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Difficulty: HardMedical History Evaluation

A 62-year-old woman is brought to the emergency department by her daughter due to severe shortness of breath and wheezing that began 24 hours ago. The patient has a history of mild intermittent asthma but has not required an albuterol inhaler in over a decade. Her past medical history is also notable for essential hypertension, hyperlipidemia, and a newly diagnosed ocular condition characterized by elevated intraocular pressure, for which she saw an ophthalmologist three weeks ago. She is a lifelong nonsmoker. Her current oral medications include amlodipine and atorvastatin. When asked about other medications, she initially states she takes nothing else, but upon targeted questioning regarding her recent ophthalmology visit, she confirms she started a new twice-daily eye drop three weeks ago. Temperature is 37.0°C (98.6°F), blood pressure is 122/76 mmHg, pulse is 52/min, and respirations are 24/min. Oxygen saturation is 91% on room air. Physical examination reveals diffuse bilateral wheezing with a prolonged expiratory phase. The skin is warm and dry, and the oral mucosa is moist. There is no excessive lacrimation, salivation, or abnormal bowel sounds. A detailed medical history reveals that the systemic absorption of her new eye medication is likely responsible for her current presentation. Which of the following is the primary mechanism of action of the most likely responsible medication?

  1. Antagonism of beta-adrenergic receptorsAnswer
  2. B
    Activation of prostaglandin F2-alpha receptors
  3. C
    Inhibition of carbonic anhydrase
  4. D
    Stimulation of alpha-2 adrenergic receptors
  5. E
    Activation of muscarinic cholinergic receptors

Answer

The correct answer is antagonism of beta-adrenergic receptors.
The correct answer identifies antagonism of beta-adrenergic receptors. The patient has classical signs of systemic non-selective beta-blockade: acute bronchospasm (beta-2 receptor blockade) and bradycardia (beta-1 receptor blockade). Non-selective beta-blocker eye drops (such as timolol), frequently used to treat open-angle glaucoma, can drain through the nasolacrimal duct and be absorbed by the highly vascular nasal mucosa. Because this route bypasses first-pass hepatic metabolism, it can produce profound systemic effects. This scenario underscores the importance of rigorous medical history evaluation, as patients often do not consider eye drops to be 'medications' and may omit them unless asked direct, targeted questions.

Step-by-Step Solution

1
Analyze the patient's acute clinical presentation.
The patient is presenting with a severe asthma exacerbation (wheezing, hypoxia, tachypnea) accompanied by notable bradycardia (pulse 52/min), despite her asthma being well-controlled for over a decade.
Identifying the paired symptoms (bronchospasm + bradycardia) provides the physiologic signature of the offending agent.
2
Correlate the physical findings with the medical history.
The onset of symptoms closely follows the initiation of a new medication for elevated intraocular pressure (glaucoma), despite the patient initially omitting the eye drops from her medication list.
Patients frequently fail to report topical medications, inhalers, or supplements during standard medication reconciliation. Targeted history evaluation is required to uncover these agents.
3
Determine the pharmacologic class of the eye drop causing the specific adverse effects.
Ophthalmic non-selective beta-blockers (like timolol) are known to cause significant systemic beta-1 and beta-2 blockade due to absorption through the nasolacrimal mucosa.
Beta-2 antagonism causes the acute bronchospasm, and beta-1 antagonism causes the bradycardia, perfectly matching the clinical picture.

Key Concept

During medical history evaluation, targeted questioning about topical therapies (such as ophthalmic drops) is essential, as systemic absorption of agents like non-selective beta-blockers (e.g., timolol) via the nasolacrimal duct can precipitate life-threatening adverse effects such as bronchospasm and bradycardia.
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Medical History Evaluation

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