Ranking in Vitro Dissolution of Inhaled Micronized Drug Powders including a Candidate Drug with Two Different Particle Sizes

Pulmonary dissolution of poorly soluble drug substances (DSs) may limit the drug absorption rate and consequently influence clinical performance. Dissolution rate is thus an important quality attribute, and its influence on in vivo drug release must be characterized, understood, and controlled early in the development process. The aim of this study is to establish an in vitro dissolution method with the capability to capture therapeutically relevant differences in the dissolution rate between drug batches and drug compounds. A method was developed by which a biorelevant aerosol fraction was captured on a filter using a sedimentation technique in a modified Andersen cascade impactor to avoid particle agglomeration. Subsequently, the filters were transferred to a commercial Transwell system where dissolution in 3 mL of phosphate buffer at pH 6.8 with 0.5% sodium dodecyl sulfate (SDS) occurred at sink conditions. Dissolved DS was quantified over time using UPLC-UV. Dissolution data was obtained on a series of micronized and aerosolized lipophilic DSs, budesonide, fluticasone furoate (FF), fluticasone propionate (FP), and AZD5423. The latter is a lipophilic AstraZeneca development compound available in two different mass median diameters (MMD), 1.3 (AZD5423(1.3)) and 3.1 mu m (AZD5423(3.1)). Dissolution data were evaluated using a Weibull fit and expressed as t(63), the time to dissolution of 63% of the initial dose. The following rank-order of t(63) was obtained (mean t(63) and MMD in brackets), budesonide (10 min, 2.1 mu m) = AZD5423(1.3) (10 min, 1.3 mu m) < AZD5423(3.1) (19 min, 3.1 mu m) < FP (38 min, 2.4 mu m) < FF (63 min, 2.5 mu m). The method could differentiate between different drug compounds with different solubility but similar particle size distribution, as well as between the same drug compound with different particle size distributions. Furthermore, a relation between the in vitro dissolution rate (t(63)) and mean pulmonary absorption time in man (literature data) was observed, indicating clinical relevance. It is thus concluded, that the method may be useful for the characterization and ranking of DSs and drug products in early development, as well as being a potential tool for the control of dissolution as a potential quality attribute.