Q. A 60-year-old patient comes to the clinic because of fatigue and muscle weakness over the last few weeks. He has been undergoing treatment for multiple myeloma. His BP is 130/88 mm Hg, heart rate is 90/min, respiratory rate is 20/min, and his temperature is 37.8 degrees Celsius. Laboratory tests reveal metabolic acidosis with a blood bicarbonate level of 15 mEq/L, hypokalemia with a potassium level of 2.5 mEq/L, and a urine pH of less than 5.5. The patient has healthy kidney function and no other underlying medical problems. Which of the following is the most likely diagnosis?