Influence of Particle Size,Air Flow,and Inhaler Device on the Dispersion of Mannitol Powders as Aerosols

Purpose. To study the effect of particle size, air flow and inhaler type on the dispersion of spray dried mannitol powders into aerosols. Methods. Mannitol powders were prepared by spray drying. The solid state properties of the powders were determined by laser diffraction, X-ray powder diffraction, scanning electron microscopy, freeze fracture, Karl Fischer titration and gas pycnometry. The powders were dispersed using Rotahaler^® and Dinkihaler^®, connected to a multistage liquid impinger at different air flows. Results. Three crystalline mannitol powders with primary particle size (MMD) 2.7, 5.0, 7.3 m and a similar polydispersity were obtained. The particles were spherical with a density of 1.5 g/cm³ and a moisture content of 0.4 wt.%. At an air flow of 30 L/min all the powders were poorly dispersed by both inhalers. With the Rotahaler^® increasing the flow (60–120 L/min) increased the fine particle fraction (FPF) in the aerosols for the 2.7 m powder, and decreased the FPF for the 7.3 m powder; whereas the FPF for 5.0 m powder was unaffected. With the Dinkihaler^®, all the powders were near complete dispersion at 60 L/min. Conclusions. The FPF in the mannitol powder aerosols was determined by an interplay of the particle size, air flow and inhaler design.     

Protein Inhalation Powders: Spray Drying vs Spray Freeze Drying

Purpose. To develop a new technique, spray freeze drying, for preparing protein aerosol powders. Also, to compare the spray freeze-dried powders with spray-dried powders in terms of physical properties and aerosol performance. Methods. Protein powders were characterized using particle size analysis, thermogravimetric analysis, scanning electron microscopy, X-ray powder diffractometry, and specific surface area measurement. Aerosol performance of the powders was evaluated after blending with lactose carriers using a multi-stage liquid impinger or an Anderson cascade impactor. Two recombinant therapeutic proteins currently used for treating respiratory tract-related diseases, deoxyribonuclase (rhDNase) and anti-IgE monoclonal antibody (anti-IgE MAb), were employed and formulated with different carbohydrate excipients. Results. Through the same atomization but the different drying process, spray drying (SD) produced small (3 m), dense particles, but SFD resulted in large (8–10 m), porous particles. The fine particle fraction (FPF) of the spray freeze-dried powder was significantly better than that of the spray-dried powder, attributed to better aerodynamic properties. Powders collected from different stages of the cascade impactor were characterized, which confirmed the concept of aerodynamic particle size. Protein formulation played a major role in affecting the powder's aerosol performance, especially for the carbohydrate excipient of a high crystallization tendency. Conclusions. Spray freeze drying, as opposed to spray drying, produced protein particles with light and porous characteristics, which offered powders with superior aerosol performance due to favorable aerodynamic properties.     

Use of Solid Corrugated Particles to Enhance Powder Aerosol Performance

Purpose. To study the dispersion performance of non-porous corrugated particles, with a focus on the effect of particle surface morphology on aerosolization of bovine serum albumin (BSA) powders. Methods. The solid-state characteristics of the spray-dried BSA powders, one consisting of smooth spherical particles and another corrugated particles, were characterized by laser diffraction, X-ray powder diffraction, scanning electron microscopy, confocal microscopy, thermogravimetric analysis, surface area analyzer, and buoyancy method. The powders were dispersed using the Rotahaler® and the Dinkihaler® coupled to a four-stage liquid impinger operating at 30 to 120 L/min. Fine particle fraction (FPF) was expressed as the wt. % of BSA particles of size 5 m collected from the liquid impinger. Results. Apart from the morphology and morphology-related properties (specific surface area, envelope density), the corrugated particles and spherical particles of BSA had very similar solid-state characteristics (particle size distribution, water content, true density, amorphous nature). Using the Dinkihaler®, the FPFs of the corrugated particles were 10-20 wt. % higher than those of the smooth particles. Similar FPF differences were found for the powders dispersed by the Rotahaler®, but the relative changes were larger. In addition, the differences were inversely proportional to the air flows (17.3% at 30 L/min, 25.2% at 60 L/min, 13.8% at 90, 8.5% at 120 L/min). Depending on the inhaler, capsule and device retention and impaction loss at the impinger throat were lower for the corrugated particles. Conclusions. Enhanced aerosol performance of powders can be obtained by surface modification of the particles. The surface asperities of the corrugated particles could lower the true area of contact between the particles, and thus reduce the powder cohesiveness. A distinct advantage of using corrugated particles is that the inhaler choice and air flow become less critical for these particles.     

