A 68-year-old man comes to the physician for a follow-up appointment. He has congestive heart failure managed with enalapril, metoprolol, spironolactone, furosemide, hydralazine, and isosorbide dinitrate. He has type II diabetes mellitus managed with meformin. Laboratory studies are shown:
Sodium 130 mEq/L
Potassium 4.0 mEq/L
Bicarbonate 24 mEq/L
Calcium 9.0 mg/dL
BUN 20 mg/dL
Which of the following is the most likely explanation for these findings?
