Parasympatholytics

Parasympatholytics are the drugs that block or inhibit the actions of acetylcholine at postganglionic nerve endings and cholinergic receptors. They are also referred to as anticholinergics or cholinergic blocking agents or antispasmodics.
Anticholinergic drugs include atropine and related drugs- atropine is the prototype. Atropine is obtained from the plant Atropa belladonna. Atropine and scopolamine (hyoscine) are the belladonna alkaloids. They compete with acetylcholine for muscarinic receptors and block this receptors-they are muscarinic antagonists.

1. PARASYMPATHO LYTICS (Anticholinergics) Prof. Amol B. Deore Department of Pharmacology MVP’s Institute of Pharmaceutical Sciences, Nashik

2. Mechanism of action of Atropine Acetylcholine Atropine binds to the same receptor sites as Acetylcholine and prevents Acetylcholine from binding smooth muscles, cardiac muscles, exocrine glands and CNS. Muscarinic receptors

3. EFFECT ON THE EYE

4. Iris Pupil

5. The smooth muscles of the iris of the eye have a dual nerve supply (parasympathetic and sympathetic nerve supply). The parasympathetic supply is carried out via oculomotor nerve and innervates circular muscles of iris. The stimulation of these muscles causes miosis ( pupil constriction). The sympathetic supply is carried out via spinal nerve and innervates radial muscles of iris. The stimulation of radial muscles causes mydriasis ( pupil dilation ).

6. As preanesthetic medication: atropine is sued to reduce salivary and bronchial mucus secretions. Hence used as preanesthetic medication. Ophthalmic uses : atropine is used to produce mydriasis and cycloplegia for measurement of refractive errors, and other diagnostic procedures. They are also used in treatment corneal ulcers, choroiditis and iridocyclitis . Atropine is a cardiac stimulant hence used in heart block due to digitalis toxicity. In urinary incontinence (enuresis) Atropine sulphate is used as antidote in Organophospharus poisoning due to its antimuscarinic actions.

7. Adverse drug reactions of atropine Dryness of mouth and throat (xerostomia): due to reduction in salivation, leading to dysphagia (difficulty for swallowing). The skin is dry, hot and red, especially in the region of the face and neck (flushing). The body temperature may be raised due to decreased sweating and reduced heat loss leading to hyperpyrexia. Increased in intraocular pressure leading to glaucoma. Blurred vision due to paralysis of circular muscles and ciliary bodies of iris (pupil dilation i.e. mydriasis). Photophobia may result due to widely dilated pupils.

8. Urinary retention may occur due to loss of bladder tone especially in elder male patients with prostate enlargement. (Urinary retention is defined as the inability to completely or partially empty the bladder. Suffering from urinary retention means you may be unable to start urination, or if you are able to start, you can't fully empty your bladder) Palpitation and tachycardia may occur due to blockade of cardiac vagus nerve. Constipation occurs due to reduced GIT motility and peristalsis.

9. Contraindications Atropine is contraindicated in patients with narrow angle glaucoma, angina pectoris, congestive heart failure and prostate enlargement .

10. ACUTE BELLADONNA POISONING It may occur accidentally by ingestion of leaves/ roots of Atropa belladonna or seeds of Dhatura stromanium or overdose of atropine or scopolamine or anticholinergic drugs.

11. Symptoms

12. THANKING YOU Prof. Amol B. Deore Department of Pharmacology MVP’s Institute of Pharmaceutical Sciences, Nashik