Cholinergic Antagonists: Relation of mechanisms of action to clinical response

• Central nervous system

  • Scopolamine used for preventing motion sickness by inhibitory effect on the vestibular apparatus

  • Treatment of Parkinson’s disease using muscarinic antagonists supplanted by L-dopa + peripheral decarboxylase inhibitors

  • Alzheimer’s disease: due to loss of cholinergic neurons, use cholinesterase inhibitors for tx

• Ophthalmology

  • Glaucoma: due to high intraocular pressure may result in blindness by damaging the optic nerve and retina

  • Closed angle glaucoma: pupillary constriction lowers the intraocular pressure by pulling the iris away from the trabeculum and opening the angle. Use cholinomimetics for tx

  • Open angle glaucoma: tx with cholinomimetics, carbonic anhydrase inhibitors, B-blockers, and epinephrine

  • Cholinomimetics most often used is prilocarpine

• Gastrointerstinal and urinary tracts

  • Cholinomimetics used to treat urinary retention and decreased stomach and bowel motility when there is no obstruction and to treat congenital megacolon

  • Muscarinic antagonist for tx of urinary incontinence and diseases characterized by bowel hypermotility

  • Peptic ulcer tx with antacids

• Respiratory tracts

  • Muscarinic antagonists are used for tx of COPD, with an inhaler

• Myasthenia gravis

  • Autoimmune disease with skeletal muscle weakness

  • Cholinesterase inhibitors will amplify the effects of the neuronal released acth making these drugs useful for restoring strength in myasthenic patients

  • Side effects: abdominal cramping and diarrhea

• Hypertensive emergencies

  • Ganglionic blockers used for emergencies ONLY

• Miscellaneous uses of cholinesterase inhibitors

  • Edrophonium will increase the refractory period of AV node, decreases the nodal conduction velocity and restores normal sinus rhythm

Category: Pharmacology Notes