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Dehydration behavior of eprosartan mesylate dihydrate.

Abstract：

:Eprosartan mesylate (SKF 108566-J; EM) is an antihypertensive agent approved for marketing in the USA. EM dihydrate was prepared by three methods, one of which included suspending the anhydrous drug in an aqueous solution of 1.0 M methanesulfonic acid to form a slurry, followed by filtration. The dehydration kinetics of EM dihydrate were derived by analyzing the fit of the isothermal thermogravimetric analytical (TGA) data to numerous kinetic models. EM dihydrate undergoes dehydration in two distinct steps, each involving the loss of 1 mol of water at 25-70 degrees C and 70-120 degrees C, respectively. Recrystallization of EM occurs at approximately 120-140 degrees C after dehydration to the anhydrous phase. This explanation is supported by variable temperature powder X-ray diffractometry. The mechanism of the dehydration reaction is complex, the dependence of the reaction rate on temperature varying as a function of the particles size. For the dihydrate of sieve fraction <125 microm, the kinetics of the first and second dehydration steps are consistent with the Avrami-Erofeev equation (A3, n = 1/3) over the temperature range studied, corresponding to three-dimensional growth of nuclei. In contrast, for the 125-180-microm and 180-250-microm sieve fractions, the kinetics are best described by the two-dimensional phase boundary reaction (R2) at a lower dehydration temperature (i.e., 28.3 degrees C), and by the Avrami-Erofeev equation (A3, n = 1/3) at a higher dehydration temperature (i.e., 93.7 degrees C). The activation energies (15-40 kcal/mol) and frequency factors of the dehydration of EM dihydrate were determined both by Arrhenius plots of the isothermal rates determined by TGA and by Kissinger plots of the nonisothermal differential scanning calorimetric data. Hot stage microscopy of single crystals of EM dihydrate showed random nucleation at the surface and dehydration with the growth of microcrystals along the needle a axis. Cerius(2) molecular modeling software showed the existence of water channels along the a axis and enabled the observed dehydration behavior of EM dihydrate crystals to be explained in terms of the bonding environment of water molecules in the crystal structure.

journal_name

J Pharm Sci

journal_title

Journal of pharmaceutical sciences

authors

Sheng J,Venkatesh GM,Duddu SP,Grant DJ

doi

10.1021/js9900250

subject

Has Abstract

pub_date

1999-10-01 00:00:00

pages

1021-9

issue

eissn

0022-3549

issn

1520-6017

pii

S0022-3549(15)50875-7

journal_volume

pub_type

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Dehydration behavior of eprosartan mesylate dihydrate.