NSG 325 Dosage Calculation and Drug Variation Questions

Dosage Calculation Module: Review, Practice, and Do

What is involved in Pediatric Dosage Calculation?

Situation;

Pediatrics covers a wide age range that includes a time of significant growth and development changes that affect how medications are handled by the body.

Children vary a great deal in height and weight and we cannot just use age to determine what is a safe or therapeutic dosage

Background:

• According to Lehne Pharmacology textbook (Burcham & Rosenthal, 2019), patients who are very young respond differently to drugs than the rest of the population…younger patients are more sensitive to drugs than adult patients and show greater individual variation.Drug variation is most often related to organ immaturity and this will change as the child matures and the organ function matures.Because of that wide variability, the effects of drugs will be variable throughout the pediatric population.
• Additionally, we have less information about how drugs used in the adult population affect the pediatric population in regard to effectiveness, adverse effects, and dosing because of limited research on children.
• Children have wide variations in weight.Children of the same age have very different weights.Additionally, the “pediatric” population is birth to age 18, so what should be given to a 15 year old will be much different from the dosage to be given to a 15 month old

Assessment:

Therefore, dosage calculation involves using the child’s weight and/or body surface area to calculate the correct and safe dosage.Doses are often estimated based on the usual adult dose, but these are approximations and the dosage may need to be adjusted based on evaluation of the child’s response and adverse effects.

Recommendation/Requirement:

Nurses do not determine what the safe dose is, but use the information provided by the manufacturer to calculate what the safe/therapeutic dose is for the individual child.And this is what you will be learning to do.

The nurse is individualizing to the dose to the individual child using information from the maker of the drug.

Safety:

• The nurse compares the ordered dose with the recommended dose, using critical thinking skills to determine whether the ordered dose of the medication is safe.
• An ordered dose of medication is considered safe if it is the same as or less than the recommended dose.
• Often, the manufacturer provides a safe dosage range.The goal is to have the ordered dose fall between the lowest number and the highest number.

Caution, sometimes the dose does fall below the “safe” dose and may be much lower than the “safe” dosage recommendation.The nurse must once again use critical thinking here.If it is too far below the recommended safe dose, the nurse should contact the physician to verify the dose.Receiving too small a dose can significantly affect treatment—think of the problem of giving too little antibiotic—the infection won’t be treated.Or, giving the patient too little anti-seizure medication.So, keep in mind, the nurse must use critical thinking in decision making.

Some reminders:

• Please make sure you are comparing the ordered dose with the correct calculated safe dose.Physicians generally order a single dose and then how frequently the individual dose should be administered.The recommended dose can be given as this many mg per kg per dose OR this many mg per day.
• Take your time and be sure you are comparing the correct things.

When calculating how much to give, always use the doctor’s order—not the recommended dosage or range—nurses give the dose ordered by the physician

Example…the nurse calculated the safe dose to be 40-80 mg per dose and the doctor has ordered 65 mg per dose.

Calculate how to deliver 65 mg, NOT 40-80 mg!

Drug available as 50 mg per mL

65 mg/50 mg times 1 mL= 0.769 mL rounded to 0.77 mL (because the nurse can use a 1 mL syringe to measure this dose

Rounding:

Always follow rounding rules.

ATI and NCLEX will tell the student exactly what to round to—follow those directions

Rounding is generally based on what can be measured—the goal is to give as close to the actual dose as possible, but rounding will be often be necessary, especially when dealing with weight based doses.

Liquids should be rounded to what can be measured in a syringe.

Please round at the end of the problem, NOT as you progress through the problem.

123 lbs divided by 2.2 lbs/kg =55.909090….Keep that in the calculator for calculating the dose and then round when calculating how much to give.

EXCEPTION TO THE ABOVE:

• Sometimes physicians order a medication as mg (or mcg or g) per kg per minute (mg/kg/minute) or hour.
• Physicians do not automatically know the patient’s weight and expect the patient to be given a certain amount of medication (the mg/mcg/g) per the patient weight per a prescribed time.
• Because the dose itself will always be different, calculating using the patient’s current weight (or sometimes the patient’s body surface area) provides the most accurate dosing.
• Most often this is done with heparin and cardiac drugs and chemotherapy, which must be calculated based on the individual patient
• In this case, the nurse does use the calculated dose for the dose to be administered.

References

Burchum, J. R., & Rosenthal, L. D. (2019). Lehne’s pharmacology for nursing care. (10th ed.). Elsevier/Saunders.

Example problem:

A child is to receive vancomycin 450mg IVPB every 6 hours.

The child weighs 70 pounds

The recommended dosage is 40-60 mg/kg/24 hours (per day) to be administered every 6 hours.

