A systematic comparison of four pharmacopoeial methods for measuring powder flowability

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Chemical Engineering

Background:

• Powder flowability significantly impacts pharmaceutical manufacturing efficiency and product quality.
• The U.S. Pharmacopoeia outlines four primary methods for assessing powder flow: angle of repose (AoR), compressibility index (CI) and Hausner ratio (HR), flow through an orifice, and shear cell analysis.
• A comparative analysis of these methods is essential for selecting appropriate techniques for powder characterization.

Purpose of the Study:

• To systematically compare the performance of four common powder flowability evaluation methods.
• To determine the correlation between different methods across a wide range of powder flow characteristics.
• To provide guidance for selecting the most suitable methods for pharmaceutical powder characterization.

Main Methods:

• Utilized 21 different pharmaceutical powders with varying flowability.
• Performed comparative analysis of Angle of Repose (AoR), Compressibility Index (CI)/Hausner Ratio (HR), flow through an orifice (minimum diameter, dmin), and shear cell methods.
• Correlated results obtained from different apparatus and measurement techniques within each method.

Main Results:

• Strong correlations were observed between different variations of AoR measurements (R² = 0.939) and between CI/HR values obtained from different tapping methods (R² > 0.9).
• AoR, CI/HR, dmin, and shear cell methods showed strong correlations for powders with poorer flowability (worse than Avicel® PH102).
• Shear cell and CI/HR methods effectively distinguished poor-flowing powders, while AoR and CI/HR were superior for differentiating good-flowing powders.

Conclusions:

• No single method is universally superior for characterizing all types of powder flowability.
• Shear cell and CI/HR methods are reliable for identifying poor powder flow.
• For comprehensive powder flow characterization, especially across a broad spectrum of flow properties, utilizing multiple complementary techniques is recommended.