Severe Hypomagnesemia in a Patient Treated Using Carboplatin Co-Administered with Vonoprazan.

Introduction: We describe a case of severe hypomagnesemia that occurred during treatment with carboplatin (CBDCA) and nanoparticle albumin-bound paclitaxel (nab-PTX) for lung adenocarcinoma when co-administered with vonoprazan. Case Presentation: A man in his 70s was diagnosed with stage IIIA lung adenocarcinoma and received CBDCA and nab-PTX as the first-line treatment. The patient had been taking omeprazole 10 mg once daily (for >3 years) for gastroesophageal reflux disease, but it was switched to lansoprazole 15 mg because of hospital's adopted medication. During the first treatment cycle, his serum creatinine levels increased from 1.0 to 1.5 mg/dL, suggesting CBDCA-associated renal impairment. Because of gastric discomfort on day 15 of the second cycle, lansoprazole was switched to vonoprazan 10 mg once daily. On day 23 of the second cycle, he developed torsades de pointes and was hospitalized; severe hypomagnesemia (0.4 mg/dL) was detected to be causing the symptoms. Discontinuation of vonoprazan and a single intravenous infusion of 60 mEq magnesium sulfate raised serum magnesium levels to 3.7 mg/dL, and the arrhythmia disappeared. Mild hypomagnesemia (1.4 mg/dL) reappeared 5 days later, and an additional intravenous infusion of 20 mEq magnesium sulfate with subsequent oral magnesium oxide (1,980 mg/day) resolved the symptoms. CBDCA was discontinued and nab-PTX monotherapy was continued. Vonoprazan was resumed owing to gastric discomfort relapse; however, grade ≥2 hypomagnesemia did not reappear later. Conclusions: This case highlights the risk of severe hypomagnesemia in patients with CBDCA and vonoprazan co-administration; therefore, regular monitoring of serum magnesium levels during the treatment is crucial.