Evaluation of preservative systems in opthalmic suspension of polymyxin B and dexamethasone by linear regression.

An ophthalmic suspension of polymyxin B and dexametasone with 13 different preservative systems was evaluated by a linear regression method for rapid screening, using D-values. The products were challenged against Pseudomonas aeruginosa, Burkholderia cepacia, Staphylococcus aureus, Candida albicans and Aspergillus niger. Since linear regression showed correlation coefficients higher than 0.84 the decimal reduction time (D-value) was then calculated. The comparison of D-values obtained for each microorganism and each product led to the selection of the formula 9 = 10, which was selected to be submitted to the efficacy of antimicrobial preservation according to the European Pharmacopoeia.