What is the recommended dosage of nitrofurantoin for a 10-year-old patient weighing 75 pounds (approximately 34 kilograms) with a urinary tract infection (UTI) and allergies to penicillin and sulfa?

Nitrofurantoin Dosing for a 10-Year-Old Child with UTI

For a 10-year-old child weighing 75 lbs (34 kg) with a urinary tract infection, nitrofurantoin should NOT be used as first-line therapy for febrile UTI or suspected pyelonephritis, as it does not achieve adequate tissue concentrations in the renal parenchyma or bloodstream. 1

Critical Contraindication for Febrile UTI

• Nitrofurantoin is explicitly contraindicated for treating febrile infants and children with UTI because it fails to achieve therapeutic concentrations in the bloodstream and renal parenchyma necessary to treat pyelonephritis or urosepsis. 1
• The American Academy of Pediatrics specifically states that agents excreted in urine but not achieving therapeutic blood concentrations, such as nitrofurantoin, should not be used for febrile UTIs. 1

When Nitrofurantoin May Be Appropriate

If this is an uncomplicated lower urinary tract infection (cystitis) without fever or systemic symptoms, nitrofurantoin could be considered:

Dosing for Uncomplicated Cystitis

• Standard pediatric dosing: 5-7 mg/kg/day divided into 4 doses (general pediatric practice)
• For this 34 kg child: approximately 170-238 mg/day divided into 4 doses, or roughly 42-60 mg four times daily
• Adult equivalent dosing referenced in guidelines: 100 mg four times daily (qid) for uncomplicated UTI 1

Treatment Duration

• 3-7 days for uncomplicated lower UTI 1
• The American Academy of Pediatrics recommends 7-14 days total antimicrobial therapy for UTI in young children, though this applies to agents that treat pyelonephritis 1

Preferred First-Line Alternatives

Given the patient's penicillin and sulfa allergies, better options include:

For Febrile UTI or Suspected Pyelonephritis:

• Ceftriaxone 75 mg/kg once daily (2,550 mg/day for this 34 kg child) 1
• Cefotaxime 150 mg/kg/day divided every 6-8 hours (5,100 mg/day divided) 1
• Gentamicin 7.5 mg/kg/day divided every 8 hours (255 mg/day divided) 1

For Uncomplicated Lower UTI (Afebrile):

• Cephalosporins (cefixime 8 mg/kg/day in 1 dose = 272 mg daily, or cephalexin 50-100 mg/kg/day in 4 doses = 1,700-3,400 mg/day) 1
• These achieve both urinary and tissue concentrations 1

Important Clinical Caveats

• Cross-reactivity concern: While cephalosporins can be used in penicillin allergy, significant penicillin allergy warrants consideration of alternative agents 1
• Fluoroquinolones (ciprofloxacin 10-20 mg/kg/dose every 12 hours = 340-680 mg twice daily) are an option but should be reserved due to resistance concerns and pediatric safety considerations 2
• Treatment duration: 7-14 days is recommended for pediatric UTI regardless of route of administration 1
• Clinical reassessment: Monitor for improvement within 24-48 hours; lack of response requires diagnostic reassessment and potential antimicrobial change 1, 2

Key Pitfall to Avoid

The most critical error would be using nitrofurantoin for a febrile child or one with suspected upper tract involvement (pyelonephritis), as this provides inadequate treatment and risks progression to urosepsis or renal scarring. 1 Always assess for fever, flank pain, or systemic symptoms before selecting nitrofurantoin.