Pediatric Amoxicillin Dose and Penicillin Allergy History
A mother brings in a prescription for her 4-year-old daughter weighing 16 kg: amoxicillin 400 mg/5 mL suspension, 5 mL PO TID for 10 days, for acute otitis media. The child has no fever now but had ear pain for two days. The mother mentions that the child "broke out in hives" after amoxicillin two years ago, but she is not sure whether it was the antibiotic or a viral rash. The child has eczema and takes no regular medications. The prescription as written provides 150 mL, which is exactly 10 days at 5 mL TID. The mother asks whether the dose is right for her daughter and whether the allergy means she cannot take it. The pharmacy has amoxicillin 400 mg/5 mL in stock.
1. Calculate the prescribed daily dose in mg/kg/day and assess whether it is appropriate for acute otitis media.
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Calculation: 5 mL × 400 mg/5 mL = 400 mg per dose. Three doses per day = 1,200 mg/day. 1,200 mg ÷ 16 kg = 75 mg/kg/day.
Assessment: For acute otitis media, high-dose amoxicillin is typically 80-90 mg/kg/day divided BID or TID. At 75 mg/kg/day, this is slightly below the high-dose range but within a commonly used range (40-90 mg/kg/day depending on risk factors). Whether to recommend high-dose depends on local resistance patterns and whether the child has recent antibiotic exposure or severe symptoms.
Practical points:
- The volume is adequate: 5 mL × 3 × 10 = 150 mL, matching the dispensed quantity.
- TID dosing is acceptable but BID is often preferred for adherence; do not change without prescriber agreement.
- Shake well and refrigerate if the label requires; discard after 14 days.
- If high-dose therapy is intended, the prescriber would need to adjust to approximately 1,300-1,440 mg/day (e.g., 6.5 mL TID or 8 mL BID). Contact the prescriber rather than adjusting silently.
2. How do you evaluate the reported "hives" reaction and what do you recommend?
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Evaluation: The history is vague - "hives" two years ago, uncertain whether it was the drug or a viral rash, in a child with eczema. This is a common scenario where true penicillin allergy is over-reported. However, hives are a type II (IgE-mediated) symptom and cannot be dismissed without assessment.
What to do:
- Ask targeted questions: timing relative to the dose (within minutes to hours suggests IgE), whether there was swelling, breathing difficulty, or hypotension, whether it resolved, and whether other drugs were taken.
- Do not label the child as penicillin-allergic without a clear history, and do not simply proceed without addressing it.
- Contact the prescriber: options include a supervised oral challenge, allergy referral, or a non-beta-lactam alternative (e.g., cefdinir if appropriate, noting cross-reactivity is low but not zero).
- If amoxicillin is given, counsel the mother on signs of anaphylaxis and when to seek emergency care.
Documentation: Record the reported reaction, the questions asked, the prescriber discussion, and the plan.
3. The prescriber decides to proceed with amoxicillin. What counselling points do you give the mother?
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Counselling:
- Dose and schedule: Give 5 mL three times daily, ideally evenly spaced. Complete all 10 days even if the child feels better.
- Administration: Shake the bottle well before each dose; measure with the oral syringe provided, not a kitchen spoon. Refrigerate if required and discard remaining suspension after 14 days.
- Allergy watch: Because of the prior hives, explain the signs of a serious reaction - facial or throat swelling, difficulty breathing, widespread hives, vomiting with lethargy - and tell her to stop the drug and call emergency services if these occur. Mild localized rash should be reported to the pharmacy or prescriber before continuing.
- Side effects: Diarrhea, nausea, and rash are possible; probiotics are optional but not required.
- Adherence tips: Pair doses with meals and use a reminder; if a dose is missed, give it when remembered unless close to the next dose, and do not double up.
- Follow-up: If ear pain or fever returns or does not improve in 48-72 hours, contact the prescriber.
- Confirm understanding: Ask her to repeat back the dose and the warning signs.