FDA Finalizes Guidance on Therapeutic Equivalence Evaluations for Generic Drugs

The US Food and Drug Administration (FDA) has finalized guidance on its approach to making therapeutic equivalence (TE) evaluations and assigning therapeutic equivalence codes for abbreviated new drug applications (ANDAs). These codes, listed in the agency's Orange Book (搜索)搜索该词条, denote a drug's bioequivalence to a reference-listed drug (RLD). The guidance is little changed from the draft guidance of the same title issued in July 2022.

The guidance clarifies the scientific and regulatory principles that underpin whether one drug product can be substituted for another, and is intended to be considered alongside the publication Approved Drug Products With Therapeutic Equivalence Evaluations (commonly known as the Orange Book (搜索)搜索该词条). While often viewed through the lens of generic drug approval and pharmacy substitution, the document's implications extend far beyond regulatory labeling, serving as a reminder that therapeutic equivalence is built upon a foundation of robust pharmaceutical development, manufacturing control, and demonstrated product performance.

The Three Criteria for Therapeutic Equivalence

The guidance explains that a product can only be considered therapeutically equivalent when three criteria are met: pharmaceutical equivalence, bioequivalence, and an expectation of the same clinical effect and safety profile under labeled conditions of use. FDA's regulations state that for products to be considered therapeutically equivalent to a reference-listed drug, they must have the same clinical effect and safety profile when administered to patients. These TE evaluations are designed to provide public information and guidance to state health agencies, prescribers, and pharmacists to assist in drug product selection.

Pharmaceutical Equivalence

To achieve the base requirement of pharmaceutical equivalence, drug products must contain the same active ingredient, dosage form, route of administration, and strength, and meet appropriate standards for identity, quality, purity, and potency. Notably, pharmaceutical equivalents do not have to contain identical excipients; differences in inactive ingredients are permitted provided the products still meet the applicable quality standards.

This places significant emphasis on formulation development, raw material control, process validation, analytical method validation, stability programs, and supplier qualification. Seemingly minor differences in excipient grade, particle size distribution, manufacturing parameters, or packaging materials can influence product performance and potentially undermine equivalence claims.

Bioequivalence and Manufacturing Consistency

The second pillar is bioequivalence, where the FDA requires evidence demonstrating that the rate and extent of absorption do not differ significantly from those of the reference product when administered at the same molar dose under similar conditions. The guidance reinforces that bioequivalence is fundamentally linked to product quality and manufacturing consistency. A successful study does not guarantee future success if the manufacturing process is not adequately controlled.

Potential process problems include variability between manufacturing batches, changes in raw material characteristics, equipment scale-up effects, process transfers between facilities, and inadequate control of critical process parameters. Each of these issues can produce material differences in dissolution characteristics or drug release profiles that may threaten continued bioequivalence.

Manufacturing Quality as a Life Cycle Responsibility

One of the most important messages in the FDA guidance is that therapeutic equivalence is inseparable from manufacturing quality. The FDA explicitly notes that approval depends upon adequate facilities, controls, manufacturing methods, and packaging systems capable of maintaining product identity, strength, quality, and purity. This means therapeutic equivalence cannot be considered solely a development function; it is a life cycle responsibility shared by pharmaceutical development, manufacturing, quality assurance, regulatory affairs, and supply chain management.

Inspectors increasingly assess whether firms maintain a state of control after approval, not simply whether they have achieved initial approval. A product that was therapeutically equivalent during registration can become non-equivalent if manufacturing control deteriorates.

Scope of Application and TE Codes

The guidance primarily applies to ANDAs submitted under Section 505(j) of the Federal Food, Drug, and Cosmetic (FD&C) Act. Sponsors of these products must show that the proposed generic product is the same as the RLD with respect to the active ingredient, conditions of use, route of administration, dosage form, strength, and labeling, and that the drug is bioequivalent to the RLD.

The agency notes that it does not routinely conduct TE evaluations for products submitted via the hybrid 505(b)(2) application pathway, nor for new drug applications (NDAs) submitted under Section 505(c) of the FD&C Act. However, a new process has been introduced for applicants of certain hybrid 505(b)(2) applications to request TE codes. The guidance now states that, in certain circumstances, a 505(b)(2) application holder may use the process described in section 505(j)(7)(A)(v)(I) to request that FDA make a therapeutic equivalence evaluation for a prescription drug in a 505(b)(2) application where the sole difference from a listed drug relied upon in the application is a difference in inactive ingredients not permitted under 21 CFR 314.94(a)(9)(iii)-(iv).

Drug products are assigned an "A" as the first letter of their TE code if the FDA considers them therapeutically equivalent to other pharmaceutically equivalent products, and these are grouped together in the Orange Book (搜索)搜索该词条. The agency assigns products an AB code if bioequivalence problems have been found. Products beginning with the letter B are not considered therapeutically equivalent to other pharmaceutically equivalent products at the time of evaluation because actual or potential bioequivalence concerns have not been adequately resolved. FDA may revise a TE evaluation if it identifies documented bioequivalence issues or significant potential for such issues for one or more applications under regulatory review.

Implications for Generic and Innovator Companies

For generic manufacturers, the guidance confirms the FDA's longstanding position that substitution relies on scientific evidence rather than commercial assumptions. A generic applicant must demonstrate pharmaceutical equivalence, bioequivalence, and manufacturing consistency. Manufacturers should avoid viewing bioequivalence studies as isolated projects, instead ensuring that commercial manufacturing processes reflect those used during development and registration.

The guidance also carries importance for innovator organizations, which often undergo process improvements, facility upgrades, technology transfers, and packaging changes. These activities require careful evaluation to ensure that post-change product performance remains consistent. A common misconception is that therapeutic equivalence is solely a generic drug concept; maintaining a consistent clinical effect and safety profile remains equally important for originator products.

Remediation and Quality Systems

When risks to therapeutic equivalence are identified, firms must demonstrate a structured remediation program. An effective strategy should include comprehensive investigation to determine whether quality defects arise from formulation changes, raw material variability, manufacturing process drift, equipment performance, environmental factors, or laboratory issues. Manufacturers should strengthen trending programs examining dissolution performance, assay results, content uniformity, stability data, complaint rates, and process capability metrics. Where significant changes occur, firms should assess critical quality attributes, process capability, batch-to-batch consistency, and the clinical relevance of observed changes.

FDA expectations are increasingly linked to pharmaceutical quality system maturity, requiring effective change control, robust deviation management, strong CAPA systems, continuous process verification, and data integrity controls. In summary, the FDA's therapeutic equivalence guidance reinforces that therapeutic equivalence is not simply a regulatory designation; it is the outcome of sound pharmaceutical science and sustained manufacturing control.