Parasympathomimetics PDF

Prasympathomimetics By Ghada Adel  Ach not used clinically because: GR 1- short duration of action 2- lack of selectivity  Postoperativeretention of urine and paralytic ileus in absence of mechanical obstruction e.g. bethanechol, carbachol.  Glaucoma e.g. carbachol , betha...

Prasympathomimetics By Ghada Adel  Ach not used clinically because: GR 1- short duration of action 2- lack of selectivity  Postoperativeretention of urine and paralytic ileus in absence of mechanical obstruction e.g. bethanechol, carbachol.  Glaucoma e.g. carbachol , bethanechol ( eye drops).  Vasodilator in treatment of peripheral vascular diseases e.g. methacholine.  Relief of attacks of paroxysmal atrial tachycardia e.g. methacholine. Adverse effects:  Nausea, vomiting, diarrhea  sweating, salivation, colic, involuntary urination and defecation, bronchial constriction ,decreased blood pressure (M3)  bradycardia (M2)  NATURALLY OCCURRING ALKALOIDS (PILOCARPINE)  Muscarinic action ; no nicotinic  Specific action on eye but no eye lid twitches (no nicotinic action) :GR  Increase salivary and sweat secretions Uses:  Glucoma  Promotes hair growth  INDIRECT ACTING CHOLINOMIMETICS A-Reversible anticholinesterase. 1- Short-acting anticholinesterase: duration of action 5-10 min e.g. Edrophonium. 2- Medium-duration anticholinesterase: duration of action 2-6 hours e.g. physostigmine, neostigmine , donepezil. B- Irreversible anticholinesterase (organophosphates): duration of action days-weeks e.g di- isopropyl-fluorophosphate (DFP). Differences between Physostigmine and Neostigmine Physostigmine Neostigmine Source Natural alkaloid Synthetic Oral absorption Good Poor CNS action Present Absent Direct action on muscular Absent Present nicotinic receptors Prominent effect on Autonomic effectors Skeletal muscle Important use Miotic Myasthenia gravis Systemic:4-6 hrs Duration of action 3-4 hrs In eye:6-24 hrs