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Which of the following medications is the most likely cause of this patient's condition?
Dr. Shoaib Ahmad Baig
January 20, 2025
🔍 Question
A 68-year-old woman is brought to the emergency department due to worsening lethargy. Her family states that the patient has had headache and nausea for the past several days, and today she was confused and lethargic.
Medical history is significant for seizure disorder, hypertension, type 2 diabetes mellitus, and bipolar disorder, for which she is on a number of medications. Vital signs are within normal limits. On physical examination, the patient is somnolent and responds to painful stimuli only. Mucous membranes are moist and jugular venous pressure is normal. The lungs are clear to auscultation and heart sounds are normal. There is no extremity edema.
Laboratory evaluation reveals severe hyponatremia with a serum sodium of 118 mEq/L; blood urea nitrogen and serum creatinine are within normal limits. Serum osmolality is low and urine osmolality is high.
Which of the following medications is the most likely cause of this patient's condition?
A. Canagliflozin
B. Carbamazepine
C. Furosemide
D. Lithium
E. Spironolactone
Correct Answer 🎯: B. Carbamazepine
⚙️
Seizure Disorder & Bipolar Disorder Management
⬇
Medication Use (Includes Carbamazepine) 🧠
⬇
Carbamazepine ↑ Vasopressin Release (SIADH Mechanism)
⬇
⬇️ Free Water Excretion (Due to ADH effects)
⬇
Water Retention
⬇
Dilutional Hyponatremia (↓ Serum Sodium 118 mEq/L)
⬇
⬇ Serum Osmolality 🧠
⬇
High Urine Osmolality (Due to inappropriate water reabsorption)
• Direct SIADH Induction
⬇
Excess Vasopressin Action 🧠
⬇
Water Retention
⬇
Hyponatremia with Low Serum Osmolality & High Urine Osmolality
• Carbamazepine acts like a faucet 🚰 that keeps pouring water into the system (↑ Vasopressin).
• SIADH locks the drain 🛠️, so water stays and dilutes everything (hyponatremia).
Symptoms Explained 🔧
• Lethargy & Confusion
⬇
Hyponatremia causes cerebral edema 🧠
⬇
Neuronal dysfunction
⬇
Altered mental status
• No Edema
⬇
SIADH retains water intracellularly 🧠
⬇
Dilution without overt fluid overload
⚖️ Explanation of Other Differentials
Differential ⚖️ | Mechanism ⚙️ | Why Incorrect? 🔴 |
|---|---|---|
A. Canagliflozin | Sodium-glucose co-transporter 2 (SGLT2) inhibitor | Results in glycosuria & osmotic diuresis ⬇ Would cause hypernatremia, not hyponatremia 🧠 |
C. Furosemide | Loop diuretic blocks Na-K-2Cl cotransporter ⬇ ⬇️ Sodium reabsorption (Urinary loss of Na) | Typically causes hypovolemic hyponatremia (Not SIADH pattern) |
D. Lithium | ADH action at the kidney 🧠 ⬇ Nephrogenic diabetes insipidus | Causes hypernatremia due to water loss |
E. Spironolactone | Aldosterone antagonist 🧠 ⬇ Hyperkalemia and mild natriuresis | Does not lead to SIADH or severe hyponatremia |
📝 Flashcards
Stay Hungry, Stay Curious!
Your Brother In This Struggle
Dr. Shoaib Ahmad
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