pH and Buffer Solutions in Drug Formulation
Start with the big picture
Formulation pH affects drug ionization and therefore solubility, permeability, and bioavailability. It also influences degradation: acid- or base-catalyzed hydrolysis and oxidation may accelerate outside a drug’s pH-stability profile. Buffers such as phosphate, citrate, acetate, TRIS, and histidine resist pH change; buffer capacity is greatest near the conjugate acid–base pair’s pKa and rises with total buffer concentration. The Henderson–Hasselbalch equation helps guide acid-to-salt ratios when targeting a pH. Formulators also consider dosage-form tolerability, ionic strength for parenterals, preservative performance, and the stability needs of proteins. The lesson connects these principles with practical formulation choices, including pH adjustment, degradation mitigation, and enteric coating behavior.
What you'll learn
- Explain how pH affects drug ionization, solubility, permeability, and bioavailability.
- Describe how pH relates to drug stability and pH-dependent degradation pathways.
- Identify common buffer systems and explain buffer capacity and its relationship to pKa.
- Apply the Henderson–Hasselbalch equation conceptually to buffer design.
- Recognize formulation considerations for parenterals, preservatives, proteins, and enteric coatings.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
