Predicting the aerosol performance of dry powder inhalation formulations by interparticulate interaction analysis using inverse gas chromatography

Previous studies have demonstrated the utility of inverse gas chromatography (IGC) in discriminating the differences in surface energy between salmeterol xinafoate (SX) powders prepared by conventional sequential batch crystallization and micronization and by supercritical fluid crystallization. In the present study, solubility parameters derived from IGC analysis at infinite dilution (zero coverage) were further utilized to evaluate the influence of solid-solid interactions on the in vitro aerosol performance of these SX samples, with or without the inclusion of a lactose carrier. To this end, the strength of cohesive SX-SX interactions and that of adhesive SX-lactose interactions were computed for the samples from the corresponding solubility parameters, and their fine particle fractions determined using a multi-stage liquid impinger. It was found that the aerosol performance of SX could be substantially improved by the addition of lactose carrier only if the adhesive SX-lactose interactions were stronger than the cohesive SX-SX interactions. The difference in strength between these two forms of interactions also displayed a significant correlation with the increase in fine particle fraction after the addition of lactose carrier. These results suggest that IGC-based interparticulate interaction measurements may serve as a useful means for predicting the aerosol performance of dry powder inhalation formulations.

(R)-albuterol elicits antiinflammatory effects in human airway epithelial cells via iNOS

Catecholamines can suppress production of inflammatory mediators in different cell types, including airway epithelium, but downstream signaling mechanisms involved in regulation of these antiinflammatory effects are largely unknown. We theorized that acute beta2-adrenergic stimulation of airway epithelial cells with albuterol could suppress the production and release of inflammatory mediators, specifically granulocyte macrophage-colony stimulating factor (GM-CSF) via a pathway involving inducible nitric oxide synthase (iNOS). Normal human bronchial epithelial (NHBE) cells in primary culture were exposed to a cytokine mixture (10 ng/ml each IFN-gamma and IL-1beta) to induce iNOS expression. (R)- and (S)-enantiomers of albuterol, as well as racemic mixtures, were added with these cytokines, and effects on GM-CSF expression and production were assessed. Specific inhibitors and activators of protein kinases (PKs), beta2-adrenergic receptor antagonists, and small interfering RNAs against iNOS were used to delineate signaling pathways involved. iNOS message was significantly upregulated in a concentration-dependent manner by the active (R)-enantiomer of albuterol. (R)-albuterol also attenuated cytokine-induced increases in GM-CSF steady-state mRNA expression and protein release. The (S)-enantomer of albuterol had no effect on these parameters. PKC, specifically, the delta isoform, was required for iNOS message increase, but PKA and PKG were not involved in the pathway. Overall, this study identifies a novel pathway by which beta2-adrenergic agonists may exhibit antiinflammatory effects in airway epithelium and surrounding milieu.

Regional lung deposition and bronchodilator response as a function of beta2-agonist particle size

RATIONALE

Aerosol particle size influences the extent, distribution, and site of inhaled drug deposition within the airways.

OBJECTIVES

We hypothesized that targeting albuterol to regional airways by altering aerosol particle size could optimize inhaled bronchodilator delivery.

METHODS

In a randomized, double-blind, placebo-controlled study, 12 subjects with asthma (FEV1, 76.8 +/- 11.4% predicted) inhaled technetium-99m-labeled monodisperse albuterol aerosols (30-microg dose) of 1.5-, 3-, and 6-microm mass median aerodynamic diameter, at slow (30-60 L/min) and fast (> 60 L/min) inspiratory flows. Lung and extrathoracic radioaerosol deposition were quantified using planar gamma-scintigraphy. Pulmonary function and tolerability measurements were simultaneously assessed. Clinical efficacy was also compared with unlabeled monodisperse albuterol (15-microg dose) and 200 microg metered-dose inhaler (MDI) albuterol.

RESULTS

Smaller particles achieved greater total lung deposition (1.5 microm [56%], 3 microm [50%], and 6 microm [46%]), farther distal airways penetration (0.79, 0.60, and 0.36, respective penetration index), and more peripheral lung deposition (25, 17, and 10%, respectively). However, larger particles (30-microg dose) were more efficacious and achieved greater bronchodilation than 200 microg MDI albuterol (deltaFEV1 [ml]: 6 microm [551], 3 microm [457], 1.5 microm [347], MDI [494]). Small particles were exhaled more (1.5 microm [22%], 3 microm [8%], 6 microm [2%]), whereas greater oropharyngeal deposition occurred with large particles (15, 31, and 43%, respectively). Faster inspiratory flows decreased total lung deposition and increased oropharyngeal deposition for the larger particles, with less bronchodilation. A shift in aerosol distribution to the proximal airways was observed for all particles.

