Review Question - QID 214488

A 33-year-old man presents to the emergency department for malaise and dark urine. The patient is seen in the hospital frequently for opiate abuse and alcohol abuse/withdrawal. Today, he is complaining of gradually worsening fatigue and states that his urine went from amber to brown over the past week. He has frequent chills. He endorses IV drug use. He recently treated himself for a sore throat, cough, and runny nose with amoxicillin he had left over. His temperature is 103°F (39.4°C), blood pressure is 130/85 mmHg, pulse is 122/min, respirations are 22/min, and oxygen saturation is 100% on room air. Physical exam reveals a patient demonstrating rigors with bilateral pulmonary crackles and a rapid heart rate. Laboratory values are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 22,500/mm^3 with normal differential
Platelet count: 331,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 4.3 mEq/L
HCO3-: 25 mEq/L
BUN: 33 mg/dL
Creatinine: 2.2 mg/dL

Urine dipstick:
Color: Brown
Red blood cells: Many
Nitrites: Negative
White blood cells: Many
Bacteria: Negative

Which of the following is the most likely diagnosis?