Amoxicillin Pediatric Dosing Calculator

An amoxicillin pediatric dosing calculator converts a child’s weight into the correct daily dose, per-dose amount, and the milliliters of liquid suspension to give, using the FDA-approved weight-based dosing bands. Pediatric amoxicillin is never dosed by age alone: two children the same age can need very different doses because dosing is set in milligrams per kilogram of body weight per day. Enter the child’s weight, pick the infection severity, and the tool does the rest.

Dosing follows three standard bands from the FDA label and pediatric guidelines. Mild to moderate ear, nose, throat, skin, or urinary infections: 25 mg/kg/day split every 12 hours, or 20 mg/kg/day split every 8 hours. Severe infections and lower respiratory tract infections: 45 mg/kg/day every 12 hours, or 40 mg/kg/day every 8 hours. High-dose therapy for resistant ear infections and pneumonia in areas with penicillin-resistant pneumococci: 80-90 mg/kg/day. Children under 3 months are capped at 30 mg/kg/day because of immature kidney function, and the typical pediatric ceiling for high-dose regimens is 4,000 mg per day.

Quick Answer

Weight, not age: how pediatric dosing is set

Children clear drugs roughly in proportion to body size, so pediatric dosing scales with weight. The unit is mg/kg/day: milligrams of drug per kilogram of body weight, per day. Multiply by the child's weight to get the total daily dose, then divide by the number of doses per day. That is the entire arithmetic behind pediatric prescribing.

Age-based shortcuts are where errors happen. A small 6-year-old and a large 4-year-old can differ by 5 kg, which at 45 mg/kg/day is a 225 mg daily difference, more than a full dose. Always use a current scale weight, and re-weigh if the prescription is a refill weeks later.

The three dosing bands

The FDA label and pediatric guidelines define the bands by infection severity. Mild to moderate ear, nose, throat, skin, and urinary infections: 25 mg/kg/day divided every 12 hours, or 20 mg/kg/day divided every 8 hours. Severe infections and all lower respiratory tract infections: 45 mg/kg/day every 12 hours, or 40 mg/kg/day every 8 hours. High-dose therapy, 80-90 mg/kg/day, is reserved for acute ear infections and pneumonia where penicillin-resistant pneumococci are a concern, such as children under 2, recent antibiotic use, or daycare attendance.

Twice-daily dosing is the modern default because families actually complete it; three-times-daily schedules use the slightly lower per-day bands shown because more frequent doses keep levels steadier. The calculator applies the right band automatically for the frequency you choose.

Turning milligrams into milliliters

The pharmacy dispenses amoxicillin as a powder that is reconstituted into a liquid suspension, and the label states the strength: 125 mg, 250 mg, or 400 mg per 5 mL are the common pediatric strengths. The conversion is mL per dose = (mg per dose ÷ strength) × 5. So a 225 mg dose from a 250 mg/5 mL bottle is (225 ÷ 250) × 5 = 4.5 mL.

Measure with the oral syringe or dosing cup that comes with the medicine. Kitchen teaspoons vary in volume and are a documented source of dosing errors in children. Shake the bottle well before each dose, store reconstituted suspension in the refrigerator, and discard leftover medicine after the date on the label, usually 14 days.

Worked example: 18 kg child, ear infection

A child weighing 18 kg is prescribed the mild-to-moderate regimen, twice daily, and the pharmacy dispensed 250 mg/5 mL suspension. The tool computes: daily dose = 18 × 25 = 450 mg; per dose = 450 ÷ 2 = 225 mg; volume = (225 ÷ 250) × 5 = 4.5 mL per dose. These are the tool's exact outputs for these inputs.

If the same child needed the severe band at 45 mg/kg/day, the numbers become 810 mg/day, 405 mg per dose, and 8.1 mL per dose. If the computed daily dose ever exceeds 4,000 mg, the calculator flags it and caps the display, because that is the standard pediatric ceiling for high-dose regimens.

What competing dosing calculators get wrong

Many online dosing tools ask for age and return a flat dose, which contradicts the FDA label's weight-based bands and can underdose larger children or overdose smaller ones. Others give the daily total in milligrams but leave parents to convert to milliliters, the exact step where kitchen-spoon errors happen. Some omit the frequency-specific bands, quoting only 25 or 45 mg/kg/day without adjusting for twice vs three times daily.

This calculator keeps weight as the single required input, applies the correct band for the chosen frequency automatically, converts to milliliters using the actual bottle strength, and enforces the 4,000 mg/day safety ceiling with a visible flag. It also states plainly what it is: an educational estimate, not a prescription.

The 10-day strep rule and finishing the course

For infections caused by group A streptococcus (strep throat), treatment must run at least 10 days even if the child feels better sooner, because shorter courses raise the risk of acute rheumatic fever. More generally, antibiotics should continue 48 to 72 hours beyond symptom resolution: stopping early lets the infection return and contributes to antibiotic resistance.

1. Give doses on schedule. Space them evenly (every 12 or 8 hours) and set reminders; missed doses lower effectiveness.
2. Measure, do not guess. Use the oral syringe every time, and shake the bottle first.
3. Watch for side effects. Mild stomach upset or loose stools are common; hives, swelling, or breathing trouble need immediate care.
4. Finish every dose. Complete the full course even after symptoms resolve, per the prescriber's duration.
5. Discard leftovers properly. Refrigerate during the course and discard after the label date; never save antibiotics for later.

Frequently Asked Questions