Powder, capsule and device: An imperative ménage à trois for respirable dry powders

The development of inhaled products to treat or to prevent lung infection is a very active research field in drug delivery. The pulmonary route is extremely attractive but very challenging. This paper reports the study of excipient, capsule brand and device influence on the aerodynamic behavior of dry powder formulations to treat tuberculosis.

A capreomycin hydrophobic salt was powdered using spray-drying and formulated using lactose (added after spray-drying, external excipient) or L-leucine (added before spray-drying, internal excipient). Aerosolization performances were investigated loading the formulations in 2 different capsule brands and aerosolizing them with 3 different devices.

Capreomycin oleate and capreomycin oleate/l-leucine powders were produced with a yield around 70%. Capreomycin oleate powder was composed of particles with an irregular surface. Particles of capreomycin oleate/l-leucine were roundish and wrinkled on the surface. Capreomycin oleate/l-leucine formulation gave the highest values of respirable fraction in all cases. Statistical analysis asserted the significant effect on the respirable fraction of the powder (p≤0.001), the capsule brand (p≤0.01) and the device (p≤0.05).

The use of L-leucine as internal excipient allows one to avoid the use of lactose, obtaining a carrier-free formulation. Even though differences are not very large, to obtain the highest RFE, the best choice between capsule and device is Quali-V(®) and model 8.