Levalbuterol hydrochloride

Racemic albuterol, a commonly used bronchodilator, is an exact 50:50 mixture of two enantiomers, R- and S-albuterol. Concern regarding increased mortality associated with the use of this beta-2 (beta 2) agonist triggered the study of both of these enantiomers separately. In vitro studies suggest that the two enantiomers have different binding affinities for beta-adrenoreceptors, may exert opposing effects on inflammation, demonstrate different effects on mucocilary transport, and display differing pharmacokinetics. Clinical studies comparing both enantiomers are few, of short duration, and often in small patient populations, and their results vary. R-albuterol has greater bronchodilatory effects than the racemate and may have anti-inflammatory properties. S-albuterol has markedly less affinity for the beta-adrenoreceptor. It was found to cause bronchoconstriction in animal models, but neither bronchoconstrictive nor pro-inflammatory effects have been conclusively demonstrated in human studies. The data available at present, while suggestive, are insufficient to conclusively recommend R-albuterol over the racemate. Further basic research and investigations in humans comparing both enantiomers at increasing doses over longer time periods are required to clarify the precise roles of R- and S-albuterol.

Respiratory deposition patterns of salbutamol pMDI with CFC and HFA-134a formulations in a human airway replica

This paper describes a technique that uses a well-defined human airway replica and gamma counting as a standard method for evaluating and comparing the performance of medical inhalers and spacers. High-fidelity replicas reproduced as needed from master casts made from human cadavers include the oropharyngeal cavity, larynx, trachea, and five to nine generations of bronchi. Deposition in the small airways and alveoli region of the cast is simulated by material that passes through the upstream airways and is collected on foam filters. Deposition patterns in the respiratory tract replica were obtained by using radiolabel in the medical inhaler and by gamma scintigraphy. This technique was used to determine respiratory deposition patterns of salbutamol in a pressurized metered dose inhaler (pMDI) with chlorofluorocarbon (CFC, in-house formulation) and HFA-134 formulations (Proventil hydrofluoroalkane [HFA]). At an inspiration flow of 30 L/min, patterns in the salbutamol/CFC formula showed a high deposition in the oropharyngeal airway (78%) and a 16% deposition in the lung, similar to in vivo measurements reported in the literature. However, the salbutamol/HFA formula showed lower oral deposition (56%) but higher lung deposition (24%). The difference in the oral deposition patterns may be attributed to lower initial spray velocity, initial droplet evaporation rate, and possibly initial droplet sizes of Proventil HFA. The small orifice diameter (0.25 mm) of the Proventil HFA actuator produced a softer plume with a smaller impact force, resulting in lower oropharyngeal deposition. Cascade impactor measurements showed similar aerodynamic particle size distribution of the CFC and HFA formulations. We also showed that using spacers in the Proventil HFA resulted in a lower oropharyngeal deposition and higher lung deposition, indicating beneficial effects. Comparison of oropharyngeal deposition and those predicted by artificial throats used in the impactor measurements showed that, in general, the artificial throat predicted a lower deposition.

The therapeutic ratio of R-albuterol is comparable with that of RS-albuterol in asthmatic patients

BACKGROUND

It has been suggested that R-albuterol produces bronchodilation that is comparable with that of racemic albuterol (RS-albuterol) on a 4:1 dose-for-dose basis but systemic side effects on a 2:1 basis, implying better therapeutic ratio for R-albuterol.

OBJECTIVE

We sought to carefully compare the bronchodilating and systemic effects of R- and RS-albuterol by using a crossover study design.

METHODS

Twenty asthmatic patients (15.1%-28.7% FEV(1) reversibility) were given R-albuterol (6.25-1600 microg), S-albuterol (6.25-1600 microg), RS-albuterol (12.5-3200 microg), or placebo in a crossover, double-blind, placebo-controlled fashion. Cumulative doses were given with a Mefar dosimeter, and FEV(1), heart rate, and plasma K(+) levels were measured 20 minutes after each dose.

