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Abstract
Although there was a great interest in solid dispersion systems during the past four
decades to increase dissolution rate and bioavailability of poorly water-soluble drugs,
their commercial use has been very limited, primarily because of manufacturing difficulties
and stability problems. Solid dispersions of drugs were generally produced by melt
or solvent evaporation methods. The materials, which were usually semisolid and waxy
in nature, were hardened by cooling to very low temperatures. They were then pulverized,
sieved, mixed with relatively large amounts of excipients, and encapsulated into hard
gelatin capsules or compressed into tablets. These operations were difficult to scale
up for the manufacture of dosage forms. The situation has, however, been changing
in recent years because of the availability of surface-active and self-emulsifying
carriers and the development of technologies to encapsulate solid dispersions directly
into hard gelatin capsules as melts. Solid plugs are formed inside the capsules when
the melts are cooled to room temperature. Because of surface activity of carriers
used, complete dissolution of drug from such solid dispersions can be obtained without
the need for pulverization, sieving, mixing with excipients, etc. Equipment is available
for large-scale manufacturing of such capsules. Some practical limitations of dosage
form development might be the inadequate solubility of drugs in carriers and the instability
of drugs and carriers at elevated temperatures necessary to manufacture capsules.