PARASYMPATHOMIMETICS (Cholinomimetics)
This group of drugs produces pharmacological effects similar to that produced by parasympathetic stimulation
Classification
1- DIRECTLY ACTING PARASYMPATHOMIMETICS They directly stimulate the cholinergic receptors.
- Acetylcholine.
- Carbachol.
- Bethanechol
- Methacholine
- Pilocarpine.
2- INDIRECTLY ACTING PARASYMPATHOMIMETICS (CHOLINE ESTERASE INHIBITORS) They inhibit cholineesterase enzymes leading to accumulation of A.ch at the receptor sites which in turn produces the cholinergic effects on (CNS, NMJ, Ganglia, wall of blood vessels… etc.).
A. Reversible cholineesterase inhibitors.
- Physostigmine
- Neostigmine (Prostigmine) and its substitutes.
- Tacrine
- Donepezil  B. Irreversible cholineesterase inhibitors. (ORGANOPHOSPHOROUS COMPOUNDS)
- Nerve gases: Sarin, Soman.
- Insect killers: Malathion, Parathion, TEPP (tetraethylpyrophosphate)
- Drugs used clinically: DFP (Diisopropyl flurophosphate)
Cholinesterase re-activators (oximes)
PARASYMPATHOLYTICS (Muscarinic antagonists)
NEUROMUSCULAR BLOCKING AGENTS
| Myasthenic crisis | Cholinergic crisis | |
|---|---|---|
| Cause | Deficient cholinergic transmission | Excessive cholinergic transmission e.g. ch. E inhibitor overdosage. |
| Nicotinic manifestations Muscarinic manifestations | Flaccid paralysis. No | Spastic paralysis. Weakness in cholinergic crisis is due to permanent depolarization of nicotinic receptors at motor end plate. ↓ H.R. – ↓ B.P. – Miosis – Colic – sweating. |
| Edrophonium test | Improves | Aggrevates. |
| Treatment | *Edrophonium or Neostigmine + Atropine. *Artificial respiration | 1-PAM (pralidoxime)+ Atropine 2. Artificial respiration 3. Stop causative drug |