Dear Alessia,

First of all you have to choose the release medium according to the dosage form of the drug, IV, IM, SC, Solution, enetric coated tablets or regular tablets. For hydrophobic drugs, PBS with pH 7.4 with 2& surfactant such as SLS (you might change the percentage of the surfactant according to the solublity of the system) and mixing by shaker at 37 degrees is generally used.

The following links contain publications for the release of hyrophobic drugs incorporated in a variety of vehicles:

https://www.google.ps/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0ahUKEwjRr__gzOPKAhXJCBoKHVZpC2gQIAhjMAk&url=http%3A%2F%2Fwebcache.googleusercontent.com%2Fsearch%3Fq%3Dcache%3AGJN7ELNzKXwJ%3Ahrcak.srce.hr%2Ffile%2F7421%2B%26cd%3D10%26hl%3Den%26ct%3Dclnk%26gl%3Dps&usg=AFQjCNEAiKcT6X4sjjty1CDhMjqXMySFCg&sig2=0M2QpjXhhHPx9gtN9xRwYw

https://www.google.ps/search?biw=1366&bih=667&q=related:pubs.acs.org/doi/abs/10.1021/am4035027+release+of+hydrophobic+drug&tbo=1&sa=X&ved=0ahUKEwjRr__gzOPKAhXJCBoKHVZpC2gQHwhaMAg

https://www.google.ps/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjRr__gzOPKAhXJCBoKHVZpC2gQIAhRMAc&url=http%3A%2F%2Fwebcache.googleusercontent.com%2Fsearch%3Fq%3Dcache%3APXHGjLiM8CMJ%3Ascitation.aip.org%2Fcontent%2Faip%2Fjournal%2Fbmf%2F9%2F5%2F10.1063%2F1.4916230%2B%26cd%3D8%26hl%3Den%26ct%3Dclnk%26gl%3Dps&usg=AFQjCNH_B7KdoqIN6i7cyPxmN7xrXiHf8w&sig2=IbF5UKBRMUf1YFOWOXuz1Q

https://www.google.ps/search?biw=1366&bih=667&q=related:www.ncbi.nlm.nih.gov/pubmed/22887492+release+of+hydrophobic+drug&tbo=1&sa=X&ved=0ahUKEwjRr__gzOPKAhXJCBoKHVZpC2gQHwhAMAU

https://www.google.ps/search?biw=1366&bih=667&q=related:www.ncbi.nlm.nih.gov/pubmed/17331574+release+of+hydrophobic+drug&tbo=1&sa=X&ved=0ahUKEwjRr__gzOPKAhXJCBoKHVZpC2gQHwg4MAQ

Hoping this will be helpful,

Rafik

I agree with Rafik

Lipid--an emerging platform for oral delivery of drugs with poor bioavailability.

Chakraborty S1, Shukla D, Mishra B, Singh S.

Abstract

The sole objective of pharmaceutical science is to design successful dosage forms which fulfill the therapeutic needs of the patients effectively. Development of new drug entities is posing real challenge to formulators, particularly due to their poor aqueous solubility which in turn is also a major factor responsible for their poor oral bioavailability. Lipids as carriers, in their various forms, have the potential of providing endless opportunities in the area of drug delivery due to their ability to enhance gastrointestinal solubilization and absorption via selective lymphatic uptake of poorly bioavailable drugs. These properties can be harvested to improve the therapeutic efficacy of the drugs with low bioavailability, as well as to reduce their effective dose requirement. The present communication embodies an in-depth discussion on the role of lipids (both endogenous and exogenous) in bioavailability enhancement of poorly soluble drugs, mechanisms involved therein, approaches in the design of lipid-based oral drug delivery systems with particular emphasis on solid dosage forms, understanding of morphological characteristics of lipids upon digestion, in vitro lipid digestion models, in vivo studies and in vitro-in vivo correlation.

http://www.ncbi.nlm.nih.gov/pubmed/19505572

Thank you all! 

I want to study delivery of drugs from polymeric formulations, produced by supercritical techniques. So I have powders to analyzed; I want  to simulate human body so I usually use PBS at different pH.

Dear Alessia,

Generally, they conduct kinetic study (release of a drug from its formulation) in three different pHs: pH = 1.5 of the stomach, pH 6.5 of the intestine and pH 7.4 of the blood circulation. PBS buffer can be appropriate for the intestine and blood circulation since you can make it 6.5 or 7.4 (adjusting pH), whereas, for the pH of the stomach you should use .01N HCl with or without pepsin.

Hoping this will be helpful,

Rafik

I agree with Rafik; your study will be more complete if you measure release at 3 different pHs that can be met thrughout the digestive tract. We use pHs 1.2 (stomach), 4.5 (upper part of small intestine) and 6.5 or 7.4 (lower part of small intestine, colon)

I agree. Thanks.

to simulate human body, go for "Fed state" and "Fasting state" studies it compliance more than normal PBS study

I agree rafik