Dispensing amoxicillin suspension for a 20 kg child

Dose calculation

$$45\ \text{mg/kg/day} \times 20\ \text{kg} = 900\ \text{mg/day}$$

$$900 \div 3 = 300\ \text{mg per dose}$$

Concentration is 250 mg/5 mL = 50 mg/mL, so

$$300 \div 50 = 6\ \text{mL per dose}$$

Course volume

$$6\ \text{mL} \times 3 \times 10 = 180\ \text{mL}$$

One 100 mL bottle gives about 16 doses, roughly 5.3 days, so two bottles are required. If both are reconstituted on day 1, the second bottle is used between day 6 and day 10, still inside the 14-day refrigerated limit - acceptable. The tidier practice is to reconstitute the second bottle only when it is opened, which removes any ambiguity.

Label and counselling

• 'Give 6 mL three times a day for 10 days.'
• Supply an oral dosing syringe marked at 6 mL; a household teaspoon is anywhere between 3 and 7 mL and must not be used.
• 'Reconstitute by adding water to the mark, shake well; store in the refrigerator; shake before every dose.'
• Write the discard date: refrigerated, 14 days from reconstitution, i.e. 17 March for a bottle opened on 3 March.
• Complete the full 10 days even if the child feels well; do not save leftovers for another illness or share with a sibling.

Do not make the change yourself, and do not simply drop the midday dose. Amoxicillin is a time-dependent antibiotic: what matters is the fraction of the dosing interval for which the free drug concentration stays above the minimum inhibitory concentration. Stretching the interval compresses that time and risks both treatment failure and selection of resistant pneumococcus, which is the specific worry in acute otitis media.

However, the practical schedule can be rescued. Three doses eight hours apart fit a school day more easily than the family thinks:

• 7.00 a.m. before leaving for school
• 3.00 p.m. immediately after school
• 11.00 p.m. at bedtime

This is genuinely eight-hourly and is far better than a 'twice daily' compromise or a missed school dose. Give the family a written timetable and, if the school permits, arrange a midday dose with the school nurse; otherwise use the 7 a.m. / 3 p.m. / 11 p.m. pattern.

If the family still cannot manage it, the correct action is to contact the prescriber, who may choose a different agent or a prescriber-sanctioned twice-daily regimen at a higher dose. Adjusting the regimen in the pharmacy without that conversation is not appropriate, and a missed-dose policy ('give it as soon as remembered, but never double up') should be explained.

Do not dispense on your own authority. A pharmacist cannot decide from a counter conversation whether this is a true penicillin allergy, and the safest action is to hold the medicine and contact the prescriber before the first dose is given.

Why the history is ambiguous. A flat, non-itchy maculopapular rash appearing on about day 5 of a course is frequently not IgE-mediated. In children it is commonly a viral exanthem (Epstein–Barr virus is the classic example) coinciding with the antibiotic, or a benign delayed drug eruption. That is different from urticaria, angioedema, wheeze, hypotension or a blistering eruption, which indicate genuine, potentially severe hypersensitivity.

What to do

1. Take a structured history: timing, itch, urticaria, swelling, breathing difficulty, mucosal involvement, what treatment was needed, and any later exposure to penicillins.
2. Contact the prescriber, record the discussion in the patient record and on the prescription, and note the reaction on the child's pharmacy record and any allergy card.
3. If the prescriber judges it a low-risk benign rash, dispensing may proceed with counselling on warning signs and when to stop and seek help.
4. If a true allergy is judged likely, the prescriber chooses an alternative agent; the pharmacist checks the choice and reinforces the allergy label. Either way, document, and never silently substitute on the basis of a parental description alone.