1. Pediatric dosage calculations
Jennifer kean MSN, RN, CCRN

2. dosing
Most drugs for children are dosed according to body weight (mg/kg) or body surface area (BSA)
Care must be taken to convert body weight from pounds to kilograms before calculating doses based on body weight
1 kg = 2.2 lbs
Doses are often expressed as mg/kg/day or mg/kg/dose
If provider writes mg/kg/d, you must clarify; it is a confusing order
Dosing also varies by indication, so diagnostic information is helpful
Most institutions have policies that require 2 nurses to check any doses or calculations

3. Example 1
Calculate the dose of amoxicillin suspension in milliliters for a 1-year-old child weighing 22 lb.
The dose required is 40 mg/kg/day divided twice daily (BID)
The suspension comes in a concentration of 400 mg/5 ml

4. Step 1
Convert pounds to kilograms
22 lb = _____ kg

5. answer
22 lb = 10 kg

6. Step 2
Calculate the dose in milligrams
40 mgx 10 kg = _______ mg/day

7. answer
40 mg x 10 kg = 400 mg/day

8. Step 3 Divide dose in half (given bid)
400 mg / 2 doses = ______ mg / dose

9. answer
400 mg / 2 doses = 200 mg / dose

10. Step 4 Convert the milligram dose to milliliters
200 mg / dose / 400 mg/ 5 ml = _____ ml

11. answer
200 mg / mg
____ _______ = ______ ml BID
x ml ml

12. answer
Since you are dividing 2 fractions, you must flip the second fraction
200 mg ml
x = _______ ml BID
x ml 400 mg

13. the answer is 2. 5 ml bid Always make sure your answer makes sense
the answer is 2.5 ml bid Always make sure your answer makes sense. This sounds right for a 1-year-old child.

14. Example 2
Calculate the dose of ceftriaxone in milliliters for meningitis for a 5-year-old child weighing 20 kg.
the dose required is 100 mg/kg/day given iv once daily
The drug comes prediluted in a concentration of 500 mg/ml

15. Step 1 Calculate the dose in milligrams
100 mg x 20 kg = _____ mg / day

16. answer
100 mg x 20 kg = 2000 mg/day

17. Step 2 Divide the dose by the frequency
2000 mg/day / 1 (daily) = 2000 mg/ dose

18. Step 3 Convert the milligram dose to ml
2000 mg / 500 mg/ml = ______ ml/ dose x 1 daily
4ml once daily

19. Problem 1 Order: amoxicillin (Amoxil) 60 mg po tid
child’s weight: 12.5 lb.
drug concentration: 125 mg/5 ml

20. formula d
x v = h

21. Problem 2 Order: ampicillin 350 mg im q6h
Child’s weight and age: 61.5 lb and 9 years old
Drug concentration: 500 mg/2 ml

22. formula d
x v h

23. Dosage per body surface area
The following information is needed to calculate the dosage:
Order with name of drug, dosage, and time frame /frequency
Child’s height, weight in kg, and age
Information on how drug is supplied
Pediatric dosage (as listed by manufacturer or hospital formulary)
Child’s bsa

24. Calculating the dose
Multiply the bsa by the minimum and maximum dose (substitute bsa for weight)
Is this a safe dose?
Calculate drug dose using d/h or by ratio/proportion

25. Problem 3 Child with rheumatic fever; 45 lb, 4 years old
Order: penicillin v potassium 250 mg po q8h
Pediatric dose: mg/kg/day
Drug concentration: 125 mg/ 5ml

26. Problem 4 Child with seizures; 7.2 kg, 9 months old
Order: phenobarbital 25 mg po tid
Pediatric dose: 5-7 mg/kg/day
Drug concentration: 20 mg/5 ml

27. Problem 5 Child with lower resp. tract infection; 17 lb, 6 months old
Order: cefprozil (cefzil), 100 mg po q12h
Pediatric dose: (> 6 months) 15 mg/kg/12h