Hi Alessia.

Yes, chemical interactions can certainly affect drug release rates. Nominally, drug molecules are released from a dosage form or complex when they interact with a solvent that acts as a diffusion medium, so the free dissolved molecules can transport away from the source to a lower concentration region. (In dissolution experiments, the solvent is usually, but not necessarily, a liquid.)  That process will occur at a rate dictated by the drug, solvent, temperature, etc., all of which affect the molecular mobility.

If there is another process affecting the location of the drug molecules that is occurring simultaneously with the diffusion of the free molecules, both must be taken into account. For instance, if there is strong binding or complexation, the source of molecules that can be dissolved is restricted. In that case, the ability of molecules to diffuse away from a source may be offset by the ability of molecules to dissolve in the first place.  In other words, complexed molecules may not be free to diffuse in a medium... any interaction that slows the rate or extent of molecules being freed up to diffuse can slow the rate of release.

For example, we see this with solubilization... if a drug is tightly bound to a water-soluble complexing agent (for instance, a polymer), it may appear to be in solution because it is out of the undissolved state, but  it may not be able to diffuse, react chemically, cross membranes, etc. because those are factors seen with free molecules.

The topic is complicated, and modeling it requires solving simultaneous differential and partial differential equations. However, you may find papers (I don't have any offhand) relating binding or complexation to drug absorptoin, or effects of binding on dialysis of free drugs, etc.

I hope this gives you some ideas to start. Good luck!

thank you Mr. Bellantone!

Hi Alessia,

This is the aim of chemically controlled release technology  used to prolong the release of drug molecules linked to a polymeric carrier. There are erodible systems  (drug release controlled by polymer degradation/erosion/dissolution) and pendant chain systems where chemical linkages (ester, amide, utethane,...) are used to link drug to polymer, the drug release being controlled by the rate of degradation of the labile bond (by hydrolytic or enzymatic degradation)

Best regards, 

the answer of Mr.Bellantone was comprehensive

Hi Alessia

Chemical interactions must affect release of medicament from dosage form, Especially if reaction leads to polymerization of monomers, so degree of polymerization can control the rate of release of drug from polymer matix. Nominally, drug are released from a dosage form or complex when they interact with a solvent via diffusion and erosion  that acts as a diffusion medium.