Acquired Bartter-Like Syndrome Following Polymyxin Therapy in an Elderly Patient: A Case Report

Introduction: Bartter syndrome is a rare inherited tubulopathy characterized by salt wasting, hypokalemia, and metabolic alkalosis. Acquired Bartter-like syndromes have been reported in association with nephrotoxic agents such as polymyxins. Polymyxin-induced nephrotoxicity, which affects up to 60% of patients, involves proximal tubular accumulation via megalin/PEPT2-mediated endocytosis, leading to tubular injury. We present a case of a 77-year-old female who developed Bartter-like syndrome following six days of polymyxin-B therapy, highlighting a rare but significant adverse effect. Case Description: A 77-year-old female with a past medical history of hypertension, hyperlipidemia, deep vein thrombosis, prediabetes, and obesity, who presented to ER with asymptomatic hypokalemia (serum potassium: 2.5 mmol/L), was detected on routine outpatient labs. She had recently been hospitalized for a left lower extremity cellulitis and was treated with initially treated with piperacillin/tazobactam, followed by Polymyxin-B and Meropenem. Patient was discharged to continue intravenous meropenem, polymyxin-B (100mg IV BID), and the addition of oral doxycycline for two weeks. During her stay at a rehabilitation facility, routine bloodwork revealed persistent hypokalemia. Laboratory investigations are shown in Table 1. Discussion: This case illustrates a polymyxin rare but important adverse effect: an acquired Bartter-like syndrome. We presume that the patient developed persistent hypokalemia, hypomagnesemia, and hypocalcemia, with borderline high bicarbonate, approximately 20-21 days after polymyxin-B exposure. Despite preserved renal function at the time of discharge and readmission, her electrolyte panel was consistent with a Bartter-like syndrome. Polymyxin-induced nephrotoxicity is well-documented, with incidence rates up to 60%, typically manifesting as acute tubular injury. Its ability to mimic Bartter syndrome through distal tubular dysfunction is less commonly recognized. Table 1 – Serum electrolytes - Prior to discharge Day 1 Day 2 Day 3 Day 4 Reference range Creatinine 1.01 1.05 1.13 1.22 1.13 0.51-0.95 mg/dL Sodium 138 128 131 134 138 136-145 mmol/L Potassium 4.2 2.7 2.6 3.1 3 3.5- 5.1 mmol/L Chloride 104 84 88 91 95 98 – 107 mmol/L Magnesium 1.7 0.6 1.2 1.5 1.2 1.5- 2.2 mg/dL Calcium 9.4 5.6(Albumin 2.9 g/dl) 6.1 6.7 6.4 8.6 - 10.4 mg/dL Bicarbonate 24 25 27 27 28 22-28 mmol/L