CONCLUSIONS

Regional targeting of inhaled beta2-agonist to the proximal airways is more important than distal alveolar deposition for bronchodilation. Altering intrapulmonary deposition through aerosol particle size can appreciably enhance inhaled drug therapy and may have implications for developing future inhaled treatments.

Comparative study of erythritol and lactose monohydrate as carriers for inhalation: atomic force microscopy and in vitro correlation

The adhesion of micronised salbutamol sulphate to two carrier excipients, lactose monohydrate and erythritol, was investigated using the atomic force microscope (AFM) colloid probe technique and correlated with their respective physico-mechanical properties and aerosolisation performance. The particle size, morphology and moisture sorption properties of the carriers were similar thereby allowing direct comparison of functionality. AFM force measurements (n = 1024 force curves) were obtained between salbutamol sulphate drug probes (n = 4) and the excipients, as 63-90 microm sieve fractions and atomically smooth crystals. In general, significant differences in drug adhesion to lactose monohydrate and erythritol were observed (ANOVA, p<0.05), with erythritol exhibiting relatively greater adhesiveness. A linear relationship between drug probe adhesion to lactose monohydrate and drug probe adhesion to erythritol was established with salbutamol sulphate-lactose monohydrate adhesion being 60-70% of that of the erythritol system. In vitro analysis suggested good correlation with the adhesion measurements. The aerosolisation of salbutamol sulphate from erythritol carrier particles was significantly less (ANOVA, p<0.05) than from lactose monohydrate, with a fine particle dose (<6.4 microm) of 41.9 +/- 7.4 microg and 24.9 +/- 3.1 microg for the lactose monohydrate and erythritol carriers, respectively (n = 3).

The correlation of urinary levels of albuterol and its metabolites isomers following inhalation from a dry powder inhaler and in vitro particle size characterisation

This study was designed to analyse the two enantiomers of abuterol in urine after the inhalation of a single dose of racemic albuterol from three dry powder inhalers by human volunteers. Urine samples were collected over 24h and analysed by HPLC-with fluorescence detection. Albuterol and its metabolites in urine could only have resulted from pulmonary absorption because gastrointestinal absorption was prevented. Unchanged albuterol and its conjugated metabolites were detected in the urine of healthy volunteers at much higher levels than in the urine of the asthmatics. Also, the amount of S-(+)-isomer excreted in urine was higher than that of the R-(--)-isomer. These differences did not arise as a consequence of either the formulation or the inter-conversion of two isomers in the urine. There is a relationship between the improvement of mid-expiratory flow (FEF(25-75)) and the amount of R-(--)-albuterol remaining to be excreted. The elimination rate constants of the parent drug in healthy volunteers of both R-(--)- and S-(+)-isomers were higher than those of the respective conjugated metabolites. The mean S/R ratio of the parent drug was about unity initially and increased to about 1.5 in the urine collected between 12 and 24h. The values of S/R ratio of the conjugated metabolites in the healthy volunteers were in the range 1.2-2.4, with the value increasing over the time of collection before reaching a plateau. This also occurred with the asthmatics, but the ratios were higher, in the range of 2.0-4.5. In summary, the urinary level of albuterol following in vivo inhalation was found to correlate with in vitro deposition data from the dry powder inhaler.

