USFDA Guidance: Physicochemical and Structural (Q3) Characterization of Topical Drug Products Submitted in ANDAs

Introduction

This guidance, "Physicochemical and Structural (Q3) Characterization of Topical Drug Products Submitted in ANDAs", published in March 2026, provides detailed recommendations for applicants submitting Abbreviated New Drug Applications (ANDAs) for topical drug products.

It focuses on physicochemical and structural (Q3) characterization, which plays a critical role in demonstrating product performance and bioequivalence (BE). Topical products, especially semisolid formulations, are considered complex products due to their formulation design and route of delivery. This guidance reflects FDA’s current thinking and is nonbinding in nature.

Background

This guidance was developed as part of FDA’s broader efforts to promote generic drug competition and accessibility.

For ANDA approval, applicants must demonstrate that the proposed generic product:

• Matches the reference listed drug (RLD) in key characteristics

• Is bioequivalent (BE) to the reference product

For topical products, even small formulation differences can impact drug delivery. Therefore, Q3 characterization becomes essential to ensure consistent quality and performance.

Purpose of Q3 Characterization

As described in this guidance, Q3 characterization serves two primary purposes.

Firstly, it helps to identify and confirm the dosage form of the topical product. Secondly, it provides a detailed understanding of properties that are critical to product performance, supporting bioequivalence.

In simple terms:

• Basic Q3 characterization → defines dosage form

• Comprehensive Q3 characterization → supports BE and performance assessment

Basic vs Comprehensive Q3 Characterization

This guidance clearly differentiates between two levels of characterization.

Basic Q3 Characterization

Basic characterization focuses on describing the physical nature of the product. It typically includes:

• Appearance and texture

• Phase states (single or multiple phases)

• Structural organisation of matter

This level of characterization ensures that the generic product has the same dosage form as the reference.

Comprehensive Q3 Characterization

Comprehensive characterization provides a deeper understanding of attributes that may influence product performance.

It includes:

• Physicochemical properties such as pH

• Structural attributes like particle or globule size

• Rheological properties such as viscosity and flow

This detailed profiling helps identify whether any differences may impact bioavailability (BA) or BE.

Key Recommendations for Q3 Characterization

This guidance provides a structured approach for building a comprehensive Q3 profile.

Applicants are expected to evaluate multiple attributes, including:

• Appearance and texture

  • Description of color, odor, smoothness, and absence of visible particles

• Phase states

  • Microscopic evaluation to determine whether the product is single-phase or multi-phase

• Structural organisation

  • Particle size distribution, globule size, and emulsion type

• Polymorphic form

  • Identification of active ingredient forms within the formulation

• Rheological behavior

  • Flow characteristics and viscosity under varying conditions

• Water activity or drying rate

  • Particularly important for formulations containing volatile components

• pH and buffering capacity

  • Measurement and evaluation of buffering systems

• Oleaginous components

  • Characterisation of petrolatum or hydrocarbon-based systems

• Specific gravity

  • Density and mass per unit volume

• Metamorphosis-related changes

  • Changes after dispensing or during shelf life

These evaluations ensure that the product maintains consistent performance under real-world conditions.

Q3 Comparability and Bioequivalence

This guidance introduces three important concepts when comparing a generic product with its reference.

Q3 Sameness

A product is considered Q3 the same when:

• All Q3 attributes fall within the acceptable range of the reference

• No differences affect drug availability

This significantly reduces the risk of BE failure and may support waivers for in vivo studies.

Q3 Similarity

A product is Q3 similar when:

• Attributes are within acceptable ranges

• Some compositional differences exist

In such cases, additional data may be required to address potential risks.

Q3 Difference

A product is Q3 different when:

• One or more attributes fall outside acceptable ranges

This increases uncertainty and may require more extensive evidence to demonstrate BE.

(A simplified illustration of these concepts is provided in Figure 1 on page 9 of the document.) 

Communication with FDA

This guidance also highlights the importance of early interaction with the FDA during product development.

Applicants can:

• Submit controlled correspondence for specific queries

• Request pre-ANDA meetings for complex products

These interactions help clarify expectations and reduce regulatory risks.

📌 Reference

For full details, refer to the official guidance, "Physicochemical and Structural (Q3) Characterization of Topical Drug Products Submitted in ANDAs (Published March 2026)