Pediatric Dosing for Injectable Cefotaxime (Monocef), Benzylpenicillin (Pan), and Ondansetron (Emset)
For a 5-year-old child weighing 17.5 kg, administer cefotaxime (Monocef) 875 mg IV every 8 hours (50 mg/kg/dose), benzylpenicillin 875–1,050 mg IV every 6 hours (50–60 mg/kg/dose), and ondansetron 3.5 mg IV (0.2 mg/kg/dose) for nausea/vomiting.
Cefotaxime (Monocef) Dosing
Standard Dosing Algorithm
- For children >1 month of age with serious infections, the recommended dose is 150 mg/kg/day divided every 8 hours (50 mg/kg per dose). 1
- For this 17.5 kg child: 50 mg/kg × 17.5 kg = 875 mg IV every 8 hours (total daily dose 2,625 mg). 1
- Maximum daily dose: Do not exceed 12 g/day for severe infections, though typical maximum is 6 g/day for most pediatric infections. 1
Clinical Context Considerations
- Cefotaxime provides excellent coverage against common pediatric pathogens including Streptococcus pneumoniae, Haemophilus influenzae, and gram-negative enteric organisms. 2
- For suspected meningitis or CNS infections, increase to 200–300 mg/kg/day divided every 6–8 hours (maximum 12 g/day). 1
- Cefotaxime has demonstrated superior efficacy compared to penicillin-gentamicin combinations in severe pediatric infections, with cure rates exceeding 94%. 3
Important Caveats
- Listeria coverage: Cefotaxime is not active against Listeria monocytogenes; if listeriosis is suspected (especially in neonates or immunocompromised patients), add ampicillin. 4, 5
- Pseudomonas coverage: Cefotaxime has limited activity against Pseudomonas aeruginosa and should not be used as monotherapy for suspected pseudomonal infections. 2
Benzylpenicillin G (Pan/Penicillin) Dosing
Standard Dosing Algorithm
- For children aged 5–14 years with suspected serious infection, the dose is 200–300 mg/kg/day divided into 6 doses (every 4 hours), with a maximum of 6 g/day. 1
- For this 17.5 kg child:
- Lower range: 200 mg/kg/day = 3,500 mg/day ÷ 6 doses = 583 mg every 4 hours
- Upper range: 300 mg/kg/day = 5,250 mg/day ÷ 6 doses = 875 mg every 4 hours
- Practical dosing: Administer 600–900 mg IV every 4 hours (or 875–1,050 mg every 6 hours if dosing every 6 hours is preferred for convenience). 1
Clinical Context
- Benzylpenicillin is highly effective against Streptococcus pneumoniae, group B streptococci, and Neisseria meningitidis. 1
- For asplenic patients or suspected pneumococcal sepsis, benzylpenicillin remains first-line therapy. 1
- The intravenous route is strongly preferred over intramuscular for serious infections. 1
Important Caveats
- Gram-negative coverage: Benzylpenicillin has poor activity against gram-negative organisms; if gram-negative sepsis is suspected, cefotaxime or an aminoglycoside must be added. 1
- Dosing frequency: The 4-hour interval is critical for maintaining therapeutic levels in severe infections; do not extend to 6-hour intervals without clinical justification. 1
Ondansetron (Emset) Dosing
Standard Dosing Algorithm
- For pediatric patients with nausea/vomiting, the typical dose is 0.15–0.2 mg/kg IV (maximum 16 mg per dose).
- For this 17.5 kg child: 0.2 mg/kg × 17.5 kg = 3.5 mg IV as a single dose or every 8 hours as needed.
- Alternative dosing: For children 4–11 years old, a fixed dose of 4 mg IV is commonly used and is within the safe range for this weight.
Clinical Context
- Ondansetron is a 5-HT3 receptor antagonist highly effective for chemotherapy-induced, postoperative, and gastroenteritis-related nausea/vomiting.
- Administration: Infuse over 2–5 minutes; rapid IV push may increase risk of QT prolongation.
Important Caveats
- QT prolongation risk: Avoid in patients with congenital long QT syndrome or those receiving other QT-prolonging medications.
- Maximum single dose: Do not exceed 16 mg per dose, even in larger children.
- Frequency: Can be repeated every 8 hours if needed, but reassess need after 24–48 hours.
Critical Prescribing Principles
Weight-Based Dosing Accuracy
- Always use actual measured weight for dose calculations; visual estimation can result in errors ranging from 300% overestimation to near-100% underestimation. 6
- For drugs with narrow therapeutic indices (e.g., aminoglycosides, sedatives), weight-based dosing is mandatory. 6
Combination Therapy Considerations
- If both cefotaxime and benzylpenicillin are prescribed together, ensure there is a clear clinical indication (e.g., suspected mixed infection with Listeria or enhanced streptococcal coverage). 4
- Penicillin-cephalosporin combinations may show antagonism against group B streptococci in vitro but are synergistic against Listeria monocytogenes. 4
- In most cases, cefotaxime alone is sufficient for empiric therapy of serious pediatric infections unless specific pathogens (e.g., Listeria) are suspected. 3, 5
Monitoring and Reassessment
- Reassess clinical response at 48–72 hours: If no improvement, consider broadening coverage (e.g., adding vancomycin for MRSA, azithromycin for atypicals) or adjusting based on culture results. 1
- Renal function: Adjust cefotaxime and penicillin doses in renal impairment; ondansetron does not require dose adjustment.
Summary Dosing Table
| Drug | Dose for 17.5 kg child | Frequency | Route |
|---|---|---|---|
| Cefotaxime (Monocef) | 875 mg | Every 8 hours | IV |
| Benzylpenicillin (Pan) | 600–900 mg | Every 4 hours | IV |
| Ondansetron (Emset) | 3.5 mg | Every 8 hours PRN | IV |