By Jack G. Saad
Zeta potential measures the stability of a suspension and is often used as a method of quality control in many common place pharmaceutical products. As the absolute value of zeta potential gets closer to 0mV, the suspension becomes less stable. Low zeta potential in an unstable suspension indicates that the particles in the suspension are likely to be attracted to each other and form flocculants or agglomerate, and possibly settle out of the medium in lumps. In finished products like vaccines, cough syrups, and other liquid medicines.
Some time-release drugs are made through spraying a suspension which contains the actual drug over small sugar spheres or beads. The suspension must have an appropriate zeta potential, along with other processing parameters, to avoid clumping up the sprayer and the uneven distribution of the drug. In the body, these sugar beads are encapsulated and the drug suspension is released at different time intervals. Many liquid medicines come with the instructions “shake well before use.” Settling or uncontrolled flocculation in these medicines can be due to low zeta potential which may cause the components of the suspension to clump together and may be due to inappropriate formulation components being used. If the zeta potential of these substances can be adjusted, a more uniformly spread suspension can be made. Therefore, measuring a correct and appropriate zeta potential value is one of the keys to a quality product.