Metformin-Associated Lactic Acidosis During Docetaxel Therapy for Castration-Resistant Prostate Cancer: A Case Report.

[INTRODUCTION] Docetaxel is a key treatment for castration-resistant prostate cancer and is administered with prednisolone, which increases the risk of steroid-induced diabetes. Its myelosuppressive effect also increases vulnerability to febrile neutropenia. Metformin is widely used for glycemic control; however, elderly cancer patients are particularly susceptible to metformin-associated lactic acidosis, necessitating careful management of sick-day and febrile neutropenia during chemotherapy.

[CASE PRESENTATION] We report a 70-year-old male with castration-resistant prostate cancer and diabetes mellitus who developed febrile neutropenia on Day 5 following docetaxel initiation. He progressed to shock with severe metabolic acidosis on Day 7 and died despite intensive care, including continuous renal replacement therapy. A retrospective review revealed continued metformin use despite prodromal fatigue and loss of appetite, likely due to impaired judgment.

[CONCLUSION] This case may have involved septic shock, but metformin likely worsened the lactic acidosis. It highlights the need for sick-day education and monitoring in elderly cancer patients.