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☕️ Which of the following medications is the most likely cause of this patient's condition?

Morning Quiz 126 ☕️

Author

Dr. Shoaib Ahmad Baig
June 15, 2025

Morning Quiz ☕️ 

A 68-year-old woman is brought to the emergency department due to worsening lethargy.

History of Present Illness

  • Family reports:

    • Headache and nausea for the past several days.

    • Today, she became confused and lethargic.

  • Medical history:

    • Seizure disorder

    • Hypertension

    • Type 2 diabetes mellitus

    • Bipolar disorder

  • Current medications: Multiple (unspecified).

Physical Examination

  • Vital signs: Within normal limits.

  • General: Somnolent, responds only to painful stimuli.

  • Cardiovascular:

    • JVP normal, heart sounds normal.

  • Respiratory: Lungs clear to auscultation.

  • Extremities: No edema.

  • Mucous membranes: Moist.

Laboratory Findings

  • Serum sodium: 118 mEq/L (normal: 135–145).

  • Renal function: BUN and creatinine within normal limits.

  • Osmolality:

    • Serum osmolality: Low

    • Urine osmolality: High

Question

Which of the following medications is the most likely cause of this patient's condition?

Options:
A. Canagliflozin
B. Carbamazepine
C. Furosemide
D. Lithium
E. Spironolactone

Correct Answer 🎯: B. Carbamazepine

⚙️

Carbamazepine (Anti-seizure & mood stabilizer)

⬇

Stimulates ADH release  (from hypothalamus/pituitary )

or ↑ Renal sensitivity to ADH

⬇

↑ ADH effect despite normal serum osmolality

⬇

↑ water reabsorption in kidneys without appropriate osmotic trigger

⬇

Dilutional hyponatremia (Serum Na⁺ 118 mEq/L, ↓ serum osmolality)

⬇

↑ Urine osmolality (Kidneys still concentrating urine due to ADH action)

⬇

↓ Plasma Na⁺ → Water shifts into brain cells (↑ ICF)

⬇

(Brain cells swell )

⬇

Cerebral edema

⬇

Headache + Nausea

(due to cerebral edema → ↑ intracranial pressure)

⬇

Neuronal dysfunction

⬇

Confusion → Lethargy → Somnolence (responds to pain only)

🧠 Syndrome of Inappropriate ADH Secretion (SIADH)

Differential Table ⚖️

Differential ⚖️

Mechanism ⚙️

Why Incorrect? 🔴

Canagliflozin(SGLT2 inhibitor)

Blocks glucose reabsorption in PCT → ↑ Glucose in tubule → Osmotic diuresis → ↑ Water loss

Causes hypovolemia + hypernatremia(opposite of this case)

Furosemide(Loop diuretic)

Inhibits Na⁺/K⁺/2Cl⁻ pump in TAL → ↓ Na⁺ reabsorption → ↓ Medullary gradient → ↓ Water reabsorption

Causes ↓ urine osmolality, hypovolemia(Not matching: urine is concentrated + euvolemic)

Lithium

Damages principal cells → Blocks ADH action → Nephrogenic DI → ↑ Water loss → ↑ Serum Na⁺

Hypernatremia + dilute urine expected (opposite of findings)

Spironolactone

Aldosterone antagonist → ↑ Na⁺ excretion, ↑ K⁺ retention → Mild volume loss

Would cause dry mucosa, ↓ JVP, ↓ BP → Not observed (mucosa moist, JVP normal)

Visual Cheat Charts 📈 

Stay Hungry, Stay Curious!

Your Brother in This Struggle

Dr. Shoaib Ahmad