the child can swallow tabletsStep 1 Convert pounds to kg:70 lb × 1 kg/2.2 lb = 31.8 kgStep 2 Calculate the dose in mg:31.8 kg × 15 mg/kg/day = 477 mg/dayStep 3 Divide the dose by the frequency:477 mg/day ÷ 3 (tid) = 159 mg/dose q8hThe total dose is 159 mg every 8 hours. Since the tablets only come in 250 and 500 mg, it is probably best to prescribe the oral suspension to be more precise.Table 3.6 Calculating the dose of amoxicillin suspension in mL for a 10‐year‐old child weighing 70 lbStep 1 Convert pounds to kg:70 lb × 1 kg/2.2 lb = 31.8 kgStep 2 Calculate the dose in mg:31.8 kg × 40 mg/kg/day = 1272 mg/dayStep 3 Divide the dose by the frequency:1272 mg/day ÷ 3 (tid) = 424 mg/dose bidStep 4 Convert the mg dose to mL:424 mg/dose ÷ 125 mg/5 mL = 3.39 mL bidStep 5 Convert mL into teaspoonfulsa3.39 mL ÷ 5 mL = 0.68 teaspoonful Rx: amoxicillin oral suspension 125 mg/5 mLDisp: 100 mL bottleSig: Take 3.4 cc orally three times a day for 7 days for dental infectionNote: mL (milliliters) is sometimes referred to as cc or cubic centimeters. Usually, a medical dropper will have markers in cc which is the same as mL. There is probably less misinterpretation when mL is used rather than cc.a Each teaspoonful is 5 mL.
How supplied: suspension comes in concentrations of 125 mg/5 mL, 250 mg/5 mL, 250 mg/mL, 400 mg/mL (100 mL bottle).
Advise the parent to get a medicine dropper/spoon rather than using an ordinary teaspoon because of variations in measurements of a teaspoonful. After amoxicillin solution is mixed, it is best to store it in a refrigerator between 2 °C and 8 °C (36–46 °F); do not freeze. Throw away any unused medicine after 14 days.
3.2.3.2 Amoxicillin Chewable Tablets (Table 3.7)
Dose required: 25–45 mg/kg/day divided bid or 20–40 mg/kg/d q8h (this is given by the manufacturer).
How supplied: chewable tabs 125, 400 mg.
3.2.3.3 Amoxicillin Capsules (Table 3.8)
Dose required: 25–45 mg/kg/day divided bid (given by the manufacturer).
How supplied: capsules 250, 500 mg.
Table 3.7 Calculating the dose of amoxicillin chewable tablets in mg for a 10‐year‐old child weighing 70 lb
| Step 1 Convert pounds to kg: | 70 lb × 1 kg/2.2 lb = 31.8 kg |
| Step 2 Calculate the dose in mg: | 31.8 kg × 30 mg/kg/day = 954 mg/day |
| Step 3 Divide the dose by the frequency: | 954 mg/day ÷ 3 (tid) = 378 mg/dose bid |
Since chewable tablets only come in strengths of 125 and 400 mg, it is recommended to always use the lower dose and then increase the number of days of therapy or to use the suspension instead, which may be more precise.
Table 3.8 Calculating the dose of amoxicillin capsules in mg for a 10‐year‐old child weighing 70 lb
| Step 1 Convert pounds to kg: | 70 lb × 1 kg/2.2 lb = 31.8 kg |
| Step 2 Calculate the dose in mg: | 31.8 kg × mg/kg/day = 1272 mg/day |
| Step 3 Divide the dose by the frequency: | 1272 mg/day ÷ 2 (bid) = 636 mg/dose bid |
The dose is 636 mg bid; either 500 mg capsules can be prescribed and increase the number of days of therapy or it may be best to use the oral suspension.
1 Q. If the child in Case 1 (above) were allergic to penicillin, what other antibiotics could be prescribed?
2 A. Clarithromycin (Biaxin®) (Table 3.9)
Dose required: 15 mg/kg/day divided q12h (Table 3.10).
How supplied: oral suspension comes in concentrations of 125 mg/5 mL, 250 mg/5 mL (100 mL bottle) (Table 3.11).
Table 3.9 Calculating the dose of clarithromycin (Biaxin) in mL for a 10‐year‐old child weighing 70 lb
| Step 1 Convert pounds to kg: | 70 lb × 1 kg/2.2 lb = 31.8 kg |
| Step 2 Calculate the dose in mg: | 31.8 kg × 15 mg/kg/day = 477 mg/day |
| Step 3 Divide the dose by the frequency: | 477 mg/day ÷ 2 (bid) = 238.5 mg/dose bid |
| Step 4 Convert the mg dose to mL: | 238.5 mg/dose ÷ 250 mg/5 mL = 4.77 mL q12h |
| Step 5 Convert mL into teaspoonfulsa | 4.77 mL ÷ 5 mL = 0.954 teaspoonful bid |
a Each teaspoonful is 5 mL.
Table 3.10 Pediatric dosage schedule
Source: Adapted from www.rxlist.com/biaxin‐drug.htm
| Weight (kg) | Weight (lb) | Dosage (q12h) (tablets) | 125 mg/5 mLa (suspension) | 250 mg/5 mL (suspension) |
| 9 | 20 | 67.5 mg q12h | 2.7 mL q12h | 1.35 mL q12h |
| 18 | 40 | 136 mg q12h | 5.4 mL q12h | 2.7 mL q12h |
| 25 | 55 | 187.5 mg q12h | 7.5 mL q12h | 3.75 mL q12h |