How Much Particle Surface Corrugation Is Sufficient to Improve Aerosol Performance of Powders?

No HeadingPurpose. The current study aimed to quantify the different degree of particle surface corrugation and correlate it to the aerosol performance of powders.Methods. Powders of different degree of surface corrugation were prepared by spray drying under varying conditions. The solid-state properties of the powders including particle size, morphology, crystal form, true density, and moisture content were characterized. The degree of surface corrugation was quantified by the surface fractal dimension (D_S) obtained by light scattering. The aerosol performance was studied by dispersing the powders using the Rotahaler at 60 L/min into a multi-stage liquid impinger. Fine particle fraction (FPF) was expressed as the wt% of BSA particles of size 5 m in the aerosol.Results. Four powders of increasing degree of particle surface corrugation were prepared, with D_S ranging from 2.06 for the least corrugated to 2.41 for the most corrugated. The powders had a similar size distribution (VMD 3 m, span 1.4–1.5) and solid-state properties. Increasing the surface corrugation, D_S, slightly from 2.06 to 2.18 enhanced the FPF significantly from 27% to 41%. This was explained by the reduced area of contacts and increased separation distance between the particles. Further increase of corrugation (D_S 2.18) did not improve FPF.Conclusion. Powders with varying degrees of corrugation were successfully obtained by spray drying with their surface roughness quantified by fractal analysis. It was shown that only a relatively small degree of surface corrugation was sufficient to accomplish a considerable improvement in the aerosol performance of the powder.     

Delivery of Nasal Powders of β-Cyclodextrin by Insufflation

Purpose. Delivery of nasal powders of granulated -cyclodextrin by insufflation was studied in order to find the relationship between powder properties and delivery behavior. Methods. Three nasal powder formulations, prepared by granulating -cyclodextrin with different binders, were delivered from a powder insufflation device, in which the dose to be emitted was loaded in a gelatin capsule. The delivery sequence of powder was recorded and characterized using an image analysis program. Results. Particle size was the main parameter affecting nasal powder delivery, both as to the amount of dose sprayed and the aspect of cloud produced. Between 50–150 µm of particle size a substantial change in delivery behavior of powders was observed. Powder of around 100 µm in size showed useful insufflation characteristics for nasal delivery. Bioavailability of nasal formulations of progesterone/-cyclodextrin powders was discussed in term of delivery behavior. Conclusions. The formulation approaches for improving nasal delivery of powders require the use of size optimized carriers. Insufflation of powders over 50 µm can favour the particle deposition by impaction, whereas for powders below 50 µm, deposition by sedimentation is moved. -cyclodextrin is a suitable carrier for achieving high systemic availability following nasal administration of powder formulations.     

Protein Deposition from Dry Powder Inhalers: Fine Particle Multiplets as Performance Modifiers

Purpose. To evaluate the use of carrier-based dry powder aerosols for inhalation delivery of proteins and examine the effect of fine particle excipients as potential formulation performance modifiers. Methods. Bovine serum albumin (BSA) was co-processed with malto-dextrin by spray-drying to produce model protein particles. Aerosol formulations were prepared by tumble mixing protein powders with -lactose monohydrate (63–90 m) or modified lactoses containing between 2.5 and 10% w/w fine particle lactose (FPL) or micronised polyethylene glycol 6000. Powder blends were characterised in terms of particle size distribution, morphology and powder flow. Formulation performance in Diskhaler^® and Rotahaler^® devices was investigated using a twin stage impinger operating at 60 1 min^–1. Results. Inhalation performance of binary ordered mixes prepared using BSA-maltodextrin and lactose (63–90 m) was improved by addition of FPL and micronised PEG 6000. For the addition of 5% w/w FPL the protein fine particle fraction (0.5–6.4 m) using the Diskhaler^® was increased from 31.7 ± 2.4% to 47.4 ± 2.2%. Inclusion of FPL and micronised PEG 6000 changed the bulk properties of inhalation powders and reduced powder flow but did not affect device emptying. Unexpectedly, improvements in performance were found to be independent of the order of addition of FPL to the ternary powder formulations. SEM studies revealed that this was probably the result of a redistribution of protein particles between the coarse carrier lactose component and added FPL during mixing. Conclusions. Fine particle excipients can be used to improve the performance of carrier-based protein dry powder aerosols. Mechanistically, enhancement of performance is proposed to result from a redistribution of protein particles from coarse carrier particles to the fine particle component in the ternary mix.     

