Effect of separation characteristics between salbutamol sulfate (SS) particles and model carrier excipients on dry powder for inhalation

Most often dry powder for inhalation are formulated as ordered mixtures of a carrier excipient and a micronized drug substance. In the present study, model powder blends were prepared from a mixture of lactose alpha-monohydra te, microcrystalline cellulose pellets or synthesized sugar as carrier part icles, and micronized salbutamol sulfate (SS). These ordered mixtures were aerosolized by the multidose JAGO dry powder inhaler (DPI) and their in vit ro deposition properties were evaluated by a twin impinger (TI). The separa tion farce between SS particles and carrier particles was investigated by t he centrifuge method. In addition, the use of the air jet sieve (AJS) metho d was investigated to assess the separation behavior of drug particles from carrier excipient. Powder blends were sieved through a 325 mesh wire scree n of an air jet sieve at an air pressure of 1500 Pa. The amount of drug dep osited at the carrier surface was analysed before and after the sieving to calculate the percentage of the drug retained. A relationship was found bet ween in vitro deposition properties (fine particle fraction, FPF) and the s eparation characteristics obtained by the centrifuge method and by the AJS method. The AJS method might be a suitable alternative for evaluating separ ation of a drug particle from carrier particles and hence can be used for t he formulation screening of the dry powder inhalation.