Peds Math

[stasiastar]

Hi all,

Please please please help me, I failed Peds and fortunately I was able to take it again without sitting out like most schools... but the math is a real problem for me.. I've tried and tried and just can't seem to catch on... I can't fail again or I'm out of the program.. I need help.. my professor is really no help.., classmates just worry about themselves... I just want to give up and remain a LPN.

[NotReady4PrimeTime, RN]

What part do you seem to struggle with? It's actually pretty straight-forward algebra. If you could provide some examples of your errors we might be able to help you better.

I'll use a 14.6 kg, 100 cm tall patient for some example equations.

Dose = what you WANT divided by what you HAVE eg Acetaminophen dose is 220 mg. Liquid is 80 mg/mL. 300/80 = 2.74 mL

Weight-based dose (1) = Cefazolin 30 mg/kg/dose eg 14.6 kg x 30 mg = 438 mg

Weight-based dose (2) = Ceftriaxone meningitis dose 100 mg/kg/day divided into 2 doses eg 14.6 kg x 100 mg = 1460 gm / 2 doses = 730 mg per dose.

Body surface area doses should never appear on a basic peds med math test.

[bjwojcik]

Here is another way to look at dosage calculations.

The patient is prescribed 220 mg but you need to end up with mL. You will use the ratio of 80 mg/mL to change mg into mL. 220 mg (1 mL/80 mg) = 2.75 mL

You can flip the ratios to suit your needs. The mg's cancel out leaving mL, ensuring that the calculation was done correctly.

14.6 kg (30 mg/kg*dose) = 438 mg/dose

(Note that 30 mg/kg/dose is mathematically equivalent to 30 mg/kg*dose)

14.6 kg (100 mg/kg*day)(1 day/2 doses) = 730 mg/dose

(Note that 100 mg/kg/day is mathematically equivalent to 100 mg/kg*day).

All units cancel out except mg/dose.

Brad Wojcik, PharmD

[stasiastar]

Hi all.. I'm glad to Report that I took Pediatrics and passed this time 84%.... yaay....thanks all.

[Jamesryan]

Wouldn't you round the dose to 2.7ml?