Glossary of reconstitution terms

Short definitions of the words that appear on vial labels, syringe packaging and reconstitution calculators, in alphabetical order. Each links to a longer guide where there is one.

Terms A to Z

Bacteriostatic water for injection: Sterile water containing 0.9% benzyl alcohol as a preservative, supplied in multiple-dose vials and used to dissolve or dilute medicines for injection. See bacteriostatic water vs sterile water.
Barrel: The tube of a syringe that holds the liquid and carries the printed scale. U-100 insulin syringes commonly have 0.3 mL, 0.5 mL or 1 mL barrels.
Benzyl alcohol: The preservative in bacteriostatic water for injection, present at 9 mg per mL. It inhibits bacterial growth.
Beyond-use date (BUD): The date assigned by a pharmacy to a compounded or repackaged preparation, after which it should not be used. Different from a manufacturer's expiration date.
Blend: A single vial containing two or more substances. Each has its own concentration after mixing, and they are always drawn together in the same proportion. See the blend calculator.
Compounded medicine: A medicine prepared by a pharmacy for an individual prescription, as opposed to a mass-manufactured product. Compounded medicines are not FDA-approved products.
Concentration: The amount of a substance in a given volume of liquid, usually written in mg/mL. It equals the amount in the vial divided by the volume of liquid. 10 mg in 2 mL is 5 mg/mL.
Diluent: The liquid added to a dry medicine to dissolve it, or to a liquid medicine to dilute it. Bacteriostatic water, sterile water and sodium chloride 0.9% are common diluents. The correct one is stated on the medicine's label.
Dose: The amount of a medicine to be taken at one time, as written on a prescription. This site converts a dose into a volume; it does not supply or suggest doses.
Expiration date: The date set by a manufacturer up to which an unopened product, stored as labelled, is expected to meet its specification.
Insulin syringe: A small syringe with a fixed fine needle and a scale printed in units instead of mL. See how to read a U-100 insulin syringe.
IU (international unit): A measure of biological activity defined separately for each substance against a reference standard. It is not a weight, and the IU-to-mg factor differs for every substance. See IU vs mg.
Lot number: A code identifying the production batch a vial came from, used for tracing and recalls. Also called a batch number.
Lyophilized: Freeze-dried. The product is frozen and the water removed under vacuum, leaving a dry powder or cake in the vial. A lyophilized vial is labelled with its total amount and has no concentration until liquid is added.
mcg (microgram): One thousandth of a milligram. 1,000 mcg = 1 mg. Also written µg or ug. See mcg vs mg.
mg (milligram): One thousandth of a gram. The usual unit for the amount of substance in a vial.
mg/mL: Milligrams per millilitre, the standard way to write concentration.
mL (millilitre): One thousandth of a litre. A unit of volume. 1 mL equals 1 cc, and equals 100 units on a U-100 syringe.
Multiple-dose vial: A vial labelled for more than one withdrawal. It normally contains a preservative. How long it may be used after first entry is set by its label and your pharmacist.
Plunger: The rod that slides inside the syringe barrel. The reading is taken at the top ring of its rubber stopper, the edge nearest the needle.
Pre-mixed vial: A vial supplied as a liquid, already in solution. Its label gives a concentration (mg/mL) and a total volume. See how to read a vial label.
Reconstitution: Adding a measured volume of diluent to a dry (lyophilized) medicine to turn it back into a liquid. The volume added sets the concentration. See how water volume changes the maths.
Single-dose vial: A vial intended to be entered once, with any remainder discarded. It contains no preservative. Sterile water for injection is supplied this way.
Sterile water for injection: Sterile water with no preservative or other additive, supplied in single-dose containers and used to dissolve or dilute medicines for injection.
Syringe units: The tick marks on an insulin syringe. On a U-100 syringe each unit is 0.01 mL. For anything other than U-100 insulin they are a measure of volume only. See units vs mg vs mL.
Tuberculin syringe: A 1 mL syringe marked in mL, typically in 0.01 mL steps, instead of units. 0.10 mL on a tuberculin syringe is the same volume as 10 units on a U-100 syringe.
U-100: An insulin strength of 100 units per mL, and the syringe scale that matches it. All calculators on this site assume a U-100 syringe.
U-40: An insulin strength of 40 units per mL, used mainly for veterinary insulin, and the syringe scale that matches it. One U-40 unit is 0.025 mL. See U-100 vs U-40 syringes.
USP: United States Pharmacopeia, the organisation that publishes quality standards for medicines and their ingredients. "USP" after a product name means it is made to the corresponding standard.
Vial: A small glass container sealed with a rubber stopper and a metal crimp, holding a medicine as a dry powder or a liquid.
Volume: The amount of space a liquid takes up, measured in mL or in syringe units. The volume to draw equals the prescribed amount divided by the concentration.

How the terms fit together

A lyophilized vial holds a fixed amount in mg. Reconstitution with a measured volume of diluent gives a concentration in mg/mL. Dividing the prescribed amount by that concentration gives a volume in mL, and multiplying by 100 gives syringe units on a U-100 syringe. The calculator does those steps, how it works shows them written out, and the tools and conversion tables cover single conversions.

Questions

What does lyophilized mean?

Lyophilized means freeze-dried. The product is frozen and its water removed under vacuum, leaving a dry powder in the vial that is dissolved again before use.

What does reconstitution mean?

Reconstitution is adding a measured volume of liquid (a diluent) to a dry medicine so that it becomes a solution. The amount in the vial divided by the volume added gives the concentration.

What is a diluent?

A diluent is the liquid used to dissolve or dilute a medicine, such as bacteriostatic water, sterile water for injection or sodium chloride 0.9%. The medicine's label states which one to use.

What does U-100 mean on a syringe?

U-100 means the syringe is marked for insulin at 100 units per mL, so 100 units on the scale is 1 mL and 1 unit is 0.01 mL.