Improved inhalation behavior of steroid KSR-592 in vitro with Jethaler by polymorphic transformation to needle-like crystals (beta-form)

Purpose. The aim of the present study was to improve the dry powder inhalation behavior of steroid KSR-592 with lactose by altering the crystal shape and the particle size of the drug for use in a newly designed inhalation device, Jethaler®. Method. The shape of the crystals was changed by polymorphic transformation of original crystal (-form) to -form by agitating -form crystals in hexane containing 5% ethanol. The inhalation properties of the resultant crystals in vitro were evaluated with a twin impinger and cascade impactor. Results. Needle-like crystals (-form) with dimensions of 1.8 m in width × 41m in length were obtained by the polymorphic transformation, the kinetics of which was described by the Avrami equation. The -form crystals loaded on lactose particles were easily separated and crushed into fine particles in the airstream produced in the Jethaler®, which increased dramatically the respirable fraction (RF) deposited in the twin impinger (43.8%) and the fine particle fraction (FPF) of the cascade impactor (FPF = 39.3%) compared with their values for the original crystals (RF = 5.8%, FPF = 4.7%). Conclusion. The dry powder inhalation properties of steroid KSR-592 (platelike crystal, -form) were improved dramatically by changing the crystal shape to a needle-like shape by the polymorphic transformation to the -form.     

Aerosol Electrostatics I: Properties of Fine Powders Before and After Aerosolization by Dry Powder Inhalers

Purpose. To evaluate the dependence of fine particle dose charge (FPD charge) generated from powder inhalers on physico-chemical properties of the inhalation powder, inhaler type, deaggregation mechanism, dose number and/or retained powder. Methods. Electrostatic charges were determined on micronized powders and aerosolized fine particle doses withdrawn from two, high efficiency, multidose powder inhalers, Turbohalerand prototype Dryhaler. The behavior of terbutaline sulfate, budesonide, albuterol (sulfate and base), beclomethasone dipropionate and lactose was assessed before and after aerosolization. Results. Both inhalers conferred triboelectric FPD charges during aerosolization in the range –400 pC through +200 pC. Specific charges (charge/unit mass) on the fine particle doses of budesonide from Dryhaler were significantly less than those from Turbohaler (p < 0.01). Electrostatic charges on the potentially respirable cloud of terbutaline sulfate generated by Bricanyl Turbohaler were positive and/or negative and unpredictable. With Pulmicort Turbohaler, FPD charges on budesonide were always positive. Dryhaler was used to determine the chemical dependence of fine particle triboelectrification during the aerosolization of pure materials. A triboelectric series was constructed from the Dryhaler results ranking the powders from positive to negative as budesonide > lactose > albuterol sulfate > terbutaline sulfate albuterol beclomethasone dipropionate. Conclusions. While there was no evidence of FPD charge dependence upon dose number with either inhaler, FPD charges were dependent upon the powder under investigation, as well as the construction and deaggregation mechanism of the inhaler. The specific charge on the fine particle dose of budesonide from Turbohaler corresponded to approximately 200 electronic charges per particle, a value which is known to affect both total and regional aerosol deposition in the human lung. Electrostatic charge effects may be important determinants of aerosol behavior and should not be neglected.     

Particle interactions involved in aerosol dispersion of ternary interactive mixtures

Purpose. To investigate the mechanism of action of ternary components within dry powder aerosols. Methods. Ternary interactive mixtures were prepared containing salbutamol sulphate (SS), coarse lactose carriers and either micronized lactose (ML) or micronized glucose (MG). In vitro drug and excipient aerosol deposition was performed using a twin-stage impinger (TSI) at 60 L/min with a Rotahaler device. Adhesional properties of the lactose carrier were examined using an atomic force microscope (AFM) colloidal probe technique. Result. The fine particle fraction (FPF) from ternary mixtures were dependent upon carrier type (p < 0.001), ternary concentration (p < 0.001) and ternary component type (p < 0.05). Ternary mixtures produced higher FPF than binary mixtures, except those containing Superfine (SF), which was attributed to the high proportion of intrinsic fine carrier particles. The higher FPF obtained from ternary mixtures was independent of the mixing order (p = 0.08). Increased adhesion force was observed on the carrier surface following the addition of ternary components (p < 0.001). Conclusion. The results confirm that ternary components increase aerosol deposition of powder mixtures. Some results were not entirely consistent with the saturation of active site theory and a hypothesis involving competitive and multilayer adhesion was proposed and requires further testing.     