Preparation and release of salbutamol from chitosan and chitosan co-spray dried compacts and multiparticulates

Chitosan microparticulates were prepared by spray drying from aqueous media containing hydrochloric acid or acetic acid. The medium affected the morphology and degree of acetylation of chitosan, the presence of acetic acid resulting in increased acetylation of the polymer during processing. Co-spray drying salbutamol sulphate/chitosan systems with the crosslinking agent formaldehyde had no detectable effect on particle morphology. However, with increasing salbutamol loading particles became less spherical, taking on a collapsed appearance. Spray dried chitosan-salbutamol sulphate microparticulates were X-ray amorphous. Chitosan-salbutamol sulphate composites were compressed into discs to quantify drug release and showed delayed release of salbutamol sulphate. The general power law equation fitted the data better than the t0.5, mono- or bi-exponential models and gave n indices greater than 0.5, i.e. in the range 0.53-0.71. Crosslinking did not dramatically alter the drug release behaviour. Both crosslinked and non-crosslinked composites swelled during release, the former to the greater extent. The release data for crosslinked composites gave slightly higher n values than the corresponding non-crosslinked composites, consistent with the increased swelling of these systems. Release studies were also conducted on the microparticulates. Because of the small particle size and large surface area present, the release of the highly soluble drug salt was extremely rapid (> 90% release in 5 min). Twin impinger analysis indicated good in vitro deposition of the microparticulates and potential for pulmonary delivery.

An in vivo and in vitro comparison of two powder inhalers following storage at hot/humid conditions

Dry powder inhalers (DPIs) are increasingly being used for the treatment of asthma and COPD. A potential drawback is that DPIs can be sensitive to humidity. Two DPIs, Symbicort Turbuhaler and Seretide Diskus, were stored 3 months at either 25 degrees C/30% RH or 40 degrees C/75% RH. After storage, delivered, as well as fine particle dose, FPD, were tested in vitro and lung deposition, of the steroid components, was assessed in vivo. After storage at 40 degrees C/75% RH, delivered dose as well as FPD from Symbicort Turbuhaler was virtually unchanged while FPD for Seretide Diskus decreased by about 50% despite no decrease in delivered dose. For both products, no difference in FPD was seen after storage at 25 degrees C/30% RH. These in vitro findings were confirmed in the in vivo part of the study. Lung deposition for Symbicort Turbuhaler was unaffected by 40 degrees C/75% RH storage, while for Seretide Diskus it was reduced with about 50%. The study extends previous in vitro observations of impaired performance of Seretide Diskus and demonstrates that this translates into decreased drug delivery to the site of action. The clinical importance of this finding has not been studied but could result in undertreatment.

Effects of extreme temperatures on drug delivery of albuterol sulfate hydrofluoroalkane inhalation aerosols

PURPOSE

The effects of extreme temperatures on drug delivery of two albuterol sulfate hydrofluoroalkane, metered-dose inhalers (MDIs) were evaluated.

METHODS

Three Proventil HFA and three Ventolin HFA MDIs were stored at room temperature and served as controls while three of each product were placed in the trunk of a vehicle in Tucson, Arizona. The temperature in the vehicle was monitored for six months. Product performance for each of the MDIs was evaluated at room temperature. An additional study was performed to investigate the performance of the two products when actuated at 4, 22, 47, and 60 degrees C.

RESULTS

The products subjected to extreme environmental temperatures had a modest increase in propellant-leak rate, but the emitted-particle size, dose per actuation, respirable mass, and non-respirable mass were unaffected. The inhalers tested at temperatures outside the recommended storage conditions exhibited a decrease in particle size, dose per actuation, shot weight, and non-respirable mass as temperature increased. Conversely, increased temperature caused an increase in respirable mass.

CONCLUSION

Despite exposure to extreme temperatures exceeding the manufacturers' recommended storage conditions, drug delivery from Proventil HFA and Ventolin HFA MDIs was not significantly altered. However, drug delivery did change appreciably when the inhalers were tested at different temperatures outside recommended storage conditions.

