Abstract
The aim of the study was to investigate the specific influence of force control agents (FCAs) (leucine, lecithin and magnesium stearate) on the interfacial properties of a salbutamol sulphate-lactose dry powder inhaler formulation. The influence of FCAs on the cohesive and adhesive force balance was directly assessed via an atomic force microscopy (AFM) colloid probe technique, with a recently developed cohesive-adhesive balance (CAB) graphical analysis procedure. Co-processing of constituent particles was conducted by a novel dry mechanical fusion method (Mechanofusion). The in vitro deposition profile of the model salbutamol sulphate formulations was investigated using a Monohaler® DPI device with a next generation impactor (NGI) apparatus. The CAB-graph analysis of a salbutamol sulphate-lactose binary system suggested a predisposition for an interactive mixture. However, the reduced intermixing coefficient (Fdrug-lactose/Fdrug-drug) suggested that a significant amount of energy would be required to overcome the strong adhesive interaction for efficient dispersion of the drug from a lactose surface. The processing of lactose with leucine, lecithin or magnesium stearate, prior to formulating with the drug, significantly reduced the adhesive interactions of the salbutamol with modified lactose samples. The CAB analyses indicated that the reduced intermixing coefficients shifted to such an extent that cohesive drug interactions dominated. These dramatic shifts in the balance of forces were shown to lead to poor blend homogeneity and potential for significant segregation between drug and carrier particles. Conversely, the conditioning of salbutamol sulphate with leucine, lecithin and magnesium stearate, which modified both the adhesive and cohesive interactions, formed homogenous interactive blends with advantageously weaker drug-lactose interactions. Formulations with pre-conditioned drug, in contrast to conditioned lactose, offered the best drug delivery performances. The use of the colloid AFM technique in combination with the cohesive-adhesive balance (CAB) approach provided a very accurate means of predicting dry powder formulation behaviour and the specific influence of particulate interactions on aerosol performance.
Highlights
Accepted: August 12, 2005** 1 Prospect West, Chippenham, SN14 6FH, UKCorresponding author †KONA No.[23] (2005)Dry powder inhalers (DPIs) represent a significant advance in pulmonary drug delivery, mainly by overcoming patient related issues of co-ordination with conventional pressurised metered dose inhaler systems
Previous studies have emphasized the relative strength of the adhesive salbutamol sulphate-lactose adhesive forces with respect to salbutamol sulphate cohesive forces26)
The initial part of this study was to investigate possible variations in formulation behaviour upon modifying the cohesive and adhesive bonds, quantified by atomic force microscopy (AFM) measurements, via the introduction of a force control agent. This was achieved by first conditioning the lactose with various force control agents using a Mechanofusion system, prior to mixing with the drug
Summary
Accepted: August 12, 2005** 1 Prospect West, Chippenham, SN14 6FH, UKCorresponding author †KONA No.[23] (2005)Dry powder inhalers (DPIs) represent a significant advance in pulmonary drug delivery, mainly by overcoming patient related issues of co-ordination with conventional pressurised metered dose inhaler systems. The f luidisation, de-aggregation and dispersion of a dry powder formulation are achieved via the patient’s inspiratory action. More so than other drug delivery platforms, the characteristic properties of the dry powder formulation are critically important to the effective performance of a DPI system[1, 2]). The fluidised powder must disperse into a fine aerosol (Ø · 5 · m) for efficient drug delivery 3, 4). This leads to the well-known paradox that respirable sized particles tend to be highly cohesive, which causes entrainment problems due to their poor flowability and limits the dispersibility into an aerosol cloud[5, 6]). Strong cohesion forces hinder the handling of the powder during manufacture
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