Freezing injectable preparations
In a functioning Centralised Reconstitution Unit, an increase in production activity means we must find ways of extending the life span of ready-to-use intravenous doses.
Freezing would appear to be an easier way of achieving this goal than modifying the galenic composition of the product. Many molecules demonstrate considerable physicochemical stability when frozen.
By reducing the temperature of storage the solution is frozen, maintained in a completely inert state throughout the period of storage, provided that the storage conditions have been optimised: freezing freezer, storage freezer, limited quantities stored in each drawer of the freezer etc.
Defrosting the solutions in a microwave oven, if well handled, can remove one of the major obstacles associated with freezing: the time the product takes to thaw. Microwave thawing seems to be more secure than other techniques (forced-ventilation ovens, water baths etc.).
Microwaves work by heating the ice. Due to their wavelength (12.2cm) they do not interfere with the molecular structure of the active ingredient. We must ensure that the heating power used does not damage the active ingredient.
Since 2002 13 additional molecules have been tested, with the results of these tests published in scientific journals. The molecules tested retained 90% of their initial concentration on the day that they were defrosted by microwave, and during several days’ storage at 4°C. All analyses were conducted using HPLC.
The freezing/microwave defrosting technique allows for the production of larger batches, making this process more labour-efficient and, beyond a certain threshold of units, more efficient in terms of materials used. These results should encourage us to investigate the possibility of extending the technique to other molecules which are regularly used in hospitals.
However the hospital must be equipped with freezers (for initial freezing and sub-zero storage) and one or several microwave ovens. Managers must also approve a defrost cycle tailored to the volume of the vessel to be thawed, monitor the temperatures of freezers and refrigerators, ensure that the laminar flow hoods and extractor fans are functioning correctly, and conduct microbiological control tests on the end products.
If well-managed, the freezing/microwave defrosting technique can allow hospitals to expand the range of intravenous medications produced in the central unit for reconstitution of injectable drugs, and increase the all-round quality of care provided to patients.