Evaluation of Nebulizer Performance under Various Humidity Conditions

Jet nebulizers are a drug delivery tool commonly used for treating respiratory diseases. When a nebulizer generates aerosols, the rate at which droplets evaporate depends on humidity conditions around the nebulizer outlet. Because the relative humidity (RH) of the air affects the evaporation rate, the aerosol distribution and drug delivery dose is also affected by RH. Four nebulizers were chosen for comparison in this study: PARI LC Plus (PARI Respiratory Equipment, Inc., Midlothian, VA), SideStream (Medic-Aid Ltd., UK), VixOne (Westmed, Inc., Tucson, AZ), and Micromist (Hudson Respiratory Care Inc., Temecula, CA). Two different formulations were used: albuterol (liquid solution) and budesonide (suspension). Particle distribution (mass median aerodynamic diameter [MMAD] and geometric standard deviation [GSD]), nebulizer efficiency (total efficiency and respirable fraction [RF] efficiency for particles less than 4.7 microm), and dead volume (the amount of solution remaining after nebulization) were compared at the RH of 5%, 50%, and 80%. Our results showed that the MMAD increased (p value varied from <0.001 to 0.016) with the increase in RH, except for with the VixOne unit with albuterol (p = 0.24). The MMAD from the budesonide always appeared higher than from the albuterol. The RF (and thus, the inhalation dose) was lower with a higher RH. Except for the PARI LC Plus with budesonide, the RF decreased approximately 15-27% when the RH rose from 5% to 50%. For the PARI LC Plus nebulizer, the lower dead volume (0.22 mL) with higher residual drugs (62.3% of total drug) was obtained at an RH of 5% comparing the RH of 50% and 80% because of the unit's unique design.

Insights into cyclodextrin interactions during sample stacking using capillary isotachophoresis with on-line microcoil NMR detection

On-line capillary isotachophoresis (cITP)-NMR experiments were used to probe the interactions of the pharmaceutical compounds S-alprenolol, S-atenolol, R-propranolol, R-salbutamol and S-terbutaline with beta-cyclodextrin (beta-CD) during cITP concentration. In cITP, ionic analytes are concentrated and separated on the basis of their electrophoretic mobility. Because neutral molecules have an electrophoretic mobility of zero, they are normally not concentrated or separated in electrophoretic experiments like cITP. Most of the analytes studied were concentrated by cITP sample stacking by a factor of around 300. For analytes that formed a strong inclusion complex, beta-CD co-concentrated during cITP sample stacking. However, once the focusing process was complete, a discrete diffusional boundary formed between the cITP-focused analyte band and the leading and trailing electrolyte, which restricted diffusion into and out of the analyte band.

Effects of salbutamol and enantiomers on allergen-induced asthmatic reactions and airway hyperreactivity

Salbutamol consists of a racemic mixture of R- and S-salbutamol. R-salbutamol (levalbuterol) is the active bronchodilating enantiomer, whereas S-salbutamol is thought to be pharmacologically inactive or to exert adverse effects. This study evaluated the bronchoprotective effects of inhalation of therapeutically relevant doses of the racemate and individual enantiomers in guinea pigs. It was found that basal airway reactivity to histamine was similarly reduced 30 min after inhalation of equivalent doses of RS- and R-salbutamol; this protective effect disappeared within 3 h. Inhalation of RS- and R-salbutamol 30 min before and 5.5 h after allergen challenge suppressed allergen-induced airway hyperreactivity to histamine after the early and late asthmatic reaction, completely inhibiting the early asthmatic reaction and tending to reduce the development of the late asthmatic reaction. At 5 h after allergen challenge, the inhibition of airway hyperreactivity was more pronounced in animals treated with R-salbutamol compared to racemate-treated animals. Both basal airway reactivity and allergen-induced hyperreactivity were not affected by S-salbutamol. Inflammatory cell infiltration was not affected by the racemate or the individual enantiomers. In conclusion, inhalation of therapeutically relevant doses of R- and RS-salbutamol effectively suppress allergen-induced airway reactivity after the early and late asthmatic reactions, the R-enantiomer being slightly more potent with respect to early airway reactivity than the racemate. No adverse effects were observed for the S-enantiomer.

Surface roughness contribution to the adhesion force distribution of salmeterol xinafoate on lactose carriers by atomic force microscopy

Adhesion force distributions of silica spheres (5 and 20 microm) and salmeterol xinafoate (4 microm) particles with inhalation grade lactose surfaces and spin coated lactose films were determined by atomic force microscopy (AFM) to investigate the influence of surface roughness on the force distributions. The roughness of lactose particles and films was determined by both AFM and confocal microscopy (CM); the lactose particles showed RMS R(q) values between 0.93 and 2.2 microm. The adhesion force distributions for silica and SX probes were significantly different for the different lactose carriers and broad, e.g., the adhesion force distribution between a 5 microm silica sphere and lactose particles ranged from 5 to 105 nN. This contrasted with distributions on smooth spin coated lactose films (RMS R(q) of 0.28 nm) which were not significantly different and were narrow, e.g., the adhesion force distribution between a 5 microm silica sphere and spin coated lactose films was between 42 and 68 nN. In addition, no significant difference in adhesion force distribution occurred with silica probe size on the lactose carrier surface. The use of X-ray photoelectron spectroscopic analysis confirmed that the lactose surfaces were free of impurities that might contribute to variation in adhesion. Although the almost atomically flat films showed some adhesion variability, the surface roughness of the lactose particles was a major contributing factor to the broad distributions seen in this study.

