A 6-year-old boy of Mediterranean descent is brought to the emergency department with acute-onset jaundice and dark urine. This started 48 hours after he began taking a fluoroquinolone for a severe skin infection. An initial screening test for Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency returns in the low-normal range, despite a very high reticulocyte count. What is the most appropriate next step in management?