEE, SPIT, and SHIT (plus urinate). Anticholinergic drugs can’t make you SEE, SPIT and SHIT.
It is essential to understand the parasympathetic and sympathetic effects before you can fully understand the action of cholinergic and anticholinergic drugs.
If the signs and symptoms affect the parasympathetic nervous system, cholinergic drugs are needed. It involves constricting (eyes and lungs), stimulating (saliva, digestion and bladder) and decreasing (cardiac activity). You’ll need Bethanechol, Pilocarpine, Neostigmine, or Donepezil. If the patient experiences cholinergic toxicity (SLUDGE-M), the antidote is Atropine.
If the signs and symptoms affect the sympathetic nervous system, anticholinergic drugs are needed. It involves dilated (eyes and lungs), inhibited (salivation, digestion, and excretion), and increased cardiac activity. The antidote of anticholinergic toxicity is Physostigmine.
Feel free to share this study guide with your friends so that they can understand this topic easily too.
