The correlation between the chemical stability and the microbiological activity of polymyxin B in phosphate buffer pH 6.0 and in proprietary eye drops was evaluated. High Performance Liquid Chromatography (HPLC) was used to quantify the amount of the main components in samples stored at 43,50,55 and 60°C for a period of 500 h. The data indicated that there are significant differences in chemical stability among the different proprietary eye drops. The accurate decomposition rate constants and shelf-lives (~o) at 4°C of two of the six formulated eye drops and the standard polymyxin B solution stored in glass containers at pH 6.0 were established. It was concluded that microbiological assay by agar diffusion was unsuitable for determining the activity of control polymyxin B in phosphate buffer and polymyxin B in eye drops. Killing time determinations for polymyxin B against cell suspensions of P. aeruginosa NCTC 6750 were consequently used. Thioglycollate broth containingp- aminobenzoic acid (PABA) 0.16 %w/v and magnesium sulphate 1 %w/v was used as an inactivating recovery medium. The effect of preservatives and of second antibacterials contained in the eye drops were tested individually and combined with polymyxin B. Thiomersal 0.001 %w/v, trimethoprim 0.02 %w/v and thiomersal 0.001 %w/v plus trimethoprim 0.02 %w/v did not have an effect on the activity of polymyxin B 2000 U/ml. Neomycin was an exception and at the concentrations in the range 0.0192 to 0.16 %w/v exhibited an antagonistic effect. Chemical interaction between polymyxin B and neomycin could not be detected and it was considered that the inhibitory effect of neomycin may be the result of competition between polymyxin B and neomycin for the same binding sites on the cell surface. Gentamicin is active against P. aeruginosa NCTC 6750 and at concentrations of 0.075 and 0.036 %w/v it exhibited an additive effect with polymyxin B 2000 U/ml against the test organism. The results obtained with the samples stored at 55°C for a period of 500 h demonstrated the critical effect of pH. At a pH of 6.0 microbiological activity and chemical stability appeared optimal. The chemical stability data of five eye drop samples correlated with microbiological activity data. Exceptions were polymyxin B in one eye drop sample and control polymyxin B. These extensively decomposed samples showed good antibacterial activity which appeared to result from the activity of decomposition products. Chemical stability data for standard polymyxin B solution at pH 6.0 also correlated to microbiological activity data over the temperature range of 92 - 115°C. The polymyxin B retained detectable microbiological activity when the amount of PB1 was greater than 20%. It is suggested that the decomposition products which occurred at these higher temperatures did not possess antibacterial activity.

Anthocyanins have been shown to possess specific antioxidant capacities, which may provide an underlying protective effect against many chronic diseases . Although the antioxidant capacity of anthocyanins has been well established, less is known about the extent to which specific anthocyanin composition affects total antioxidant capacity . The aim of the present study was to compare the antioxidant capacity of two different soft fruits, blackcurrant and grape, which have distinctly different anthocyanin profiles. The anthocyanin profiles of grape and blackcurrant were characterized by HPLC/MS coupled with a diode array detector. Results showed that blackcurrant contained four predominant anthocyanins, cyanidin 3-glucoside, delphinidin 3-glucoside, cyanidin 3-rutinoside, and delphinidin 3-rutinoside . In contrast, malvidin 3-glucoside, delphinidin 3-glucoside, cyanidin 3-glucoside, petunidin 3-glucoside, and peonidin 3- glucoside were the major anthocyanins found in grape . The concentration of individual anthocyanins in all berries was quantified with HPLC/UV using cyanidin 3-glucoside as an external standard . Finally, results showed a greater (p<0.05) antioxidant capacity of blackcurrant compared to grape. The total antioxidant capacity of crude extracts from each was measured by Oxygen Radical Absorbance Capacity (ORAC) and ABTS assays. Anthocyanin antioxidant capacity index (AACI), derived from the product of antioxidant (ORAC) activity for each of major anthocyanin present in blackcurrant and grape, was also used to determine whether the antioxidant capacity of crude anthocyanin fractions represents either the sum total anthocyanin content or, alternatively, a synergy between different anthocyanins components . Our results indicated that a plausible potential synergy between anthocyanin components in regards to ORAC antioxidant capacity existed in blackcurrant and grape semi-purified anthocyanin extracts. Furthermore, it could be concluded that both total anthocyanin content as well as the composition of individual anthocyanins in soft fruits is important to assess total antioxidant capacity of different berry sources .

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