Review Question - QID 213682

A 22-year-old man with a history of depression presents to the emergency department after ingesting an unknown substance in a suicide attempt. The patient and his parents state the attempt occurred 30 minutes ago. His parents promptly brought the patient to the hospital afterwards. The patient is currently asymptomatic. The patient states he attempted suicide yesterday with a similar method but "did not take enough pills." His temperature is 97.5°F (36.4°C), blood pressure is 122/82 mmHg, pulse is 85/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is notable for a calm young man with a withdrawn affect. Abdominal exam and dermatologic exam are unremarkable. Initial laboratory values are drawn as seen below.

Serum:
Na+: 141 mEq/L
Cl-: 100 mEq/L
K+: 4.4 mEq/L
HCO3-: 25 mEq/L
BUN: 24 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.6 mg/dL
Ca2+: 10.2 mg/dL
AST: 505 U/L
ALT: 720 U/L

Which of the following is the most appropriate initial step in management?