The Pulmonary Absorption of Aerosolized and Intratracheally Instilled rhG-CSF and monoPEGylated rhG-CSF

Purpose. The objective of this study was to highlight differences in the pulmonary absorption of a monoPEGylated rhG-CSF and rhG-CSF after intratracheal instillation and aerosol delivery. Methods. Male Sprague Dawley rats (250 g) were anesthetized and intratracheally instilled (IT) with protein solution or were endotracheally intubated and administered aerosol for 20 min via a Harvard small animal ventilator. A DeVilbiss Aerosonic nebulizer containing 5 ml of protein solution at 3 mg/ml was used to generate aerosol. The volume of protein solution deposited in the lung lobes was estimated to be 13 µl after delivery of Tc-99m HSA solutions. The PEGylated proteins consisted of a 6 kDa (P6) or 12 kDa PEG (PI2) linked to the N-terminus of rhG-CSF. rhG-CSF also was administered IT in buffers at pH 4 and pH 7 and in dosing volumes ranging from 100 to 400 µl. Blood samples were removed at intervals after dosing and the total white blood cell counts (WBC) were determined. Plasma was assayed for proteins by an enzyme immuno assay. Results. The plasma protein concentration v. time profiles were strikingly different for aerosol v. IT delivery. The C _max values for rhG-CSF and P12 after aerosol delivery were greater than found after IT (Aerosol: 598 ± 135 (ng/ml) rhG-CSF; 182 ± 14 P12 v. IT: 105 ± 12 rhG-CSF; 65.9 ± 5 P12). Similarly, T_max was reached much earlier after aerosol administration (Aerosol: 21.7 ± 4.8 (min) rhG-CSF; 168 ± 31 P12 v. IT: 100 ± 17 rhG-CSF; 310 ± 121 P12). Estimated bioavailabilities (F_lung %) were significantly greater via aerosol delivery than those obtained after IT (Aerosol: 66 ± 14 rhG-CSF; 12.3 ± 1.9 P12 v. IT: 11.9 ± 1.5 rhG-CSF; 1.6 ± 0.1 P12). An increase in circulating WBC counts was induced by all proteins delivered to the lungs. The rate and extent of absorption of rhG-CSF was not influenced by the pH employed nor the instilled volume. Conclusions. Estimates of bioavailability are dependent upon the technique employed to administer drug to the lungs. Aerosol administration provides a better estimate of the systemic absorption of macromolecules.     

Artificial Neural Network Prediction of Aerosol Deposition in Human Lungs

Purpose. To develop a rapid and reliable method for predicting the pattern of aerosol particle deposition within the human lungs, using artificial neural networks (ANNs). Methods. Experimental data from the literature were used to train multi-layer perceptron (MLP) networks to allow for prediction of regional and total aerosol particle deposition patterns in human lungs. These data covered particle sizes in the range 0.05-15 m and three different breathing patterns (ranging from quiet breathing to breathing under physical work conditions). Three different MLPs were trained, to provide separate predictions of aerosol particle deposition in the laryngeal, bronchial, and alveolar regions. The total deposition fraction for a given set of breathing conditions was computed simply as the sum of the outputs produced from the corresponding regional deposition MLPs. Results. The ANNs developed are shown to give highly accurate predictions for both regional and total aerosol deposition patterns for all particle sizes and breathing conditions (with errors typically less than 0.04%). Conclusions. We conclude that the current set of ANNs can be used to give good predictions of particle deposition from polydisperse pharmaceutical aerosols generated from breath-actuated dry powder inhalers, nebulizers, and metered dose inhalers with spacers.     

