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Parasympathomimetic Drugs- Everything You Need To Know

Parasympathomimetic drugs also called as cholinomimetic or cholinergic drugs, these are actually the drugs which produce effects same as those produced by the incitement of parasympathetic nervous system on the particular organs.

Neurotransmitter contains acetylcholine. Most of the peripheral autonomic nervous system fibers produce the secretion that cause synthesis and release of acetylcholine. However, results in activation of the parasympathomimetic system, thus named as cholinergic fibers.

All preganglionic and some parasympathomimetic postganglionic with postganglionic sympathetic fibers, adrenal medulla and skeletal somatic muscle fibers compose the cholinergic fibers.

Parasympathomimetics were found from an alkaline muscarine alkaloid that took from natural resource, which produces effects by affecting target organs akin to parasympathetic system, and these receptors are termed as muscarinic receptors.

Muscarinic receptors basically are membrane-bound proteins having an extracellular domain that composes a recognition chemical site for acetylcholine (ACh); combination of Ach along with the receptor start off a physiologic change like, slowing of heart beat, increased glandular secretory activity etc. Muscarinic receptors are to be distinguished from nicotinic receptors.

While, nicotine was found to act on skeletal muscle and autonomic ganglia, such receptors were called nicotinic. Later, it was further enhanced by Dale.

Contents

Parasympathomimetic Drugs Classification:

They are classified as into two types:

  • Direct-acting parasympathomimetic agents.
  • Indirect-acting parasympathomimetic agents.

parasympathomimetic drugs

Direct-acting Parasympathomimetic agents:

Choline Esters:

  1. Acetylcholine.
  2. Carbachol.
  3. Methacholine.
  4. Bethanechol.

Cholinomimetic Alkaloids:

  1. Muscarine.
  2. Pilocarpine.
  3. Arecholine.
  4. Oxotramorine.
  5. Cevimeline.
  6. Nicotine.
  7. Lobeline.
  8. Dimethyl phenyl piperazinium (DMPP).
  9. Varenicline.

Tertiary alkaloids:

  1. Pilocarpine.
  2. Nicotine.
  3. Lobeline.

Quaternary amines:

  1. Muscarine.

Indirect-acting parasympathomimetic agents:

Reversible:

  1. Carbamates.
  2. Alcohols.

Irreversible:

  1. Therapeutically useful.
  2. War Gases.
  3. Insecticides.

Parasympathomimetic side effects:

Pilocarpine, a parasympathomimetic drug utilized in the analysis of glaucoma, produces a different ocular and systemic adverse chemical reactions. Ocular side effects composes meiosis, frontal headaches, twitching lids, conjunctival injection, cataractous alternates, allergic chemical reactions, iris cysts, retinal separation, increased permeability of the blood-aqueous barrier, anterior chamber narrowing, and the potential for incorporating an acute angle-closure attack respectively. However, the Systemic side effects incorporating nausea, vomiting, tenesmus, abdominal spasm, salivation, lacrimation, sweating, pulmonary edema, and bronchial spasm. The systemic side effects can be controlled before through proper utilization of the medication and as well nasolacrimal occlusion. The Ocusert, a prolong-acting pilocarpine-included ocular insert, is a recent advance in delivery technique that gives an sufficient hypotensive action with minute side effects. Pilopex is a brand new exploratory pilocarpine polymer brine salt shortly being examined in Israel. Photomydriasis, a procedure including the utilization of a laser to extend miotic understudies and additionally gives assistance for these patients. N-demethylated carbachol is another parasympathomimetic medication as of now under study for glaucoma treatment. Beginning results demonstrate that it might have significant visual hypotensive activity with less unfriendly impacts.

Additional knowledge:

What is the action of Direct-acting parasympathomimetic agents?

React with muscarinic receptors directly; mimic action of acetylcholine as agonists.

What are the long-acting synthetic derivatives of acetylcholine?

Bethanechol +, (methacholine +, carbachol +).

What is pilocarpine?

Naturally occurring alkaloids that are direct-acting parasympathomimetic agents.

What is the basic action of Indirect-acting parasympathomimetic agents?

Inhibit acetylcholinesterase by binding to its anionic/esteratic site, site, thus protecting from destruction of acetylcholine, increase synaptic levels of Ach, stimulate more receptors and prolong and intensify Ach effects on cholinergic receptors.

What affect does irreversible anticholinesterases have?

New acetylcholinesterase must be synthesized for activity to recover and having long side effects.

What type of component is irreversible anticholinesterases?

Organophosphorous components/organophosphates are basically those substances.

What are the routes of parasympathomimetic agents?

Oral, SC, topical, and many other routes.

How are substances with positive charge absorbed?

Substance with a positive charge shows erratic absorption from GI-tract and could not cross BBB..

Are Organophosphorous compounds well absorbed from skin?

Absolutely Yes! They can absorbed well from the skin.

What is the pharmacological affect of parasympathomimetic drugs in lungs (M)?

The very first is Bronchoconstriction, whilst the second one is decrease in airflow.

What is the pharmacological affect of parasympathomimetic drugs in Heart (M)?

These are following causes; decreased rate, contractility, conductance and slight decrease in blood pressure.

What is the pharmacological affect of parasympathomimetic drugs in Eyes (M)?

Well this is probably cause due to, constriction of pupil (miosis) and constriction of ciliary muscle.

What is the pharmacological affect of parasympathomimetic drugs in Glands (M)?

However, in this case it is most cause because of stimulation of secretion.

What is the pharmacological affect of parasympathomimetic drugs in CNS (M,N)?

Stimulation and/or inhibition, and slight boost in cognition.

What happens when there is an overdose of parasympathomimetic drugs?

These are full complete list that are, bradycardia, hypotension, dyspnea, skeletal muscle and respiratory paralysis and you know it is so awful for human body.

How does PAM work?

It has a function to remove covalently bound organophosphorous component from active-site of enzymes.

What happens in GI or GU atony and why?

This is because when after the surgery of intestines or gall bladder result in becoming of atonic and stimulation of muscarinic receptors restores activity (bethanechol).

How is open angle glaucoma corrected?

This can happens because of the stimulation of M receptors on ciliary body contracts ciliary body, pulls on longitudinal structures attached to trabecular meshwork and boosts the outflow with reduction in IOP (pilocarpine).

What complete action occur during erection?

During sexual anxious, muscarinic receptors are stimulated resulting cGMP formation and vessel dilation in the penis.

What do few drugs like sildenafil do to treat erectile dysfunction?

This is occur by the cause of Block PD, PD, long term chemical action of cGMP (catalyst) and occurs long lasting vasodilation with enhanced and longer erection.

How can adrenal medulla stimulate neuromuscular junction along with Ganglionic agonists?

They bind to Nn receptor at the adrenal medulla (Nn) and stimulate EPI, which create a bond to the Nm receptor at neuromuscular junction and increase muscle activity.

What are the actions of autonomic ganglia stimulation?

Pupillary and ciliary body constriction, bradycardia, decreased airflow, increased GI/GU activity, sweating (all parasympathetic) and blood vessel constriction (sympathetic).

What is the action of high dose of nicotine?

Nausea, salivation, vomiting, increase followed by decrease in blood pressure, irregular heart rate, blurred vision, severe diarrhea, urination, sweating, confusion, muscular weakness, paralysis, confusion, respiratory failure, death.

Hi, This is Hamza Khan from Peshawar, Pakistan. I am a 2nd prof MBBS Student at Bannu Medical College and a hobby Blogger. The Purpose of this site is to share my knowledge and Guide new Medical Students.

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