RESULTS

Both R- and RS-albuterol produced dose-related improvement in FEV(1) and, at higher doses, increased heart rate and decreased plasma K(+) levels. Neither placebo nor S-albuterol had any significant effect. Individual estimates of the potency ratio for R-albuterol/RS-albuterol were calculated and summarized across all subjects. The geometric mean potency ratio for effects on FEV(1) was 1.9 (95% CI, 1.3-2.8), on HR of 1.9 (95% CI, 1.3-2.9), and on K(+) level of 1.7 (95% CI, 1.3-2.1).

CONCLUSION

All pharmacologic effects of RS-albuterol reside with the R-enantiomer, and S-albuterol is clinically inactive. The R-albuterol/RS-albuterol potency ratios for local (FEV(1)) and systemic effects (heart rate and K(+)) are similar, suggesting a comparable therapeutic ratio for R-albuterol and RS-albuterol in asthmatic subjects.

Formulation and evaluation of controlled-release transdermal patches of theophylline-salbutamol sulfate

Transdermal formulations containing theophylline and salbutamol sulfate (SS) were formulated using hydroxypropylmethylcellulose. Theophylline was loaded by adsorption with the aid of the coadsorbate sodium chloride. The formulations were subjected to in vitro release studies, and the dose of salbutamol and theophylline was optimized to yield the desired flux. The films were uniform and 93 +/- 5.4 microm thick. The in vitro fluxes of theophylline and salbutamol sulfate from the formulation were 1.22 +/- 0.4 mg/h/cm2 and 13.36 +/- 1.02 microg/h/cm2, respectively. The formulation was subjected to pharmacodynamic studies in guinea pigs. The preconvulsive time (PCT) of guinea pigs increased significantly after 4 h, and the same was observed even after 24 h Pharmacokinetic studies were carried out in healthy human volunteers. Theophylline was analyzed in saliva, and salbutamol was analyzed in the blood plasma. The Tmax of the drugs was 3 h, and appreciable concentrations of the drugs above their MEC could be analyzed even after 12 h. The elimination half-life of the drugs was significantly prolonged compared to that for tablets. There were no signs of erythema or edema in the volunteers during observation for a period of 7 days.

Evaluation of flow properties of dry powder inhalation of salbutamol sulfate with lactose carrier

The effects of the flow and packing properties of a drug/carrier powder mixture on emission of drug adhering to the carrier from capsules and inhalation devices were investigated. Model powder mixtures were designed consisting of lactose carriers with different particle shapes were prepared by surface treatment and micronized salbutamol sulfate. These powder mixtures were aerosolized by a Spinhaler, and in vitro deposition properties of salbutamol sulfate were evaluated by a twin impinger. The flow properties of the mixed powders were evaluated by the Carr's flowability index (FI) and Hausner's ratio (HR). The packing properties of the mixed powders were determined employing the tapping method. Compared with the powder mixed with the untreated lactose carrier, the FI, HR, and the constant K in Kawakita's equation of the powder mixture prepared using the surface-treated lactose carrier were significantly different, showing that the flow and packing properties of the drug/carrier powder mixture were improved. Using this surface-treated system, the handling of the powder mixture when packing into capsules is improved, which is desirable for handling dry powder inhalants. The fraction (%) of drug emitted from capsules and devices (EM) and the FI of the powder mixture were correlated. As the flow properties improved, the outflow of the powder mixture from capsules and devices became easier, and emission of drug adhering on the carrier from capsules and devices improved. Improvement of the inhalation process, such as the drug particles emitted from the inhalation system, is valuable for increasing inhalation properties of dry powder inhalation.

