A 6-year-old boy presents with a 1-week history of bilateral ear pain, more severe on the right. He has also had a creamy, non-foul-smelling discharge from his right ear for 2 days. On otoscopy, the right external auditory canal is swollen and erythematous, and the tympanic membrane is obscured by debris and discharge. The left ear canal is mildly erythematous. He is tender on palpation of the right tragus. What is the most appropriate topical treatment?