Anesthesia Pharmacology: Autonomic Pharmacology: Cholinergic Drugs

 

• Clinical Applications of Cholinergic Receptor Blockers

  • Anticholinergic Drugs -- Anesthesia Applications/Issues

    • Overview:

    • Preoperative medication

    • Management of reflex bradycardia

    • Use in antagonism of nondepolarizing neuromuscular-blocking agents

  • Common Applications-- anesthesia related (anticholinergic agents)

    • Preoperative medications

    • Management of reflex bradycardia

    • Combinations with anticholinesterase agents during pharmacological antagonism of nondepolarizing neuromuscular-blocking agents

  • Other Applications of anticholinergic drugs:

    1. Bronchodilation (e.g.,asthma)

    2. Biliary/ureteral smooth muscle relaxation

    3. Causing mydriasis/cycloplegia

    4. Inhibition of parietal cells acid secretion

    5. Prevention of motion sickness (nausea)

    6. Component in cold remedies

  • Central Nervous System Effects of Antimuscarinic Agents

    • In normal doses, atropine produces little CNS effect.

      • In toxic doses, CNS excitation results in restlessness, hallucinations, and disorientation.

    • At very high doses, atropine can lead to CNS depression which causes circulatory and respiratory collapse.

    • By contrast, scopolamine at normal therapeutic doses causes CNS depression, including drowsiness, fatigue and amnesia.

      • Scopolamine also may produce euphoria, a basis for some abuse potential.

    • Scopolamine may exhibit more CNS activity than atropine because scopolamine crosses the blood brain barrier more readily.

    • Antimuscarinics are used clinically as preanesthetic medication to reduce vagal effects secondary to visceral manipulation during surgery.

      • Antimuscarinics with L-DOPA are used in Parkinson's disease.

    • Extrapyramidal effects induced by some antipsychotic drugs may be treated with antimuscarinic agents.

    • Scopolamine (transdermal) is effective in preventing motion sickness.

    •  Atropine is also an effective antidote to excessive cholinergic stimulation following organophosphate intoxication.

      • By blocking muscarinic receptors, the consequences of cholinesterase inhibition is attentuated.

      • Atropine may be used in conjunction with 2-PAM which may reactivate phosphorylated, inhibited acetylcholinesterase by nucleophilic displacement.

Taylor, P. Agents Acting at the Neuromuscular Junction and Autonomic Ganglia In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, pp.193-195. Adapted from Table 9-3.