Weight based calculations

[RNSAINT41]

I have some weight based dosage calculation questions.

1. 5 year old patient weighs 14 lbs doctor orders Tylenol 15mg/kg available 160mg/5ml how many mls do you administer?

First I convert 14lbs to 6.4 kg (round to nearest tenth kg) multiply times 15 equals 96mg divided by 160mg times 5 mls equals 3 mls which is the answer.

2. Doctor orders amoxicillin 100 mg TID for 6 year old patient that weighs 32lbs recommened dose is 5mg/kg-12mg/kg per day is this a safe dose ordered?

first convert patient weight to kg and round to nearest tenth kg 14.5kg.

Multiply 14.5 kg times 5mg equals 72.5mg

Multiply 14.5kg times 12mg equals 174mg

this is a safe dose.

In my book it says the weight must first be converted and rounded to nearest tenth kg before proceeding with math problem.

[NotReady4PrimeTime, RN]

Is there a question there? You've done the math correctly.

[KelRN215, BSN, RN]

You missed something on question 2. Order is 100 mg TID but the safe range is listed in mg/kg/day. You would need to convert the ordered dose to the daily dose to determine if it's in the safe range.

Though in reality the recommended dose of amoxicillin is much more than 5-12 mg/kg/day. Did you mean to say that the recommended dose is 5-12 mg/kg/dose? Even that might be low depending on the infection.

[sergel02, BSN]

I just gotta say that a 5 year old weighing 14 pounds sounds super funny to me lol

[PeakRN]

I just gotta say that a 5 year old weighing 14 pounds sounds super funny to me lol

And apparently we aren't weighing kids in kilograms either...

[bjwojcik]

For question #1) If you set the problem up like this, you can check your work before you do any calculations.

14 lb (1 kg/2.2 lb)(15 mg/kg)(5 mL/160 mg) = 3 mL.

Also, just an FYI, you should leave a space between the number and the unit per SI rules.

Brad Wojcik, PharmD