Beta2-agonist eutomers: a rational option for the treatment of asthma?

Beta2-adrenoceptor agonists (beta2-agonists) such as albuterol (salbutamol) and terbutaline and their long-acting analogs salmeterol and formoterol are widely used as bronchodilators in the treatment of asthma. They are chiral drugs historically marketed as racemic mixtures of an active (eutomer) and essentially inactive (distomer) stereoisomer. Despite their obvious therapeutic value and widespread use, beta2-agonists have been implicated, somewhat controversially, in causing an increase in asthma mortality and a deterioration of asthma control by a mechanism that remains elusive. Inherent toxicity of the distomers has been widely touted as an explanation and has given rise to pressure for the replacement of the racemates with pure eutomer formulations (the so-called chiral or racemic switch). This has culminated in the recent introduction into clinical practice of the single active stereoisomer of albuterol (levalbuterol) and the promise of other pure beta2-agonist eutomer formulations to follow. This article examines the evidence on which these chiral switches are based. Clinical studies designed to reveal negative effects of beta2-agonists have searched for reductions in lung function, increases in airway responsiveness to bronchoconstrictor mediators and worsening of asthma control. Crossover studies administering the pure stereoisomers and racemate of albuterol have not shown a clear superiority of the pure eutomer formulation over the racemate in terms of either bronchial hyperresponsiveness, tachyphylaxis to bronchoprotective effects or improvements in lung function. Clinical toxicity of beta2-agonist distomers on any aspect of asthmatic lung function has also not been demonstrated in the relatively short-term inhalational studies (single dose or repeated dose studies <1 week) that have been carried out. In animal studies, the administration of beta2-agonist racemates and distomers has been shown to enhance bronchial hyperresponsiveness but only in ovalbumin-sensitized animals where the relevance to humans is questionable. The pharmacokinetics and metabolism of beta(2)-agonist stereoisomers appear to be essentially similar whether administered as single stereoisomers or as racemates. Levalbuterol may be slightly more potent than an equivalent dose given as racemate, but there is some evidence that it forms a small amount of the distomer in vivo which detracts somewhat from its purported benefits over use of the racemate. Whilst there remains a clear need for studies of longer duration with sensitive clinical endpoints to evaluate the benefits of beta2-agonist eutomers and to investigate distomer toxicity, the chiral switch for beta2-agonists in general, and for albuterol in particular, does not appear to be justified on the basis of the evidence available to date.

Evaluation of SCF-engineered particle-based lactose blends in passive dry powder inhalers

The objective of this study was to assess the performance of SCF-engineered budesonide and albuterol sulfate powder blends in passive dry powder inhalers (DPI) relative to micronized drug blends. A number of lactose grades for inhalation were screened and the appropriate carrier and drug-to-lactose blending ratio were selected based on drug content and emitted dose uniformity. Aerosol performance was characterized by Andersen cascade impaction. Blend formulations of SEDS (solution enhanced dispersion by supercritical fluids) budesonide and albuterol exhibited a significant drug content uniformity (7-9% RSD) improvement over micronized drug blends (16-20% RSD). Further, the SEDS formulations demonstrated higher emitted dose and reduced emitted dose variability (10-12% RSD) compared to micronized powders (21-25% RSD) in the Turbospin, albeit without significant enhancement of the fine particle fraction. In contrast, SEDS powders exhibited increased fine particle fractions over micronized blends in the Clickhaler; improvements were more pronounced with albuterol sulfate. The performance enhancements observed with the SEDS powders are attributed to their increased surface smoothness and reduced surface energy that are presumed to minimize irreversible drug-carrier particle interactions, thus resulting in more efficient drug detachment from the carrier particle surface during aerosolization. As demonstrated for budesonide and albuterol, SEDS may enhance performance of lactose blends and thus provide an attractive particle engineering option for the development of blend formulations for inhalation delivery.

