Micro-dosing of powders into capsules using a new automated micro-dosing system: effect of powder characteristics and operating conditions on the filling of 0.5 mg–100 mg weights

Objective: To demonstrate the applicability of a novel micro-dosing system for precisely filling low powder doses (down to a few mg) into capsules along with weighing the filled powder mass accurately. Methods: Ten commonly used pharmaceutical powders, ranging from cohesive to free-flowing, were selected and filled at three target fill weights (0.5, 1, and 10 mg), to investigate the effect of distinct powder properties on the filling performance. The fill weight and variability, filling speed and yield (% and number of conforming capsules out of all capsules collected), as well as the system’s long-term performance were assessed. Results: The filling accuracy was found to be good for all investigated powders. In particular, the results demonstrate that the tested powders, including the challenging cohesive ones, could be dosed at standard deviations within 0.23 mg at a 10 mg target weight, within 0.07 mg at a 1 mg target weight, and within 0.05 mg at a 0.5 mg target weight. In all cases, free-flowing powders showed lower standard deviations. Intermediate and cohesive powders had slightly higher standard deviations but were still within an acceptable range. Conclusion: The study shows the suitability of the tested micro-dosing system for filling low powder doses into capsules, which is of particular importance for dosing active pharmaceutical ingredients (APIs) directly in capsules, i.e. an API-in-capsule (AIC) approach for clinical trials (often in conjunction with highly potent APIs), and for low-dose powder filling for inhalation applications.