Conductimetric determination of reproterol HCl and pipazethate HCl and salbutamol sulphate in their pharmaceutical formulations

A simple and sensitive conductimetric method for the determination of salbutamol sulphate and reproterol and pipazethate hydrochlorides is presented based on their ion associates with phosphotungstic and phosphomolybdic acids. The effect of solvent, molar ratio, reagent concentration and temperature were studied, and the solubility products of the formed ion associates were calculated. The method was applied to the determination of the drugs in their pure state or pharmaceutical preparations with mean recovery values of 99.82-100.54, 99.75-100.12 and 99.95-100.40%, and coefficient of variation 0.28-0.52, 0.16-0.36 and 0.19-0.33 for salbutamol sulphate, reproterol HCl and pipazathate HCl, respectively.

Definition of a solvent system for spherical crystallization of salbutamol sulfate by quasi-emulsion solvent diffusion (QESD) method

In this paper we describe how the spherical crystallization process by QESD method can be applied to a water-soluble drug, salbutamol sulfate. The type of solvent, antisolvent, and emulsifier and the concentration of emulsifier to be used for the production of spherical particles with a size range 80-500 microm are determined. Furthermore, the solvent/antisolvent ratio and the temperature difference between them (Delta T) are studied. It was observed that, in the case of salbutamol sulfate, the Delta T value has no influence on the formation of spherical particles. A very large metastable zone of salbutamol sulfate in water could explain this phenomenon. Finally, the influence of emulsifier concentration and of maturation time on the size of spherical particles is studied. The results show that these two parameters must be fixed to control the size of the recovered particles.

Determination of apparent binding constants of drugs by capillary electrophoresis using beta-cyclodextrin as ligand and three different linear plotting methods

Capillary electrophoretic estimation of apparent binding constants (Kapp) for naproxen, salbutamol, indomethacine and procaine with beta-cyclodextrin is presented. While with naproxen and indomethacine this approach was straightforward and gave well compatible results by three different linearization plots (double reciprocal, x reciprocal and y reciprocal), with salbutamol a higher value than reported for the electromigration estimation of this magnitude was obtained (a fourfold increase). This difference is ascribed to the fact that the measurements were done in the acid region (while the reported values were obtained at higher pH values). As a matter of fact the values of Kapp, reported in this communication for salbutamol comply better with the value of Kapp (69.3) obtained by the solubility method.

Characterisation of the aggregation behaviour in a salmeterol and fluticasone propionate inhalation aerosol system

The nature of the drug-drug aggregation phenomena between salmeterol xinafoate and fluticasone propionate used in a metered-dose inhaler system has been examined. Interactions between the drugs in the solvents 1,1,2-trichlorotrifloroethane (CFC-113) and 1,1,1,2-tetrafluoroethane (HFA-134a) have been characterised using a focused beam reflectance measurement probe by measuring the average floc size of the drug particles individually and in combination as a function of stirrer rate. The floc composition in the CFC-113 system, where the drug particles cream, was determined by high-performance liquid chromatography analysis. The aggregation behaviour of the individual drugs was shown to depend on the physical and chemical properties of both the drug substance and the media. Larger flocs were observed for salmeterol xinafoate compared with fluticasone propionate, while both drugs formed larger aggregates in HFA-134a compared with in CFC-113. The floc composition studies demonstrated that, in the combined formulation in CFC-113, salmeterol xinafoate and fluticasone propionate aggregate together to form hetero-flocs. The interaction between the two drugs was such that they did not separate on creaming, despite having different densities. The average floc size of the combined drug suspension was also found to depend on the dispersion medium.

Characterization of two polymorphs of salmeterol xinafoate crystallized from supercritical fluids

PURPOSE

To characterize two polymorphs of salmeterol xinafoate (SX-I and SX-II) produced by supercritical fluid crystallization.

METHODS

SX-I and SX-II were crystallized as fine powders using Solution Enhanced Dispersion by Supercritical Fluids (SEDS). The two polymorphs and a reference micronized SX sample (MSX) were characterized using powder X-ray diffractometry (PXRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), aqueous solubility (and dissolution) determination at 5-40 degrees C, BET adsorption analysis, and inverse gas chromatography (IGC).