Effect of nanoprecipitation on the physicochemical properties of low molecular weight poly(l-lactic acid) nanoparticles loaded with salbutamol sulphate and beclomethasone dipropionate

A modified nanoprecipitation (interfacial polymer deposition following solvent displacement) method was used to produce nanoparticles from low molecular weight poly(L-lactic acid). Model drugs, either salbutamol sulphate or beclomethasone dipropionate, were encapsulated in the particles. The influence of the preparation method on the physicochemical state of the polymer and the drugs as well as on the drug-polymer interactions were studied by electron microscopy, X-ray diffractometry, thermal analysis and infrared spectroscopy. Nanoprecipitation lowered the crystallinity of the PLA polymer. The crystallinity of the polymer was higher in the particles containing salbutamol sulphate then those containing beclomethasone dipropionate. The crystal form of beclomethasone dipropionate was changed from an anhydrate to a monohydrate as a result of nanoprecipitation. Although changes in the crystallinity of the polymer and the model drugs were seen, no clear interactions between the polymer and the drug were detected.

Probing the beta2 adrenoceptor binding site with catechol reveals differences in binding and activation by agonists and partial agonists

The beta(2) adrenergic receptor (beta(2)AR) is a prototypical family A G protein-coupled receptor (GPCR) and an excellent model system for studying the mechanism of GPCR activation. The beta(2)AR agonist binding site is well characterized, and there is a wealth of structurally related ligands with functionally diverse properties. In the present study, we use catechol (1,2-benzenediol, a structural component of catecholamine agonists) as a molecular probe to identify mechanistic differences between beta(2)AR activation by catecholamine agonists, such as isoproterenol, and by the structurally related non-catechol partial agonist salbutamol. Using biophysical and pharmacologic approaches, we show that the aromatic ring of salbutamol binds to a different site on the beta(2)AR than the aromatic ring of catecholamines. This difference is important in receptor activation as it has been hypothesized that the aromatic ring of catecholamines plays a role in triggering receptor activation through interactions with a conserved cluster of aromatic residues in the sixth transmembrane segment by a rotamer toggle switch mechanism. Our experiments indicate that the aromatic ring of salbutamol does not activate this mechanism either directly or indirectly. Moreover, the non-catechol ring of partial agonists does not interact optimally with serine residues in the fifth transmembrane helix that have been shown to play an important role in activation by catecholamines. These results demonstrate unexpected differences in binding and activation by structurally similar agonists and partial agonists. Moreover, they provide evidence that activation of a GPCR is a multistep process that can be dissected into its component parts using agonist fragments.

Evaluation of particle size distribution of albuterol sulfate hydrofluoroalkane administered via metered-dose inhaler with and without valved holding chambers

BACKGROUND

Administration of inhaled medications via metered-dose inhaler (MDI) to pediatric patients younger than 4 years usually requires use of a holding chamber or spacer with an attached face mask.

OBJECTIVE

To determine the particle size distribution and overall dose of albuterol from the albuterol sulfate hydrofluoroalkane delivered in conjunction with 2 US-marketed valved holding chambers (VHCs) compared with the dose delivered via MDIs without VHCs.

METHODS

Cascade impaction methods with high-performance liquid chromatography were used to evaluate the fine particle mass (FPM) of albuterol administered without and with the use of 2 commercially available VHCs.

RESULTS

Particle size distributions for the 2 VHCs and the control were similar. The mean FPM values for the 2 VHCs and the control were 32, 28, and 30 microg, respectively. Statistical comparison of the FPM shows a similar profile when differences from the albuterol hydrofluoroalkane without a spacer were evaluated.

CONCLUSIONS

In vitro results obtained under these test conditions demonstrate that all the FPM values for the VHCs tested were within 15% of the control range, a difference that is unlikely to be clinically meaningful. These results do not warrant a change in the recommended dose of albuterol hydrofluoroalkane administered when using the VHCs tested. The use of an MDI in conjunction with a VHC provides a reasonable therapeutic approach for administration of albuterol hydrofluoroalkane to young children and other patients who have difficulty administering the MDI alone.

