Cholinergic Drugs – Pharmacology B. Pharma 5th Semester PDF Notes

Cholinergic Drugs

Cholinergic-Drugs

Content

ANS

     Cholinergic drugs

     Pharmacology of acetylcholine

     Organophosphorous poisoning and its treatment

Intended Learning Outcomes

At the end of this lecture, student will be able to

     List the cholinergic drugs

     Explain the pharmacology of acetylcholine

     Describe pharmacokinetic of Ach

     Explain organophosphorus poisoning

     Describe treatment of poisoning

Cholinergic Drugs (Parasympathomimetics)

     + effector cells innervated by cholinergic nerves

     Ester of choline

    Acetylcholine, methacholine, carbachol, bethanechol

     Cholinomimetic alkaloids

    Pilocarpine, muscarine, arecholine

     Choline esterase inhibitors (Anticholine esterase)

    Physostigmine, neostigmine, organophosphorus compounds

Pharmacological Actions of Acetylcholine

CVS

     Heart

    + vagus nerve

    Depress SA Node: negative chronotropic

    Decrease FOC:  negative Inotropic

    May cause AV block

    Increase CV

     Blood vessels

    Dilate skin, mucous membrane blood vessels

    M3 – R: release NO

    Dilates coronary arteries

    Doubtful effect: cerebral, pulmonary vessels

    IV: transient flushing, sense of warmth in skin, throbbing headache

    Decrease PR – BP Falls

Smooth muscle

       GIT: increase tone and peristalsis

       Gall bladder: Contraction

       Bladder: Detrusor muscle contraction, trigonal sphincter relaxation

       Bronchial smooth muscle: constriction, bronchospasm

       Ureter: usually contraction

       Uterus: inconsistent response

Secretions

       Increase gastric, intestinal, pancreatic, bronchial, salivary, lacrimal, nasopharyngeal

       Increase bronchial secretion: accompanied by bronchospasm

       May result in cough and dyspnea

       Salivary: profuse and watery

       Sweat glands: increase sweating

Eye

       Instillation – no effect

       Intracarotid injection: miosis

       Contraction of circular muscle fibers

       Decrease IOP

       Increase the drainage of ocular fluid through canal of Schlemm

       Contraction of ciliary muscle

       Relaxation of suspensory ligaments

       Lens bulge into the anterior chamber

       Increase thickness, decrease focal length

       Vision fixed for short-distance

       Spasm of accommodation

Autonomic ganglia

       Ach+ ganglia

       Post ganglionic site: Increase NA/ Ach

       NA:   BP- Peripheral vasoconstriction

       Large dose: Adrenal medulla +

       Sustained increase in BP

Myoneural Junction

       Contraction of skeletal muscle

       High conc: paralysis by persistent depolarisation

Miscellaneous

       Essential for normal behaviour and cognition

       Does not cross BBB

Uses

       Extreme transient action

       Not used in clinical practice

       Substitutes : Effective orally

       More selective in actions

Cholinergic Drugs

Cholinomimetic alkaloids

       Pilocarpine (P. microphyllus, P. jaborandi)

       Muscarine (Amanita muscaria)

       Arecholine (Areca catechu)

       Cevimeline

      M3 agonist

      Incerase salivary and lacrimal secretion

      Used in dry mouth

Choline esterase inhibitors (Anticholine esterases)

       Inhibits true and peudo choline esterase

       Prevent inactivation of Ach

Reversible choline esterase inhibitors

       Natural: Physostigmine

       Synthetic: Neostigmine, pyridostigmine, ambenonium, demecaium, edrophonium, tacrine, rivastigmine

Irreversible choline esterase inhibitors

       OPC

       Useful: Di isopropyl fluorophosphate, metrifonate, echothiophate

       Insecticides: Fenthion, malathion, sumithion, monocrotophos, octamethyl pyrophosphotetramide

Uses of reversible Anti ChE

       Glaucoma

       For decurarisation, Curare poisoning

       MG

       GIT: Post-operative paralytic ileus

       Urinary retention (Rare)

