The U.S. Food and Drug Administration (FDA) has issued important guidance for generic drug manufacturers seeking waivers for differences in pH adjusters compared to reference listed drugs (RLDs) intended for parenteral, ophthalmic, or otic use. This guidance explains how and when applicants can request a waiver under 21 CFR 314.99(b) to use pH adjusters that differ qualitatively (Q1) or quantitatively (Q2) from the RLD, and what scientific information they must provide.
Typically, generic drugs must contain the same inactive ingredients as the RLD in the same concentrations. However, pH adjusters -usually acids or bases- function uniquely by adjusting the solution’s pH to maintain stability, solubility, and patient comfort. Because the amount of pH adjuster required can vary from batch to batch to achieve a target pH range, the FDA recognizes that certain differences may be acceptable.
The guidance clarifies that a waiver for pH adjusters may be appropriate if the proposed changes do not adversely affect the drug product’s safety, efficacy, or physicochemical characteristics, such as pH, buffer capacity, osmolality, viscosity, and overall performance. Applicants must submit scientific evidence demonstrating that the differences will not impact these critical properties.
Not all differences qualify for a waiver; those resulting in a new active ingredient form, novel excipients lacking safety data, or significant alterations affecting drug performance will be denied. Early interaction with the FDA via controlled correspondence or pre-ANDA meetings is recommended to discuss waiver strategies and data requirements.
Key scientific considerations supporting waiver approval include comparative physicochemical testing to confirm similar pH levels and buffer capacities, ensuring the drug’s stability and quality. Additional data from the FDA’s Inactive Ingredients Database (IID) can support safety claims. Where appropriate, bioequivalence studies -either in vivo or in vitro- may further justify the waiver request.
Applicants must clearly describe the Q1 or Q2 differences in the pH adjuster, provide comprehensive supporting data, and identify the specific sections of the ANDA submission containing the waiver request. The FDA will evaluate the waiver during the ANDA’s scientific review and inform applicants of the decision upon acting on the application.
A granted waiver affects eligibility for certain bioequivalence study approaches. Specifically, an ANDA with a granted pH adjuster waiver is ineligible for an automatic in vivo bioequivalence waiver but may pursue alternative scientifically justified methods to demonstrate equivalence.
In conclusion, this guidance balances regulatory flexibility and patient safety by allowing scientific and risk-based justification for pH adjuster differences in complex generic drug formulations. It aims to facilitate greater access to safe and effective generic versions of parenteral, ophthalmic, and otic drug products that require pH adjustment.
Learn more: FDA Guidance for Industry
