Case Presentation: An 88-year-old woman comes to the emergency department with a four-day history of left-sided flank pain associated with nausea and emesis. She has a history of essential hypertension, dyslipidemia, anxiety, and diverticulitis, with a prior history of partial colectomy. For hypertension, she has been on triamterene-hydrochlorothiazide 75 mg-50 mg once daily for several years. Blood work revealed a white blood cell (WBC) count of 7600/µL, sodium of 138 mmol/L, potassium of 3.4 mmol/L, blood urea nitrogen (BUN) of 18 mg/dL, creatinine of 1.30 mg/dL. CT scan of the abdomen and pelvis showed a 4 mm obstructing distal left ureteral stone. Given intractable pain, the patient was admitted and was placed on intravenous hydration, oral tamsulosin, and oral and intravenous pain medications to be given as needed. She eventually passed the stone, with relief in her symptoms. Analysis of the stone revealed that it was composed of 100% triamterene. The patient was advised to stop taking triamterene and was switched to spironolactone.
Discussion: Triamterene is a potassium-sparing diuretic, usually given with a thiazide diuretic such as hydrochlorothiazide for managing hypertension or edema. About 50% of triamterene is excreted in the urine, 20% as triamterene, and 80% as a metabolite [1]. Studies have shown that when given in higher doses (50 mg to 100 mg), it can induce the formation of triamterene crystals and granular casts in most patients [2,3]. Among the potassium-sparing diuretics, this crystal and cast formation appears to be specific to triamterene [2,3]. Triamterene can rarely result in the formation of renal calculi [1,4,5]. The patients with triamterene calculi usually have a prior history of nephrolithiasis [1,5]. A study by Ettinger et al. showed that triamterene was detected in 0.4% of all the renal stones analyzed [6]. Stones with triamterene usually have other components, such as calcium oxalate monohydrate or dihydrate, apatite, or uric acid [5,7]. Ettinger et al. studied that about one-third of the stones containing triamterene were composed mainly or entirely of triamterene [6]. Another study by Sorgel et al. showed that half of 66 triamterene-containing stones that they studied had less than 5% triamterene, and none had more than 75% [7]. These studies indicate that the presence of 100% triamterene in a stone is a rare phenomenon. The case discussed here is unique on two fronts: firstly, the absence of a prior history of renal calculi, usually present in triamterene stones. Secondly, the composition of the stone is entirely triamterene, a rare and unusual occurrence.
Conclusions: Triamterene, a potassium-sparing diuretic, carries the risk of crystalluria, granular casts, and, rarely, nephrolithiasis. Renal calculus, composed entirely of triamterene, as described in this case report, is unusual. Physicians and advanced practice clinicians should be aware of these potential adverse events when prescribing triamterene.