![]() ![]() Physicochemical properties of excipients have been shown to significantly affect the adsorption of small drug particles. 11įactors that affect adsorption of small drugs are summarized in Table 1. As particles are smaller than 100 μm, the electrostatic forces of adhesion become negligible compared with van der Waals forces involved in surface adsorption. Four significant forces may be present at the surface of fine particles: van der Waal's, electrostatic, adsorption and valency. ![]() 10 As a solid particle is reduced to a very fine level, surface effects become significant compared with the original particles. Greco reported that adsorption generally plays a role when the average particle size is 400 μm in mixing. Among those approaches, adsorption of drugs at the surface of excipients plays an important role. Many approaches have been used to achieve content uniformity for low-dose drugs, such as ordered mixing pre-mixing with surface adsorbent to facilitate distribution co-milling/sieving and the addition of low-dose drugs in solution spray. ![]() 3,4 Surface adsorption has also been involved in other pharmaceutical applications such as drug oxidation, 5 granulation for oily medicines, 6,7 and some special formulation designs. 1,2 For poorly water-soluble drugs, adsorbing small drug particles at the surface of large excipients can increase the dissolution rate by increasing drug surface area, and/or transforming drug from crystalline form to the amorphous form. One of the frequently used approaches is adsorbing small drug particles at the surface of large excipients by geometric mixing. Achieving good content uniformity is a common challenge when manufacturing solid dosage formulations. Adsorption of small drug particles on the surface of large excipients has been widely used in the pharmaceutical industry for various purposes, such as improving content uniformity of low-dose drugs, enhancing the dissolution rate for poorly water-soluble drugs and enhancing some special formulation designs. ![]()
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