A 10-year-old boy is brought to the clinic after developing a rash on his right thigh. The rash began 5 days ago and has gradually expanded. The boy reports no fever, joint pain, or other systemic symptoms. His medical history is unremarkable, but his parents mention they recently returned from a family hiking trip in the northeastern United States. Physical examination reveals a large, annular rash with central clearing and a red, advancing edge. Which of the following is the most appropriate treatment?
