A patient is using a drug solution containing 10 mg of clindamycin per ml in a 30 ml package. What is the strength of clindamycin in the solution used by the patient?

Step 1 is to identify the definition of percentage weight-in-volume (% w/v) Percentage w/v = (grams of drug ÷ 100 mL of solution) Step 2 is to convert the given concentration (mg/mL) into grams per milliliter 10 mg ÷ 1,000 = 0.01 Result at this step = 0.01 g/mL Step 3 is to calculate the amount of drug in grams per 100 mL (0.01 × 100) = 1 Result at this step = 1 g per 100 mL Step 4 is to express this as a percentage 1 g per 100 mL = 1% Result at this step = 1%