2.3. pH Adjusting ExcipientsThe pH

2.3. pH Adjusting ExcipientsThe pH of the boundary layer (or stagnant diffusion layer) on the surface of solid drug particlesis of special importance for the dissolution of weak acidic and basic drugs [27]. It is possible toimprove the dissolution rate of weak acidic and basic drugs by including pH-adjusting excipients in aformulation that is capable of changing the pH of the stagnant diffusion layer or micro-environment.pH-adjusting excipients are mixed with the other ingredients of a solid oral dosage form prior to beingcompressed into tablets or filled into capsule shells. When disintegration of the dosage form takesplace, these excipients dissolve in the fluids of the gastrointestinal tract. These excipients then cause a pH adjustment of the stagnant diffusion layer due to provision of H+ or OH− ions (depending onwhether decreasing or increasing of pH is desired) that favors the dissolution of the active ingredientby forcing its molecules to exist more in the ionized state [28–30].