Transdermal application can be an alternative drug delivery route for ondansetron, an antiemetic drug. Previous studies found that fatty acids, namely oleic and lauric, were the most effective penetration enhancers. The aim of this study was to investigate the formation of an ion pair between ondansetron and lauric acid as a possible mechanism of its enhancing action. Several techniques were used to reveal the formation of an ion pair complex. Partitioning experiments, where the n-octanol/water coefficient was measured, showed an increase in the distribution coefficient in the presence of the acid, possibly as a result of the formation of more lipophilic ion pairs between the charged molecules of ondansetron and lauric acid. Further evidence of complex formation between ondansetron and lauric acid, was gained from the 13C-nuclear magnetic resonance (13C-NMR) spectra of ondansetron, lauric acid, and their mixture (molar ratio 1:1). The NMR spectra revealed alterations to the magnetic environment of the carbon atoms adjacent to the ionized group, which are the carbonyl group of the acid and the nitrogen of the imidazole ring of ondansetron. This evidence substantiates the theory of ion pair formation. Finally, thermal analysis of the binary mixtures of ondansetron and lauric acid revealed the formation of an additional compound, with different melting point from pure ondansetron and lauric acid, which is thermodynamically favored.
The effects of coating thickness, type of adhesive, and type and concentration of enhancer on the mechanical properties of two acrylic pressure-sensitive adhesives (PSAs) were investigated using a 2(4) factorial design and an optimization technique. Sixteen formulations containing 0% or 10% of either caprylic acid or methyl laurate in two different PSAs, namely Duro-Tak 87-2196 and Duro-Tak 87-2097, were prepared. The adhesive properties of these laminates were evaluated by applying the 90 degrees Dynamic Adhesive Strength Peel Test (90 degrees DASPT) and 1800 Release Liner Peel Test (180 degrees RLPT). Coating thickness, concentration of enhancer, and type of adhesive did affect the 90 degrees DASPT. For the 180 degrees RLPT, the most significant factors were coating thickness and concentration of enhancer, with a strong interaction observed between the two. Coating thickness and concentration of enhancer were also used to create mathematical models that correlated these factors with the mechanical properties of the PSAs. For this purpose, the optimization technique 3(2) was applied. It was found that the correlation of the above factors can be adequately described with polynomial equations, which can be used for predicting the mechanical properties of the laminates containing the above PSAs and methyl laurate (0%-10%).
The in vitro permeation of ondansetron through human cadaver epidermis, as a preliminary step toward the development of a transdermal therapeutic system, was investigated. In vitro release studies were carried out using modified Franz diffusion cells and human epidermis, taken from cadaver skin by heat separation technique. To estimate the effect of the type and concentration of the penetration enhancers and the skin from different donors, an 8(1)3(2) asymmetrical factorial design was used. Formulations containing lauric acid and oleic acid as penetration enhancers, showed the largest Q values [amounts of ondansetron permeated per unit area of epidermal membrane (microg/cm2)] at 24, 48, and 72 hr, as well as steady-state flux values, among all formulations tested. The other enhancers increased the flux in the following order: lauryl alcohol>glycerol monooleate>Azone >cineole>oleyl alcohol>1-methyl-2-pyrrolidinone. Moreover, the concentration of the penetration enhancer and the type of the skin were proved to significantly affect the permeation rate of ondansetron through human epidermis. From the results obtained, it was shown that the formulations containing lauric acid or oleic acid at 5% or 10% could increase sufficiently the permeation of ondansetron. Therefore, the transdermal administration of ondansetron seems feasible.
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