RESULTS

Compared with SX-I, SX-II exhibited a lower enthalpy of fusion, a higher equilibrium solubility, a higher intrinsic dissolution rate, a lower enthalpy of solution (based on van't Hoff solubility plots), and a different FTIR spectrum (reflecting differences in intermolecular hydrogen bonding). Solubility ratio plot yielded a transition temperature (-99 degrees C) below the melting points of both polymorphs. MSX showed essentially the same crystal form as SX-I (confirmed by PXRD and FTIR), but a distinctly different thermal behaviour. Mild trituration of SX-I afforded a similar DSC profile to MSX while prolonged grinding of SX-I gave rise to an endotherm at -109 degrees C, corresponding to solid-solid transition of SX-I to SX-II. Surface analysis of MSX, SX-I, and SX-II by IGC revealed significant differences in surface free energy in terms of both dispersive (nonpolar) interactions and specific (polar) acid-base properties.

CONCLUSIONS

The SEDS-processed SX-I and SX-II display high polymorphic purity and distinctly different physical and surface properties. The polymorphs are related enantiotropically with SX-I being the thermodynamically stable form at room temperature.

Agonist-induced conformational changes in the G-protein-coupling domain of the beta 2 adrenergic receptor

The majority of extracellular physiologic signaling molecules act by stimulating GTP-binding protein (G-protein)-coupled receptors (GPCRs). To monitor directly the formation of the active state of a prototypical GPCR, we devised a method to site specifically attach fluorescein to an endogenous cysteine (Cys-265) at the cytoplasmic end of transmembrane 6 (TM6) of the beta(2) adrenergic receptor (beta(2)AR), adjacent to the G-protein-coupling domain. We demonstrate that this tag reports agonist-induced conformational changes in the receptor, with agonists causing a decline in the fluorescence intensity of fluorescein-beta(2)AR that is proportional to the biological efficacy of the agonist. We also find that agonists alter the interaction between the fluorescein at Cys-265 and fluorescence-quenching reagents localized to different molecular environments of the receptor. These observations are consistent with a rotation and/or tilting of TM6 on agonist activation. Our studies, when compared with studies of activation in rhodopsin, indicate a general mechanism for GPCR activation; however, a notable difference is the relatively slow kinetics of the conformational changes in the beta(2)AR, which may reflect the different energetics of activation by diffusible ligands.

Evaluation of stereoselective dissolution of racemic salbutamol matrices prepared with commonly used excipients and 1H-NMR study

The purpose of this work was to examine the in vitro enantioselective dissolution of salbutamol from matrix tablets containing various chiral excipients, such as gamma cyclodextrin (gamma-CD), heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD), sulfobutyl-beta-cyclodextrin (SBE-beta-CD), hydroxypropylmethylcellulose (HPMC), and egg albumin. In this study, two types of tablets were prepared; the coated tablet contained the complex of racemic salbutamol and cyclodextrin (gamma-CD, DM-beta-CD, and SBE-beta-CD), and the uncoated tablet was composed of the drug with either HPMC or egg albumin. Subsequently, these formulations were evaluated for enantioselective release. The results revealed that the formulations containing either SBE-beta-CD, HPMC, or egg albumin had no enantioselective release, while the formulation with DM-beta-CD gave slightly different release of the two enantiomers at the end of the dissolution profile. The formulation containing gamma-CD provided significant stereoselectivity throughout the dissolution profile. The release of the eutomer R-salbutamol was higher than that of the distomer S-salbutamol from the gamma-CD tablet. In addition, the enantioselective interaction for the gamma-CD inclusion complex was investigated by 1H-NMR (nuclear magnetic resonance) spectroscopy and gave evidence to support the enantioselectivity obtained on dissolution.

