states pharmacopeia usp xxii 1990 antimicrobial preservative effectiveness standards was performed against staphylococcus aureus for the compositions shown in the following table the screen entailed challenging the formulations with the gram positive bacteria s aureus and sampling at 7 and 14 days the initial preservative efficacy test for the formulations had indicated that the formulations had poor preservation only against s aureus whereas the formulations exhibited appropriate preservative efficacy according to usp against the other organisms such as gram negative pseudomonas aeruginosa and fungi aspergillus niger at 7 and 14 days ______________________________________formulationingredient a b c d______________________________________caffeine 0 0 0 2 0 75 1 25diclofenac sodium 0 1 0 1 0 1 0 1vitamin e tpgs 1 5 1 5 1 5 1 5tromethamine 1 2 1 2 1 2 1 2boric acid 0 6 0 6 0 6 0 6disodium edta 0 1 0 1 0 1 0 1bac 0 01 0 01 0 01 0 01mannitol 4 4 4 4 3 8 3 2hpmc 0 1 0 1 0 1 0 1naoh or hcl qs to 7 4 7 4 7 4 7 4adjust ph topurified water qs to 100 100 100 100______________________________________ according to the usp preservative efficacy standards for s aureus a formulation has to exhibit a minimum of 3 0 log reduction on day 14 and no increase in count between 14 to 28 days fig1 shows the results for the s aureus screen for the formulations in the above table the formulations had similar compositions except for the varying concentrations of caffeine from 0 0 to 1.