Pediatric Dosing and Compounding of an Oral Suspension
A 4-year-old girl weighing 16 kg is prescribed amoxicillin 45 mg/kg/day divided every 12 hours for acute otitis media. The pharmacy has only 500 mg capsules and amoxicillin powder for oral suspension 250 mg/5 mL. The suspension label states reconstitute with 60 mL of water to yield 100 mL. The child refuses the commercially flavored suspension, and the prescriber asks whether a compounded suspension can be made from capsules using a 1:1 simple syrup and purified water vehicle. The pharmacy has no suspending agent other than the syrup. The prescription is for 10 days. The mother reports the child had a rash with penicillin as an infant, described as a mild flat rash that resolved without treatment.
1. Calculate the dose and total quantity needed, and evaluate whether the requested compounded preparation is pharmaceutically appropriate.
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Dose calculation. 45 mg/kg/day x 16 kg = 720 mg/day, divided every 12 hours = 360 mg per dose. Rounding to a measurable volume, 360 mg is not a convenient multiple of 250 mg/5 mL (which gives 50 mg/mL). 360 mg / 50 mg/mL = 7.2 mL per dose. Practically, the prescriber may round to 7.5 mL (375 mg) per dose, giving 750 mg/day (46.9 mg/kg/day), which is acceptable.
Total quantity. 7.2 mL x 2 doses x 10 days = 144 mL. Using 7.5 mL, 150 mL. The commercial bottle yields only 100 mL after reconstitution, so two bottles would be needed, or a compounded preparation of adequate volume.
Pharmaceutical evaluation of the requested compound. A 1:1 simple syrup and water vehicle is a solution, not a suspension. Amoxicillin powder from capsules will not remain dispersed; it will settle and dose non-uniformly, risking under- or over-dosing. Without a suspending agent (for example methylcellulose, xanthan gum, or a commercial suspending vehicle), the preparation is not pharmaceutically acceptable. Additionally, amoxicillin is unstable in aqueous solution and requires refrigeration and a short beyond-use date (typically 14 days refrigerated for the commercial product; extemporaneous preparations are usually limited to 14 days refrigerated). A 10-day course fits within this window, but the lack of a suspending agent does not.
Recommendation. Use the commercial suspension, or if flavor is the issue, consider a different compatible flavoring or a commercial suspending vehicle that has stability data for amoxicillin. Document the calculation and the refusal to compound an unstable, non-suspendable product.
2. How should the reported infantile penicillin rash influence the plan?
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A mild, flat, non-urticarial rash in infancy is often a benign maculopapular reaction, frequently associated with a viral illness rather than true IgE-mediated penicillin allergy. It does not automatically contraindicate amoxicillin, but it should not be dismissed without assessment.
Approach.
- Take a structured history: timing relative to the dose, presence of hives, swelling, wheeze, vomiting, or hypotension, and whether the child has taken penicillin since without reaction.
- Classify the reaction. A non-urticarial maculopapular rash without systemic features is low-risk. An urticarial or anaphylactic reaction is high-risk and requires avoidance.
- For low-risk histories, direct oral challenge or graded challenge under supervision may be appropriate, but this requires prescriber involvement and a setting where reactions can be managed.
- If the reaction is judged high-risk or cannot be clarified, choose a non-beta-lactam alternative for otitis media (for example, depending on local resistance, a macrolide or other agent), recognizing that amoxicillin is first-line for most cases.
Practical point. The pharmacist should not simply dispense amoxicillin because the rash was 'mild.' Document the history, discuss with the prescriber, and record the allergy classification in the patient record so future decisions are informed. If amoxicillin is given, counsel the mother on what to watch for and when to seek emergency care.
3. The prescriber agrees to use the commercial suspension but wants 375 mg twice daily. Write the dispensing instructions and counseling points, including what to do about the volume shortfall.
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Dispensing. Amoxicillin 250 mg/5 mL suspension, two bottles to provide at least 150 mL. Reconstitute each bottle with 60 mL of water per the label, shake well, and label 'refrigerate, discard after 14 days.'
Directions. Give 7.5 mL (375 mg) by mouth every 12 hours for 10 days. Provide an oral dosing syringe calibrated in 0.5 mL increments; household spoons are inaccurate.
Counseling points.
- Shake the bottle well before every dose; the drug settles.
- Refrigerate; do not freeze.
- Complete the full 10 days even if the child feels better, to prevent relapse and resistance.
- Common effects: loose stools, mild nausea, rash. Seek urgent care for hives, facial swelling, wheezing, or severe watery/bloody diarrhea.
- Give with or without food; if stomach upset, give with food.
- If a dose is missed, give it as soon as remembered unless it is almost time for the next dose; do not double up.
- Keep out of reach of children.
Volume shortfall. Because the total needed (150 mL) exceeds one bottle (100 mL), dispense two bottles and instruct the mother to finish the first bottle before opening the second, or to use the second only if the first runs out. Alternatively, verify whether the prescriber will accept 7.2 mL (360 mg) per dose, which still requires 144 mL, so two bottles remain necessary. Document the quantity dispensed and the calculation.