A nurse practitioner prepares an injection of promethazine, an antihistamine used to treat allergic rhinitis. If the stock bottle is labeled 30. mg/mL and the order is a dose of 10.0mg, how many milliliters will the nurse draw up in the syringe?

With a dose order of 10mg and the stock bottle being labeled 30mg/mL, the nurse will need to draw up. 33mL. We come to this answer by taking the dose order of 10mg and multiplying by the stock bottle amount of 1mL/30mg. The 30mg/mL was inverted to account for units so that mg cancels out and we are left with mL answer.

Total mL needed = 10mg * (1mL/30mg) =.33mL