Abstract
The kinetics of passive transport of ketoprofen and metformin, as model substances for high and low permeability, respectively, across the artificial membrane under the influence of the pH of donor solution was investigated. There was an upward trend in the apparent permeation coefficient (Papp) of ketoprofen with the decrease in pH to a value close to pKa. At the pH value below pKa the permeation coefficient had lower value, due to the higher retention of ketoprofen in the artificial membrane. Metformin is a low permeable compound, and the highest permeation values were recorded at pH 7.4. Two dissociation constants determine that metformin at physiological pH exists as a hydrophilic cationic molecule, i.e. predominantly in ionized form. At pH values below 2.8, metformin mainly exists in diprotonated form, and it was, thus, very poorly permeable. The highest retention, i.e. affinity of both ketoprofen and metformin to the membrane, was at the lowest pH values, which is explained by different mechanisms. At higher pH values of donor compartment the substances showed significantly less affinity to the membrane. The obtained values of apparent permeation coefficients at studied pH values showed good correlation with the obtained experimental values by other in vitro methods.
Highlights
The oral route is the most preferred route of drug administration
The donor compartment contained a solution of 500 μmol L-1 of active substance in 100 mL of phosphate buffer of different pH values
Permeations of ketoprofen and metformin were monitored in this experimental work at different pH values of the donor compartment, while the pH of the acceptor compartment was 7.4 in all cases
Summary
The oral route is the most preferred route of drug administration. It is considered safe, effective, and readily available, with minimal discomfort to the patient compared to other routes [1]. The absorption of orally administered drugs is a function of its dissolution, solubility and permeability of the substance along the length of the gastrointestinal tract (GIT) [2]. The absorption of active substances varies depending on the pH along the gastrointestinal tract [3]. The absorption of active substances mainly takes place in the small intestine, i.e. in the jejunum which has the largest absorption surface [4].
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