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Microbial toxicity of isopropyl myristate used for sterility testing of petrolatum-based ophthalmic ointments
Abstract:
The toxicity of isopropyl myristate (IPM) to microorganisms varies from lot to lot and between manufacturers. The toxicity is not directly proportional to the number and level of IPM homologues present nor to the small quantities of fatty acids, alcohols, aldehydes, or ketones found in both filter- and heat-sterilized IPM. The toxicity of IPM, both filter- and heat-sterilized, has no correlation with the usual physical and chemical characteristics of IPM but shows excellent correlation (correlation coefficient, r = 0.88) with the pH of a water extract of IPM. The toxic compounds can be removed and the toxicity of both filter- and heat-sterilized IPM can be reduced by basic alumina treatment. These findings may indicate that trace amounts of acidic catalysts remaining after production of IPM are responsible for the toxic effect.
Insights
Isopropyl myristate (IPM) toxicity to microbes varies significantly. This toxicity correlates with pH, not chemical composition, suggesting residual acidic catalysts are the cause.
Area of Science:
- Microbiology
- Chemical Engineering
- Cosmetic Science
Background:
- Isopropyl myristate (IPM) is a common cosmetic ingredient.
- The antimicrobial toxicity of IPM varies between batches and manufacturers.
- Standard quality control measures do not predict IPM toxicity.
Purpose of the Study:
- To investigate the factors influencing the variable toxicity of isopropyl myristate (IPM) to microorganisms.
- To identify reliable indicators of IPM toxicity.
- To explore methods for reducing IPM's antimicrobial toxicity.
Main Methods:
- Assessing the toxicity of various IPM lots to microorganisms.
- Analyzing the correlation between toxicity and IPM composition (homologues, fatty acids, alcohols, aldehydes, ketones).
- Evaluating the relationship between toxicity and physical/chemical characteristics, including the pH of water extracts.
- Testing the efficacy of basic alumina treatment in reducing toxicity.
Main Results:
- IPM toxicity showed no correlation with homologue levels or common impurities.
- A strong correlation (r = 0.88) was found between IPM toxicity and the pH of its water extract.
- Basic alumina treatment effectively removed toxic compounds and reduced IPM's toxicity.
- Sterilization methods (filter vs. heat) did not alter the toxicity-pH correlation.
Conclusions:
- The antimicrobial toxicity of isopropyl myristate is primarily linked to its water extract pH.
- Residual acidic catalysts from the manufacturing process are likely responsible for IPM's toxic effects.
- Basic alumina treatment offers a viable method for mitigating IPM toxicity.