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Autonomic Nervous System
Lecture 2
Cholinergic Drugs
Parasympathetic Nervous System
• Works to save energy, aids in digestion,
and supports restorative, resting body
functions...
Body Responses – “rest and digest”
• Dilation of blood vessels in skin
• Decrease heart rate (bradycardia)
• Increase secr...
Cholinergic Receptors
M1 Secretory glands salivation, stomach acid,
sweating, lacrimation
M2 Heart Decreases heart rate 
...
Cholinergic Drugs
• Often called parasympathomimetic drugs, because
their action mimics the action of the PSNS.
• Also cal...
Direct acting cholinergic agonist
• They act by binding directly to cholinoceptors. Direct acting
cholinergics are lipid i...
Drug Effects of Cholinergic Agents
• Cardiovascular effects
– Decreased heart rate( Bradycardia)
– Vasodilation (NO mediat...
Drug Effects of Cholinergic Agents
• Stimulate pupil
– Constriction (miosis), Spasm of accomodation
– Reduced intraocular ...
Drug Effects of Cholinergic Agents
“MSLUBDD”
Many Smart Ladies Ultimately Bring Disaster for
Dudes!
Miosis
Salivation
Lacr...
Acetylcholine
• One of the main neurotransmitters of the ANS is
acetylcholine
• Acetylcholine is released at preganglionic...
Bethanechol
• Not hydrolyzed by acetylcholinesterases
• Actions
• Directly stimulates M receptors causing increased
intest...
Pilocarpine
An alkaloid, lipid soluble & is stable to hydrolysis
by cholinsterases.
Actions:
When applied locally to corne...
Indirect acting Cholinergic agonists
• They act through inhibition of Acetyl cholinesterase
enzyme, so increases Acetylcho...
• Reversible: Irreversible:
• Neostigmine Organophosphates
• Physostigmine Dyflos,
Echothiopate
• Pyridostigmine Parathion...
• Physostigmine - only anticholinesterase
capable of crossing the blood brain barrier. Is
more lipid soluble. Used as an a...
• Neostigmine - prototype anticholinesterase agent.
Used for long-term treatment of myasthenia gravis
and as an antidote f...
Uses of Indirect Cholinergic agonists
• Glaucoma – Pilocarpine, Physostigmine
• Edrophonium to test Myasthenia gravis,
Neo...
• Cobra bite – edrophonium (prevent respiratory
paralysis.
• atropine poisoning – Physostigmine
(antogonizes both central ...
Cholinergic Agents: Side Effects
Side effects are a result of overstimulation
of the PSNS.
• Cardiovascular:
– Bradycardia...
Cholinergic Agents: Side Effects
• Respiratory:
–Increased bronchial secretions,
bronchospasms
• Other:
–Lacrimation, swea...
Acute toxic effects of irreversible
cholinesterase inhibitors (OP poisoning )
• These agents are lipid soluble
• Can enter...
• Cholinergic crisis occurs because the
irreversible anticholinesterase poison binds to
the enzyme acetylcholinesterase an...
Treatment of OP poisoning
Emergency treatment includes:
• Decontamination of clothing
• Flushing poison from skin and eyes...
• To relieve the neuromuscular blockade by
nicotinic effects, give pralidoxime, a
cholinesterase reactivator.
• Pralidoxim...
Thank you!
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Cholinergic drugs

  1. 1. Autonomic Nervous System Lecture 2 Cholinergic Drugs
  2. 2. Parasympathetic Nervous System • Works to save energy, aids in digestion, and supports restorative, resting body functions. –Decrease in heart rate –Increased gastro intestinal tract tone and peristalsis –Urinary sphincter relaxation –Vasodilation – decrease in blood pressure
  3. 3. Body Responses – “rest and digest” • Dilation of blood vessels in skin • Decrease heart rate (bradycardia) • Increase secretion of digestive enzymes • Constriction of smooth muscle of bronchi • Increase in sweat glands - cooling • Contraction of smooth muscles of urinary bladder • Contraction of smooth muscle of skeletal system
  4. 4. Cholinergic Receptors M1 Secretory glands salivation, stomach acid, sweating, lacrimation M2 Heart Decreases heart rate  bradycardia M3 Smooth muscle (GI/GU/Resp) Contraction of smooth muscles (some)  diarrhea, bronchospasm, urination M3 Pupil and ciliary muscle Contracts  Miosis Increased flow of aqueous humor Nm Skeletal muscle end plate Contraction of skeletal muscle Nn Autonomic ganglia, Adrenal Medulla Secretion of Epinephrine Controls ANS
  5. 5. Cholinergic Drugs • Often called parasympathomimetic drugs, because their action mimics the action of the PSNS. • Also called as cholinomimetic. • Stimulate parasympathetic nervous system in same manner as does acetylcholine • May stimulate cholinergic receptors directly or slow acetylcholine metabolism at synapses (affect the enzyme acetylcholinesterase) • Cholinergic agonists are two types : 1.Direct acting 2.Indirect acting
  6. 6. Direct acting cholinergic agonist • They act by binding directly to cholinoceptors. Direct acting cholinergics are lipid insoluble. • Do not readily enter the CNS so effects are peripheral. • Resistant to metabolism by acetylcholinesterase. • Effects are longer acting than with acetylcholine. • Acetylcholine • Methacholine Muscarine • Carbachol Pilocarpine • Bethanechol Arecoline
  7. 7. Drug Effects of Cholinergic Agents • Cardiovascular effects – Decreased heart rate( Bradycardia) – Vasodilation (NO mediated) • Stimulate intestine and bladder – Increased gastric secretions – Increased gastrointestinal motility – Increased urinary frequency
  8. 8. Drug Effects of Cholinergic Agents • Stimulate pupil – Constriction (miosis), Spasm of accomodation – Reduced intraocular pressure (increased outflow) • Respiratory effects – Bronchial constriction, narrowed airways • Increased salivation and sweating
  9. 9. Drug Effects of Cholinergic Agents “MSLUBDD” Many Smart Ladies Ultimately Bring Disaster for Dudes! Miosis Salivation Lacrimation Urination Bronchoconstriction Defaecation Decreased heart rate
  10. 10. Acetylcholine • One of the main neurotransmitters of the ANS is acetylcholine • Acetylcholine is released at preganglionic fibers of both the sympathetic and parasympathetic nervous system • Also released from postganglionic sympathetic neurons that innervate the sweat glands and from motor neurons that innervate the skeletal muscles • It is a quaternary ammonium compound so cannot penetrate the membrane. • Does not have any therapeutic importance, because rapid inactivation by acetylcholinesterases. • It has both Muscarinic & Nicotinic actions .
