during a comparison between nano liposomes loaded with antibiotic and antibiotic itself in invitro antimicrobial assessment , we found that the antibiotic showed more inhibition for the bacterial than the nano liposomes. how can we solve this issue ?
Hi Hesham,
These questions need to be answered first:
1- What is the purpose of formulating the antibiotic into liposomes? I assume you want to achieve some delivery benefits (enhanced skin permeation, enhanced tissue deposition, longer plasma circulation, etc.).
2- What is the purpose of this in vitro test? What are you expecting?
3- It is expected that the liposomal antibiotic shows slower inhibition compared to free antibiotic. Liposomes provide slow drug release, but they also provide better skin permeation (in some cases), higher cellular uptake (also in some cases), longer plasma circulation (if they are injected IV), or different tissue/organ distribution.
In conclusion, liposomes should provide slow inhibition in vitro. You may use this test to confirm that the antibiotic is actually encapsulated inside the liposomes. I'd be surprised if the liposomes are faster than the free antibiotic in bacterial inhibition.
what if the free antibiotic itself is not diffusing the media because of its low solubility, Could nanoliposomes offer a delivery system that increases the solubility and diffusion in media, therefore enhance the antibacterial activity?
I still need to know the purpose of the formulation. What is the proposed route of administration?
This agar-based in vitro test only aims to differentiate between different molecules with different antibacterial activities. Diffusion through the medium wouldn't predict any therapeutic benefit because it doesn't mimic any in vivo condition.
Also the agar medium has a network structure that may need be a valid test for the solubility of the molecule. In all cases, nanoliposomes are not expected to improve solubility of the molecule, because it is an encapsulation system. If you do a nano-range size reduction (without encapsulation), this may improve solubility. Also, most antibiotics have salt forms that are more soluble.
If you want to deliver the liposome topically, you need an in vitro test that mimics in vivo situation (Franz diffusion cells or any similar device).
If you want to deliver it through mucosa (nasal drops, etc.), you need to prove that it penetrates mucosa or shows sufficient mucosal deposition (e.g. Ussing diffusion cells, etc.).
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