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.