Cholinergic Drugs (cholinomimetics)
Cholinergic drugs, also known as cholinomimetics, mimic the effects of acetylcholine and stimulate the parasympathetic nervous system. These drugs can be classified into two main categories: direct-acting and indirect-acting cholinergic agonists.
- 1. Classification of Cholinergic Drugs
1.1 Direct-Acting Cholinergic Agonists
- Mechanism: Directly stimulate cholinergic receptors (muscarinic and nicotinic).
- Examples:
- Acetylcholine
- Bethanechol
- Carbachol
- Pilocarpine
1.2 Indirect-Acting Cholinergic Agonists
- Mechanism: Increase acetylcholine concentration by inhibiting acetylcholinesterase (AChE).
- Reversible Inhibitors:
- Neostigmine, Pyridostigmine, Physostigmine
- Donepezil, Rivastigmine
- Irreversible Inhibitors:
- Nerve gases, Organophosphates
Pharmacodynamics of Cholinergic Drugs
2.1 Direct Cholinomimetics
- Mechanism: Act by directly stimulating muscarinic and nicotinic receptors.
- Physiological Effects:
- M2 receptors (heart): Decrease heart rate (negative chronotropic effect) and contractility (negative inotropic effect).
- M3 receptors (GI tract, eye, and lungs):
- Increase gastrointestinal motility and secretion.
- Bronchoconstriction and increased bronchial secretions.
- Miosis (pupil constriction) and accommodation in the eye.
- Relaxation of sphincters.
2.2 Indirect Cholinomimetics
- Mechanism: Increase acetylcholine levels by inhibiting AChE.
- Effects: Enhance cholinergic transmission, improving conditions like myasthenia gravis and Alzheimer’s disease.