Solubility, Polymorphism, Crystallinity, Crystal Habit, and Drying Scheme of (R, S)-(±)-Sodium Ibuprofen Dihydrate - Pharmaceutical Technology

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Solubility, Polymorphism, Crystallinity, Crystal Habit, and Drying Scheme of (R, S)-(±)-Sodium Ibuprofen Dihydrate
The racemic compound (R, S)-()-ibuprofen is a popular and well understood active pharmaceutical ingredient, but it has several disadvantageous formulation properties such as poor solubility, low melting point, and potential esterification with excipients containing an hydroxyl group. The authors investigate the use of an (R, S)-()-ibuprofen salt to evaluate these problems using various analytical methods to determine the polymorphism, crystallinity, and drying scheme.


Pharmaceutical Technology


Solubility studies. Because of the expensive nature of (R, S)-()-sodium ibuprofen dihydrate, its solubility was determined by the gravimetric titration method that required a relatively small amount of material (13). Although the gravimetric titration method had an inherent error of about 20% because the solvent volume used was assumed to be the same as the solution volume (13) and was less accurate than the well-known UV-visible spectroscopic technique (16) and the evaporation-weighing technique (17), it was rapid, robust, and more suited for the initial screening. Unlike the other two techniques, the gravimetric titration method did not require establishing time-consuming calibration curves of (R, S)-()-sodium ibuprofen dihydrate concentration in every solvent and did not produce any unforeseen solvates that could interfere with the true mass of the dihydrate solids after removal of the solvents.

Solvent-miscibility studies. The miscibility tests were performed by mixing two solvents from the 23 solvents in a 20-mL scintillation vial (13). The number of miscible and immiscible solvent pairs from the miscibility investigations and the API solubility in the 23 single solvents from the Solubility Studies Section (13) were combined to deduce a form space. The form space is defined as the total number of solid-generation experiments in pure-solvent, cosolvent and antisolvent systems (13).

Polymorph, crystallinity, and crystal-habit studies. Solids were produced in the good solvents ferreted out by the Solubility Studies Section (13). The polymorphism, crystallinity, and crystal habit of the solids were determined by DSC, TGA, PXRD, OM, and SEM, respectively.

Scanning electron microscopy. Solids of racemic (R, S)-()-sodium ibuprofen dihydrate compound grown from water were filtered, rinsed with acetone, and vacuumed-dried at 40 C or 4 h. The anhydrous (R, S)-()-sodium ibuprofen solids were mounted on an aluminum stub by a double-sided carbon conductive adhesive tape (Product number 16073, Ted Pella Inc., Redding, CA). The solid sample was sputter-coated with a 6-nm thick gold film in an Hitachi E-1010 Auto Sputter Coater (Hitachi Ltd., Tokyo, Japan).

SEM was carried out using an Hitachi S-3500N (Hitachi Ltd., Tokyo, Japan) instrument equipped with a tungsten filament cathode source. Gold-coated samples were examined with beam energies of 15 kV with a chamber pressure of 10-5 Pa (resolution ~3 at these voltages).

Drying-scheme studies. Filtered solids of the racemic (R, S)-()-sodium ibuprofen dihydrate compound were dried by three various modes in a DOV-40 oven (Dengyng Instrument Co., Ltd., Taiepi, Taiwan) at 40 C for 4 h in air, at 40 C for 4 h under vacuum, and 90 C for 2 h under vacuum. A vacuum of 6.7 10-2 Pa was generated by the GVD-050A vacuum pump (Ulvac Kiko Inc., Yokohama, Japan).


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