What are the signs of overdose to look out for in a 13-year-old male after accidental ingestion of Risperidone (risperidone) up to 20mg?

Risperidone Overdose in a 13-Year-Old: Critical Monitoring Parameters

Monitor primarily for extrapyramidal symptoms (EPS), sedation, and cardiovascular effects—these are the most common and clinically significant manifestations of risperidone overdose in this age group and dose range. 1, 2, 3

Immediate Neurological Monitoring (Highest Priority)

Extrapyramidal Symptoms

• Acute dystonia is the most concerning early complication, particularly in children who are more susceptible than adults at lower doses 2, 3

  • Watch for involuntary upward eye gaze (oculogyric crisis), facial grimacing, neck twisting (torticollis), and jerky limb movements 2
  • Symptoms typically appear within the first 9-12 hours post-ingestion 2
  • Have diphenhydramine 1-2 mg/kg IV/IM immediately available as it provides rapid reversal of dystonic reactions 2, 4

• Akathisia and tremor may develop, presenting as motor restlessness, inability to sit still, and parkinsonian tremor 5, 6

• Muscle rigidity and parkinsonism can occur, though less common in acute overdose 5, 6

Central Nervous System Effects

• Drowsiness and sedation are the most frequently reported symptoms in overdose, occurring in 58-70% of cases 1, 4, 3
• Monitor Glasgow Coma Scale—significant CNS depression is uncommon at 20mg but possible 3
• Seizures are rare but have been documented in overdose cases 1

Cardiovascular Monitoring

Vital Signs

• Tachycardia occurs in approximately 58% of risperidone-alone overdoses, defined as heart rate ≥100 bpm 3
• Orthostatic hypotension is common and requires serial blood pressure measurements in both supine and standing positions 5, 6, 4
• Hypotension requiring vasopressor support is uncommon at this dose level 4, 3

Cardiac Rhythm

• Obtain baseline ECG and repeat monitoring for the first 12-24 hours 1, 4
• QTc prolongation can occur but is typically minimal (0-5 ms mean increase) 5, 6
• QRS widening >120 milliseconds is rare but has been reported in larger overdoses 1, 3
• Dysrhythmias are uncommon in risperidone-alone overdoses 4, 3

Metabolic and Laboratory Monitoring

Essential Laboratory Tests

• Complete blood count to monitor for leukocytopenia, though this is more relevant to chronic use 6, 7
• Liver function tests as transaminase elevations can occur 5, 7
• Electrolytes including sodium and potassium, as hyponatremia and hypokalemia have been reported in larger overdoses 1

Timeline of Symptom Onset and Resolution

• Peak symptoms typically occur within 3-4 hours of ingestion, corresponding to peak plasma levels 8
• Most symptoms resolve within 24 hours in the majority of patients 4
• All patients are typically asymptomatic by 72 hours post-ingestion 4
• Extended monitoring for 33-48 hours may be warranted given the case report of a 3.5-year-old requiring diphenhydramine doses up to 24 hours post-discharge 2

Management Considerations

Decontamination

• Activated charcoal may be considered if presentation is within 1-2 hours of ingestion 2
• Gastric lavage is generally not recommended unless massive ingestion 2

Symptomatic Treatment

• Diphenhydramine 1-2 mg/kg IV/IM for acute dystonic reactions—expect immediate response 2, 4
• Lorazepam 1-2 mg IV/IM for severe agitation if needed 7
• Supportive care with IV fluids for hypotension 1, 4

Observation Period

• Minimum 12-16 hours of observation is recommended based on median length of stay data 3
• Consider extended observation to 24-33 hours given pediatric cases showing delayed symptoms 2

Critical Pitfalls to Avoid

• Do not assume benign course based on dose alone—children are more susceptible to EPS at lower doses than adults 2
• Do not discharge without ensuring resolution of orthostatic hypotension—falls risk is significant 6
• Do not overlook subtle dystonic reactions—hand tremor, body shivering, and eye wandering may be early signs requiring treatment 2
• Consider coingestants—mixed overdoses have higher complication rates including seizures and prolonged sedation 4

Reassuring Prognostic Features

• At 20mg ingestion, intensive care admission and mechanical ventilation are unlikely based on overdose case series 3
• Cardiac toxicity is uncommon in risperidone-alone overdoses at this dose range 3
• Mortality is extremely rare—no deaths reported in risperidone-alone overdoses in the literature 1, 4, 3
• Complete recovery is expected with appropriate supportive care and symptom management 4, 3