Excipients for Semisolid Formulations

Semisolids dosage forms, as a class, are plastic in behavior, i.e., they retain their shape until acted upon by an outside force, in which case they deform and the deformations are permanent. The common denominator to all semisolid systems which gives them their special rheological character is that they all have a permanent three-dimensional structure. This structure is sufficient when undisturbed to impart solid-like properties but which is easily broken down and realigned under some strain or applied force (4). The semisolid systems used pharmaceutically include 

While these studies indicate that DSC and TSR are powerful tools for examining cetostearyl alcohol creams, it is also clear that pharmaceutical scientists must generate 

Antioxidants are often used to reduce oxidation of active substances and excipients in creams. There most common types of oxidants have been recognized (24). Table 1 lists each class of antioxidants and the most common antioxidants used in pharmaceutical creams. 

Type of antioxidant Definition Most commonly used 

True antioxidants These are thought to Butylated hydroxyanisole, 

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Some tablet formulations call for the inclusion of a small amount of semisolid, or even semiliquid, ingredient. It is highly desirable that any such component should be adsorbed onto, or absorbed into, one of the powders. In cases where none of the other excipients in the formulation is able to act as a carrier, an... 

On the other hand, the comparability of the drug substance and excipients with those of the innovators product listed by the FDA as the Reference Listed Drug (RLD), assumes (under the FDA s SUPAC guidelines) considerably greater importance for sterile and non-sterile semisolid formulations than, for solid oral dosage forms. With the semisolid dosage forms, the FDA uses various types of diffusion analyses in lieu of dissolution as a surrogate for in vivo bioequivalence. 

Nasal preparations can be formulated as liquid, semisolid or solid preparations and can contain one or more active substances. Whether intended for local or systemic action, the mucociliary function of the nose should be disturbed as httle as possible by the preparation However, it is well known that active substances as weU as excipients may have a negative influence on the mucociliary clearance, in other words may be cdiotoxic. In the formulation of nasal preparations one should take into consideration the possible damage to the cilia in relation to the indication and the period of use. 

The formulation of aqueous pastes strongly resembles the formulation of cutaneous suspensions (see Sect. 12.5.5.2). Aqueous pastes contain, however, a higher percentage of solid substances which makes them semisolid. For typical excipients see Sect. 12.5.1. The formulation of an aqueous paste with colloidal aluminium magnesium silicate as viscosity enhancer is described here. Propylene glycol preserves the aqueous phase. 

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