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ARPN Journal of Science and Technology >> Volume 7, Issue 1, January 2017

ARPN Journal of Science and Technology

Preformulation Study of Saquinavir: pH-Dependent Solubility, Ionization and Partition Coefficients

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Author Obonga, WO, Nnadi, CO, Onyechi, AA
ISSN 2225-7217
On Pages 551-556
Volume No. 3
Issue No. 5
Issue Date June 01, 2013
Publishing Date June 01, 2013
Keywords Preformulation study, saquinavir, pH, spectrophotometry, partition coefficient


Solubility, ionization and lipophilicity of a drug molecule are known to affect its transportation, distribution and permeation properties. The determination of physicochemical properties of saquinavir (SQV) was carried out to design alternative or improve on the available dosage form(s) of the compound capable of circumventing the obvious challenges with current available formulation while improving bioavailability and compliance. Solubility, pKa and octanol-water partition coefficient were determined by UV spectrophotometry in different buffer systems (pH 3-11, ionic strength 0.10 M at 25 C) and in selected solvent systems: polysorbate 80, PEG 400 and glycerol. Log P was determined by shake flask method, solubility was measured by adding excess SQV in 10 ml of buffer or solvent system at 25 C for 48 h, centrifuged, supernatant filtered, diluted and absorbance recorded at 265 nm to obtain solubility from a pre-calibrated and validated Beers plot. The pKa was estimated from the point of inflection of first derivative plot of ?Abs/?pH versus pH, Handerson-Hasselbach, intrinsic solubility and Bates-Schwarzenbach methods. A maximum aqueous solubility (1358 g/ml) was observed around the pKa value. PEG 400 (10 %v/v) improved the solubility of SQV (2756 g/ml). The log P measurements show a value >1.0 in buffer systems (pH 3-11 at 25 C). The order of solubility of SQV for the solvents are PEG 400>polysorbate 80>glycerol. The pKa of SQV ranges from 6.998 to 7.15 in buffer system at 25 C, 0.1 M. The physicochemical parameters found in this study could serve as veritable tool for possible further development of topical SQV capable of improving bioavailability and compliance.

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