Article — Amoxicillin Pediatric Dosage
Amoxicillin pediatric dosage calculator
Pediatric amoxicillin is dosed by body weight, typically 25-50 mg/kg/day for mild infections and 80-90 mg/kg/day for acute otitis media or pneumonia, divided into 2 or 3 daily doses. The maximum daily dose is 3000 mg (the adult cap). This calculator converts weight in kg or pounds into milligrams per dose and milliliters of suspension based on AAP-aligned ranges.
The math is identical for any weight-based antibiotic: weight times mg/kg target divided by daily frequency. What changes between infections is the target dose and the duration. Below is the practical breakdown clinicians and parents need.
Before amoxicillin and its predecessors, group A strep pharyngitis carried roughly a 3% risk of acute rheumatic fever in untreated children during epidemics, with today's antibiotic-treated risk below 0.1%. Finishing the course matters more than the brand on the bottle.
What is amoxicillin pediatric dosing
Amoxicillin is a beta-lactam antibiotic in the aminopenicillin family. It targets the bacterial cell wall and is first-line for most childhood respiratory and ear infections caused by Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, and Moraxella catarrhalis. Pediatric dosing is weight-based because children's pharmacokinetics scale with body size rather than age.
The American Academy of Pediatrics publishes the Red Book annually with current pediatric amoxicillin recommendations. The two main targets families encounter are 45 mg/kg/day for routine sinusitis or strep, and 80-90 mg/kg/day high-dose regimens for acute otitis media in children at risk of resistant pneumococcus.
Standard amoxicillin dose ranges
Dosing varies by indication. The table below summarizes the most commonly prescribed regimens. Always verify against your prescriber's order — these are reference ranges, not orders.
- Acute otitis media (high-dose) = 80-90 mg/kg/day divided BID, 5-10 days
- Group A strep pharyngitis = 50 mg/kg/day (max 1000 mg) once daily or BID, full 10 days
- Acute bacterial sinusitis = 45-90 mg/kg/day divided BID, 10-14 days
- Community-acquired pneumonia = 90 mg/kg/day divided BID or TID, 5-7 days
- Uncomplicated UTI = 25-50 mg/kg/day divided TID, 7-10 days
- Adult maximum daily dose = 3000 mg (reached around 33-37 kg at 90 mg/kg/day)
How to use this amoxicillin calculator
Enter the child's measured weight, the mg/kg/day target your prescriber chose, the daily frequency (twice or three times daily), and the suspension strength on the bottle. The calculator returns milligrams per dose, milliliters per dose, total daily dose, and a warning if the daily dose exceeds 3000 mg.
A worked example: a 20 kg child, 45 mg/kg/day, BID, 250 mg/5 mL suspension. Daily dose = 20 x 45 = 900 mg. Per dose = 900 / 2 = 450 mg. Volume = 450 / 50 = 9 mL twice daily. Many parents are surprised by the volume — that is normal at this strength. Switching to 400 mg/5 mL would drop the per-dose volume to about 5.6 mL.
125 mg/5 mL 25 mg per 1 mL250 mg/5 mL 50 mg per 1 mL400 mg/5 mL 80 mg per 1 mLkg from lb lb ÷ 2.2046Choosing the right suspension
Pediatric amoxicillin comes in three common oral suspension strengths and several solid forms. The 125 mg/5 mL suspension is the original pediatric formulation, used heavily for infants and toddlers under 10 kg where dose volumes stay reasonable. The 250 mg/5 mL is the workhorse for school-age children, and 400 mg/5 mL exists specifically to keep volume manageable on high-dose otitis regimens.
Concentration matters because volume tolerance is real. A toddler given 18 mL of 125 mg/5 mL twice daily will frequently refuse the second dose. The same 450 mg as 9 mL of 250 mg/5 mL is much more likely to land. Talk to your pharmacist about switching strengths if your child resists the prescribed volume.
BID vs TID amoxicillin dosing
Twice-daily (BID, q12h) and three-times-daily (TID, q8h) dosing produce different pharmacokinetic profiles. BID gives higher peaks and longer troughs, which suits pneumococcus where time-above-MIC is the key parameter and high-dose strategies improve middle ear penetration. TID gives steadier serum levels and is preferred for more sensitive organisms like group A strep, where 50 mg/kg once daily also works because penicillins kill streptococci at relatively low concentrations.
For school-age children, BID dosing avoids the awkward midday dose at school. If your prescription allows BID and your child is at school, ask the prescriber to confirm BID is appropriate — for most amoxicillin indications it is.
Amoxicillin safety and side effects
Common side effects include diarrhea (10-25% of children), nausea, abdominal discomfort, and a non-allergic rash that appears 5-10 days into the course. The non-allergic rash is benign and usually resolves on its own — but distinguishing it from true penicillin allergy needs a clinician's eye. Stop the medicine and call the prescriber for any wheezing, facial swelling, or hives.
Children with a documented penicillin or cephalosporin allergy must not receive amoxicillin. The cross-reactivity rate is low but the risk of anaphylaxis is real. Always confirm allergy history at the prescriber's office, not at the pharmacy counter.
Common pediatric dosing mistakes
The most frequent dosing errors fall into a few categories. Using a kitchen teaspoon (which can hold anywhere from 3 to 7 mL) instead of the supplied oral syringe overdoses or underdoses by 25-50%. Stopping the antibiotic after 5 days because the child feels better — particularly for group A strep — sets up a rebound infection and rare but serious complications like acute rheumatic fever. Storing reconstituted suspension on the counter instead of in the refrigerator drops potency below the therapeutic range within days.
Equally common is double-dosing after vomiting. If the dose comes back up within 15 minutes, redose; after 30 minutes, the dose has likely been absorbed and the next scheduled dose should proceed normally. When in doubt, call the prescriber's office or a 24-hour nurse line rather than guessing.
Renal function adjustments are another underappreciated source of error. Children with chronic kidney disease or acute kidney injury need extended dosing intervals, not lower per-dose amounts. The dose calculator on this page assumes normal renal function. Newborns under one month also need separate pediatric infectious disease guidance — their hepatic and renal clearance pathways are still developing, and standard mg/kg dosing can produce supratherapeutic levels.
Storage of the reconstituted suspension matters more than parents usually realize. Most US amoxicillin suspensions are stable for 14 days when refrigerated at 2-8°C after mixing. Once that window closes, the active drug has degraded enough that residual doses may be subtherapeutic. Throw the bottle out at day 14 even if it looks fine, and never freeze it — freezing fractures the suspension and changes how the drug delivers per milliliter.