Pharmaceutical Calculations

%w/v = grams of solute per 100 mL of solution. To convert to mg/mL, multiply the percent by 10. Example: a 2% w/v lidocaine solution = 2 g/100 mL = 20 mg/mL.

%w/w = grams of solute per 100 g of total product. Example: 30 g of zinc oxide in 120 g of ointment = (30/120)x100 = 25% w/w.

%v/v = milliliters of solute per 100 mL of solution. Example: 25 mL of ethanol in 500 mL solution = (25/500)x100 = 5% v/v.

Grams = (% / 100) x volume(mL). Example: how much drug in 250 mL of 4% w/v solution? (4/100) x 250 = 10 g.

Ratio strength 1:r means 1 g (or mL) of solute in r mL (or g) of product. %strength = (1/r) x 100. Example: 1:1000 epinephrine = (1/1000) x 100 = 0.1% w/v = 1 mg/mL.

Ratio strength 1:r where r = 100/percent. Example: 0.25% w/v -> r = 100/0.25 = 400, so 1:400.