A 9-year-old male with autism spectrum disorder (level 2) is brought to the clinic by his parents for escalating aggression including hitting, kicking, and property destruction that occurs daily, primarily when routines are disrupted or sensory demands are overwhelming. He attends a specialized school program and receives applied behavior analysis therapy 20 hours per week. Despite behavioral interventions for the past 6 months, aggression episodes have increased in frequency and intensity, resulting in suspension from school and injuries to caregivers. He is 32 kg, has no medical comorbidities, and takes no medications. Behavioral data confirm the aggression is not solely attention-maintained. Which pharmacologic treatment plan is most appropriate?