The angle of internal flow as an indicator of filling and drug release properties of capsule formulations

Effects of powder flow properties on capsule filling weight uniformity

Filling capsules with the right amount of powder ingredients is an important quality parameter. The purpose of this study was to develop effective laboratory methods for characterizing flow properties of pharmaceutical powder blends and correlating such properties to weight variability in filled capsules. The methods used for powder flow characterization were bulk and tapped density, gravitational displacement rheometer (GDR) flow index, Freeman Technology V.4 (FT4) powder rheometer compressibility, FT4 basic flow energy (BFE), and cohesion parameters [cohesion, (C) and flow factor (ffc)] measured in a shear cell also using the FT4. Capsules were filled using an MG2-G140 continuous nozzle dosator capsule-filling machine. Powder flow properties were the most predominant factors affecting the weight and weight variability in the filled capsules. Results showed that the weight variability decreased with increasing bulk and tapped density, ffc and BFE, while the weight variability increased with increasing compressibility, cohesion and GDR flow index. Powder flow properties of the final blends were significantly correlated to the final capsule weight and weight variability of the filled capsules.

Predictive and correlative techniques for the design, optimisation and manufacture of solid dosage forms

There is much interest in predicting the properties of pharmaceutical dosage forms from the properties of the raw materials they contain. Achieving this with reasonable accuracy would aid the faster development and manufacture of dosage forms. A variety of approaches to prediction or correlation of properties are reviewed. These approaches have variable accuracy, with no single technique yet able to provide an accurate prediction of the overall properties of the dosage form. However, there have been some successes in predicting trends within a formulation series based on the physicochemical and mechanical properties of raw materials, predicting process scale-up through mechanical characterisation of materials and predicting product characteristics by process monitoring. Advances in information technology have increased predictive capability and accuracy by facilitating the analysis of complex multivariate data, mapping formulation characteristics and capturing past knowledge and experience.

Rational design of powder formulations for tamp filling processes

Tamp filling processes are widely used for the filling of powders into hard gelatin capsules, whereby capsule fill weight is controlled by the formation of a loosely packed plug of material that is dispensed into the capsule shell. To rationally design formulations for tamp filling processes the formulator must have an intimate knowledge of the synergy between machine parameters and powder properties and the corresponding effect on product quality. However, despite ubiquitous use throughout the pharmaceutical industry, relatively little is understood about the design of powders for tamp filling processes. The aim of the following review is to summarize the published literature to date from a formulation design perspective and to provide a framework for future scientific research.

The filling of powders into two-piece hard capsules

The factors that influence the filling of powders into hard capsules are reviewed. Powder properties that affect machine performance and influence plug formation are highlighted. The use of instrumented machines and machine simulators in formulation development are described. The properties of excipients that are required for uniform filling are identified. The use of optimisation techniques to produce rational formulations is discussed.

Powder filling into hard gelatine capsules on a tamp filling machine

A series of pharmaceutical excipient powders used in capsule formulations as fillers have been filled into hard gelatine capsules on a Bosch GKF-400S tamp filling machine. These machines depend on pushing pins through a powder bed so that a unit dose is transferred into a dosing disc. This dose is then ejected into the capsule body. The results indicate that the range of powders that can be filled on this type of machine exceeds that applicable to a dosator nozzle system. Filling problems due to powder flooding could be solved by increasing the powder bed height in the powder bowl. The fact that such powders usually do not form a firm plug was not reflected in the coefficient of fill weight variation, and uniform filling could hence be achieved without problems. The influence of the powder bed height on the capsule fill weight increased with decreasing powder flow. The influence of the setting of the tamping pins on the capsule fill weight was comparatively small and further decreased with a decrease in powder flow. However, when a granulated product (Elcema G250) was filled, the tamping pin setting was more important than the influence of the powder bed height on the capsule fill weight. For moderate flowing powders the coefficient of fill weight variation appeared to be nearly independent of powder bed height or tamping pin setting. However, the filling performance of powders with poor flow properties could be adjusted by optimising both machine settings. Very complex relationships were found between the powder properties such as angle of internal flow, dynamic densification profile, Carr's compressibility index and particle size and shape, and the filling behaviour.