The thermo-softening excipients, such as the Gelucire product line (Gattefosse S.A.), must be melted in order to (preferably) solubilize or, alternatively, suspend the drug in the excipient matrix which is subsequently filled into hard gelatin capsules in the molten state; the relatively low melting temperature of soft gelatin capsules (40°C) usually precludes the use of these capsules with thermo-softening excipients. Additional excipients, such as glyceryl monostearate and PEG esters, may be incorporated into the molten excipient matrix to prevent uncontrolled polymorphic changes subsequent to congealing of the matrix, which can adversely affect the dissolution profile and potentially reduce drug absorption in vivo (27).
It should also be noted that colloidal silicon dioxide may be added to fluid lipid excipients to yield thixotropic formulations useful for preparing lipid suspensions of solid drug substances. For this purpose, hydrophilic colloidal silicon dioxide is used for preparing immediate release formulations, whereas the hydrophobic form finds application in the preparation of controlled release formulations (27).
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