Introduction to Safe Range / Weight-Based
Safe Range / Weight-Based Conversions
Nurses are often required to calculate weight-based doses that utilize a patient’s body weight to determine a personal and appropriate medication dose. This will prevent the patient from receiving too much or too little medication. Safe ranges of dosages are provided in drug reference materials. Nurses are most likely to encounter weight-based dosing when calculating doses for a child. Medication errors often occur in children, who have smaller ranges of safe dosage than adults due to their smaller weight.
When verifying that a dosage is within a safe range based on a patient’s weight, begin by completing the dosage calculation. Then, calculate the low and high ends of the safe dosage range. Finally, verify that the calculated dose is within this range.
Safe Range / Weight-Based Example 1
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 minimum and maximum of the recommended safe dose.
mg → [latex]10mg x 7kg = \frac{70mg}{dose}[/latex] (min)
mg → [latex]15mg x 7kg = \frac{105mg}{dose}[/latex] (max)
2. Compare to the prescribed dosage.
Minimum → Prescribed → Maximum
70mg → 100mg → 105mg
3. Solve.
This prescribed dosage fits between the minimum and maximum range and, therefore, is safe to administer.
Safe Range / Weight-Based Example 2
Order: Phenytoin 75 mg by mouth every 12 hours for a child weighing 50 lb.
On Hand: Dilantin chewable 50 mg tablets.
The recommended oral dose for a child is 5 to 7 mg/kg/day in divided doses every 12 hours. Is this dose within the safe range?
If yes, how many tabs would the nurse give?
1. Calculate the minimum and maximum of the recommended safe dose.
mg → [latex]5mg x \frac{1kg}{2.2lbs} x 50lbs = \frac{113.64mg}{day} = \frac{56.8mg}{dose}[/latex] (min)
mg → [latex]7mg x \frac{1kg}{2.2lbs} x 50lbs = \frac{159.09mg}{day} = \frac{79.5mg}{dose}[/latex] (max)
2. Compare to the prescribed dosage.
Minimum → Prescribed → Maximum
56.8mg → 75mg → 79.5mg
This prescribed dosage fits between the minimum and maximum range and, therefore, is safe to administer.
3. Calculate to the appropriate number of tablets.
Tabs → [latex]\frac{1tab}{50mg} x 75mg = 1.5 tabs[/latex]
Safe Range/ Weight-Based Video Tutorial[1]
- WisTech Open. (2024, August 12). Nursing dosage calculations - Safe range/Weight-based dosages [Video]. YouTube. CC BY 4.0. https://www.youtube.com/watch?v=BbBMtn4SR8c ↵
