What is the appropriate dose of promethazine (25 mg/mL) for a child weighing 13.43 kg?

Promethazine Dosing for a 13.43 kg Child

For a child weighing 13.43 kg who is 2 years or older, administer promethazine at 1.1 mg/kg (approximately 14.8 mg or 0.59 mL of the 25 mg/mL solution) via deep intramuscular injection only, with the dose not exceeding half the adult dose. 1

Critical Age Verification

• Promethazine is absolutely contraindicated in children under 2 years of age due to fatal respiratory depression risk. 1
• Before administering, confirm the child is at least 2 years old—age takes precedence over weight in this safety determination. 1

Exact Dosing Calculation

• Weight-based dosing: 1.1 mg/kg × 13.43 kg = 14.77 mg (round to 14.8 mg). 1
• Volume to draw: 14.8 mg ÷ 25 mg/mL = 0.59 mL of the 25 mg/mL solution. 1
• Maximum dose rule: This calculated dose must not exceed half the adult dose (12.5 mg for most indications), so the practical maximum would be 12.5 mg (0.5 mL). 1
• For premedication specifically: The FDA label states 1.1 mg/kg, which would be the full 14.8 mg dose. 1
• For nausea/vomiting or allergic conditions: Use the lower end, capping at 12.5 mg (0.5 mL). 1

Administration Route: Deep IM Only

• Deep intramuscular injection is the only acceptable route for this child—this is the FDA's preferred parenteral route. 1
• Never give subcutaneously (contraindicated—causes tissue necrosis). 1
• Never give intra-arterially (causes arteriospasm and gangrene). 1
• IV administration requires extreme caution: If absolutely necessary, dilute to ≤25 mg/mL, infuse at ≤25 mg/minute through a functioning IV line, and stop immediately if the patient reports pain. 1
• The Institute for Safe Medication Practices and American Society of Health-System Pharmacists recommend removing injectable promethazine entirely from clinical settings due to tissue injury risks. 2

Respiratory Monitoring Requirements

• Continuous observation is mandatory because promethazine causes respiratory depression, especially in children. 1
• Respiratory depression has occurred even at recommended doses (0.07 mg/kg), with one case requiring naloxone and another developing respiratory arrest within 30 minutes. 3
• Avoid combining with other respiratory depressants (opioids, benzodiazepines, barbiturates)—if combination is necessary, reduce doses of both agents. 1
• Monitor respiratory rate, oxygen saturation, heart rate, and level of consciousness at 30-minute intervals for at least 2 hours post-injection. 4

Frequency and Maximum Daily Limits

• For nausea/vomiting: Do not repeat more frequently than every 4 hours. 1
• For allergic conditions: May repeat within 2 hours if necessary, then transition to oral route. 1
• Do not use antiemetics for vomiting of unknown etiology in children and adolescents. 1

Common Pitfalls to Avoid

• Extravasation causes severe tissue injury: Inspect the injection site and stop immediately if pain occurs during administration. 1
• Sedation duration is prolonged: Expect the child to sleep within 27 minutes, sit upright at 103 minutes, and return to normal behavior in 19 hours on average. 4
• Insufficient sedation occurs in 29% of cases when used for procedures, so have backup plans ready. 4
• Promethazine has no evidence base for sleep and should not be used as a sleep aid, particularly in patients with psychiatric conditions. 5