What is the appropriate starting dose of Risperidone (risperidone) for a 16-year-old male with Autism Spectrum Disorder (ASD) weighing approximately 63.5 kilograms (140 pounds)?

Risperidone Dosing for 16-Year-Old Male with Autism Spectrum Disorder

For a 16-year-old male with Autism Spectrum Disorder weighing approximately 140 pounds (63.5 kg), the appropriate starting dose of risperidone is 0.5 mg once daily, with gradual titration based on response and tolerability.

Initial Dosing Algorithm

1. Starting dose:

   • 0.5 mg once daily (as per FDA guidelines for adolescents ≥20 kg) 1
   • Can be administered in the morning or evening

2. Titration schedule:

   • Maintain initial dose for a minimum of 4 days
   • After 4 days, may increase to 1 mg daily if needed
   • Maintain this dose for a minimum of 14 days to assess response
   • Further increases should occur at intervals of 2 weeks or greater
   • Increase in increments of 0.5 mg per day

3. Target dose range:

   • Effective dose range: 0.5 mg to 3 mg per day 1
   • Most adolescents respond to 1-2.5 mg per day
   • No additional benefit has been observed above 2.5 mg per day in pediatric patients

Administration Considerations

• If persistent somnolence occurs (reported in up to 51% of pediatric patients), consider:

  • Administering the dose at bedtime
  • Dividing the total daily dose into two administrations
  • Reducing the dose 2, 1

• Conservative dosing is recommended as adolescents with ASD may be more sensitive to medication side effects 3

Monitoring Parameters

1. Effectiveness monitoring:

   • Irritability and aggressive behaviors (primary target symptoms)
   • Sleep patterns (risperidone may improve sleep-onset delay) 3
   • Social functioning and repetitive behaviors

2. Side effect monitoring:

   • Weight gain (significant concern, monitor BMI) 4
   • Somnolence (most common side effect, occurring in up to 51% of patients) 3, 2
   • Metabolic parameters (glucose, lipids)
   • Prolactin levels (asymptomatic increases common) 3
   • Extrapyramidal symptoms

Duration of Treatment

• After achieving sufficient clinical response, consider gradually lowering the dose to achieve optimal balance of efficacy and safety 1
• Periodically re-evaluate the long-term risks and benefits of continued treatment 1
• Evidence supports persistent efficacy for intermediate-length treatment (6 months) 5
• Discontinuation after 6 months may lead to rapid return of disruptive behaviors in many patients 5

Important Cautions

• Weight gain is a significant concern and may limit long-term use 6
• Higher risperidone plasma concentrations are associated with greater weight gain, sedation, and prolactin elevation, but also better effectiveness 4
• Withdrawal dyskinesias have been reported in 15.4% of children after long-term treatment 7
• Consider risperidone as a "last resort" option after behavioral interventions have been inadequate 8

Risperidone has demonstrated effectiveness in reducing irritability, aggression, and self-injurious behaviors in adolescents with ASD, with effects typically appearing within 2 weeks of initiation 3. However, the benefit-risk profile must be carefully considered given the potential for significant adverse effects.