Effect of the amphoteric properties of salbutamol on its release rate through a polypropylene control membrane

The permeation of salbutamol from aqueous vehicles with different pH values through the Celgard 2500 polypropylene membrane was studied, the goal being to assess the effect of the amphoteric properties of the drug on its release by the membrane. Permeation rates were generally low, which was related to the fact that purely aqueous vehicles were not imbibed into the pores of the membrane and therefore permeation took place through the amorphous polypropylene domains. Permeability coefficients were not proportional to the fraction of uncharged drug at different bulk pH values, indicating that either a pH gradient between the bulk and the membrane surface exists and/or charged drug species can permeate the hydrophobic membrane. Calculated hypothetical pH values of the membrane surface, assuming permeation of the uncharged drug only, failed to provide a consistent explanation of the experimental permeabilities. Permeability coefficients of the different ionization forms of the drug assuming no pH gradient were calculated from a system of linear equations, each one of them corresponding to a specific bulk pH. These were for the anionic and the cationic species one to two orders of magnitude smaller than for the combined uncharged and zwitterionic species. It is possible that both, a pH difference between bulk and membrane surface and permeation of ionized molecules were simultaneously responsible for the observed permeation rates.

Dry powder inhalers: the influence of device resistance and powder formulation on drug and lactose deposition in vitro

It is a principal in the formulation of a dry powder aerosol that the device should enable a high fine particle fraction (FPF) of drug to be delivered to the lung whilst any carrier, such as lactose, should remain in the upper airways. Both the device and the dry powder formulation itself contribute to the resultant FPF and few studies have considered the deposition of lactose carrier. It was the purpose of this study to determine the effect of the resistance of the device and the influence of powder formulation on the deposition of drug and carrier. Measurement of the pressure drop across the devices investigated in this study showed that the two types of Inhalator Ingelheim had the highest resistance, whilst lower pressure drops were found across the Diskhaler, Cyclohaler and Accuhaler devices. The lowest pressure drops were measured across the Rotahaler and Spinhaler devices. Employing Rotacaps 400 capsules as the formulated salbutamol product, the FPF of drug was greater from the high resistance devices, being in the order Inhalators Ingelheim>Cyclohaler>Rotahaler=Spinhaler. However, the Diskhaler, employing its own developed formulation, produced the highest FPF, approximately twice that from the Accuhaler. There was no statistical difference between the FPF of salbutamol (approximately 20% nominal dose) from the Rotacaps formulation when aerosolised using high resistance devices (Inhalators Ingelheim) operated at 30 l min-1, a medium resistance device (Cyclohaler) operated at 60 l min-1 and low resistance devices (Spinhaler and Rotahaler) operated at a flow-rate of 90 l min-1. The Ventolin Diskhaler using its own formulation operated at 60 l min-1 gave a FPF of 40.33%, but the FPF obtained was sensitive to flow, being only 25.65% of the nominal dose at 30 l min-1. Whereas no lactose was found in the FPF from the Accuhaler operated at 60 l min-1, 100, 400 and 3500 microg were obtained from the Diskhaler, Rotacaps and micronised lactose formulation, respectively, when operated at the same flow-rate. An in-house formulation comprising salbutamol sulphate blended with micronised lactose in a weight ratio of 1:67.5 and aerosolised from a Cyclohaler produced a similar FPF to the Diskhaler at 60 l min-1. When air flow was reduced to 30 l min-1, the FPF from the in-house formulation was reduced considerably less than that from the Diskhaler formulation.

Measurement of electrostatic charge decay in pharmaceutical powders and polymer materials used in dry powder inhaler devices

The electrostatic charge generated on drug/excipient particles during the formulation, manufacture, and use of pharmaceutical dry powder inhaler (DPI) devices may significantly affect the performance of such devices. An experimental investigation has been undertaken of charge accumulation and decay on compacts of selected powders (lactose and salbutamol sulfate) and a device material (polyvinyl chloride, PVC) used during the formulation, manufacture, and use of DPIs. Significant differences in charge acquisition and decay for the three materials have been demonstrated after charging using a corona electrode. PVC acquired the highest charge, which decayed rapidly in 30 min toward the value prior to exposure to corona. Lactose and salbutamol acquired similar charge values, which decayed to zero after 30 min for lactose, whereas salbutamol retained a significant charge after 120 min. The significant differences in charging propensity among drug, excipient, and device materials may have relevance in DPI formulation, manufacture, and use.

