pH modulation: a mechanism to obtain pH-independent drug release.

IMPORTANCE OF THE FIELD: In formulation development, weakly acidic or basic drugs pose a major challenge as the solubility depends significantly on pH of the dissolution media. This gives rise to pH-dependent drug release, as the formulation is exposed to different pH ranges in the gastrointestinal tract. This indicates a need to carry out formulation optimization for such drugs while developing them into a dosage form. AREAS COVERED IN THIS REVIEW: For overcoming pH-dependent behavior of drugs, pH-modifying excipients (which alter the microenvironment pH inside the formulation) are most commonly used. A combination of enteric and sustained release polymers can be used for weakly basic drugs. Other strategies include conversion of crystalline drug to amorphous form, enhancement of partitioning of unionized fraction of drug from the formulation, and using a combination of pH modifier and enteric polymer, micellar solubilization and inclusion complexation. WHAT THE READER WILL GAIN: Readers will gain an insight into various formulation techniques for obtaining pH-independent drug release for weakly acidic and basic drugs. TAKE HOME MESSAGE: Readers will be able to evaluate the different formulation strategies in terms of their applicability and best use of the available strategies when designing their own research work for such drugs.