Severe tolvaptan-associated hyperglycemia: a case report.

Background: Tolvaptan-associated hyperglycemia has rarely been described in literature.

Case presentation: A 95-year-old East Asian (Chinese) male patient with hyponatremia started on tolvaptan treatment at a dosage of 15 mg per day. The patient had a serum sodium concentration of 124.5 mmol/L at baseline; this concentration increased to 138.3 mmol/L over the ensuing 5 months of treatment. Moreover, the patient's fasting blood glucose dramatically increased from 6.3 to 17.2 mmol/L with tolvaptan treatment, and his glycated hemoglobin A1c increased from 5.8% to 9.4%. Tolvaptan was withdrawn owing to hyperglycemia, and insulin pump treatment was started. The serum sodium concentration decreased to 123 mmol/L after tolvaptan withdrawal. The higher levels of blood glucose, insulin, and C-peptide did not return to their previous levels for 5 months after the withdrawal of tolvaptan.

Conclusion: We reported a rare case of tolvaptan-associated chronic severe hyperglycemia with a Naranjo probability scale score of 6. Our findings increase clinical knowledge and indicate the need for proactive blood glucose monitoring during prolonged tolvaptan use in clinical practice.