Medical Emergencies · patient case question
What electrolyte disturbance does the combination of triamterene and hydrochlorothiazide prevent?
Patient case: Blood pressure, potassium and a pounding headache
demo: 63-year-old male
chief: Presents for extraction of a hopeless mandibular molar.
history: Hypertension for fifteen years. He tells you he ran out of his tablets ten days ago. His father died of a subarachnoid haemorrhage.
meds: Lisinopril 20 mg daily. Triamterene with hydrochlorothiazide, one tablet each morning.
findings: Blood pressure on arrival is 204/122 mmHg in both arms, repeated after five minutes of rest. He describes a severe occipital headache that began this morning and some blurring of vision.
Show answer and explanation
Correct answer: A. Hypokalaemia
- A. Correct. Hydrochlorothiazide increases sodium delivery to the collecting duct, which drives potassium loss and causes hypokalaemia. Triamterene blocks the epithelial sodium channel there and spares potassium, so the fixed combination gives the diuretic benefit without the potassium fall.
- B. Thiazides cause hyponatraemia, not hypernatraemia, and this is one of their more common clinically significant adverse effects in older patients.
- C. Thiazides increase distal calcium reabsorption, so they tend to raise serum calcium slightly rather than lower it. This is why thiazides are sometimes chosen in patients who form calcium stones.
- D. Hyperkalaemia is the risk of triamterene used alone, particularly with renal impairment or alongside an ACE inhibitor. The combination is designed to balance potassium, not to raise it.
Note: Note that this patient is on both a potassium-sparing diuretic and an ACE inhibitor, a combination that genuinely can push potassium too high. It needs monitoring.
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