Pharmaceutical suspensions: relation between zeta potential, sedimentation volume and suspension stability

Area of Science:

• Pharmaceutical Sciences
• Colloid and Surface Chemistry

Background:

• Understanding drug suspension stability is crucial for effective drug delivery.
• Surface-active agents (surfactants) are commonly used to modify suspension properties.
• The DLVO theory is a foundational model for explaining colloid stability.

Purpose of the Study:

• To investigate the impact of various ionic and non-ionic surfactants on the sedimentation volume of four model drug suspensions.
• To correlate sedimentation behavior with zeta potential measurements.
• To assess the applicability of the DLVO theory to coarse pharmaceutical suspension systems.

Main Methods:

• Preparation of drug suspensions (betamethasone, griseofulvin, nalidixic acid, thiabendazole) with varying concentrations of ionic and non-ionic surfactants.
• Measurement of sedimentation volume.
• Measurement of zeta potential.
• Analysis of results in the context of colloid stability theories.

Main Results:

• Surfactant addition resulted in coagulated, deflocculated, or sterically stabilized systems.
• Sterically stabilized systems were predominantly formed using mixtures of ionic and non-ionic surfactants.
• Non-ionic surfactants alone provided significant stability against caking.
• Secondary minimum flocculation was not readily observed, potentially due to the examination method.

Conclusions:

• The study confirms that DLVO theory, including steric interactions, can effectively model the stability of coarse pharmaceutical suspension systems.
• Controlled coagulation and steric stabilization are important mechanisms for achieving desired suspension properties.
• Careful selection of surfactant combinations is essential for optimizing drug suspension performance and preventing caking.