Ratio & Proportion Pediatric Dosages
The Ratio & Proportion Method is so easy to calculate dosages, all you have to do is cross multiply and divide. Let's start off with some examples!
Ex 1) Order: Give "Drug A" IV piggyback for a child weighing 66 Ib, at a dosage of 50 mg/kg/day in divided doses q6h. How many mg would each dose contain?
Step 1: Convert the divided doses q6h
24 / 6 = 4x a day
Step 2: Convert Ib to Kg
66 Ib / 2.2 = 30 Kg
Step 3: Figure the amount of mg given a day for a 30 Kg individual by using the Ratio & Proportion
If 50 mg = 1 kg
Then X mg = 30 kg ----< 50 mg x 30 kg / 1 kg = 1500 mg/day
Step 4: Figure the amount of mg given per dose for a 30 Kg individual by dividing
1500mg / 4 (q6h) = 375 mg/dose
How many mg would each dose contain? 375 mg Answer
Ex 2) Order: Cefadyl 5 mg qid IM for a child weighing 44 Ib. The PDR recommends 1-3 mg/kg/day. Is the ordered dose safe?
Step 1: Decipher qid
4x a day
Step 2: Convert Ib to Kg
44 Ib / 2.2 = 20 Kg
Step 3: Calculate doctor's total mg given a day from the order
5 mg x 4 = 20 mg/day
Step 4: Calculate 20 Kg into the PDR recommended dose range by using the Ratio & Proportion
If 1 mg = 1 kg
Then x mg = 20 kg ---< 1 mg x 20 kg / 1 kg = 20 mg/day
If 3 mg = 1 kg
Then x mg = 20 kg ---< 3 mg x 20 kg / 1 kg = 60 mg/day
Step 5: Recommeded dose range for a 20 kg individual is
20 mg - 60 mg per day
Step 6: Is the order safe?
Well the doctor's total order dose is 20 mg/day (from Step 3) so YES it is safe because 20 mg/day falls within the recommended dose range of 20 mg - 60 mg per day (from Step 5).
Ex 3) Order: Tetracycline Elixir qid for a child weighing 50 Ib at a dosage of 8 mg/kg/day in equally divided doses. How many mg would one dose contain? Tetracycline is supplied at 50 mg per 7 ml. How many ml should be administered?
Step 1: Decipher qid
4x a day
Step 2: Convert Ib to Kg
50 Ib / 2.2 = 22.7 kg
Step 3: Figure the amount of mg given a day for a 22.7 Kg individual by using the Ratio & Proportion
If 8 mg = 1 kg
Then x mg = 22.7 kg ---< 8mg x 22.7 kg / 1 kg = 181.6 mg/day
Step 4: Figure the amount of mg given per dose for a 22.7 Kg individual by dividing
181.6 mg / 4 (qid) = 45.4 mg/dose
How many mg would one dose contain? 45.4 mg Answer
Step 5: Figure the amount of ml to be administered by using the Ratio & Proportion
If 50 mg = 7 ml
Then 45.4 mg = x ml ---< 45.4 mg x 7 ml / 50 mg = 6.4 ml
How many ml should be administered? 6.4 ml Answer
1.) Order: Ampicillin IVPB for a child weighing 55 Ib at a dosage range of 20 mg/kg/day in 4 equally divided doses. How many mg would be given per dose? The Ampicillin is supplied as 250 mg in 1.5 ml after reconstitution, give ________ ml.
Answer: 125 mg/dose, 0.75 ml
2.) Order: Garamycin 35 mg IM q6h for a child weighing 42 Ib. The recomended dose is 6-7.5 mg/kg/day given at 6 hour intervals. Is the order within the safe range?
Answer: You tell me :-)
czamudio18@yahoo.com
3.) Order: Give "Drug C" IV piggyback for a child weighing 77 Ib, at a dosage of 60 mg/kg/day in divided doses q6h. How many mg would each dose contain?
Answer: 525 mg/dose
