11.1 Medicines that require reconstitution
These include medicines, e.g. amoxicillin, that are presented as a dry powder and therefore need to be reconstituted before use. Further dilution may be necessary. The advantage of this type of formulation is that it enables prolonged storage of products that are unstable in solution.
There are a number of disadvantages, including the following:
- They need to be reconstituted, which is time consuming, particularly if the preparation is difficult to dissolve.
- All manipulations pose the risk of environmental and microbial contamination of the solution.
- They may be complex to prepare, particularly if they require special diluents or multiple transfers of fluid. The greater the complexity, the greater the chance of an error being made during preparation.
- Some medicines are susceptible to ‘foaming’, e.g. teicoplanin and asparaginase. If doses are drawn up from foam, part of the dose may be left in the vial. Foaming of protein drugs sometimes inactivates them.
- If the product is presented as glass ampoules that require snapping, there is a danger of glass particles getting into the preparation, staff injuries and the risk of medicine droplets polluting the environment.
- Pressure differentials in vials with a rubber septum may be difficult to manage (see below).
11.1.1 Equalising pressure in the vial
Some vials are manufactured with a vacuum inside, and it is important that the effects of this are corrected during reconstitution. If the vial has a vacuum inside it will be obvious when trying to add diluent because the diluent will be ‘sucked’ into the vial.