Generation of Micro-Particles of Proteins for Aerosol Delivery Using High Pressure Modified Carbon Dioxide

Purpose. To investigate the feasibility of using the Aerosol Solvent Extraction System (ASES) to generate microparticles of proteins suitable for aerosol delivery from aqueous-based solutions. Methods. The ASES technique using high- pressure carbon dioxide modified with ethanol was utilised for the generation of microparticles of proteins (lysozyme, albumin, insulin and recombinant human deoxyribonuclease (rhDNase)) from aqueous solutions. Particle size, morphology, size distributions and powder aerosol performance were examined. The biochemical integrity of the processed proteins was assessed by testing the level of molecular aggregation using size exclusion chromatography and by bioassay technique for lysozyme. Results. Proteins were precipitated as spherical particles ranging in size from 100 to 500 nm. The primary nano-sized particles agglomerated to form micron-sized particles during the precipitation process. The median size of the particles was a function of the operating conditions. In-vitro aerosol performance tests showed that the percent fine particle mass (< 5m) was approximately 65%, 40% and 20% for lysozyme, albumin and insulin, respectively. Negligible loss in the monomer content or biological activity was observed for lysozyme. Insulin exhibited slight aggregation and 93% of the monomer was retained after processing. Albumin was affected by processing and only 50-75% of the monomer was retained compared with 86% in the original material. However, rhDNase was substantially denatured during processing as shown by the significantly reduced monomer content. Conclusions. Micron-sized particles of lysozyme, albumin and insulin with satisfactory inhalation performance were successfully generated from aqueous solutions using the modified ASES technique. The biochemical integrity of the processed proteins was a function of the operating conditions and the nature of the individual protein.     

Adhesion of Powders for Inhalation: An Evaluation of Drug Detachment from Surfaces Following Deposition from Aerosol Streams

Purpose. To evaluate micronized powder retention and detachment from inhaler surfaces following reproducible deposition by impaction, coupled with centrifugal particle detachment (CPD). Methods. Micronized albuterol sulfate (AS) and beclomethasone dipropionate (BDP) were aerosolized as dry powders and deposited by cascade impaction onto different contact surfaces. Drug detachment from the surfaces was characterized using CPD, coupled with HPLC assay and scanning electron microscopy. Results. Drugs which accumulated as aggregates on model surfaces detached with distinctive profiles for % remaining vs. applied centrifugal force; each profile showed reproducible values for the minimum force required to initiate drug detachment, F_yield. While differences occurred in the observed detachment profiles for different drugs and contact surfaces (polyacetal vs. aluminum), the deposited drug particle size had the most significant effect on these profiles, e.g., F_yield for AS (2.1-3.3 m) was 383 12.7 N compared with 18 13.8 N for AS (4.7-5.8 m). Conclusions. A technique was developed which enabled the experimental review, and subsequent data analysis, of the adhesive properties between different DPI construction materials and drug substances deposited from aerosol clouds. The technique appears to be of greater relevance to inhaler design decisions than earlier studies in the literature claiming to show differences in the adhesion of single drug particles to surfaces.     

The Effect of Formulation Excipients on Protein Stability and Aerosol Performance of Spray-Dried Powders of a Recombinant Humanized Anti-IgE Monoclonal Antibody1

Purpose. To study the effect of trehalose, lactose, and mannitol on the biochemical stability and aerosol performance of spray-dried powders of an anti-IgE humanized monoclonal antibody. Methods. Protein aggregation of spray-dried powders stored at various temperature and relative humidity conditions was assayed by size exclusion chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Protein glycation was determined by isoelectric focusing and affinity chromatography. Crystallization was examined by X-ray powder diffraction. Aerosol performance was assessed as the fine particle fraction (FPF) of the powders blended with coarse carrier lactose, and was determined using a multiple stage liquid impinger. Results. Soluble protein aggregation consisting of non-covalent and disulfide-linked covalent dimers and trimers occurred during storage. Aggregate was minimized by formulation with trehalose at or above a molar ratio in the range of 300:1 to 500:1 (excipient:protein). However, the powders were excessively cohesive and unsuitable for aerosol administration. Lactose had a similar stabilizing effect, and the powders exhibited acceptable aerosol performance, but protein glycation was observed during storage. The addition of mannitol also reduced aggregation, while maintaining the FPF, but only up to a molar ratio of 200:1. Further increased mannitol resulted in crystallization, which had a detrimental effect on protein stability and aerosol performance. Conclusions. Protein stability was improved by formulation with carbohydrate. However, a balance must be achieved between the addition of enough stabilizer to improve protein biochemical stability without compromising blended powder aerosol performance.     

