Tips for Drug Calculations
Ø Always convert everything to the same units before solving the calculation.
Ø Complete work from left to right.
Ø Follow the ‘one unit’ or by proportion rule: what you do to one side of an equation, do the same to the other side.
Ø Write out the calculation clearly.
Ø Write down every step. Do not take short cuts; you are more likely to make a mistake.
Ø If you are copying formulas from a reference source, double-check your work.
Ø Try not to depend on your calculator. Gestimate your answer, then if you make a mistake on the calculator, you are more likely to know that an error has been made.
Ø If you are in doubt about a calculation, stop and get help.
Ø When administering intravenous (IV) infusions, you need to know: the flow rate, infusion time, and total volume.
Use the following equations:
ü flow rate (mL/hr) = total volume (mL) ÷ infusion time (hr)
ü infusion time (hr) = total volume (mL) ÷ flow rate (mL/hr)
ü total volume (mL) = flow rate (mL/hr) × infusion time (hr)