Abstract: SA-PO0595
Pembrolizumab-Associated Distal Renal Tubular Acidosis: A Rare Immune-Related Adverse Event
Session Information
- Fluid, Electrolyte, and Acid-Base Disorders: Case Reports - 2
October 24, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Fluid, Electrolytes, and Acid-Base Disorders
- 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical
Authors
- Kinane, Jenny, St. Vincent's University Hospital, Dublin, Ireland
- Cullen, Roisin, St. Vincent's University Hospital, Dublin, Ireland
- Arbuthnott, James, St. Vincent's University Hospital, Dublin, Ireland
- Kant, Sam, St. Vincent's University Hospital, Dublin, Ireland
Introduction
As Immune Checkpoint Inhibitor (ICI) therapy becomes more widespread, recognition of immune-related adverse events (irAEs) remains critical to therapeutic success. Nephrotoxicity beyond acute kidney injury is increasingly recognised. Acid–base disturbances in this setting should prompt consideration of an ICI-associated irAE. A systematic approach to electrolyte abnormalities is essential in establishing causality.
Case Description
A 73-year old female was admitted with nausea, fatigue and anorexia. Past medical history was significant for metastatic non-small cell lung cancer on treatment with Pembrolizumab (cycle 32). The patient reported two episodes of vomiting prior to admission and had no further significant GI losses during her admission. Serum potassium was low at 2.7mmol/L and was refractory to treatment with multiple doses of IV potassium. Labs revealed a non-gap metabolic acidosis with serum bicarb of 14mmol/L. The anion gap was 9.5. Urine K:Creatinine ratio was 8.6mEq/mmol, supporting a renal rather than gastrointestinal cause. Urine Osmolar Gap was 73mOsm/kg, suggestive of impaired ammonium excretion. Urine pH was 7 prior to any alkaline therapy, and the patient had no features of Fanconi's syndrome, thus a diagnosis of Distal RTA secondary to Pembrolizumab was made. The patient was commenced on oral potassium citrate. Serum potassium recovered to 3.7mmol/L on day 2 of treatment and the patient was discharged home shortly after. Given the effective response to treatment and stability of renal function, Pembrolizumab therapy could continue.
Discussion
The postulated mechanism for ICI related dRTA from previous reports is reduction of the H+ secreting V-ATPase in the distal tubule. This case highlights the importance of recognising RTAs as a potential adverse effect of ICIs, even in the absence of renal impairment or interstitial nephritis, requiring careful analysis and interpretation of investigations to confirm the underlying aetiology.