Long-chain formoterol analogues: an investigation into the effect of increasing amino-substituent chain length on the beta2-adrenoceptor activity

The synthesis of a series of long-chain formoterol analogues in which the terminal ether residue of the beta-phenethyl-amino-substituent has been extended beyond the methyl ether residue present in the parent compound are described. Evaluation of these analogues as beta(2)-adrenoceptor agonists was used to provide an insight into the factors controlling the magnitude and duration of receptor activation.

Surface characterization of salmeterol xinafoate powders by inverse gas chromatography at finite coverage

In our previous studies, surface analysis by inverse gas chromatography (IGC) at infinite dilution (zero coverage) was performed on four salmeterol xinafoate (SX) powdered samples, viz, two supercritical CO2-processed Form I (SX-I) and Form II (SX-II) polymorphs, a commercial granulated SX (GSX) raw material and its micronized product (MSX). Both GSX and MSX are also of the same Form I polymorph. To further probe the differences in surface properties between the samples, the present study has extended the IGC analysis to the finite concentration range of selected energy probes. The adsorption isotherms of the SX samples were constructed using (nonpolar) octane, (polar acidic) chloroform, and (polar basic) tetrahydrofuran as liquid probes. Type II adsorption isotherms with weak knees were observed with each probe for all SX Form I samples. The extents of probe adsorption by the samples at various relative pressures follow the rank order: SX-II > GSX approximately MSX > SX-I, indicating that the SX-I has fewer high-energy adsorption sites than GSX and MSX. Type III isotherms were observed for SX-II with the two polar probes, indicative of weak adsorbate-adsorbent interactions. The additional information generated shows that IGC analysis at finite coverage is a valuable complementary tool to that at infinite dilution.

Effects of surface processing of lactose carrier particles on dry powder inhalation properties of salbutamol sulfate

The effects of the surface processing of lactose carrier particles on the dry powder inhalation properties of salbutamol sulfate were investigated. Lactose carrier particles were processed using a high-speed elliptical-rotor-type powder mixer (Theta-Composer). In the present study, drug/carrier powder mixtures were prepared, consisting of micronized salbutamol sulfate and coarse lactose carriers with various particle surface conditions prepared by surface processing. These powder mixtures were aerosolized by a Jethaler, and the in vitro inhalation properties of salbutamol sulfate were evaluated with a twin impinger. Compared with those of the powder mixed with unprocessed lactose carriers, the in vitro inhalation properties of the powder mixture prepared using the surface processed lactose carriers were significantly different, showing that the in vitro inhalation properties of salbutamol sulfate were improved. The in vitro inhalation properties increased with the rotor rotation rate. Using this surface processing system would thus be valuable for increasing the inhalation properties of dry powder inhalation with lactose carrier particles.

Determining the critical relative humidity for moisture-induced phase transitions

A new method to determine the onset relative humidity for a glass transition and crystallization processes in amorphous or partially amorphous materials was developed using dynamic gravimetric vapor sorption (DVS). Water vapor can act as a plasticizing agent in amorphous materials, thus lowering the glass transition temperature below room temperatures. Additional water sorption can lead to a crystallization event below the glass transition temperature. On spray-dried lactose the glass transition RH and crystallization RH values were 30 and 58% at 25 degrees C, respectively. Glass transition and crystallization RH values were also measured at 5, 15, 25, 35, and 45 degrees C on a spray-dried salbutamol sulfate sample. The glass transition RH values for the salbutamol sulfate sample ranged from 64.5% RH (5 degrees C) to 32.8% RH (45 degrees C) while the crystallization RH values ranged from 81.0% RH (5 degrees C) to 50.4% RH (45 degrees C). The results clearly show that the glass transition and crystallization humidity values decrease as the sample temperature increases.

Enantiomeric separation of basic compounds using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin in combination with potassium camphorsulfonate in nonaqueous capillary electrophoresis: optimization by means of an experimental design

The enantiomeric separation of a series of basic pharmaceuticals (beta-blockers, local anesthetics, sympathomimetics) has been investigated in nonaqueous capillary electrophoresis (NACE) systems using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) in combination with potassium camphorsulfonate (camphorSO3-). For this purpose, a face-centered central composite design with 11 experimental points was applied. The effect of the concentrations of HDMS-beta-CD and camphorSO3- on enantioresolution was statistically evaluated and depended largely on the considered analyte. The presence of camphorSO3- was found to be particularly useful for the enantioseparation of compounds with high affinity for the anionic CD. CamphorSO3- seems to act as a competitor, reducing the affinity for the CD, probably by ion-pair formation with these analytes. For compounds with lower affinity for HDMS-beta-CD, the combination of camphorSO3- and the CD appeared to have a favorable effect on enantioresolution only if the optimal CD concentration could be reached. On the other hand, for compounds characterized by a very low affinity for the anionic CD, the association of camphorSO3- and HDMS-beta-CD is always unfavorable. Finally, experimental conditions were selected by means of the multivariate approach in order to obtain the highest resolution (Rs) value for each studied compound.