The child’s weight in kg is _______ kg. 70/2.2 = 31.818181

The recommended safe dosage range for this child is _______ mg/DAY

31.818181 kg times 40 mg/kg = 1272.72 mg/day—this represents the lowest amount to be given per day

31.818181 kg times 60 mg/kg = 1909.09 mg/day—this represents the highest amount to be given per day

The recommended dosage is to be divided into 4 doses given every 6 hours.What is the individual recommended safe dosage range for this child?

1272.72 mg/4= 318.18 mg PER DOSE– this represents the lowest amount to be given per dose

1909.0 mg/4 = 477.27 mg PER DOSE– this represents the highest amount to be given per dose

NOW IS THE TIME TO COMPARE WHAT IS ORDERED TO WHAT IS SAFE—

The order is for 450 mg per dose

The safe per dose range is 318.18 to 477.27 mg per dose

450 mg is between the low and high allowed and is safe

Is the dose ordered safe?

What would the nurse do if the ordered dose was not considered safe?

(This dose is safe, but if it was not, the nurse would call the physician and ask for the correct dose)

Practice Problems (33 possible points):

• The physician orders Amoxil 180 mg by mouth every 8 hours for a child who weighs 35 pounds.Recommended dose is 25-50 mg/kg/24 hours divided into doses every 6 to 8 hours.See the label below to see how Amoxil is provided.
• The physician orders vancomycin 330 mg by mouth every 6 hours for a child who weighs 74 by pounds.The recommended daily oral dose is 40 mg/kg/24 hours to be given in equally divided doses every 6 hours.The medication is available as Vancomycin 250 mg/5 mL.
• The physician has ordered Phenobarbital 72 mg by mouth daily for a child with a seizure disorder.The child weighs 37 pounds.
• The physician orders Biaxin 300 mg by mouth twice a day for a child who weighs 92 pounds.The recommended daily oral dose is 15 mg/kg/24 hours to be given in equally divided doses every 12 hours.The medication is available as Biaxin 125 mg/5 mL.
• The physician orders gangcyclovir 13 mg IV every 12 hours for a newborn with congenital CMV infection.The infant weighs 6.6 pounds.The recommended IV dose for newborns is 6mg/kg/dose twice a day.
• A child weighing 66 pounds is prescribed epinephrine subcutaneous injection for an allergic reaction.The physician ordered epinephrine 0.3 mg subcutaneously now.

Child’s weight in kg is _______ kg

The recommended dosage range per day is _______ mg to _______ mg per day

The physician has ordered the medication be given every 8 hours, so calculate the recommended individual dose for this child.

_______ mg to _______ mg/dose

Compare what the physician has ordered with what is considered a safe dosage range.Is the dose safe?

If it is, how much will the nurse administer? ___________ mL (figure out the answer even if it is not safe)

What would the nurse do if the ordered dose was not considered safe?

Child’s weight in kg is _______ kg

The recommended dosage per day (24 hours) is _______ mg

The recommended dosage per dose (is to be given every 6 hours)is _______ mg by mouth every 6 hours

Is the ordered dose safe?

If the ordered dose is safe, the nurse will administer ________ mL by mouth every 6 hours. (calculate the answer even if it is not deemed safe)

What would the nurse do if the ordered dose was not considered safe?

The recommended safe dosage range for this medication is 4 to 6 mg/kg/24 hours administered once or twice a day.

The medication is available as Phenobarbital 20 mg/5 mL

Child’s weight in kg is _______ kg

The recommended dosage range per day is _______ mg to _______ mg per day

The physician has ordered the medication to be administered once a day, so the ordered dose should be compared with the range for the daily dose that was just calculated.

Is the dose safe?

If the ordered dose is safe, the nurse will administer ________ mL by mouth daily (calculate the answer even if it is not deemed safe)

What would the nurse do if the ordered dose was not considered safe?

Child’s weight in kg is _______ kg

The recommended dosage per day (24 hours) is _______ mg

The recommended dosage per dose (is to be given every 12 hours)is _______ mg by mouth every 12 hours

Is the ordered dose safe?

If the ordered dose is safe, the nurse will administer ________ mL by mouth every 12 hours (calculate the answer even if it is not deemed safe)

What would the nurse do if the ordered dose was not considered safe?

What is the child’s weight in kg? (You can divide 6.6 by 2.2, just as any other weight—the 0.6 is NOT ounces, but is 6/10^th of a pound) _______ kg

What is the recommended individual dose for this child?_______ mg IV

Is the ordered dose safe for this patient?

The recommended safe dose is 0.01 mg/kg subcutaneous every 20 minutes

What is the child’s weight in kg?_______ kg

What is the recommended safe dose for this child?

Is the ordered dose safe?

If it is safe, the nurse will administer ________ mL subcutaneously now. (calculate the dose even if it is not deemed safe)