Pediatric dosage calculations Jennifer kean MSN, RN, CCRN

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

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

Step 1 Convert pounds to kilograms 22 lb = _____ kg

answer 22 lb = 10 kg

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

answer 40 mg x 10 kg = 400 mg/day

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

answer 400 mg / 2 doses = 200 mg / dose

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

answer 200 mg / 400 mg ____ _______ = ______ ml BID x ml 5 ml

answer Since you are dividing 2 fractions, you must flip the second fraction 200 mg 5 ml x = _______ ml BID x ml 400 mg

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.

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

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

answer 100 mg x 20 kg = 2000 mg/day

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

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

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

formula d x v = h

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

formula d x v h

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

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

Problem 3 Child with rheumatic fever; 45 lb, 4 years old Order: penicillin v potassium 250 mg po q8h Pediatric dose: 25-50 mg/kg/day Drug concentration: 125 mg/ 5ml

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

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