Prescribing Skills (Part 5 of 8 - Drug Calculation Skills)

Drug Calculation Skills

Calculations

CALCULATION AND PRESCRIBING PRINCIPLES.


1) Use the same units on both sides when calculating

2) Try and use whole numbers rather than fractions.

3)  Ensure final value is practical. Look in the BNF to see if the drug is deliverable at that dose. For example Gentamicin comes in 40mg/mL vials. Prescribing 32.5 mg would mean 0.8125 ml of gentamicin which is difficult to measure. Round this up to 30mg, which is 0.75 mL and measurable.

Mutliple Choice Question

You have been asked to prescribe a GTN infusion for your patient. The dose required is 10 micrograms/ minute. You look at the BNF and note that they come in 5mg/mL ampoules, and has to be diluted in glucose or sodium chloride 0.9% before administration.


You dilute 50mg of GTN to make up a 500mL infusion and set up an infusion pump. What is the rate of administration in ml/hour to administer the above dose?