Resolution of racemic albuterol via diastereomeric salts formation with di-p-toluoyl-D-tartaric acid

A convenient method is described for the resolution of racemic Albuterol by selective crystallization of its di-p-toluoyl-D-tartrate salt. The separation resulted in a 38% yield of the (R)-enantiomer. Racemization of the (S)-enantiomer occurs in diluted H2SO4 at 100 degrees C in 80% yield. This racemic mixture was recycled to the diastereomer salt, in order to improve the overall yield. The (R)-Albuterol tartrate salt was decomposed in a sulfuric acid solution, and the (R)-Albuterol was isolated as its sulfate salt with 67% overall yield with 99.5% optical purity.

Functional properties of atypical beta-adrenoceptors on the guinea pig duodenum

In this study, we attempted to further characterize atypical beta-adrenoceptors on the guinea pig duodenum. (-)-Enantiomers of isoprenaline and noradrenaline were more potent than its (+)-enantiomers. The isomeric activity ratios ((+)/(-)) were less than those obtained in the guinea pig atria and trachea. The concentration-response curves to catecholamines ((-)-isoprenaline, (-)-noradrenaline and (-)-adrenaline), to the selective beta(3)-adrenoceptor agonist, BRL37344 ((R*, R*)-(+/-)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid sodium), and to the non-conventional partial beta(3)-adrenoceptor agonist, (+/-)-CGP12177A ((+/-)-[4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazol-2-one] hydrochloride), were resistant to blockade by (+/-)-pindobind, the beta-adrenoceptor alkylating agent. (-)-Noradrenaline and (-)-adrenaline were more potent than dopamine and (-)-phenylephrine, respectively. Selective beta(2)-adrenoceptor agonists possess agonistic activities at atypical beta-adrenoceptors. (+/-)-Propranolol and (+/-)-bupranolol had no agonistic effect, whereas (+/-)-alprenolol, (+/-)-pindolol, (+/-)-nadolol, (+/-)-CGP12177A and (+/-)-carteolol exhibited agonistic activities at atypical beta-adrenoceptors. These results suggest that pharmacological properties of atypical beta-adrenoceptors differ from those of conventional beta(1)- and beta(2)-adrenoceptors on the guinea pig.

Solubility prediction of salmeterol xinafoate in water--dioxane mixtures

The mole fraction solubility of salmeterol xinafoate was determined in various concentrations of dioxane in aqueous binary mixture. Maximum solubility was observed in 90% v/v dioxane and solubility parameter of the solute was estimated from solubility peak equal to 24.99 MPa(0.5). The predicting capability of four different cosolvency models was also evaluated employing a five data point training set. The solubility data at other cosolvent concentrations were predicted using the trained models, with percentage average errors for 28 drug solubility data sets in water-cosolvent mixtures lying between 12.5 and 15.0%. Further predictive model is proposed for accurate solubility predictions based on a minimum number of experiments. The percentage average error where tested was 10.6%.

Single-isomer beta-agonists

A new generation of bronchodilators is being developed for acute asthma management-single-isomer beta-agonists. These drugs consist only of the active bronchodilatory isomer (eutomer); they do not have the inactive and potentially harmful isomer (distomer) that is present in marketed racemic beta-agonists. Clinical studies comparing the effectiveness of (R)-albuterol (levalbuterol) with racemic albuterol established a strong rationale for using single-isomer beta-agonists in place of the racemic mixture: reduced dosages provide equivalent bronchodilatory effects with fewer beta-mediated side effects. Higher dosages achieve superior bronchodilation in episodes of severe asthma and may reduce costs of emergency department treatment.

