Dose By Weight

Medications can be a patient-specific dose, notably based on the patient’s weight. This can be very beneficial when dosing a child, or an adult with abnormal weight. Since we commonly use pounds and ounces to describe a person’s weight in the United States, we will first have to convert patient weight to kilograms. Remember there are 16 ounces in a pound and 2.2 pounds in a kilogram. See other unit conversions.

Patient-Specific Dose Example

Milly weighs 105 pounds. She is prescribed a drug with dosing of 0.8mg/2kg. What dose in milligrams should Milly be given?

As you can see, the denominators’ measurement units do not match so we have to convert kilograms to pounds before we can cross-multiply. If needed, review setting up ratios and proportions.

Convert Kilograms to Pounds

For every kilogram, there are 2.2lbs so we will multiply 2 by 2.2 to the medication’s converted measurement.

2 * 2.2 = 4.4lbs

4.4x = 0.8 * 105

4.4x = 84

x = 19.1mg

Based on this patient-specific dosing, Milly’s dose is 19.1mg.

Concentrated Dosing

Patient-specific dosing by weight can also be applied to concentrated medications as well. Consider the above example is available as a 100mg/5mL concentrated solution. What would Milly’s dose be per milliliter? We already have her dose needed per milligram from the previous example.

100x = 95.5

x = 0.96mL

If Milly is given a dose from the concentrated solution, her dose is slightly less than 1mL. She will be given 0.96mL per dose.