Is the indirect method (free drug concentration in supernatant) considered as exact as the indirect one? which method one is more reliable?
I fell dialysis method easy and relabel method.
Were u have to dialysis your polymer/nanoparticulate solution with know volume of dialysate for a period of time. Amount of drug in dialyzes fluid can be determined using UV or HPLC.
U can refer the folowing article for detailed methodology:
International Journal of Biological Macromolecules 51 (2012) 1109– 1115.
You can also try centrifugal method. Where you have to centrifuge your sample solution at high rpm for a period of time.
Note: %EE may not give you accurate results. Its always suggested to carryout drug content studies.
You can use either the direct method which is this one (what is encapsulated into the particles) or the indirect (what was not encapsulated into the nanoparticles) in order to calculate the encapsulation efficiency. in the first method as you nicely describe you will have to dissolve the nanoparticles and the encapsulated drug (nanoformulation) in the same solvent and measure the concentration of the drug with any analytical method suits you best. With the indirect method you can measure the drug that was not encapsulated (measure the supernatant after the procedure of encapsulation and the isolation of the nanoparticles (centrifugation). Please check also if you like the papers mentioned bellow
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Article: Novel self-assembled core-shell nanoparticles based on crystalline amorphous moieties of aliphatic copolyesters for efficient controlled drug release
Sofia Papadimitriou · Dimitrios Bikiaris
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Full-text · Article · Jun 2009 · Journal of Controlled Release
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Entrapment efficiency gives you an idea about the %drug that is successfully entrapped/adsorbed into nanoparticles. It is calculated as follows:
%EE = [(Drug added - Free "unentrapped drug")/Drug added] *100
Example: If the %EE is 30%, it means that 30% of your drug is entrapped into the nanoparticles.
Loading capacity helps you to deal with nanoparticles after their separation from the medium and to know their drug content. It is calculated using the following equation:
%LC = [Entrapped Drug/nanoparticles weight] * 100
Example: If the loading capacity is 30%, it means that 30% of the nanoparticles weight is composed of the drug! i.e. Each 1 mg nanoparticles contains 0.3 mg drug.
I will suggest you to use both direct and indirect methods if feasible, although direct method is considered more accurate. The problem with indirect method is that whole un-entrapped drug may not get into supernatant due to low solubility. On the other hand, un-entrapped drug may precipitate out with nanoparticles in direct method and, erroneously, be regarded as encapsulated (false positive result) when precipitate is dissolved in appropriate solvent. However, this problem can be overcome to some extent by washing nanoparticles with water/ethanol etc. The problem with dialysis method is that encapsulated drug may be released from nanoparticles when placed in excess of medium. The problem of drug release from nanoparticles release may also be observed during washing of nanoparticles in direct method. In this scenario, another option (which I also use sometime) is to measure amount of drug in supernatant of formulation as well as supernatant of first (few) washings to calculate amount of un-entrapped drug in indirect method.
Therefore, you must check solubility of drug, drug release pattern and time for each procedure while making selection of process.
It is an indirect method. Further confirmation of the encapsulation effiiciency can be made by drug release studies in PBS.
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