Microbial toxicity of isopropyl myristate used for sterility testing of petrolatum-based ophthalmic ointments

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.

Antimicrobial activity of neomycin C against Staphylococcus epidermidis

In vitro studies indicate that neomycin C is 50% as active as neomycin B against Staphylococcus epidermidis (ATCC 12228).

Microcount method for petrolatum-based topical ointments containing waxes

A practical solvent system for the detection of microorganisms in topical ointments has been developed. The method involves dissolving 0.5 g of topical ointment in 50 ml of a solvent mixture (92 parts isopropyl myristate, 6 parts carbon disulfide, and 2 parts xylene) and filtering it through a 0.45-mum membrane filter. Residual solvent is then washed from the filter pad with 200 ml of sterile 0.5% Brain Heart Infusion broth containing 0.1% Tween 80. The filter pad is then removed and placed on a petri plate containing Trypticase Soy Agar medium. The petri plates thus prepared are then incubated at 37 C for 7 days, and the colonies produced are then counted. The toxicity of the solvent mixture was determined against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella newington, and spores of Bacillus subtilis and was found to be less toxic than the heat-sterilized isopropyl myristate and comparable to the filter-sterilized isopropyl myristate.

Sterility test method for petrolatum-based ophthalmic ointments

A sensitive sterility testing procedure for the detection of microbial contamination in petrolatum-based ointments is described. The method involves dissolving the ointment in filter-sterilized isopropyl myristate and filtering through a membrane filter. Improved sensitivity is obtained by blending the membrane in Trypticase Soy Broth before incubation. Filter-sterilized isopropyl myristate is shown to be less toxic to microorganisms than heat-sterilized isopropyl myristate. The isopropyl myristate method is more sensitive than the polyethylene glycol-ether method for the detection of microbial contamination.