Quantitative determination of clenbuterol, salbutamol and tulobuterol enantiomers by capillary electrophoresis

Enantiomers of clenbuterol, salbutamol and tulobuterol were directly separated and quantitated from a spiked sample by capillary electrophoresis (CE) using sulfaited beta-cyclodextrin (SCD) as chiral selector and phosphate as running buffer. The SCD and buffer concentration, pH and field strength were the parameters studied to optimize the separation. Optimal separation was obtained using 50 mM of phosphate monobasic at pH = 2.24, 0.25% (w/w) of sulfated cyclodextrin and a field strength of 10 kV, with 20 min total time analysis. Comparison between two different injection modes (hydrodynamic and electrokinetic) was made. In the hydrodynamic mode, repeatability (expressed as relative standard deviation, RSD) was less than 1.2% for migration times for all the analyte peaks and less than 2% for peak area percentages. With respect to reproducibility, RSD was less than 3.8% for migration time and less than 3% for peak area percentages. Calibration curves were set up for two different sample concentration ranges (1 to 10 microg mL(-1) and 160-800 ng mL(-1), of each of the racemates studied). Although the electrokinetic injection mode for an aqueous sample appeared to suffer from some enantiodiscrimination, calibration curves were linear in the range between 1 and 10 ng mL(-1) with regression coefficients ranging from 0.9996 to 0.9952. As in the case of hydrodynamic injection, the method was tested with a spiked sample.

The pharmacokinetics of levosalbutamol: what are the clinical implications?

Salbutamol (albuterol) is a beta2-adrenoceptor agonist used as a bronchodilator for the treatment of asthma and as a uterine relaxant for the suspension of premature labour. Salbutamol has been marketed as a racemic mixture, although beta2-agonist activity resides almost exclusively in the (R)-enantiomer. The enantioselective disposition of salbutamol and the possibility that (S)-salbutamol has adverse effects have led to the development of an enantiomerically pure (R)-salbutamol formulation known as levosalbutamol (levalbuterol). Salbutamol is metabolised almost exclusively by sulphotransferase (SULT) 1A3 to an inactive metabolite. (R)-Salbutamol is metabolised up to 12 times faster than (S)-salbutamol. This leads to relatively higher plasma concentrations of (S)- salbutamol following all routes of administration, but particularly following oral administration because of extensive metabolism by the intestine. Enantiomer concentrations are similar for the first hour following an inhaled dose, reflecting the fact that salbutamol in the lung probably undergoes little metabolism. Subsequently, (S)-salbutamol predominates due to absorption and metabolism of the swallowed portion of the inhaled dose. Following oral or inhaled administration of enantiomerically pure salbutamol, a small amount (6%) is converted to the other enantiomer, probably by acid-catalysed racemisation in the stomach. Tissue binding of salbutamol is not enantioselective and plasma protein binding is relatively low. Both enantiomers are actively excreted into the urine. Compared with healthy individuals, patients with asthma do not have substantially different pharmacokinetics of the salbutamol enantiomers, but they do appear to have less drug delivered to the lung following inhaled administration because of their narrowed airways. Levosalbutamol elicits an equal or slightly larger response than an equivalent dose of the racemic mixture. This is probably due to competitive inhibition between the enantiomers at beta-adrenoceptors. Pharmacokinetic-pharmacodynamic relationships for levosalbutamol show relatively large interindividual variations. Functionally significant genetic polymorphisms have been identified for beta2-adrenoceptors, SULT1A3 and organic action transporters, all of which affect the disposition or action of levosalbutamol. Animal, in vitro and some clinical studies have reported deleterious effects of (S)-salbutamol on smooth muscle contractility or lung function. However, well-designed clinical studies in patients with asthma have failed to find evidence of significant toxicity associated with (S)-salbutamol. The clinical consequences of relatively higher plasma concentrations of (S)-salbutamol following administration of racemate remain unclear, but in the absence of clear evidence of toxicity the clinical superiority of levosalbutamol over racemic salbutamol appears to be small.

