Correlation between inertial impaction and laser diffraction sizing data for aerosolized carrier-based dry powder formulations.
OBJECTIVE
The purpose of the study was to determine whether the drug fine particle fraction (FPF) from different dry powder aerosol formulations measured by laser diffraction at a range of flow rates correlated with that measured by inertial impaction.


METHODS
Ten binary formulations were prepared containing 1.5% w/w salbutamol base or sulphate, blended with the sieved (63-90 microm) fraction of different sugars (regular lactose, spray-dried lactose, sorbitol, dextrose or maltose). A further six ternary formulations were prepared containing 1.5% w/w salbutamol sulphate, 97% coarse lactose (63-90 microm) and 1.5% micronised or intermediate-sized lactose (1-50 microm). The FPF particles (< 5 microm) of these formulations were measured by laser diffraction and inertial impaction at flow rates between 28.3 and 100 l min(-1).


RESULTS
When only the particles with diameter < 60 microm obtained by laser diffraction were considered the FPF (< 5 microm) could be determined and this enabled the aerosolisation of all 16 blends to be feasibly compared at flow rates ranging from 28.3 to 100 l min(-1). A significant linear correlation was found between the fine fractions measured by laser diffraction and the salbutamol fine fractions determined by inertial impaction (r2 = 0.934). Such correlation was also confirmed for formulations containing added fine lactose.


CONCLUSIONS
Particle size measured by laser diffraction under the employed conditions reflected the aerodynamic properties of the drug. Laser diffraction can be used as on-, in- and/or at-line measurements and controls for dry powder aerosol formulations.
Zeng
Xian-Ming
XM
King's College London, Pharmaceutical Science Research Division, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK.
MacRitchie
Helen B
HB
Marriott
Christopher
C
Martin
Gary P
GP
D000318:Adrenergic beta-Agonists / Q000008:administration & dosage / Q000737:chemistry; D000336:Aerosols; D000420:Albuterol / Q000008:administration & dosage / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D004339:Drug Compounding; D005079:Excipients; D007834:Lasers; D008953:Models, Anatomic; D010316:Particle Size; D011208:Powders; D015203:Reproducibility of Results
D000318:Adrenergic beta-Agonists; D000336:Aerosols; D005079:Excipients; D011208:Powders; D000420:Albuterol