Parasympathomimetic or cholinergic drugs mimic the action of the stimulated parasympathetic nervous system. They are classified as direct-acting cholinergic agonists that directly bind to cholinergic receptors, or indirect-acting agonists that inhibit acetylcholinesterase to prolong the action of acetylcholine. Direct agonists like bethanechol are used to treat atonic bladder while indirect agonists like physostigmine and neostigmine are used to treat myasthenia gravis by blocking the antibodies that inhibit acetylcholine receptors. Myasthenia gravis is an autoimmune disorder where antibodies block acetylcholine receptors at the neuromuscular junction, weakening muscles.
3. INTRODUCTION
PARASYMPATHOMIMETICS OR CHOLINERGIC DRUGS ARE THOSE DRUGS WHICH MIMIC THE
ACTION OF STIMULATED PARASYMPATHETIC SYSTEM.
ACTIONS OF PARASYMPATHOMIMETICS ARE-
EYES- MIOSIS [CONTRACTION OF PUPIL]
LACRIMAL GLANDS- STIMULATE TEARS
SALIVARY GLANDS-WATERY SECRETION
HEART- DECREASE
B.P.- DECREASE
TRACHEA AND BRONCHI- CONTRACTION
GIT-THE MUSCLE MOTILITY AND TONE
ON BLOOD VESSEL- DILATION
10. ACTING CHOLINERGIC AGONIST
• CHOLINERGIC AGONIST MIMIC THE EFFECT OF ACH BY BINDING DIRECTLY TO
CHOLINORECEPTORS.
• IT IS STRUCTURALLY RELATED TO THE ACH IN WHICH ACETATE IS REPLACED BY CARBAMATE
AND CHOLINE IS METHYLATED. IT LACKS NICOTINIC ACTIONS BUT DOES HAVE STRONG
MUSCARINIC ACTIVITY.
• ACTIONS- IT DIRECTLY STIMULATE MUSCARINIC RECEPTOR, CAUSING INCREASED INTESTINAL
MOTILITY AND TONE.
• TH. USE- IT IS USED TO STIMULATE ATONIC BLADDER; ALSO USED TO TREAT NEUROGENIC
ATONY AS WELL AS MEGACOLON.
• ADVERSE EFFECTS- BETHANECHOL CAUSE THE EFFECTS OF GENERALIZED CHOLINERGIC
STIMULATION. THESE INCLUDE SWEATING.
11. INDIRECT ACTING CHOLINRGIC AGONIST
• ACETYLCHOLINESTERASE IS AN ENZYME THAT SPECIFICALLY CLEAVES ACH TO ACETATE AND
CHOLINE AND THUS TERMINATES ITS ACTIONS. INHIBITION OF ACETYLCHOLINESTERASE
INDIRECTLY PROVIDE A CHOLINERGIC ACTIONS BY PROLONGING THE LIFETIME OF ACH. THIS
RESULTS ACCUMULATION OF ACH IN SYNAPTIC SPACE.
• EG- PHYSOSTIGMINE, NEOSTIGMINE
12. • PHYSOSTIGMINE IS AN NITROGENOUS CARBAMIC ACID ESTER FOUND NATURALLY IN PLANTS.
• ACTIONS- PHYSOSTIGMINE HAS A WIDE RANGE OF EFFECTS OVER MUSCARINIC AND NICOTINIC
SITES OF ANS.
• IT CAN ENTER AND STIMULATE CHOLINERGIC SITES AT ANS.
• TH. USE – INCREASE INTESTINAL AND BLADDER MOTILITY ; PLACED TOPICALLY IN EYES, IT
PRODUCE MIOSIS. IT IS USED TO TREAT GLAUCOMA. IT IS ALSO USED IN THE TREATMENT OF
OVERDOSE OF DRUGS WITH ANTICHOLINERGIC ACTIONS LIKE ATROPINE ETC.
• ADVERSE EFFECT – IF HIGH DOSES ARE USED, MAY LEAD TO CONVULSION, BRADYCARDIC AND
A FALL IN CARDIAC OUTPUT MAY ALSO OCCURS. SOMETIME, PARALYSIS OF SKELETAL MUSCLES
ALSO OCCURS.