Identification of a key amino acid of the beta2-adrenergic receptor for high affinity binding of salmeterol

Transmembrane domains (TMDs) I, II, and VII of the beta2-adrenergic receptor (beta2AR) were replaced, individually or in combination, with the corresponding regions of the beta1AR, and vice versa. The beta2-selective binding of salmeterol was not affected by the exchange of TMD I between the beta1- and beta2ARs. The affinity of salmeterol was slightly decreased (32-fold) by replacement of TMD II of the beta2AR with the homologous region of the beta1AR; the affinity was strongly decreased (1870-fold) for the beta2AR with TMD VII of the beta1AR. The affinity of salmeterol was partially restored by the introduction of TMD VII, but not TMD II, of the beta2AR into the beta1AR. By analyzing alanine-substituted mutants, we found that Tyr308 in TMD VII was mainly responsible for the high affinity binding of salmeterol. Two salmeterol derivatives with the ether oxygen at different positions in the side chain showed 33- and 64-fold decreased affinities for the wild-type beta2AR, and a derivative with no ether oxygen showed 147-fold decreased affinity for the wild-type beta2AR. These results indicate that Tyr308 in TMD VII is the major amino acid conferring the beta2-selective binding of salmeterol to the beta2AR and that the position of the ether oxygen in the side chain is also important for beta2-selective binding. A three-dimensional model of the salmeterol-beta2AR complex shows that the phenyl group of Tyr308 interacts with methylene groups near the protonated amine of salmeterol and the ether oxygen interacts with Tyr316.

Determination of the enantiomers of albuterol in human and canine plasma by enantioselective high-performance liquid chromatography on a teicoplanin-based chiral stationary phase

A sensitive enantioselective high-performance chromatographic (HPLC) method was developed validated to determine low levels of (-)-R and (+)-S-albuterol in plasma. Baseline resolution was achieved by using a teicoplanin-based chiral stationary phase with a polar organic mobile phase consisting of methanol/ acetonitrile/glacial acetic acid/diethylamine, 40:60:0.3:0.2, (v/v/v/v) and a flow-rate of 1.0 ml/min. Enantioselectivity (alpha) equaled 1.18 and resolution (RS) equaled 1.8. By using fluorescence detection maximized at 230 and 310 nm for excitation and emission, respectively, concentrations of each enantiomer could be measured down to 125 pg/ml from a 1-ml plasma sample. Initially, the method was applied to plasma samples from a small single-dose inhalation study of racemic albuterol in a human volunteer and, later, to in vivo samples from a canine inhalation study of the single enantiomer, (-)-R-albuterol. Results from the canine study showed that no chiral inversion of (-)-R-albuterol occurs in the dog.

Thermodynamic analysis of moisture sorption isotherms

This article illustrates how thermodynamic functions can be calculated from moisture sorption isotherms for water-solid systems. The materials evaluated include the drugs albuterol sulfate and indomethacin, the carbohydrates sucrose, raffinose, and trehalose, and the polymers poly(vinyl pyrrolidone) and microcrystalline cellulose. The results demonstrated that significant positive and negative deviations from ideality occurred for water and solid components, respectively, producing higher free energy materials than for the ideal mixtures. The calculations quantitatively discriminated major differences in thermodynamic activity and free energy for all of the solid phases studied, arising from the uniqueness in chemical interactions. This approach to analyzing moisture sorption data is invaluable in advancing our understanding of the physical chemistry of water-solid systems.

Physical characteristics and release behavior of salbutamol sulfate beads prepared with different ionic polysaccharides

Salbutamol sulfate beads were prepared using anionic and cationic polysaccharides, Gelrite and chitosan, respectively. Alginate beads were also prepared for comparison. The mean diameter, porosity, and drug content of the beads were determined. The beads were examined by scanning electron microscopy (SEM), DSC, and x-ray diffraction. The drug release from the beads was studied in 0.1 N HCl (pH 1.2), distilled water, and phosphate buffer (pH 7.4). The physical examination of the beads indicated the presence of drug crystals with no interaction between the drug and polymers. The drug release was dependent on the ionic properties of the polymers and the pH of the release media. In acidic pH, chitosan beads showed a rapid drug release, whereas a sustained drug release was obtained from Gelrite beads. In contrast, the drug release in phosphate buffer was rapid from Gelrite, and chitosan showed a sustained drug release. The results of drug release from Gelrite were comparable to that from alginate beads. Gelrite is recommended as an anionic polysaccharide for sustained-release preparations.

Iontophoretic transdermal delivery of salbutamol: methyl-orange ion-pair

The influence of pulsed current duty cycle, addition of electrically neutral species and pH on iontophoretic transdermal delivery of an organic ion-pair salbutamol:methyl orange through excised rabbit abdominal skin is described. It was compared with salbutamol sulphate and salbutamol:sulphate ion-pair. It was found that there exists an optimum duty cycle range (1:3-1:4) at which iontophoretic flux of the ion-pair was at a maximum because of partition-electric current synchronization. Addition of mannitol decreases the flux of the ion-pair showing the important role of electroosmosis in ion-pair transport. The extremes of pH decrease the flux rates.

