Preparation of respirable nanoparticle agglomerates of the low melting and ductile drug ibuprofen: impact of formulation parameters

Ductile and low melting point drugs exhibit challenging behaviour during both particle size reduction and spray drying as considerable amount of heat is involved in both processes. In this study, a systematic approach was employed to understand the preparation and in-vitro performance of respirable nanoparticle agglomerates by coupling wet milling and spray drying for ibuprofen, which is a drug with a low melting point and challenging mechanical properties. Wet milling in the presence of two stabilizers differing in their thermal properties and subsequent spray drying of the suspensions were employed after the addition of mannitol and/or leucine. The effects of the stabilizer type and the amounts of mannitol (matrix former) and leucine (dispersibility enhancer), on the yield of the process, the particle size, the redispersibility (i.e. reformation of nanoparticles upon rehydration) and the aerosolization (fine particle fraction, FPF%) of the nanoparticle agglomerates were evaluated using standard least squares model and a 23 full factorial design (3 factors at 2 levels plus four centre points). All factors investigated were found to have a significant effect on the yield of nanoparticle agglomerates (p < 0.05). The size of the nanoparticle agglomerates was mainly dependent on the leucine to drug ratio and the type of stabilizer (p < 0.05), while mannitol to drug ratio was the only significant factor affecting the redispersibility of the formulations (p < 0.05). The FPF%, determined using a fast screening impactor, was found to be dependent on both the leucine and mannitol to drug ratio (p < 0.05). This study demonstrates the successful preparation of respirable nanoparticle agglomerates of low melting point and ductile ibuprofen and the usefulness of the design of experiments as a tool to understand the impact of the formulation parameters on their fabrication and in-vitro performance