Mechanism for further enhancement in drug dissolution from solid-dispersion granules upon storage

The present study was performed to investigate the further increase in drug dissolution on storage of ternary solid-dispersion granules containing poorly water-soluble drugs. Ternary solid-dispersion granules of the drug, a dispersion carrier, and a surface adsorbent were prepared using hot-melt granulation. Two proton-donating drugs, BAY 12-9566, naproxen, and a nonproton-donating drug, progesterone, were studied. Gelucire 50/13 and polyethylene glycol 8000 were evaluated as solid-dispersion carriers with low melting point. Neusilin US2 (magnesium aluminosilicate), a proton acceptor, was used as the surface adsorbent. The proposed mechanism for further increase in drug dissolution (BAY 12-9566 and naproxen) on storage at 40 degrees C/75% RH (relative humidity) is based on hydrogen bonding between the proton-donating drugs and the surface adsorbent, Neusilin US2 (proton acceptor). We propose that there is enough mobility in the solid-dispersion granules at elevated temperatures of storage to allow an increase in the ratio of the hydrogen bonded drug to the crystalline drug. These changes are mediated through the saturated solid solution state, and manifest themselves as increased drug dissolution upon storage. Fourier transform infrared spectroscopy studies are indicative of an increase in the amount of drugs (BAY 12-9566 and naproxen) hydrogen bonded to Neusilin on storage. A corresponding decrease in the crystallinity of these drugs was measured using x-ray powder diffractometry. Granules containing progesterone (a nonproton-donating drug) do not show an increase in the amount of drug hydrogen-bonded to Neusilin upon storage. In contrast to the proton-donating drugs, decreased drug dissolution was found on storage of progesterone-containing granules.