Characterisation of a preservative system in an oily preparation.

The influence of three variables, i.e. the concentrations of benzyl alcohol (BA), butylated hydroxytoluene (BHT) and tert-butyl-4-hydroxyanisol (BHA), on the preservative efficacy and antioxidant activity of an oily veterinary formulation was investigated using quantitative experimental designs and applying pharmacopoeial methods as part of the robustness-evaluation. Preservative Efficacy Tests (PETs) were performed using the validated European Pharmacpoeia (EP) methodology with 7 test-organisms over one month on lab-scale test-formulations. These were independently prepared according to a Box-Behnken experimental design with a triplicate central point at 0.75% m/V BA, 0.05% mN BHT and 0.05% m/V BHA, and with an additional control-point outside the Box-Behnken cube containing no preservative ingredient. The preservative efficacies were evaluated against the USP and EP criteria for formulations for oral use, as well as by the statistical comparison of the slopes obtained by linear regression of the log of CFU/g versus time. The peroxide values were determined after two months storage at 50 degrees C, using the EP titrimetric method. No interactions between the preservatives were observed for any of the seven tested micro-organisms in the PETs. BA had a very significant preservative effect against several of the tested microorganisms, while no antimicrobial effect for BHT and BHA was observed. Aspergillus niger was the most preservative-resistant micro-organism, while Staphylococcus aureus was the most sensitive test-germ. Compliance with USP-PET criteria was found for all formulations tested, even those without preservatives, while the EP-PET criteria showed compliance for those formulations with the highest BA concentration only. Stored in glass vials, a statistically significant antioxidant effect was demonstrated for BA only, although all tested formulations showed acceptable anti-oxidative properties. No significant antioxidant effects were shown for BHT or BHA.

The importance of the cosolvent propylene glycol on the antimicrobial preservative efficacy of a pharmaceutical formulation by DOE-ruggedness testing.

The aim of this study was to statistically evaluate the influence of the concentration of the co-solvent propylene glycol on the preservative efficacy of a complex pharmaceutical suspension-emulsion formulation containing methyl- and propylparaben. Preservative Efficacy Tests (PETs) were performed using the validated pharmacopoeial methodology with five test organisms over 1 month on lab-scale test formulations. These were independently prepared according to a Box-Behnken experimental design with a triplicate central point at 0.22% m/m methylparaben, 0.22% m/m propylparaben, and 2.75% m/m propylene glycol, and with an additional corner point of the Box-Behnken cube. We evaluated the preservative efficacies against the criteria of the United States Pharmacopeia (USP) and European Pharmacopoeias (PhEur) for formulations for oral use, as well as by the statistical comparison of the slopes obtained by linear regression of log (CFU/g) vs. time. With an initial bacterial challenge of 10(6) CFU/g for each of the three bacterial strains, no survivals were detected after 7 days. For the two fungal strains, box plots and analysis of variance showed significant, concentration-dependent, main effects: the three variables significantly influenced the kill-rate of C. albicans, while A. niger was predominantly influenced by the cosolvent propylene glycol, and only to a minor extent by methylparaben and not at all by propylparaben. These findings were confirmed by taking the pharmacopoeial criteria as the evaluation basis, where the dominant influence of propylene glycol concentration is apparent. It was concluded that the cosolvent propylene glycol is at least of equal preservative importance than both parabens.