Physical Stabilizing Effect of Biopolymers on Solid Dispersions Containing Indomethacin and Polyethylene Glycol

Solid dispersions of poorly water-soluble drug, indomethacin (IMC), and carriers at a ratio of 1:9 were prepared by melting method. The carriers used in this study were polyethylene glycol 4000 (PEG4000), hydroxypropyl methylcellulose (HPMC) and pectin. The solid dispersions obtained were characterized by powder x-ray diffractometry (PXRD) and dissolution studies. PXRD patterns showed that all solid dispersions led to amorphous products while their physical mixture still showed the crystalline state of drug. Crystalline drug was clearly detectable in solid dispersion products containing only IMC and PEG4000 after storage for 2 months. The formulations with biopolymer (i.e., HPMC, pectin or their combination) showed no drug crystal after storage. More than 80% of IMC dissolved within 5 minutes for all formulations after preparation while less than 40% of IMC dissolved, within 5 minutes, from the formulations containing IMC, PEG4000 and HPMC after storage for 2 months. The slower drug dissolution may be due to the gel-forming properties of HPMC as well as the agglomeration of the products after storage. The results suggested that either HPMC or pectin in solid dispersions can help to prevent the crystallization of amorphous IMC in solid dispersion, probably by a polymer anti-plasticizing effect. Pectin showed superior stabilizing effect with no retardation effect on drug dissolution.