Effect of Spray Drying and Subsequent Processing Conditions on Residual Moisture Content and Physical/Biochemical Stability of Protein Inhalation Powders

Purpose. To understand the effect of spray drying and powder processing environments on the residual moisture content and aerosol performance of inhalation protein powders. Also, the long-term effect of storage conditions on the powder's physical and biochemical stability was presented. Methods. Excipient-free as well as mannitol-formulated powders of a humanized monoclonal antibody (anti-IgE) and recombinant human deoxyribonuclease (rhDNase) were prepared using a Buchi 190 model spray dryer. Residual moisture content and moisture uptake behavior of the powder were measured using thermal gravimetric analysis and gravimetric moisture sorption isotherm, respectively. Protein aggregation, the primary degradation product observed upon storage, was determined by size-exclusion HPLC. Aerosol performance of the dry powders was evaluated after blending with lactose carriers using a multi-stage liquid impinger (MSLI). Results. Spray-dried powders with a moisture level (~ 3%) equivalent to the freeze-dried materials could only be achieved using high-temperature spray-drying conditions, which were not favorable to large-male manufacturing, or subsequent vacuum drying. These dry powders would equilibrate with the subsequent processing and storage environments regardless of the manufacturing condition. As long as the relative humidity of air during processing and storage was lower than 50%, powders maintained their aerosol performance (fine particle fraction). However, powders stored under drier conditions exhibited better long-term protein biochemical stability. Conclusions. Manufacturing, powder processing, and storage environments affected powder's residual moisture level in a reversible fashion. Therefore, the storage condition determined powder's overall stability, but residual moisture had a greater impact on protein chemical stability than on powder physical stability.     

Surface-modified Antiasthmatic Dry Powder Aerosols Inhaled Intratracheally Reduce the Pharmacologically Effective Dose

Purpose. The aim of this study was to construct a reliable dry powder inhalation (DPI) testing system for use in guinea pigs. Using this system, we were able to demonstrate the superiority of pulmonary administration of hydrophilically surface-modified pranlukast hydrate powder (SM-DP) over IV and PO administration as reflected in improved pharmacological action. Our ultimate aim is the development of an ideal treatment system for bronchial asthma involving topical administration to the lung. Methods. The reliability of the present DPI system was validated by continuously monitoring the concentration and particle size distribution of aerosols generated with an ambient particulate monitor and an Andersen air sampler, respectively. The pharmacological effect of SM-DP intratracheally administered to guinea pig was investigated by measuring the degree of bronchoconstriction and microvascular leakage induced by leukotriene D₄. Results. The mass concentration of aerosols generated by the DPI system was stable and the mass median aerodynamic diameter of aerosols insufflated from the respirator of the DPI system ranged from 1.4 to 1.7 m, within respirable limits. Inhibition of bronchoconstriction and airway microvascular leakage induced by leukotriene D₄ was achieved successfully with a dramatically lower dose of DP, or a further lower dose of SM-DP, comparable with that of the drug solution injected intravenously. The plasma pranlukast hydrate level with SM-DP at 50% inhibition of bronchoconstriction and airway microvascular leakage was reduced to 1/10 or less that following IV and PO administration. Conclusions. The hydrophilically surface-modified pranlukast hydrate powders were ideally aerosolized by the present DPI system, and were uniformly deposited in the lung lobes after inhalation. The pulmonary administration system with SM-DP is strongly recommended as an ideal system for the treatment of bronchial asthma in order to avoid systemic side-effects due to a dramatically reduced ED₅₀, comparable with or lower than IV, and the low plasma concentration of drug, 1/12 or less than that following IV and PO administration.     

The Liposome Partitioning System for Correlating Biological Activities of Imidazolidine Derivatives

The partitioning of 10 imidazolidines in various liposome/buffer systems (log K _m) has been determined and compared to partitioning in the n-octanol/buffer system (log P). The log K _m, which was generally greater than the log P, increased or decreased upon the addition of dicetylphosphate (DCP) or stearylamine (STA), respectively, to dimyristoylphosphatidylcholine (DMPC) liposomes. Quantitative correlations of ₂-adrenergic potencies of imidazolidines have been made by regression analyses with log P, log K _m, binding affinity, and intrinsic activity. Both central and peripheral potencies correlated with log K _m but not with log P Multiple regressions yielded improved predictable quantification of these potencies. Thus, the liposomal membrane system shows certain advantages over the n-octanol/buffer system for the prediction of biological activities of the imidazolidines.     

