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Muscarinic Agonists

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Muscarinic Agonists

Key Points

  • Pilocarpine is a muscarinic receptor agonist used to lower intraocular pressure in glaucoma.
  • Pilocarpine contracts the ciliary muscle and improves aqueous-humor drainage from the anterior chamber.
  • After eye-drop instillation, apply light pressure over the lacrimal sac for about 2 minutes to reduce systemic absorption.
  • Remove contact lenses before administration.
  • Cholinergic adverse effects follow the DUMBBELSS pattern and require respiratory/cardiac surveillance.
  • Teach caution with night driving because miosis can impair low-light vision.

Mechanism of Action

Muscarinic agonists stimulate muscarinic cholinergic receptors. In glaucoma care, pilocarpine causes ciliary-muscle contraction and facilitates aqueous-humor outflow, lowering intraocular pressure.

Indications

  • Glaucoma treatment to control elevated intraocular pressure.

Nursing Considerations

  • Verify the correct eye and baseline ocular symptoms before instillation.
  • Remove contact lenses before administration.
  • Instruct the patient to apply gentle pressure to the lacrimal sac for about 2 minutes after instillation to limit systemic absorption.
  • Monitor for cholinergic adverse effects that can affect airway, cardiovascular status, and GI function.

Adverse Effects

Use DUMBBELSS for rapid recall of cholinergic toxicity pattern:

  • Diarrhea
  • Urination
  • Miosis
  • Bronchospasm
  • Bradycardia
  • Excitation (skeletal muscle/CNS)
  • Lacrimation
  • Sweating
  • Salivation

Additional symptoms reported with pilocarpine include light-headedness, nausea, vomiting, and abdominal cramping.

Health Teaching

  • Use caution with night driving and other low-light activities.
  • Report wheezing, shortness of breath, marked dizziness, severe GI symptoms, or slow pulse promptly.
  • Reinforce correct drop technique and no-touch bottle-tip handling.

Clinical Judgment Application

Clinical Scenario

A patient newly prescribed pilocarpine asks why pressing the inner eye corner is necessary and later reports dizziness after dosing.

  • Recognize Cues: Pilocarpine therapy, potential systemic symptoms, and uncertainty about administration technique.
  • Analyze Cues: Inadequate lacrimal occlusion can increase systemic absorption and cholinergic effects.
  • Prioritize Hypotheses: Priority is preventing cardiopulmonary complications while preserving glaucoma control.
  • Generate Solutions: Re-teach instillation and lacrimal-pressure technique; reassess pulse, blood pressure, breathing, and symptom severity.
  • Take Action: Hold further dosing if severe symptoms appear and notify the provider for evaluation.
  • Evaluate Outcomes: Confirm symptom improvement, correct return demonstration, and safe continuation plan.

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