Pediatric Dosage Calculations

Hey guys, in this lesson we are going to briefly talk about how to calculate pediatric medication dosages and then I’ve made some scenarios for you to practice with. We are going to look at how we calculate doses, some basic rules to follow and then look at the practice scenarios.

The main thing to remember when giving any kind of medication to a child is that we have to take into account the age and the size of the child. At different ages kids will have different metabolisms and will process and use medications at different speeds. So you may see drug guides vary doses based on age. The most common ways to account for these variables are to use weight or body surface area to calculate doses. Body Surface Area is the most accurate way to calculate meds and it is usually used when prescribing chemotherapy. We are going to focus on mg/kg dosing here because it’s most common. You may see other units like grams or units but the math you need to be able to do will be the same just with different units! Often drug guides will give a range for what is considered safe. So you may see something like 10-15 mg/kg/dose listed as the safe range. Any dose that is prescribed between these two numbers would be considered therapeutic and safe. Another variable to consider for children that doesn’t come up as often with adults is giving liquids and suspensions. This means there’s an extra calculation that has to be done to figure out how many milliliters should be given to give the correct dosage in mg. These added variables and need for more calculations mean that there is an increased risk for error when giving medications to kids. Make sure you always double check your math and that you are aware of your high risk meds that require double verification. And really anytime you aren’t certain get a fellow nurse to help or ring your pharmacist.

Okay so while we are going through these practice problems pause the video and practice working through it yourself. When you have an answer restart the video and I’ll walk you through the calculations! Alright our first practice problem … A 1 month old baby, named Anna, has been admitted to hospital with a high fever, lethargy and poor feeding. A full septic work up has been done, including lumbar puncture with culture, blood culture and urine culture. While waiting for these test results the baby will be admitted and given IV antibiotics. She has been prescribed Ceftriaxone and Ampicillin. Anna weighs 8 lbs 4 ounces. What is her weight in kilograms? Remember there are 16 ounces in a pound so 4 ounces equals .25 of an pound 4/16 = 0.25 8.25/2.2 = 3.75 kg

Let’s calculate what would be a safe dose for her for both of these medications.

Ceftriaxone Safe dose = 100 mg/kg/day given once daily or every 12 hours

• 100 mg x 3.75 kg= 375 mg/day
• Once a day dosing = 375 mg
• BID dosing = 187.5 round up to 188 mg

Okay, moving on to ampicillin,

Safe dose = 25-200 mg/kg/day given every 6 hours

• 25 mg x 3.75 kg= 93.75 round up to 94 mg 94 mg/4 doses = 23.5 round up to 24 mg/dose
• 200 mg x 3.75 kg= 750 mg 750 mg/4 doses = 187.5 round up to 188 mg/dose
• Safe range = 24 mg/dose – 188 mg/dose
•  

Our 2nd scenario is A 10 year old boy called Jakob, who weighs 35 kg, has come to the ER with a wheeze. He is a known asthmatic and has already been started on nebulized albuterol. Now he needs an oral steroid, called prednisolone (Orapred).

Prednisolone (Orapred)
Safe dose = 1-2 mg/kg/day given once daily or divided q12 hours

• 1 mg x 35 kg = 35 mg/day
• 2 mg x 35 kg = 70 mg/day
• Safe range = 35 mg/day – 70 mg/day

The pharmacy provides Prednisolone oral suspension 25mg/5 ml. How many ml’s would you give if Jakob was prescribed 70 mg.

• 25 mg/5 ml = 70 mg/X ml 25 X = 70 x 5 = 350 X = 350/25 X = 14 ml

Now, let’s look at scenario 3.  A 5 year old girl, named Carla, has pyelonephritis. She has already started her antibiotics, but she is still fevering. Her mom requests some acetaminophen to bring the fever down and help with pain. She weighs 15 kg. She is prescribed 225 mg of acetaminophen q 6 hours PRN pain/fever.

Safe dose = 10-15 mg/kg/dose

• 10 mg x 15 kg = 150 mg/dose
• 15 mg x 15 kg = 225 mg/dose
• Safe range = 150 mg – 225 mg/dose

The pharmacy provides acetaminophen oral suspension 160 mg/5 ml. How many mls would you give for the 225 mg dose?

160 mg/5 ml = 225 mg/X ml 160 X = 1125 X = 1125/160 X = 7.03 round down to 7 ml