Dr. Asmaa Fady's Academic Background Quiz

Indirect Cholinergic Drugs

• Cholinergic drugs mimic or enhance the effects of acetylcholine (ACh), a neurotransmitter.

• Indirect cholinergic drugs, also called anticholinesterases, work by inhibiting the enzyme acetylcholinesterase, preventing the breakdown of ACh. This results in increased ACh concentrations and subsequent stimulation of cholinergic receptors.

• Anticholinesterases have various actions, including muscarinic and nicotinic actions, as well as potential effects in the central nervous system (CNS).

Learning Objectives

• Students should be able to classify indirect-acting cholinomimetics.

• Describe the mechanism of action, kinetics, dynamics, and applications of anticholinesterases.

• Identify the main side effects and contraindications of anticholinesterases.

• Describe organophosphate toxicity's symptoms and treatment.

• Identify the key side effects of direct cholinomimetics.

Classification

• Cholinergic agonists are categorized into direct-acting and indirect-acting.

• Direct-acting agonists directly stimulate cholinergic receptors.

• Indirect-acting agonists work by inhibiting acetylcholinesterase.

• Anticholinesterases are further classified as reversible or irreversible.

Indirect Cholinergic Drugs (Anticholinesterases)

• Anticholinesterases structurally resemble ACh.

• They bind to cholinesterase instead of ACh.

• Mechanism of Action: Anticholinesterases stop ACh hydrolysis by the cholinesterase inhibiting the enzyme, thus resulting in increased ACh concentrations and actions on cholinergic receptors.

• Anticholinesterase effects occur at muscarinic and nicotinic receptors, and in the neuro muscular junction and CNS.

Anticholinesterases: Reversible Agents

• Short-Acting: Alcohol, Edrophonium

• Intermediate-Acting: Carbamate esters (Physostigmine, Neostigmine, Pyridostigmine, Ambenonium)

Anticholinesterases: Irreversible Agents

• Very Long-Acting: Phosphate esters (Isoflurophate, Ecothiophate)

Pharmacological Actions of Indirect Cholinergic Drugs

• All anticholinesterases have muscarinic and nicotinic effects.

• Some anticholinesterases can affect the CNS, but only those that are lipid-soluble.

Muscarinic Actions

• Eye: Miosis, contraction of ciliary muscles
• Heart: Bradycardia, NO release, vasodilation
• Lung: Bronchial constriction, increased secretions
• Gastrointestinal (GI) Tract: Increased motility, sphincter relaxation, increased secretions
• Urinary Bladder: Contraction of muscles, sphincter relaxation
• Exocrine Glands: Increased secretions (sweat, saliva, tears, etc.)

Nicotinic Actions

• Neuromuscular junction: Therapeutic dose causes muscle contraction; toxic dose causes paralysis. This action is at the neuro muscular junction
• Ganglia: Stimulates both sympathetic and parasympathetic ganglia.
• Adrenal medulla: Causes catecholamine release (epinephrine and norepinephrine).

Reversible Anticholinesterase Agents: Details

• Edrophonium: Short-acting, primarily peripheral action, used for diagnosing myasthenia gravis.

• Physostigmine: Intermediate-acting, penetrates CNS, used for glaucoma and reversing anticholinergic toxicity.

• Neostigmine: Intermediate-acting, doesn't penetrate CNS, used for myasthenia gravis.

Adverse Effects of Anticholinesterases

• Parasympathetic excess: Sweating, salivation, flushing, diaphoresis, nausea, abdominal pain, diarrhea, urinary urgency, decreased BP, bradycardia, bronchospasm.

Organophosphate Toxicity

• Highly toxic compounds, including nerve gases and insecticides.

• Irreversible inhibition of acetylcholinesterase.

• Muscarinic and nicotinic effects similar to those of anticholinesterases, leading to the increased concentration of ACh

• CNS effects include headache, dizziness, tremor, restlessness, anxiety, confusion, convulsions, coma.

Treatment of Organophosphate Toxicity

• Supportive measures (maintaining respiration).
• Atropine: Blocks muscarinic receptors.
• Pralidoxime (2-PAM): Reverses the effects of organophosphates (if given before aging of enzyme)

Summary Table of Anticholinesterase Agents

(Refer to provided table for specific details on these agents).

Summary of Other Information

• Donepezil: Used in Alzheimer's disease; primarily CNS action. GI distress is a side effect.

• Key drugs for various conditions (e.g., glaucoma, myasthenia gravis, Alzheimer's disease) are detailed in the provided summary tables.

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