13. • A NUMBER OF SYNTHETIC ORGANOPHOSPHATE COMPOUNDS HAVE THE CAPACITY TO BIND
COVALENTLY TO ACETYLCHOLINESTERASE . THE RESULT IS A LONG LASTING INCREASE IN ACH
AT ALL SITES WHERE IT IS RELEASED.
• EG- ECHOTHIOPHATE
• ECHOTHIOPHATE IS AN ORGANOPHOSPHATE COMPOUND HAVE THE CAPACITY TO BIND VIA ITS
PHOSPHATE GROUP TO –OH GROUP AT THE ACTIVE SITES OF ACETYLCHOLINESTERASE. ONCE
THIS OCCURS, ENZYME IS PERMANENTLY INACTIVATED AND RESTORATION OF
ACETYLCHOLINESTERASE ACTIVITY REQUIRES SYNTHESIS OF NEW ENZYME MOLECULES.
• ACTION- GENERALIZED CHOLINERGIC STIMULATION .
• TH. USE- USED TO TREAT OPEN ANGLE GLAUCOMA ; POTENTIAL RISK OF CONTRACT LIMITS
USE OF GLAUCOMA.
• ADVERSE EFFECT – PARALYSIS OF MOTOR FUNCTION [CAUSING BREATHING DIFFICULTIES] AND
14. MYASTHENIA GRAVIS
• IT IS AN AUTOIMMUNE NEUROMUSCULAR DISORDER , IN WHICH WEAKNESS IS
CAUSED BY CIRCULATING ANTIBODIES.
• ANTIBODIES BLOCK ACH RECEPTOR AT POST SYNAPTIC NEUROMUSCULAR
JUNCTION , INHIBITING THE STIMULATIVE EFFECT OF N.T. ACH.
15. SIGNS AND SYMPTOMS
• - WEAKNESS IN ARMS, LEGS, NECK
• - CHANGE IN FACIAL EXPRESSION
• - DYSPHAGIA [ DIFFICULTY IN SWALLOWING ]
• - DOUBLE VISION
• - SHORTNESS OF BREATH
• - IMPAIRED SPEECH
16. CAUSES
• - CAUSED BY DEFECT IN TRANSMISSION OF NERVE IMPULSE TO MUSCLES ,
OCCURS WHEN NORMAL COMMUNICATION BETWEEN NERVE AND MUSCLE IS
INTRUPTED AT THE NEUROMUSCULAR JUNCTION.
• - IN MYASTHENIA GRAVIS , ANTIBODIES BLOCK ACH RECEPTOR AT POST
SYNAPTIC NEUROMUSCULAR JUNCTION , INHIBITING THE STIMULATIVE EFFECT
OF ACH.
• - MYASTHENIA GRAVIS IS AN AUTO IMMUNE DISEASE BECAUSE THE IMMUNE
SYSTEM MISTAKENLY ATTACK ITSELF.
17.
18.
19. TREATMENT
- TREATMENT IS BY MEDICATION /SURGERY.
- MEDICATION CONSISTS-
CHOLINESTERASE INHIBITOR TO MUSCLE FUNCTION
IMMUNOSUPPRESSANT DRUGS TO REDUCE AUTOIMMUNE PROCESS
- THYMECTOMY IS A SURGICAL METHOD TO TREAT MG.
- FOR EMERGENCY TREATMENT, PLASMAPHERESIS OR IVIG CAN BE USED AS TO
REMOVE
ANTIBODIES FROM THE BLOOD CIRCULATION.
20. REFERENCES
• HTTPS://WWW.SLIDESHARE.NET/UDDENT/3CHOLINERGIC-DRUGS
• TRIPATHI K. D. , ‘ESSENTIAL OF MEDICAL PHARMACOLOGY’ 6TH EDITION 96-
105
• HTTP://MYASTHENIAGRAVIS.CO.ZA/ABOUT.HTML
• ://SIMPLIFASTER.COM/HTTPSARTICLES/AUTONOMIC-NERVOUS-SYSTEM/
• HTTP://WWW.THEMEDNOTE.COM/2011/08/15/CHOLINERGIC-RECEPTORS/
