Bioavailability micellar solubilization

Mydriatic activity on rabbits and humans, and cycloplegic activity on humans were tested. It was found that tropicamide bioavailability, both in rabbits and in humans, was not decreased by micellar solubilization. The conclusion was that some poloxamers perform satisfactorily as solubilizing vehicles for tropicamide, producing neutral 1.0-1.5% drug solutions that are better tolerated and more effective than the standard aqueous eyedrops. 

The use of the lauric acid salt of propranolol for extended release also resulted in increased bioavailability possibly linked to micellar solubilization, ion pair formation, and preferential lymphatic uptake. 

Although the micellar solubilization can be demonstrated in vitro there is no warrant for a corresponding enhancement of bioavailability by the oral route in any case. With particular combinations of drug substance and surfactant, even reduced instead of improved bioavailability has been observed. Such effects depend on the concentration of the surfactant and may have various reasons such as shift of equilibrium in favour of micellar inclusion or formation of other types of drug-surfactant aggregates. 

The normal micelles and reverse micelles solubilize both hydrophilic and lipophilic drugs. The normal micellar solubilization increases the bioavailability of the poorly soluble drugs, whereas, the reverse micellar solubilization allows sustained release of the medicament. 

Solubilization capacity is defined as solubilization effect of polymers on active ingredients in an aqueous solution. Needless to say, if the polymer can retain the drug in supersaturation state in the GI tract, it will significantly enhance bioavailability. Of all polymers used in ASD, amphiphilic polymers such as Soluplus have better solubilization capacity due to their ability to create micellar structures. On the other hand, most of ionic polymers such as methacrylate copolymers can create complexes with the drug and thus increase its solubility. 

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