Anticholinergic System And Drugs Question And Answers

What Are Parasympatholytics? Classify Them. Describe Pharmacological Action, Therapeutic Uses, And Side Effects Of Atropine.
Answer:

Parasympatholytics are also known as anticholinergic drugs.

These drugs block the action of acetylcholine mediated through muscarinic receptors.

Classification Of Parasympatholytics

1. Natural alkaloids: Atropine, hyoscine

2. Semisynthetic derivatives: Hyoscine butyl bromide, homatropine, atropine mononitrate, ipratropium bromide, Tiotropium bromide.

3. Synthetic compounds:

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- Quaternary Compounds: propantheline, oxyphenonium, aclidinium, isopropamide, glycopyrrolate.
- Tertiary amines: dicyclomine, valethamate, pirenzepine.

4. Vasicoselective: Oxybutynin, Flavoxate, Tolterodine.
5. Antiparkinsonism: Trihexiphenydyl, procyclidine, biperiden.

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Anticholinergic System And Drugs Question And Answers

“Global prevalence of autonomic dysfunction and its management”

Atropine

Pharmacological Actions

CNS: Atropine at its therapeutic dosages produces a mild CNS stimulant effect. It reduces cholinergic overactivity in basal ganglia and produces anti-parkinsonian activity.
It also suppresses vestibular disturbance and produces anti-motion sickness effect. At its high doses, it leads to restlessness, excitement, agitation, hallucination, medullary paralysis, coma, and death.
CVS: Atropine at its low dosages causes blockage of presynaptic muscarinic autoreceptors on vagal nerve endings and produces mild bradycardia.
At its therapeutic doses, it blocks M2 receptors of the heart and produces tachycardia. It improves AV conduction too. At its high doses, it leads to flushing of the face and hypotension.
Glands: All secretions, i.e. sweat, salivary, lacrimal, tracheobronchial, nasal, etc. under cholinergic influence decrease due to blockage of M3 receptors. It produces dryness of skin and mucous membranes.

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Eye: Atropine blocks M3 receptors and causes paralysis of constrictor pupillae muscles which leads to passive mydriasis.
Atropine due to blockage of M3 receptors also causes paralysis of ciliary muscles which causes loss of accommodation which leads to cycloplegia.
GIT: Atropine reduces the tone as well as motility of the gut and increases the tone of the sphincter which can cause constipation. Atropine causes relaxation of the smooth muscle of the gallbladder.
Bronchi: It causes relaxation of bronchial smooth muscle. It decreases bronchial secretion and also leads to mucociliary clearance which causes formation of mucous plug which blocks the airway.
Urinary bladder: Atropine causes relaxation of the detrusor muscle of the bladder and increases the tone of the sphincter which leads to urinary retention.

Therapeutic Uses

In ophthalmic system
- It is used as mydriatic and cycloplegic for testing the refraction.
- It is used as a mydriatic for fundoscopic examination.
- It is used in iridocyclitis to break and prevent adhesion between the iris and lens.
Preanesthetic medication: Atropine is used before giving general anesthesia to:
- Prevent vagal bradycardia at the time of anesthesia.
- Prevent laryngospasm by decreasing respiratory secretions.

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In poisoning
- It acts as a life-saving drug in organophosphorus poisoning.
- In some of the mushroom poisonings, it is the first drug of choice to be used.
As antispasmodic: Atropine is used as antispasmodic drug indysmenorrhea, intestinal colic and renal colic.
As vagolytic: It is useful for treating sinus bradycardia and partial heart block which occur due to an increase in vagal activity. Due toitsvagolyticeffctitimprovesAVconduction.
In peptic ulcer: It decreases gastric secretion in fasting as well as in the neurogenic phase and provides symptomatic relief in peptic ulcer.
In pulmonary embolism: Atropine provides benefits by reducing the reflex secretions.
In bronchial asthma and COPD: Atropine leads to the drying of the secretion in the respiratory tract and leads to the plugging of bronchioles.

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Adverse Effects

GIT: Xerostomia, dryness of throat, dysphagia, constipation, etc.
Eye: Headache, photophobia, blurring of vision, in elderly patients it can precipitate acute congestive glaucoma.
Urinary tract: Presence of urinary retention, difficulty in micturition.
CNS: At high doses, it leads to delirium, excitement, and hallucination.
CVS: Atropine causes hypotension, tachycardia and palpitation.
Acute belladonna poisoning: In severe poisoning, it can lead to coma and convulsion.

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