Some medications, particularly for children may be prescribed according to the person's body weight (kg) or body surface area (mē). Simply multiply the dose by the weight to determine the dose required which may then be placed in other formula.
Example
2mg / kg of a drug is required in a single dose. The child weighs 18 kg. How many milligrams will you give?
2 x 18 = 36 mg
Example
Amoxicillin is prescribed at 35 mg per kg / 24 hrs in 3 divided doses. The patient's weight is 12 kg. On hand you have 125 mg in 5 ml Suspension. How many millilitres will you administer in a single dose? (Round to 1 decimal point)
First determine the dose required in 24 hours:
= 35 mg X 12 kg
= 420 mg
Now determine the amount required in a single dose:
= 420mg / 3 doses
= 140 mg / dose
Now use the result in the formula to calculate fluid dosages
140 milligram of amoxicillin is prescribed. On hand you have 125 milligram in 5 millilitres.
The formula to use is:
| Required Dose | x | Stock Volume | = Volume to be given |
| Stock Dose | 1 |
Place the values in the formula
| 140mg | x | 5 ml | = Volume to be given |
| 125mg | 1 |
= 1.12 X 5
= 5.6 millilitres
| Other Calculations | |||||
| Metric Conversions | Body Mass Index | Tablet Dosages | Fluid Dosages | IV Flow Rates | Dosage by Weight |