As a pharmacist, I want to explain an important finding from a recent study that helps ensure the safety and effectiveness of medicines. AstraZeneca scientists conducted research to understand how freezing and thawing medicines affects tiny living organisms, like bacteria, that could potentially contaminate them. The study found that repeatedly freezing and thawing medicines weakens these microorganisms more than thawing them just once. While freezing can reduce the number of microbes, it may not completely eliminate them, which is why careful handling is so important during the manufacturing and storage of medicines.
The researchers tested eight different types of microorganisms in three different liquids commonly used in medicine production: tryptone soya broth (a nutrient-rich liquid), purified water (water that has been cleaned to remove impurities), and phosphate-buffered saline (a liquid that helps maintain a stable environment for the microbes). They stored these mixtures at -20°C (a typical freezer temperature) and then thawed them either once after four weeks or multiple times over the same period. They measured how many microbes survived using two methods: membrane filtration and counting colonies of bacteria.
The scientists expected that repeated freezing and thawing would cause more damage to the microbes than a single thaw. They also thought that the microbes would survive best in the nutrient-rich broth and worst in the purified water. Their results mostly matched these expectations, showing that repeated freezing and thawing generally reduced the number of surviving microbes more than a single thaw. However, the exact effects varied depending on the type of microorganism and the liquid it was in. For example, certain types of bacteria with a thin outer layer (called Gram-negative bacteria) were more affected by freezing and thawing than others.
Even though no new microbes grew during the thawing process, the findings highlight the importance of minimizing contamination risks during the handling of thawed medicines. The researchers suggested that future studies should test these effects using actual medicine formulations to make the results even more practical for drug development and manufacturing.
This study provides strong evidence to support the current practices of carefully managing freezing and thawing steps in the production and storage of medicines. This helps ensure that the medicines we use are as safe and effective as possible. The research was published in the journal EJPPS.