🔍 Question of the day

A 78-year-old woman presents to the hospital with a 2-day history of nausea, vomiting, abdominal pain, and headache. She has a past medical history of chronic obstructive pulmonary disease (COPD), managed with theophylline. Recently, she was hospitalized for a stroke, during which she developed a urinary tract infection and experienced delirium. On examination, her temperature is 37°C (98.6°F), blood pressure is 110/70 mm Hg, pulse is 118/min, and respirations are 22/min. She appears restless and agitated, with a coarse tremor noted in her outstretched arms. Auscultation of the lungs reveals mild expiratory wheezing. Laboratory results show markedly elevated serum theophylline levels.

Which of the following medications is most likely responsible for her current symptoms?

• A. Amoxicillin

• B. Cephalexin

• C. Ciprofloxacin

• D. Haloperidol

• E. Nitrofurantoin

  

Correct Answer 🎯:C. Ciprofloxacin

⚙️

Theophylline Metabolism

Theophylline → 🧠 Metabolized by Cytochrome P450 (CYP1A2) in the liver

↑ Sensitivity to drug interactions

⬇

Introduction of Ciprofloxacin

Ciprofloxacin → 🧠 Potent CYP1A2 inhibitor

Effect: ↓ Theophylline metabolism

⬇

↑ Serum Theophylline Levels

Result of CYP1A2 inhibition

⬇

Toxic Effects of Theophylline

• CNS: Agitation, restlessness, coarse tremors, headache

• GI: Nausea, vomiting, abdominal pain

• Cardiovascular: ↑ Heart rate (tachycardia)

⬇

Outcome: Clinical Signs & Symptoms

• Tachycardia (pulse 118/min), tremor, agitation

• GI distress (nausea/vomiting)

Think of : 

CYP1A2 Enzyme ⚙ = A drainpipe

Ciprofloxacin = A clog in the drain → Blocks metabolism → Overflow of theophylline ↑ (toxicity).

Toxicity as an overflowing bucket 🪣

Theophylline fills the bucket; ciprofloxacin prevents the bucket from draining → Overflow = toxicity.

How To Approach this Question? 🏗️

Patient Presentation

Symptoms: GI (nausea, vomiting), CNS (tremor, agitation), cardiovascular (tachycardia).

🔍 What links these?

🧠 Consider theophylline toxicity ⚙.

⬇

Key History Clues

Recent UTI → Treated with antibiotics (likely ciprofloxacin 🧠).

Preexisting COPD → On theophylline.

⬇

Theophylline Metabolism ⚙

Liver enzyme CYP1A2 metabolizes theophylline.

🧠 Ciprofloxacin inhibits CYP1A2 ⚙ → ↓ Clearance of theophylline ↑.

⬇

Result: Theophylline Toxicity

⚙ Mechanism:

• ↑ Theophylline levels →

  • GI: Nausea, vomiting.

  • CNS: Agitation, tremor.

  • CV: Tachycardia.

⬇

Differentiating from Other Drugs ⚖

🧠 Ciprofloxacin fits all mechanisms; others do not.

⚖ Amoxicillin, Cephalexin, Nitrofurantoin → No CYP1A2 inhibition.

⚖ Haloperidol → Causes agitation but unrelated to theophylline.

⚖️ Explanation of Other Differentials

📝 Flashcards

Stay Hungry, Stay Curious!

Your Brother In This Struggle

Dr. Shoaib Ahmad

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