Metformin induced severe hypophosphatemia in a patient on hemodialysis.

A 67-year-old diabetic and hypertensive woman presented to us with very low serum phosphate levels (PO₄⁻ =1.1 mg/dL) about 40 days after initiation of hemodialysis (HD). The phosphate binders were discontinued, because they were thought to be the cause of hypophosphatemia. However, the serum phosphate levels continued to remain low during subsequent follow-up visits over one month (PO₄⁻⁻⁻ = 0.7 and 0.6 mg/dL respectively). The patient had been started on metformin hydrochloride (850 mg thrice a day) about 18 days after the beginning of HD. The drug was stopped immediately (approximately 50 days after it was started) and the serum phosphate levels increased progressively, reaching 4.3 mg/dL. During the period with hypophosphatemia, the patient suffered from very intense fatigue and weakness (she was unable to walk), anorexia, diarrhea and tenesmus. There were no features suggestive of rhabdomyolysis, hemolysis, low blood pressure or hypoglycemia; she had low white blood cell and platelet counts. The patient was in good clinical condition 2-3 days after the discontinuation of metformin and she recovered totally 15 days later. This case is presented due to its rarity as well as the observation that despite the patient having severe hypophosphatemia, she showed only side effects of metformin. Hypophosphatemia caused only intense fatigue and no other symptoms.