Dosing Recommendations for 18-Month-Old Child (11 kg)
Cetirizine Dosing
For an 18-month-old child weighing 11 kg, administer cetirizine 0.25 mg/kg twice daily, which equals approximately 2.75 mg (or 2.5-3 mg) twice daily, for a total daily dose of 5-6 mg. 1, 2
- The weight-based dosing of 0.25 mg/kg twice daily has been specifically validated in infants and very young children aged 6-46 months in prospective, randomized, double-blind, placebo-controlled studies 1, 2
- This twice-daily regimen is necessary in very young children because levocetirizine (the active enantiomer) oral clearance is rapid and increases with body weight and age, requiring more frequent dosing than in older patients 1
- The safety profile at this dose has been well-established, with no differences in adverse events compared to placebo, and actually showed a trend toward fewer sleep-related disturbances 2
- No cardiac effects (QT prolongation) were observed at this dosing in infants 2
Common pitfall to avoid: Do not use the standard adult dose of 10 mg once daily in this age group, as pharmacokinetic studies demonstrate that young children require weight-based, twice-daily dosing for optimal efficacy 1
Amoxicillin Dosing
For an 18-month-old child weighing 11 kg, the amoxicillin dose depends on the indication:
For Mild-to-Moderate Respiratory Tract Infections:
- Administer 45 mg/kg/day divided every 12 hours, which equals 250 mg (approximately 5 mL of 250 mg/5 mL suspension) twice daily 3
For Severe Infections or High Pneumococcal Resistance Areas:
- Administer 90 mg/kg/day divided every 12 hours, which equals 495 mg (approximately 500 mg or 10 mL of 250 mg/5 mL suspension) twice daily 3
For Group A Streptococcal Infections:
Administer 50-75 mg/kg/day divided into 2 doses for 10 days, which equals 275-410 mg (approximately 5.5-8 mL of 250 mg/5 mL suspension) twice daily 3
The higher dose regimen (90 mg/kg/day) is specifically indicated for children <2 years old, those attending daycare, recent antibiotic exposure within 30 days, or areas with >10% penicillin-resistant S. pneumoniae 3
Treatment duration should be 7-10 days for most respiratory infections, with pneumonia specifically requiring 10 days 3
Clinical improvement should be evident within 48-72 hours; if no improvement occurs, reevaluation is necessary 3
Critical consideration: For β-lactamase-producing organisms (H. influenzae, M. catarrhalis), use amoxicillin-clavulanate (Augmentin) at 90 mg/kg/day of the amoxicillin component instead of amoxicillin alone 3
Ondansetron Dosing
For an 18-month-old child weighing 11 kg, administer ondansetron 0.15 mg/kg per dose (maximum 8 mg), which equals approximately 1.65 mg (round to 1.5-2 mg) per dose.
- Ondansetron can be administered orally or intravenously depending on the clinical situation and severity of vomiting
- The dose can be repeated every 8 hours as needed for nausea and vomiting
- For oral administration, ondansetron disintegrating tablets (ODT) are preferred in young children for ease of administration
- Maximum single dose should not exceed 8 mg regardless of weight
Common pitfall to avoid: Do not exceed the maximum single dose of 8 mg, even if weight-based calculation suggests a higher dose, as this increases risk of QT prolongation without additional benefit.