reconstitution

Reconstitution is turning a powdered medication into a liquid by adding a diluent, which gives the vial a known concentration: 500 mg of powder with 5 mL of diluent makes 100 mg per mL. The label or the question states both the amount of drug and the volume of diluent, and the concentration that matters is what the vial holds after the diluent is added, not the powder's volume. That single point decides most reconstitution questions. Divide the drug by the final volume to get the concentration, then use it in the same proportion setup as any liquid dose. Two wrinkles are worth expecting: some questions specify a concentration the prescriber wants, so the diluent volume has to be solved for rather than assumed; and an unreconstituted vial cannot be measured in milliliters at all, which is why a question asking for an injection volume always tells you the diluent.