- Gary C Curhan, MD, ScD
Gary C Curhan, MD, ScD
- Section Editor — Chronic Kidney Disease
- Editor-in-Chief emeritus
- Harvard Medical School
Triamterene is a potassium-sparing diuretic that is commonly used in the treatment of hypertension in combination with a thiazide diuretic. It is not widely appreciated, however, that triamterene is a potential nephrotoxin, occasionally inducing crystalluria and cast formation, and rarely causing stone formation or reversible acute kidney injury [1,2].
CRYSTALLURIA AND CAST FORMATION
Triamterene can induce the formation of both triamterene crystals (which are usually brown in color, spherical, and appear as a "Maltese cross" under polarized light) and granular casts (which can look identical to brown pigmented casts), at least when used in higher doses. The following studies illustrate this effect:
●In a study of 20 healthy adults who ingested 100 mg of triamterene, all 20 excreted triamterene crystals, and 17 out of 20 excreted granular casts, which were present within 11 hours of taking the drug . Alkalinization of the urine to a pH of 7.5 or higher prevented the appearance of crystals.
●In a study of 26 hypertensive patients given 50 mg of triamterene, crystals and casts were seen in 14 (54 percent) .
Whether crystals and casts commonly occur with 37.5 mg of triamterene (a more typical dose) is unknown. The mechanism responsible for the cast formation is unclear but appears to be specific to triamterene, as this finding is not seen with amiloride, another potassium-sparing diuretic [3,4].
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