The poor aqueous solubility of drugs is a challenging problem faced by pharmaceutical scientists\nin drug formulation. Cosolvency and micellization techniques have been severally used to enhance\nthe solubility of poorly aqueous soluble drugs. Mirtazapine, a tetracyclic antidepressant used for\nthe treatment of moderate to severe depression and anxiety, has very poor aqueous solubility. The\nobjective of the study was to investigate the effect of solubilizing agents (cosolvents and surfactants)\non the aqueous solubility of mirtazapine while envisaging that any significant improvement\nin its aqueous solubility could contribute towards alleviating the withdrawal symptoms often associated\nwith the drug. The solubility of mirtazapine was determined at room temperature in\naqueous mixtures of cosolvents (propylene glycol and polyethylene glycol 400) and surfactants\n(polysorbate 20, polysorbate 80 and sodium lauryl sulfate). An exponential increase in mirtazapine\nsolubility was observed when total drug solubility in water-cosolvent system was plotted\nagainst cosolvent fraction volume. Polyethylene glycol 400 gave larger solubilization capacity ()\nwhen compared to propylene glycol. With the surfactants, linear relationship between the total\nsolubility of the drug in water-surfactant mixtures and surfactant concentration was noted. Sodium\nlauryl sulfate showed the largest solubilization power (k) when compared to the nonionic\nsurfactants (polysorbate 20 and polysorbate 80 respectively). A linear relationship between standard\nfree energy and partition coefficient was also observed. The result of the study shows that\naqueous solubility of mirtazapine is significantly improved by cosolvency and micellization and\ntherefore there exists the possibility of improving the withdrawal symptoms often experienced\nwith the drug. It also suggests that large free energy is required for drugs with high partition coefficients\nto permeate the biological membrane.
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