Molecular modeling (MM2 and PM3) and experimental (NMR and thermal analysis) studies on the inclusion complex of salbutamol and beta-cyclodextrin

The inclusion complex of salbutamol and beta-cyclodextrin (beta-CD) is studied by computational (MM2 and PM3) and experimental techniques. Molecular modeling calculations predict two different orientations of salbutamol in the beta-CD cavity in vacuo and in aqueous solution. In vacuo calculations show that the introduction of the aromatic ring of salbutamol is preferred to the introduction of the tert-butyl group into the beta-CD cavity. However, in aqueous solution both computational methods predict the introduction of the alkyl chain instead of the aromatic ring in the beta-CD cavity contrary to experimental results published previously. These quantitative predictions were experimentally confirmed here by studying the inclusion complex in solution by NMR. A 1:1 stoichiometry was found by (1)H NMR studies for this complex. A 2D ROESY (rotating-frame Overhauser enhancement spectroscopy) experiment shows that there are no cross-peaks between the aromatic protons of salbutamol and any of the protons of beta-CD. Cross-peaks for the protons of the tert-butyl group and protons inside the cavity of beta-CD demonstrate the full involvement of this group in the complexation process and confirm the orientation of the complex predicted by molecular modeling. The solid-state complex was prepared and its stoichiometry (beta-CD.C(13)H(21)NO(3).8H(2)O) and dissociation process studied by thermogravimetric analysis.

The use of different sugars as fine and coarse carriers for aerosolised salbutamol sulphate

The aim of this study was to investigate the dispersion and deaggregation of a model drug, salbutamol sulphate (SS), using lactose, mannitol or sorbitol as coarse and fine carriers. Binary and tertiary formulations containing micronised salbutamol sulphate (SS) and sieved (63-90 microm) coarse sugar crystals or salbutamol sulphate (SS) with a mixture of coarse and fine sugar particles were prepared. Factorial design was employed to investigate the effects of three variables, i.e. the chemical entity of the coarse sugar carrier, the chemical entity of the fine sugar and the concentration of fine sugar, on the dispersion and deaggregation of salbutamol sulphate after aerosolisation at 60 l/min via a Rotahaler(R) into a twin stage liquid impinger (TSI). The binary formulations containing the different sugar entities produced differences in the fine (<6.4 microm) particle fraction (FPF) of SS in a decreasing order of mannitol >sorbitol >lactose, but failed to produce efficient dispersion of SS since the FPF was <10%. Adding fine sugar particles and increasing their concentration to the binary mixtures generally resulted in an increase in the FPF of salbutamol sulphate. The chemical nature of the fine carriers was found to play a less important role in determining respirable fraction of the drug than the coarse carriers. In conclusion, other sugars such as mannitol or sorbitol, besides lactose, may be employed as coarse and/or fine carriers for incorporation into dry powder aerosol formulations to increase FPF.

Effect of aging on the release of salbutamol sulfate from lipid matrices

The aim of the present work was to evaluate the influence of aging that might condition the release of salbutamol sulfate from oral formulations (lipid matrices) using Gelucire as lipid excipients. Gelucires are essentially characterized by their melting point and their hydrophilic-lipophilic balance. The release profiles of salbutamol sulfate from the capsules elaborated were dependent on the type of Gelucires, fast release, in the case of Gelucire 35/10, a slower release for Gelucire 48/09 and a slow release for Gelucire 46/07. Differential scanning calorimetry was used to study the physical state of drugs in the matrices. Gelucires may exhibit aging effects, whereby a range of physical properties may change upon storage. In the case of Gelucire 35/10, which presents a fast release of salbutamol sulfate, storage produces a decrease in the values of dissolution constant for all capsule sizes. Gelucire 48/09 showed a slower release rate than Gelucire 35/10, and after 1 year of storage, a decrease in the salbutamol dissolution rate for capsule number 3 and 4 was observed. Gelucire 46/07 presented the slowest dissolution rate, but there were not statistically significant differences. These results show that the faster the dissolution rate, and the larger the capsule size, the higher is the influence of storage.

