Nursing Pharmacology Chapter 5:  Autonomic Pharmacology: Cholinergic Drugs

 

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 Cholinoceptor-Blocking Drugs

Nursing Implications:  Cholinergic Drugs: Antimuscarinic agents and Bethanechol
  • Anticholinergic (antimuscarinic) antagonists or blockers have many therapeutic applications.

      • Atropine injection:  Kaiser Permanente.
    • With respect to patient assessment prior to administration, one keeps in mind both the range of applications and the need to identify patients who may be at particular risk.

    • For example, the prototypical drug in this category is atropine which may be used for management of:

      • biliary colic

      • intestinal hyperactivity

      • bradycardia,

      • in preanesthetic medication for reduction of secretion and

      • as an antidote for muscarinic agonist poisoning.

    • Some patients should not receive atropine or other similar muscarinic blockers.

      • These patients include those with urinary tract obstruction, tachycardia, and glaucoma.

        • Cautious use in the context of asthma has been suggested.

  • Atropine may be administered by several routes including oral, by intravenous administration, subcutaneously, and by intramuscular administration.

  • Dry mouth associated with muscarinic antagonism may be profound and may even interfere with swallowing.

    • Accordingly, patients may be advised to sip water prior to oral atropine or atropine-like drugs.

    • Dry mouth due to agents with prominent anticholinergic effects is far more substantial than dry mouth occurring in a normal physiological setting.

  • Treatment with atropine or other antimuscarinic agents as well as agents which exhibit substantial anti-muscarinic side effects, such as first-generation tricyclic antidepressants, require awareness of certain prominent adverse effects as well as the advisability of preparing patients for these effects.

    • In the case of dry mouth, also known as xerostomia, patients may benefit by chewing gum, sipping fluids, or sucking hard candy, all of which may provide some relief from dry mouth,  which occurs as a result of reduce salivation.

    • Antimuscarinic drugs may also have effects on vision due to  blockade of the ciliary muscle which results in blurred vision, a reduction in visual acuity.

      • Preparing a patient for this possible side effect is advantageous, allowing the patient to avoid activities made dangerous as a result of decreased visual acuity.

      • Blockade of pupillary muscarinic receptors is effective in inhibiting pupillary constriction, even when the eye is subject to bright light.

      • Visual discomfort in the hospital setting may be reduced by darkening the hospital room; whereas, outside, the patient should be encouraged to wear sunglasses.

  • The patient may also experience, as a result of muscarinic receptor blockade, difficulty in urination, manifest as urinary hesitancy or retention.

    • To mitigate these effects, the patient might be advised to void just before taking the anticholinergic medication.

    • Sometimes in cases with severe urinary retention, catheterization may be needed.

      • Another option might be using a muscarinic agonists, such as bethanechol in order to promote voiding.

  • Whereas muscarinic agonists (e.g. bethanechol) increase intestinal motility, the antimuscarinic agents can cause constipation.

    • The likelihood of constipation can be decreased by increasing both dietary fiber and fluids.

      • However, severe constipation may require the use of laxatives.

  • Muscarinic antagonists also suppressed sweating, which may result in hyperthermia.

    • Patients may be warned of this possible side effect and adjust their behavior to avoid significant exercise in warmer environments.

  • Lastly, since the heart is mainly under parasympathetic (muscarinic) dominance, with the typical effect is slowing, administration of a muscarinic antagonist (muscarinic receptor blocker) would cause an increase in rate.

    • This increase in rate may result in tachycardic condition; accordingly, monitoring of pulse rate is appropriate and significant increases in rate should be reported.

  • The likelihood of adverse drug-drug interactions may be reduced by avoiding concurrent administration of atropine or atropine-like drugs with other agents that exhibit prominent anti-muscarinic side effects.

    • Drugs that exhibit these anti-muscarinic side effects are associated with certain particular drug categories such as:

      • first-generation tricyclic antidepressants

      • phenothiazine-type antipsychotic drugs and

      • first-generation antihistamines (sedating).

  • Overdose toxicities due to with antimuscarinic agents ingestion are associated with varied symptoms including:

    • blurred vision

    • sensitivity to light (photophobia)

    • hyperthermia

    • delirium

    • hallucinations and

    • dry mouth.

    • The skin becomes characteristically hot, dry and flushed and represents an important indication in acute toxicity.

    • Furthermore, toxicity due to antimuscarinic receptor blockade must be discriminated from psychosis.

    • The treatment of acute overdose toxicity depends on two approaches.

      • The first approach emphasizes limiting absorption of ingested antimuscarinic drug, perhaps by administering an absorbent, such as activated charcoal into the stomach.

      • The second approach is based on increasing the concentration of the neurotransmitter acetylcholine which can overcome the muscarinic receptor blockade.

        • Increased acetylcholine synaptic concentration may be accomplished by inhibiting the activity of acetylcholinesterase, an enzyme which degrades acetylcholine.

        • Drugs which act as acetylcholinesterase inhibitors include physostigmine.

  • Bethanechol

    • Bethanechol may be used to treat nonobstructive urinary retention.

      • With respect to baseline patient information, fluid intake and output should be recorded.

      • Certain "high-risk" patients with respect to bethanechol administration have been identified.

        • For example, bethanechol is contraindicated in those patients with:

          • peptic ulcer disease

          • intestinal obstruction

          • hypertension

          • asthma

          • coronary insufficiency

          • hypothyroidism and

          • urinary tract obstruction.

Lehne RA Pharmacology for Nursing Care, Sixth Edition, Chapter 14:  Muscarinic Agonists and Antagonists, Saunders/Elsevier, 2007, pp130-131.

Brown, J.H. and Taylor, P. Muscarinic Receptor Agonists and Antagonists, In, Goodman and Gillman's The Pharmacological 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.149-150

 
 
 
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