A 9-year-old boy is brought to clinic for an itchy scalp rash and hair loss for 3 weeks. His mother reports several classmates have had similar symptoms. Examination shows a single 4-cm round patch of alopecia with fine scale; within the patch, the hairs are broken off at a similar short length. There is no fluorescence under Wood lamp examination. Which of the following is the most appropriate treatment?

(Assume no medication allergies.)