The effects of carrier size and morphology on the dispersion of salbutamol sulphate after aerosolization at different flow rates

We have investigated the interdependence of various factors (particle size, surface smoothness, carrier particle shape, inhalation flow rate) on the deposition of a model drug (salbutamol sulphate) after aerosolization from a model inhaler device (Rotahaler). Different batches of alpha-lactose monohydrate were prepared to have different particle size, particle shape and surface smoothness. Each batch of lactose was then mixed separately with salbutamol sulphate in a ratio of 67.5 : 1 (w/w), under similar conditions. Drug deposition from each formulation was investigated using a 4-stage liquid impinger after aerosolization at 28.3, 60.0 and 96.0 L min(-1) via a Rotahaler. At a flow rate of 28.3 L min(-1), a large portion of drug particles was not emitted from the inhaler, the % emission varying from 29.6% to 66.6% for all formulations investigated. Drug emission tended to increase with particle size of the carrier whilst fine particle fraction, fine particle dose and dispersibility appeared to increase with decreasing particle size but increasing elongation ratio of the carrier particles. Increasing the flow rate to 60.0 L min(-1) was shown to increase drug emission since > 75% total dose was found to be emitted from the inhaler. Again, smaller or more elongated lactose particles resulted in a higher fine particle dose or fine particle fraction of salbutamol sulphate than the coarser carrier, although they produced a similar (analysis of variance P > 0.05) drug emission. Increasing the flow rate to 96.0 L min(-1) did not increase drug emission. Increasing the flow rate resulted in an increase in the fine particle fraction and fine particle dose of salbutamol sulphate from all formulations. The flow rate of the airstream appeared to play the most important role, followed by particle size and elongation ratio of the carrier particles, with the surface smoothness relatively less significant in determining the deposition of salbutamol sulphate from the Rotahaler.

Discrimination of prohibited oral use of salbutamol from authorized inhaled asthma treatment

BACKGROUND

The administration of salbutamol is permitted only by inhalation by the International Olympic Committee (IOC) for the management of asthma and exercise-induced asthma in athletes. The establishment of criteria to distinguish between the (IOC) authorized use (inhaled) and the (IOC) prohibited use (oral) of salbutamol appeared possible using simultaneous evaluation of variables based on the concentration of nonconjugated enantiomers of salbutamol excreted in urine.

METHODS

Urine was collected from asthmatic and nonasthmatic swimmers who had received various preexercise doses of oral (five doses of 4 mg) or inhaled (two doses of 100 microgram) salbutamol. Urine was also obtained from subjects who had received the maximum dosage of inhaled salbutamol advisable for competing athletes to provide protection from exercise-induced asthma and treatment of asthma (1600 microgram in 24 h, 800 microgram being in the last 4 h). All samples were analyzed to determine the total amount of unchanged salbutamol excreted in urine and the ratio between the S: and R: enantiomers.

RESULTS

The discriminant function D = -3.776 + 1.46 x 10(-3) ([S:(+)] + [R:(-)]) + 1.012 ([S:(+)]/[R(-)]) can be used to classify data into two groups, inhaled and oral. The confirmatory criterion suggested (cutoff at D = 1.06, 4 SD from the mean D value of the inhaled distribution) has been verified in different sets of samples showing suspicious concentrations by conventional screening procedures in doping control. An 11.8% false-negative (oral classified as inhaled) rate is assumed with the confirmatory criterion proposed, but virtually no false positives (inhaled classified as oral) are obtained (<1 in 33 000).

CONCLUSIONS

The overall procedure recommended is to screen all samples and to apply the confirmation criterion proposed to samples showing free racemic salbutamol concentrations >500 microgram/L by gas chromatography-mass spectrometry or free + conjugated racemic salbutamol concentrations >1400 microgram/L by ELISA.

Introduction of a single isomer beta agonist

The release of levalbuterol offers the first approved single-isomer beta agonist for oral inhalation. Data from in vitro studies support the concept that S albuterol is not inactive and may have properties antagonistic to bronchodilation. There is some variability in the results of clinical studies with the separate isomers of albuterol, which suggests the need for further study. The introduction of levalbuterol into general clinical use in managing asthma and chronic obstructive disease should begin to offer additional information on the effects of a single isomer beta agonist in comparison to previous racemic mixtures.