The aim of the study was to evaluate, in comparison to the reference product, the effect of the hydrophilic nonionic polymers: methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), as well as the anionic polymers - copolymers of acrylic acid, on the release kinetics of a calcium dobesilate hydrogel formulation intended for application on the skin. In this work, we used an ointment cell for the release of the active pharmaceutical ingredient (API) from the formulations. This release was performed by employing the paddle method at 100 rpm, with the extraction cells placed in the release vessels in two different positions: with the semipermeable membrane faced to the top, or to the bottom of the vessel. Released API percentage was assessed via the validated spectrophotometric method. In the study with standard placement of the ointment cell, the release rates ranged from 4.45×10-3 min-1 for a formulation containing polyacrylic acid (PA), to 6.96 × 10-3 min-1 for a formulation based on HPMC. In the group of nonionic polymers, the release rate is higher in the case of HPMC, and lower in the case of MC. In the group of anionic polymers, the release rate is higher with the formulation of a modified copolymer of acrylic acid 11 (PC11), while release from a formulation comprising a polymer PA is rather prolonged. We found that the placement of the extraction cell does not affect the alignment of the formulations investigated in terms of the release rates in the group of non-ionic formulations: HPMC > MC, and in the group of preparation of ionic polymers: PC11 > PA.
A shortage of available experimental data exists in the available bibliography on the release rate of calcium dobesilate (CD) from hydrogel formulations. Thus, the aim of the study was to evaluate the effect of selected hydrophilic nonionic polymers and anionic polymers on the release rate of CD from formulation provided for dermal application, as compared to the reference product in the market. The work utilized excised pork skin, while, Methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), and anionic polymers (copolymers of acrylic acid) were used as CD carriers. The release study was executed by the pharmacopoeial paddle method, with extraction cells and fresh excised porcine skin as a membrane. CD in aqueous acceptor fluid was quantified by UV-VIS spectrometry at 300 nm. Subsequently, the kinetic curves were fitted to a zero-order kinetics model, a first-order kinetics model, a second-order kinetics model, as well as to the Higuchi model. The work saw that porcine ear skin influences the release pattern of the CD, compared to the artificial membrane. In the study, the evaluated formulations with MC, polyacrylic acid (PA) and polyacrylate crosspolymer 11 (PC-11) deliver over 60% of the active component (AC), within 250 min, through the excised porcine ear skin, to the acceptor compartment. Moreover, the release observed via porcine ear skin to the aqueous acceptor compartment is congenial to zero-order or first-order kinetics. In addition, the formulations prepared on the basis of MC and PA appear to control AC delivery, independently of actual concentration of AC.
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