Review Question - QID 213813

A 27-year-old man is brought to the emergency department from prison for back pain. He complains of worsening back pain, localized to the lower back, and states that he is now unable to urinate. He denies any trauma, endorses chills at night, and states he has intermittent diarrhea. The patient has a past medical history of IV drug abuse, homelessness, antisocial personality disorder, malingering, and multiple sexually transmitted infections. His temperature is 98.2°F (36.8°C), blood pressure is 127/77 mm Hg, pulse is 70/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is notable for a normal S1 and S2 and clear bilateral breath sounds. Rectal exam reveals good rectal tone, and the patient has no sensory or strength deficits. Paraspinal muscle tenderness is noted with pain worsened when the patient touches his toes. Nursing attempts to catheterize the patient for a urine sample; however, the patient refuses and volitionally urinates instead with a post-void residual volume of 50 mL. Laboratory studies and urinalysis are seen below.

Serum:
Na+: 140 mEq/L
Cl-: 100 mEq/L
K+: 4.0 mEq/L
HCO3-: 24 mEq/L
BUN: 22 mg/dL
Glucose: 116 mg/dL
Creatinine: 1.2 mg/dL
Ca2+: 9.9 mg/dL
C-reactive protein (CRP): 1.0 mg/L

Urine:
Benzodiazepines: Positive
Opioids: Positive

A chest radiograph and ECG are unremarkable. Which of the following is the most appropriate next step in management?