Some patients being treated with a thiazide diuretic may develop hyponatremia.
Possible mechanism: reduced free water clearance
Hyponatremia refers to a serum sodium < 130 mmol/L (normal 135-145 for an adult).
Risk factors for hyponatremia may include:
(1) older age (highest risk if >= 80; increased risk if >= 60)
(2) female gender
(3) greater comorbidity burden (highest if >= 3; increased if >= 1)
(4) higher hydrochlorothiazide dose
(5) concurrent drugs (NSAIDS, carbamazepine, SSRI, etc.)
(6) increased water intake
(7) potassium depletion
Clinical features may include:
(1) malaise or lethargy
(2) dizziness
(3) nausea
(4) headache
(5) vertigo
(6) seizures
(7) falls
(8) confusion
Supportive findings:
(1) appearance of hyponatremia after starting the thiazide
(2) absence of an alternative diagnosis that can explain the hyponatremia
(3) normalization of the serum sodium after discontinuing the thiazide or reducing the dose
