Small Volume Parenteral Solutions

Small volume parenteral (SVP) solutions are usually 100 ml or less and are packaged in different ways depending on the intended use. If the SVP is a liquid that is used primarily to deliver medications, it is packaged in a small plastic bag called a minibag of 50 - 100 ml (minibags look like small plastic LVP bags). SVPs can also be packaged as ampules, vials, and prefilled syringes. Liquid drugs are supplied in prefilled syringes, heat-sealed ampules, or in vials sealed with a rubber closure. Powdered drugs are supplied in vials and must be constituted (dissolved in a suitable liquid) before being added to any solution. SVPs packaged as ampules, vials, or prefilled syringes are typically added to a minibag or a LVP but they may also serve as the final container. The term admixture is used to denote a solution where such an additive has been added to a minibag or LVP.

Ampules are sealed glass containers with an elongated neck that must be broken off. Most ampules are weakened around the neck for easy breaking; these will have a colored band around the neck. If the ampule is not weakened, it must first be scored with a file; otherwise the top may shatter. A 5 micron filter needle should be used when drawing the contents of an ampule into a syringe since glass particles may have fallen inside the ampule when the top was snapped off. The filter needle should be removed and replaced with the regular needle before injecting the drug into any solution. In addition, it is useful to wrap an alcohol wipe or small piece of gauze around the top of the ampule before breaking it. This will provide some protection to the fingers if the ampule shatters and will also reduce the possibility of glass splinters becoming airborne.

Drugs and other additives are packaged in vials either as liquids or lyophilized powders. Vials are made of glass or plastic and are sealed with a rubber stopper. A needle is used to add contents to or withdraw contents from the vial. Before withdrawing contents from a vial, an equal volume of air is usually injected into the vial to pressurize the vial and aid in withdrawing the contents. However, some medications are packaged under pressure or may produce gas (and therefore pressure) upon reconstitution. In these situations, air should not be injected into the vial before withdrawing the solution.

Dry powder formulations are lyophilized or freeze-dried powders that must be reconstituted with some suitable solvent to make a liquid formulation before being withdrawn from the vial. Some drugs are not stable in liquid form and so these drugs are put into the powder form and reconstituted just prior to use. There are several solvents that might be used to reconstitute the dry powders; the appropriate solvent is indicated in the product information insert. The most common solvents are Sterile Water for Injection, Bacteriostatic Water for Injection, Sodium Chloride Injection, and Ringer's Injection.

Vials may be designated for single-dose or multi-dose use. Single-dose vials do not contain preservatives and should be discarded after one use. Multidose vials contain a preservative to inhibit bacterial contamination once the vial has been used. Also, the rubber closure will reseal on a multidose vial. This provides a vial from which a number of doses of variable volume can be withdrawn.

There are two varieties of prefilled syringes. One type, a cartridge type package, is a single syringe and needle unit which is to be placed in a special holder before use. Once the syringe and needle unit is used, they are discarded but the holder is used again with a new unit. The other type of prefilled syringe consists of a glass tube closed at both ends with rubber stoppers. The prefilled tube is placed into a specially designed syringe that has a needle attached to it. After using this type or prefilled syringe, all of the pieces are discarded.

Ready-to-mix systems consist of a specially designed minibag with an adapter for attaching a drug vial. The admixing takes place just prior to administration. The major advantages of ready-to-mix systems include a significant reduction in waste and lower potential for medication error because the drug vial remains attached to the minibag and can be rechecked as needed. However, the systems do cost more, and there is the potential that the system will not be properly activated so that the patient receives only the diluent or a partial dose of drug.