  11. 11. Bethanechol • Not hydrolyzed by acetylcholinesterases • Actions • Directly stimulates M receptors causing increased intestinal motility & tone • It stimulates detrusor muscle of the bladder while trigone & sphincters are relaxed causing expulsion of urine • Therapeutic Uses: • Paralytic ileus • Urinary retentions • Helpful for postsurgical atony of the bladder and GI tract
  12. 12. Pilocarpine An alkaloid, lipid soluble & is stable to hydrolysis by cholinsterases. Actions: When applied locally to cornea Produces rapid miosis & contraction of ciliary muscle produces spasm of accommodation & vision is fixed at particular distance making it impossible to focus for far situated objects Therapeutic Use : In Glaucoma it opens trabecular meshwork around schlemm’s canal • causes drainage of aqueous humor • IOP immediately decreases.
  13. 13. Indirect acting Cholinergic agonists • They act through inhibition of Acetyl cholinesterase enzyme, so increases Acetylcholine level in the synapse. • Accumulation of acetylcholine then occurs which enhances the activation of the nicotinic and muscarinic receptors. • Anticholinesterase drugs are either reversible or irreversible inhibitors of acetylcholinesterase
  14. 14. • Reversible: Irreversible: • Neostigmine Organophosphates • Physostigmine Dyflos, Echothiopate • Pyridostigmine Parathion, Malathion • Edrophonium Tabun, Sarin, Soman • Tacrine Carbamates • Donepezil Carbaryl, Propoxur(baygon)
  15. 15. • Physostigmine - only anticholinesterase capable of crossing the blood brain barrier. Is more lipid soluble. Used as an antidote for overdosage of anticholinergics such as: atropine, antihistamines, TCA, phenothiazines. May also be used in treatment of glaucoma. • Pyridostigmine - is the maintenance drug of choice for patients with Myasthenia gravis.
  16. 16. • Neostigmine - prototype anticholinesterase agent. Used for long-term treatment of myasthenia gravis and as an antidote for tubocurarine and other non- depolarizing agents in surgery. • Donepezil - • Used in the treatment of mild to moderate Alzheimer’s disease. • Helps to increase or maintain memory and learning capabilities.
  17. 17. Uses of Indirect Cholinergic agonists • Glaucoma – Pilocarpine, Physostigmine • Edrophonium to test Myasthenia gravis, Neostigmine and pyridostigmine in treatment of M.gravis. • Postoperative paralytic ileus - Neostigmine • Postoperative decurarization – Neostigmine(reverses muscle paralysis)
  18. 18. • Cobra bite – edrophonium (prevent respiratory paralysis. • atropine poisoning – Physostigmine (antogonizes both central and peripheral effects). • Alzheimer’s Disease – Donepezil, galantamine, tacrine, rivastigmine. • TCA, Phenothiazines, overdose – Physostigmine.
  19. 19. Cholinergic Agents: Side Effects Side effects are a result of overstimulation of the PSNS. • Cardiovascular: – Bradycardia, hypotension, conduction abnormalities (AV block and cardiac arrest) • CNS: – Headache, dizziness, convulsions • Gastrointestinal: – Abdominal cramps, increased secretions, nausea, vomiting
  20. 20. Cholinergic Agents: Side Effects • Respiratory: –Increased bronchial secretions, bronchospasms • Other: –Lacrimation, sweating, salivation, loss of binocular accommodation, miosis
  21. 21. Acute toxic effects of irreversible cholinesterase inhibitors (OP poisoning ) • These agents are lipid soluble • Can enter the body by the eye,skin, respiratory system and GI tract. • organophosphate insecticides (malathion, parathion) or nerve gases (sarin, tabun, soman) • These agents cause excessive cholinergic stimulation (muscarinic) and neuromuscular blockade
  22. 22. • Cholinergic crisis occurs because the irreversible anticholinesterase poison binds to the enzyme acetylcholinesterase and inactivates it. Thus, acetylcholine remains in cholinergic synapses causing excessive stimulation of muscarinic and nicotinic receptors.
  23. 23. Treatment of OP poisoning Emergency treatment includes: • Decontamination of clothing • Flushing poison from skin and eyes • Activated charcoal and lavage for GI ingestion • Atropine to counteract the muscarinic effects (2mg IV every 10 min till pupil dilates, max 50-100mg)
  24. 24. • To relieve the neuromuscular blockade by nicotinic effects, give pralidoxime, a cholinesterase reactivator. • Pralidoxime causes the anticholinesterase poison to release the enzyme acetylcholinesterase. • Give Pralidoxime as soon as possible as if too much time passes, the poison bond becomes too strong (aging) for the pralidoxime to work. • Other oximes- obidoxime, diacetylmonoxime
  25. 25. Thank you!
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Cholinergic drugs and their pharmacology.

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