Limits for the Scaled Average Bioequivalence of Highly Variable Drugs and Drug Products

Purpose. To provide a rational procedure for establishing regulatory bioequivalence (BE) limits that can be applied in determinations of scaled average BE for highly-variable (HV) drugs and drug products. Methods. Two-period crossover BE investigations with either 24 or 36 subjects were simulated with assumptions of a coefficient of variation of 10, 20, 30, or 40%. The decline in the fraction of accepted studies was recorded as the ratio of geometric means (GMR) for the two formulations was raised from 1.00 to 1.45. Acceptance of BE was evaluated by scaled average BE, assuming various BE limits, and, for comparison, by unscaled average BE. A procedure for calculating exact confidence limits in two-period studies is presented, and an approximate method, based on the linearization of the regulatory model, is applied. Results. A mixed model is proposed for average BE. Accordingly, at low variabilities, the BE limit is constant, ±BEL_o, generally log(1.25). Beyond a logarithmic, limiting, switching variability (_o), in the region of HV drugs, the approach of scaled average BE is applied with limits of ±(BEL_o /_o). It is demonstrated that the performance of the mixed model corresponds to these expectations. The effect of _o and of the resulting BE limits is also demonstrated. Scaled average BE, with all reasonable limits for HV drugs, requires fewer subjects than an unscaled average BE. In two-period studies, the exact and approximate methods calculating confidence limits yield very comparable inferences. Conclusions. Scaled average BE can be effectively applied, with the recommended limits, for determining the BE of HV drugs and drug products. The limiting, switching variability (_o) will have to be established by regulatory authorities.     

Tetrafluoroethane (RFC 134A) Propellant-Driven Aerosols of Proteins

Purpose. Develop metered-dose propellant-driven aerosols of proteins using tetrafluoroethane (HFC 134A) as propellant. Methods. Proteins were lyophilized with the propellant-soluble surfactants Triton X-100, Triton X-405, Laureth-9, Brij-30, Nonidet-40, and diethylene glycol monoethylether and then charged with propellants. Results. Small particle aerosols of the experimental protein bovine gamma globulin were produced. The fraction of aerosolized respirable-sized protein particles (<4–5 m) increased after dispersion of particles in propellant with agitation by shaking. Scanning electron microscopy of respirable-sized protein aerosols demonstrated bead-like particles in grape-like clusters. Vigorous shaking of propellant-suspended particles for 2 minutes or more reduced the size of clusters and reduced the diameters of the protein-containing subparticles that constituted the clusters. A 50:50 ratio of HFC 134A and dimethylether (DME) propellants improved the respirability of protein aerosols compared to HFC 134A as the sole propellant. Protein/surfactant particles first dispersed in DME and then diluted in HFC 134A propellant most efficiently produced respirable-sized, propellant-driven, protein aerosols. Conclusions. Metered-dose aerosols of respirable-sized proteins can be generated using HFC 134A and HFC 134A:DME blended propellants as an alternative to nebulized aqueous aerosols for delivering peptide-based pharmaceuticals to the respiratory tract.     

The AERX™ Aerosol Delivery System

Purpose. We describe the AER_X aerosol delivery system, a new, bolus inhalation device that is actuated at preprogrammed values of inspiratory flow rate and inhaled volume. We report on its in vitro characterization using a particular set of conditions used in pharmacokinetic and scintigraphic studies. Methods. Multiple doses of aerosol were delivered from single use collapsible plastic containers containing liquid formulation. The aerosol was generated by forcing the formulation under pressure through an array of 2.5 micron holes. Air was drawn through the device at 70 LPM, and the aerosol was collected onto a filter or Andersen cascade impactor. The emitted dose was quantified from the filter collection data, and the particle size distribution was obtained from the best fit log-normal distribution to the impactor data. Results. 57.0 ± 5.9% of the dose of drug placed as an aqueous solution in the 45 L collapsible container was delivered as an aerosol (n = 40). The best fit size distribution had an MMAD = (2.95 ± 0.06) m and a geometric standard deviation _g = 1.24 ± 0.01 (n = 6). Conclusions. The AER_X aerosol delivery system generates a nearly monodisperse aerosol with the properties required for efficient and repeatable drug delivery to the lung.