Primidone Usage as a Rare Cause of Drug-Induced Hyperkalemia

Hyperkalemia is a life-threatening electrolyte disorder. Elderly patients are more prone to developing hyperkalemia due to age-related decline in glomerular fi ltration rate. An 81-year-old female patient previously diagnosed as having diabetes mellitus, hypertension and chronic kidney disease who was on amlodipine and basal insulin therapy, was administered primidone 31.25 mg/day orally for the treatment of essential tremor. After 2 days, serum potassium increased to 7.6 mEq/L from the baseline level of 5.3. Urinary potasium level was 11.4 mEq/L, and transtubular potasium gradient (TTKG) 2.1%. Since no predisposing factor for hyperkalemia could be detected, primidone was discontinued. After 7 days, the serum potassium level returned to normal. Irregular distribution of potassium between the intracellular and extracellular space and imbalance between intake and excretion are the main factors in hyperkalemia pathogenesis. A TTKG value <5% is highly suggestive of hypoaldosteronism. The relatively low TTKG in the present case suggests a mineralocorticoid insuffi ciency probably due to primidone usage . Recently administered drugs without a known hyperkalemia-inducing effect may be an etiologic factor in hyperkalemia in elderly patients who are at risk of developing hyperkalemia due to comorbid diseases or have potassium levels within upper range of normal.