What is buffer capacity and why is it important in parenteral formulations?

• A. The ability of a buffer to release buffer components.
• B. The ability of a buffer to resist pH change; important for maintaining drug stability and ensuring compatibility with physiological pH and container materials.
• C. The maximum solubility of salt in the buffer.
• D. The buffer's color change upon pH shift.

Answer: (B)

Buffer capacity is the ability of a buffer to resist changes in pH when small amounts of acid or base are added or when the solution is diluted. In parenteral formulations, this matters because many drugs are unstable outside a narrow pH range, and their solubility and chemical stability depend on pH. A formulation with adequate buffer capacity can maintain its pH during manufacturing, handling, and administration, reducing the risk of drug degradation, precipitation, irritation at the injection site, or adverse interactions with container materials. Buffer capacity depends on how much buffering species is present and how close the pH is to the buffer’s pKa; it is greatest near pKa and decreases as pH moves away. For IV products, keeping the pH near physiological levels minimizes tissue irritation and compatibility issues, so strong buffering helps ensure safety and efficacy throughout use.