What is the recommended dose of Pedicloryl (chlorpromazine and promethazine) and Phenargan (promethazine) for sedation in a 20kg child with no significant past medical history or allergies?

Critical Safety Warning: Do Not Use This Combination

I strongly recommend against using the combination of Pedicloryl (chlorpromazine/promethazine) and Phenergan (promethazine) for sedation in a 20kg child, as this represents dangerous duplicate dosing of promethazine and these agents have fallen out of favor due to unpredictable responses, prolonged recovery, and serious safety concerns. 1

Why This Combination is Problematic

Black Box Warning for Promethazine

• Promethazine (Phenergan) carries a black box warning regarding fatal respiratory depression in children younger than 2 years 1
• Promethazine is contraindicated for children under 2 years of age 2
• The combination you're asking about would result in duplicate and excessive promethazine dosing, significantly increasing toxicity risk 2

Historical Context and Current Evidence

• The "DPT" or "MPC" cocktail (meperidine/Demerol, promethazine/Phenergan, chlorpromazine/Thorazine) was historically used but has fallen out of favor because of unpredictable responses and prolonged recovery 1
• Two deaths were reported in infants with congenital heart disease sedated with DPT 3
• Respiratory depression occurred in 0.6% of patients, with some requiring naloxone 4
• Drugs with long duration of action (including phenothiazines like promethazine and chlorpromazine) are no longer recommended due to prolonged recovery and risk of re-sedation after discharge 1

Safer Alternative Sedation Options for a 20kg Child

First-Line Recommendations

For painless diagnostic procedures:

• Midazolam: 0.5 mg/kg PO (maximum 20 mg) or 0.05-0.10 mg/kg IV over 2-3 minutes (maximum 5 mg per dose) 1
• Pentobarbital: 3-6 mg/kg IV (typical range for children) with 99% success rates 1

For painful procedures:

• Ketamine: 1-2 mg/kg IV or 4-5 mg/kg IM, with consistent safety and efficacy demonstrated across multiple reviews 1, 5
• Nitrous oxide: Safe (0.1% incidence of respiratory events) and effective in cooperative children 5

Critical Safety Requirements

• Continuous monitoring with pulse oximetry and cardiorespiratory assessment is mandatory 1
• Emergency equipment must be immediately available, including age-appropriate airways, bag-valve-mask, and resuscitation drugs 1
• Personnel trained in pediatric advanced life support must be present 1
• Children should be monitored until they return to baseline vital signs and level of consciousness 1

If Historical DPT/MPC Dosing is Absolutely Required (Not Recommended)

Only if no safer alternatives are available and with extreme caution:

• Historical maximum dose: 2 mg/kg meperidine : 1 mg/kg promethazine : 1 mg/kg chlorpromazine 3, 4
• For a 20kg child: Maximum 40mg meperidine, 20mg promethazine, 20mg chlorpromazine 3, 4
• Never exceed 50mg/25mg/25mg total dose regardless of weight 4

High-Risk Populations Requiring Extra Caution

• Patients with abnormal mental status or underlying neurologic abnormalities have significantly increased complication rates 4
• Head injuries are associated with higher rates of sedation failure 4
• Infants under 12 months experience more delayed recovery (≥24 hours) 6

Common Pitfalls to Avoid

• Do not combine promethazine-containing products - this creates dangerous duplicate dosing 2
• Do not discharge children prematurely - 31% experience motor imbalance, 23% gastrointestinal effects, and 19% agitation after discharge 6
• Do not use in children under 2 years due to black box warning for promethazine 1, 2
• Do not assume adequate sedation means safe sedation - one child had inadequate sedation in hospital but became difficult to arouse at home 6
• Expect prolonged effects - only 48% of children return to baseline within 8 hours, and 5% require up to 48 hours for full recovery 6