It’s August of 1970 and you have discovered a mysterious rash on your arm after applying a copious amount of your favourite moisturising cream. Being that this is your favourite cream, you only apply it on special occasions. The container has been sitting in your bathroom’s vanity cupboard for about 3 months. You noticed that the smell had soured slightly, but that didn’t deter you. Hospital testing has confirmed that you have a skin infection likely caused by a Staphylococcus spp. One month later, antimicrobial effectiveness testing first appears as a General Chapter in the United States Pharmacopoeia, 18th Edition. This testing could have prevented you from the agony experienced one month prior.
Antimicrobial preservatives can be added to aqueous pharmaceutical products during the manufacturing process to inhibit any growth from organisms that may have been introduced during production. They can also be added to multiple-dose products to inhibit growth from organisms introduced through repeated usage. There is always one or more antimicrobial preservative(s) in all sterile multiple-dose products. Without the addition of preservatives, bacterial proliferation can run rampant. Bacteria are able to grow rapidly with a high efficiency/ low failure rate due to their robust cell cycle. Contamination from microorganisms can cause skin irritation (if in contact with skin; especially sensitive skin or open wounds) and other types of infection.
There are two types of preservatives that can be added to pharmaceutical products to inhibit microbial growth; antimicrobials and antioxidants. Both are used to extend the shelf life and facilitate the stability of pharmaceutical and cosmetic products, but they have distinct purposes and differences.
Antimicrobial preservatives are essential for preventing the growth of microorganisms in pharmaceutical products. Contamination during manufacturing or patient use can not only spoil the product but also pose significant health risks. These preservatives are particularly important in liquid (aqueous) formulations, such as eye drops, topical creams, and other water-containing products, which are more susceptible to microbial contamination. Common examples include benzalkonium chloride, widely used in eye drops; methylparaben and propylparaben, often found in topical and oral formulations; and phenol and chlorocresol, which are used in injectable medications.
