What is the appropriate dose of Ceftriaxone (Ceftriaxone) for a 4-year-old female patient weighing 18.9 kg with pyelonephritis, and is 100mg/kg acceptable?

Ceftriaxone Dosing for Pediatric Pyelonephritis

For a 4-year-old female weighing 18.9 kg with pyelonephritis, 100 mg/kg/day of ceftriaxone is excessive and not recommended—the appropriate dose is 50-75 mg/kg/day (approximately 950-1,420 mg/day for this patient), given once daily or divided every 12-24 hours. 1, 2

Standard Pediatric Dosing Algorithm

For infants and children beyond the neonatal period with pyelonephritis:

• Standard dose: 50-75 mg/kg/day given once daily or divided every 12-24 hours 1, 2
• For this 18.9 kg patient: 945-1,418 mg/day (practical dosing would be 1,000 mg once daily)
• Maximum daily dose: 2 grams for non-meningeal infections 2

Why 100 mg/kg Is Not Appropriate

The 100 mg/kg/day dosing is reserved for specific severe infections, NOT routine pyelonephritis:

• Bacterial meningitis: 100 mg/kg/day divided every 12-24 hours (maximum 4 g daily) 2
• Severe pneumonia with documented penicillin-resistant pneumococcus: 100 mg/kg/day 2
• Gram-negative enteric bacilli with CNS involvement: 100 mg/kg/day 2

For uncomplicated pyelonephritis, even if severe, the standard 50-75 mg/kg/day range is appropriate and effective. 1, 2

Evidence Supporting Standard Dosing for Pyelonephritis

Clinical studies demonstrate excellent efficacy with standard dosing:

• A prospective study of 34 children with acute pyelonephritis used 50 mg/kg/day (maximum 2 g/day) with successful eradication in all cases 3
• Comparative study showed once-daily ceftriaxone was superior to twice-daily cefotaxime for childhood upper UTIs, with better cure rates and fewer recurrences 4
• The once-daily dosing advantage makes ceftriaxone particularly attractive for pediatric pyelonephritis compared to other agents requiring multiple daily doses 4

Practical Dosing Recommendation

For this 18.9 kg patient with pyelonephritis:

• Recommended dose: 1,000 mg (approximately 53 mg/kg) IV/IM once daily 1, 2
• Alternative: 500 mg IV every 12 hours (total 1,000 mg/day) 1, 2
• Duration: 7-10 days based on clinical response 3, 4

Important Safety Consideration

Reversible biliary pseudolithiasis can occur even with standard dosing:

• Gallbladder precipitates developed in 15% of children receiving 50 mg/kg/day for pyelonephritis after only 3-5 doses 3
• All cases were asymptomatic and resolved spontaneously 2-5 months after discontinuation 3
• This is not a contraindication to use, but clinicians should be aware to prevent unnecessary anxiety or cholecystectomy 3
• The antibacterial and pharmacokinetic benefits outweigh this reversible complication 3

Common Pitfall to Avoid

Do not extrapolate meningitis dosing (100 mg/kg/day) to other infections. The higher dose is specifically for achieving adequate CNS penetration and treating resistant organisms in the central nervous system. 2 For pyelonephritis, standard dosing provides excellent urinary and tissue concentrations without the need for higher doses that increase the risk of adverse effects including biliary sludging. 3