I use agar well diffusion method for antimicrobial assay. My samples are semisolid cream which can not dissolve in water.
I use two model drugs, one is hydrophobic and another one can be incorporated into both hydrophobic and hydrophilic carrier.
For positive control, I use one commercial ointment (because cream is not available in the market for my model drug).
The problem that I face is, positive control and the hydrophobic drug loaded formulations didn't show activity after putting directly into wells. Another drug loaded preparations showed clear zones.
So, I tried to dissolve in different solvents,such as DMSO, Tween 80 and Methanol. The commercial ointment showed clear zones after dissolving into Tween 80.But hydrophobic one didn't showed activity after dissolving into these three.
Please,could someone suggest me again for that problem? Should I change solvent or change to another method?
Your problem comes from the difficulties of the preparation in its diffusion in the MH agar, which is water based. The problem will also persist in case you would try the dilution method to define the antimicrobial capacity., since it is being done in a watery environment, which is broth.
You could try to use the emulsifying agent, such as Arlacel. Arlacel™ 165 is an acid-stable self-emulsifying glycerol monostearate. It has numerous uses, of which one is as emulsifiers in anhydrous cream bases (5 to 25%), this is why I think it could help.
If you think that is of help, you could keep me informed on your progress.
Hope Marina's suggestion might have solved your problem. You may also try addition of tween in agar medium also.
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