Rheological data is crucial for the consistency evaluation of generic drugs. Whether it is raw materials, formula screening and process optimization, or final data declaration, it involves the processing of numerous rheological parameters. We will treat this issue in two parts here. The first step is to determine which data can be used for further data processing after completing the rheological test. The following sections are based on personal experience, and we hope that experts and peers can provide more criticism and corrections.

1. Viscosity: viscosity at a single shear rate (such as η 100)
For topical preparations for application, according to the consensus of FDA experts, viscosity data of η 20 can also be used as a reference. For oral, suspension, injection and other preparations, based on the properties of the formula, areas where viscosity does not change significantly with rate can be selected for characterization (refer to the flow curve); For patches, viscosity characterization can be performed under temperature conditions after the softening point or after the flow point.

2. Complete flow curve: viscosity under low, medium, and high shear rate conditions
EMA requires an upward and downward trend and separate curve fitting. Temperature has a significant impact on the repeatability of flow curves for certain formulations, and temperature optimization may be necessary; The size and type of rotor, as well as the speed range, have a significant impact on repeatability.
3. Yield stress (LVR): platform elastic modulus and loss modulus, endpoint stress of linear viscoelastic zone, intersection stress of modulus
Some fluids do not yield stress, and the choice between amplitude scanning or rotational stress scanning depends on the type of formulation. It is recommended to choose amplitude scanning mode for semi-solid formulations.
4. Linear viscoelastic response: elastic modulus and loss modulus under 0.1, 1, 10Hz conditions, phase angle (EMA requirement)
5. Thixotropic Ring: EMA Requirement, Relative Thixotropic Ring Area
6. Creep response: viscoelasticity ratio, zero shear viscosity
Optimization of methods is crucial for the repeatability of creep recovery, including time, applied stress, temperature, and appropriate testing gaps; Creep recovery can obtain many parameters, and it is recommended to select stable and repeated parameters for consistency evaluation based on the differences in formulations; Can evaluate the cold flow of the patch.
7. Temperature scanning: patch and temperature sensitive gel need to be carried out, and it is recommended to report the temperature of phase change point
Recommend reporting the glass transition temperature, flow point, and softening point temperature of the patch; Thermosensitive gel and other preparations need phase change temperature, gel time at specific temperature, and even self-healing experiment (in-situ gel).