Effects of particle size and adding sequence of fine lactose on the deposition of salbutamol sulphate from a dry powder formulation

Ternary mixtures composed of coarse lactose (CL) (90.8 μm), salbutamol sulphate (SS) (5.8 μm) and either micronised lactose (ML) (5 μm) or intermediate sized lactose (IML) (15.9 μm) in a ratio of 66.5:1:1 w/w were prepared using different mixing sequences of the various components. In addition, a binary mixture composed of CL and SS (67.5:1 w/w) was also prepared as the control. The in vitro deposition of SS was measured using a twin stage impinger after aerosolisation at 60 and 90 l min −1 via a Rotahaler®. The aerodynamic particle size distribution of both the aerosolised SS and lactose was further analysed using an Andersen cascade impactor at 60 l min −1. All ternary mixtures produced a significantly higher (analysis of variance, P