Capecitabine-induced severe diabetes and hypokalemia: a case report

BACKGROUND: Capecitabine is widely used in chemotherapy for breast, colorectal, and gastric cancers. The frequent adverse reactions of capecitabine mainly include gastrointestinal side effects, anemia, and cardiovascular toxicity. Here, we report a rare case of severe hyperglycemia and hypokalemia during long-term treatment with capecitabine. CASE PRESENTATION: A 48-year-old Chinese female was hospitalized with the complaint of breathlessness and weakness after activity, for 1 month. Her past history is significant for a diagnosis of right-sided breast cancer 7 years ago. She underwent right mastectomy, following which capecitabine was started 1.5 years prior to the current admission as part of her primary treatment at the discovery of systemic osseous metastasis. Her fasting plasma glucose and hemoglobin A1c levels were quite normal 7 months ago but increased to 15.3 mmol/L and 11.2%, respectively, at the present admission. Her serum potassium level was as low as 2.5 mmol/L. Plasma autoantibodies related to islets and insulin were all negative. Capecitabine was discontinued, and an insulin pump and potassium supplement were given after admission. Her blood sugar and potassium levels returned to their normal ranges soon. Self-injection of insulin was withdrawn completely at 2 months after discharge, and no oral hypoglycemic agents were added. Her plasma glucose and electrolyte levels were at normal levels at her 1-year follow-up. CONCLUSION: Glucose intolerance and hypokalemia may be rare but serious adverse effects during long-term chemotherapy with capecitabine.