# Best practice: Using a weighing scale to calculate drug dosages

Pictured Above: Marsden M-125 Column Scale.

Drugs are generally dosed according to one of three approaches: fixed dosing, weight-based dosing and body surface area-based dosing.

Fixed dosing means that the dose is constant, no matter what size the patient. With weight or BSA-based dosing, the drug dosage is proportionate to size.

In a world exclusive for 2017, Marsden became manufacturer of the only weighing scales to feature a BSA calculator - so you now need just one device to provide all the measurements you need to calculate drug dosages. Body Surface Area is recommended as the principle measure for drug dosages.

But how do you use the scale to work out BSA? And how can drug dosage be calculated from this information? Our latest best practice blog post explains.

## Using a weighing scale to calculate BSA

Several formulas can be used to calculate BSA. Marsden scales use the DuBois formula, the most common method for calculating BSA.

To use the function, first turn the scale on by pressing the ON/ZERO/OFF button in the centre of the indicator. You will then need to follow steps to calculate BMI before BSA can be worked out.

The patient should first stand on the scale. Hold down the HOLD/BMI button and then the extreme left digit will flash and the patient’s height can be entered into the scale. To move to the next digit press SEND and when all digits have been entered, press ON/ZERO/OFF to confirm.

BSA can then be displayed by pressing the TARE/BSA button.

## Using BSA to calculate drug dosage

Determine the dose of drug by multiplying the dosage (e.g., 30 mg/m2) by the patient’s BSA (m2). Check that this is not a dosage in mg/kg. Before administering the drug dosage, ensure it is double-checked to avoid any mistakes.

### Scales with BSA function

Marsden M-125 Column Scale: This is a highly accurate column scale with BSA function. The scale features an optional height measure which can be used as part of the BMI/BSA calculations.

Marsden M-225 Chair Scale: For patients who are unable to stand, the M-225 Chair Scale is ideal. It is fitted with brakes, armrests and footrests for patients who cannot be seated. For further help in using chair scales, use our previous best practice blog post: how to weigh patients who can’t stand.

Marsden M-545 Floor Scale: This Floor Scale is perfect for GP surgeries and clinics. The remote indicator keeps weight readings private in sensitive environments.

Marsden M-565 Slimming Scale: For slimming groups and sports clubs, the M-565 Slimming Scale is a portable but robust floor scale. It features a remote display and is unit switchable, weighing in kg or lb.