5.12 Safe Dosage Range

When administering calculated liquid medication, it is essential to ensure that the dosage falls within a safe range to prevent underdosing or overdosing. Safe dosage ranges are typically provided in drug reference materials, such as pharmacology textbooks, electronic drug databases, or institutional protocols. Medication errors are particularly common in pediatric patients, who have narrower safe dosage ranges than adults due to their smaller size and differences in metabolism.

When verifying that a dosage is within a safe range based on a patient’s weight, the nurse should begin by accurately performing the dosage calculation, converting units if necessary (e.g., pounds to kilograms). Next, the nurse determines the low and high ends of the safe dosage range by multiplying the patient’s weight by the minimum and maximum recommended milligrams per kilogram (mg/kg) for that medication. The final step is to compare the calculated dose to this range to confirm it is safe before administration. Nurses should also consider other patient factors that may affect dosing, such as renal or hepatic function, and always double-check calculations, particularly when working with high-risk medications or pediatric patients.

Practice Problem: Safe Dosage Range

Declan is an 8-month-old infant who weighs 7 kg. He has been prescribed acetaminophen 100 mg every 4-6 hours PO for a fever. The recommended dosage range for infants is 10-15 mg/kg/dose. Calculate the acceptable dosage range for Declan and determine if the prescribed dose is safe.

1. Calculate the low end of the safe dosage. Start by identifying the goal unit. For this problem we want to know the dose in milligrams:

2. To set up the problem, match the numerator in the first fraction to the desired unit to be solved, which in this case is mg. Based on information known from the problem, we know that the recommended low dose is 10 mg per kg, so add 1 kg to the denominator:

3. Create the second fraction with the intent to cross out units. Place kg in the numerator. Look to the problem for information related to kg. We know that Declan weighs 7 kg, so place 7 in the numerator and 1 in the denominator with the intent to cross off units:

4. Cross off units. Multiply across the numerators and then the denominators, and then divide the final fraction for the final low dose answer in mg:

5. Calculate the high dose. Set up a similar equation, but this time using the high dose information of 15 mg per kg:

6. Based on the calculations, the safe dosage range for Declan is 70 mg – 105 mg. Compare the prescribed dose to the low- and high-dose range calculations to determine if it is safe. Declan was prescribed 100 mg. It falls within the calculated safe dosage range of 70 – 105 mg, so, yes, this is a safe dose for Declan.

Practice dosage range calculations with the interactive activity below.