Injection Force Measurements
The rapidly expanding biopharmaceutical sector has significantly increased the number of injectable dosage forms available in the pharmaceutical marketplace. For protein-based products, the subcutaneous route is preferred due to avoidance of biological barriers and ease of administration. Self-injection is more convenient for the patient and reduces healthcare costs. However, highly concentrated, and thus highly viscous, formulations are required to deliver a therapeutic dose. If the force required for injection is too high, drug delivery may be precluded, inconvenient or difficult for some patient groups (e.g. the elderly). To ensure discreet injection devices and easy-to-use delivery platforms, quantitative measurements of injection force are extremely useful. The injection force instrument has been designed and constructed especially to support this aspect of biopharmaceutical formulation development. The apparatus is also suitable for the study of conventional medical and dental drug products.
Applications
- In-vitro testing of injectability
- Injectability refers to the performance of a formulation during injection. The apparatus allows the evaluation of injectability and factors which can be evaluated include:
- § Force or pressure required for injection
- § Evenness (smoothness) of flow during delivery
- § Tendency of the formulation to clog or cause blockages in the delivery system
The instrument may be used to evaluate whether a given formulation is compatible with the selected syringe-needle system, thereby reducing injectability failures. Injection forces experienced using different syringes (geometries, manufactures etc) and needles (length, gauge and wall thickness) may be compared and optimised.
Injection-related instability
For biopharmaceutical formulations, the physical stability of protein-based products is a significant concern. By simulating drug delivery, the injection force instrument provides the opportunity to assess whether the injection process itself will lead to protein instability. Following injection, various analytical techniques (such as AUC or DLS) may be applied to identify or quantify self-associates or aggregates over the physiological timescale.
Viscosity measurements
The injection force instrument may be operated as a micro-capillary rheometer for the calculation of viscosities under clinically-relevant injection speeds. The apparent viscosity can be calculated using the Poiseuille equation if the dimensions of the needle and syringe are accurately known:
Table Accuracy of the injection force micro-capillary rheometer comparing calculated values compared with those certified by the manufacturer.
General specifications