Modified push-pull osmotic system for simultaneous delivery of theophylline and salbutamol: development and in vitro characterization

An oral osmotic system which can deliver theophylline and salbutamol sulphate simultaneously for extended period of time was developed and characterized in a view to reduce the problems associated with the multidrug therapy of asthma. Simple controlled porosity osmotic pump contained both drugs (in freely soluble form) did not provide satisfactory extended release of theophylline. A modified two-layered, push-pull osmotic system was developed by using the basic designs of various oral osmotic pumps, such as controlled porosity osmotic pump (CPOP), elementary osmotic pump (EOP) and push-pull osmotic pump (PPOP). Scanning electron microscopy of cellulose acetate coating membrane after dissolution revealed that 25% (w/w) of sorbitol can be used as an optimized concentration of pore forming agent with 25% (w/w) of plasticizer, which was kept constant. Formulations were initially developed for theophylline and the release was optimized by using two different soluble forms of theophylline with varying amount of hydrophilic polymer mixture in upper layer and polyethylene oxide (expandable hydrogel) in lower layer. Further, the release of salbutamol sulphate was optimized by keeping the drug in upper or lower layer or both layers. In vitro release studies showed satisfactory controlled release profiles of both drugs. The release profiles of both drug statistically compared with respective marketed controlled release formulations. An optimized system was selected to study the effect of concentration of pore forming agent and orifice diameter on the release of both drugs.

Development and validation of HPLC methods for the enantioselective analysis of bambuterol and albuterol

Suitable HPLC methods for the direct separation of bambuterol and albuterol enantiomers were developed. The enantioseparation was tested on numerous commercial chiral HPLC columns. For bambuterol the most convenient separation was determined on amylose Chiralpak AD column, and for albuterol on vancomycine Chirobiotic V column. The mobile phase compositions were systematically studied to obtain the optimal chromatographic methods. Validation of methods in selected conditions shows that the chosen methods are selective and precise with linear response of detector for both pairs of enantiomers.

Single-isomer R-salbutamol is not superior to racemate regarding protection for bronchial hyperresponsiveness

Bronchial hyper-reactivity (BHR) has been suggested to follow cessation of regular medication with racemic salbutamol. This study aimed at investigating the effects from medication with R,S- and R-salbutamol on bronchial response to provocation with isocapnic hyperventilation of cold air (IHCA). Twenty-six patients with mild to moderate asthma were enrolled in a double-blind, randomised, cross-over study. Bronchial response to provocation was measured before and after 1 week's medication. Doses of 0.63 mg R-salbutamol or 1.25 mg R/S-salbutamol were inhaled three times daily during medication-weeks and a wash-out week intervened. Tests were performed 6 h after the last dose of test drug. Impulse oscillometry and forced expiratory volume during one second were methods used to identify bronchial response to provocation. Two patients withdrew from the investigation due to side-effects, one from R- the other from R,S-salbutamol. Comparable resting bronchial conditions were indicated by differences in baseline lung function values of <2% between study days. No statistically significant medication-dependent differences in BHR could be demonstrated between treatment groups. However, 15 patients exhibited higher (P = 0.03) post-treatment BHR after pure R-salbutamol than after R,S-salbutamol. Furthermore, plasma concentrations of R-salbutamol tended to be lower (P = 0.08) after medication with R- than after R,S-salbutamol despite equal doses of R-salbutamol given during the two separate treatment periods. We also found that considerable amounts of S-salbutamol were retrieved in plasma after medication with pure R-salbutamol. We conclude that we were unable to demonstrate favourable effects of R-salbutamol over R,S-salbutamol regarding response to provocation with IHCA after regular medication of 1 week's duration.