       AD

       Snake venom poisoning

Irreversible Anti ChE

       Absorbed by all the routes

       Cross BBB

       Glaucoma: echothiophate

       Worm infestation: dichlorvos, dichlorofos (Not used)

       Toxicological importance

OPC Poisoning

Muscarinic effects

       Eyes: Miosis, spasm of accommodation, headache, conjunctival hyperemia

        inhalation: bronchospasm, cough, increased secretions, tightness in the chest

       Ingestion: anorexia, nausea, vomiting, abdominal cramps, tenesmus, and diarrhea

       Severe bronchospasm, pulm. edema – fatal

Nicotinic effects

       Fasciculations, twitching, generalized weakness, depolarisation type paralysis

Central effects

       Giddiness, anxiety, confusion, ataxia, hypotension, respiratory depression, convulsion, coma

       Death – due to respiratory paralysis

Neurotoxic effects

       Demyelination of nerve tracts in CNS & PNS

       Permanent functional derrangements

       Not related to ChE inhibition

       Weakness, fatiguability, twitching, loss of tendon reflexes

Treatment of acute OPC Poisoning

       Remove soiled clothes

       Wash soiled skin/ eyes

       Nurse in prone position

       Clear mouth, throat

       Insert airway/ intubate

       Gastric lavage

       Atropine in sufficient qty.

       ChE activator: Pralidoxime (1-2 g)

       Supportive measures: Oxygen, shock treatment

       Convulsion: Diazepam

       Vigilance for delayed toxicity

       Note: Mouth-to-mouth respiration to be avoided

FAQ

Are Cholinergic Drugs addictive?

Cholinergic Drugs, when used as prescribed by a healthcare professional, are generally not considered addictive. However, like many medications, dependence can develop if they are misused or abused. It’s crucial to follow the recommended dosage and consult with a healthcare provider to minimize the risk of addiction.

Can these medications improve cognitive function in healthy individuals?

While Cholinergic Drugs are primarily prescribed for treating neurological disorders, some individuals may use them off-label in an attempt to enhance cognitive function. The evidence supporting cognitive enhancement in healthy individuals is limited, and the use of these medications for this purpose should be approached with caution. Always consult with a healthcare professional before considering such use.

What are the long-term effects of Cholinergic Drug use?

The long-term effects of Cholinergic Drug use can vary depending on the specific medication and individual factors. In some cases, prolonged use may lead to tolerance or diminishing therapeutic effects. Long-term use should be monitored by a healthcare provider to assess both the benefits and potential risks associated with continued medication.

How quickly do Cholinergic Drugs take effect?

The onset of action for Cholinergic Drugs varies among different medications. Some may act relatively quickly, while others may require more time to exert their effects. It is essential to follow the prescribed dosage and be patient with the treatment process. If there are concerns about the medication’s efficacy, consult with a healthcare professional.

Are there natural alternatives to Cholinergic Drugs for cognitive enhancement?

Yes, several natural alternatives are believed to support cognitive function. These include a healthy diet rich in antioxidants, regular exercise, and sufficient sleep. Additionally, certain supplements like omega-3 fatty acids and vitamins may contribute to cognitive well-being. However, always consult with a healthcare provider before incorporating any supplements into your routine.

Can Cholinergic Drugs be used to treat Alzheimer’s disease?

Cholinergic Drugs, such as acetylcholinesterase inhibitors, are commonly prescribed to manage symptoms of Alzheimer’s disease. These medications aim to enhance acetylcholine levels in the brain, which can temporarily improve cognitive function in individuals with Alzheimer’s. However, they do not cure the disease, and their effects may vary from person to person.

Summary

       Cholinergic drugs stimulate effector cells innervated by cholinergic nerves

       Cholinergic drugs: Ester of choline, Cholinomimetic alkaloids, Choline esterase inhibitors (Anticholine esterase)

       Acetylcholine actions – mostly inhibitory; stimulatory on digestion and exocrine glands

       Pralidoxime is the antidote for OPC poisoning

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