The effect of ionic strength on liposome-buffer and 1-octanol-buffer distribution coefficients

The distribution of salmeterol and proxicromil between unilamellar vesicles of dioleoylphosphatidylcholine (DOPC) and aqueous buffer at pH 7.4 has been studied, using an ultrafiltration method, as a function of compound concentration, DOPC concentration, and buffer ionic strength. The binding of these ionized lipophilic compounds to neutral DOPC vesicles induces a surface charge, which causes the observed membrane distribution coefficient D(mem)obs to vary significantly with bound compound to DOPC ratio and with ionic strength. This variability is shown to be well-described with use of the Gouy-Chapman theory of the ionic double layer and is contrasted with the ideal behavior shown by the neutral compound clofibrate. Increasing ionic strength is also shown to increase the observed 1-octanol-buffer distribution coefficients D(o/w)obs of proxicromil but through a very different mechanism involving the extraction of ion pairs. This study highlights the experimental difficulty in determining concentration-independent liposome distribution coefficients of ionized lipophilic compounds and describes when deviations will be significant and how observed values may be corrected for such effects. The general effect of ionic strength on membrane-buffer distribution and 1-octanol-buffer distribution is discussed with particular reference to the very different propensity for ion pair formation shown by the two systems, and the most suitable experimental conditions that should be used with each system.

[Osmolarity of solutions used in nebulization]

Inhaled medications are widely used in patients suffering from bronchial diseases. Beside their pharmacological properties, nebulised solutions have physico-chemical characteristics that can alter bronchial reactivity. Non-isotonic solutions can induce a bronchial hyperresponsiveness and/or a severe bronchonconstriction. Nevertheless, multiple drugs are used for nebulisation despite their unknown osmolarity. The aim of this study was to measure the tonicity of drug solutions commonly used for nebulisation in patients suffering from bronchial disease. Drug solutions were prepared either according to manufacturer recommendations or by diluting the stock in 5 ml of NaCl (0.9%) or H2CO3 (0.14%). Although bronchodilatator solutions (i.e. salbutamol, terbulatine, ipratropium bromide) were nearly isotonic, some drugs prepared for nebulisation had either a very high (e.g. mesna, netilmicine) or a very low (e.g. gomenol, sodium cromoglycate) tonicity. These values may be responsible for bronchoconstriction. Some hypertonic solutions, prepared with drugs such as acetylcytein or netilmycin, are not commercialised for nebulisation but are commonly used for aerosol therapy. In addition, solutions initially isotonic could become significantly hypertonic towards the end of nebulisation. Taken together, these results suggest that non-isotonic solutions should be used with caution specially in patients with bronchial hyperresponsiveness, even when aerosol therapy is prescribed for upper airways.

Sympathomimetic enantiomers and asthma

Airways of asthma patients can become hyperresponsive to airway spasmogens following regular use of isoprenaline or beta 2-selective sympathomimetics. Hyper-reactivity that results from acute exposure of animals to these drugs is pre-empted by vagal section (a procedure which does not influence spasmolytic efficacy of sympathomimetics), is not diminished by antagonism of beta 2-adrenoceptors and is not associated with loss of responsivity of beta 2-adrenoceptors in the airways. Since activation, modulation, or blockade of beta 2-adrenoceptors does not determine this form of hyperreactivity, the possibility that distomers may induce hyperreactivity must be considered. Ocular and vascular responses to distomers of sympathomimetics have long been recognised and, more recently, comparable observations have been made for the airways. Thus, reactivity of guinea-pig airways to spasmogens was increased following exposure to S-isoprenaline, S-salbutamol, or S-terbutaline and exposure to S-isoprenaline or S-salbutamol can intensify symptoms in asthmatics. Regular exposure to the racemate, especially during or following an allergic reaction, predisposes to expression of hyper-reactivity, which is nullified, acutely, by the eutomer. These observations imply that biological effects of sympathomimetic distomers may contribute to morbidity and mortality in asthma patients.

Effects of the enantiomers of R,S-salbutamol on incompletely fused tetanic contractions of slow- and fast-twitch skeletal muscles of the guinea-pig

1. The effects of racemic R,S-salbutamol, and its individual enantiomers have been studied on incompletely fused (sub-tetanic) contractile responses of fast- and slow-contracting isolated skeletal muscles of the guinea-pig. 2. R,S-salbutamol (2-4 microM) decreased the peak force of sub-tetani in the slow-contracting soleus muscle and increased the peak force of sub-tetani in the fast-contracting peroneus longus muscle. It also increased the force of the first twitch of sub-tetani in both muscles. The decrease in the peak force of sub-tetani in the soleus muscle was due to defusion of the individual twitches caused by a shortening of their time course. 3. The effects of 4 microM of the racemate on both fast- and slow-contracting muscles were mimicked by 2 microM R-salbutamol (levalbuterol). However, 2 microM S-salbutamol was devoid of activity in both muscles. 4. We concluded that all the effects of R,S-salbutamol on guinea-pig skeletal muscles are due to the activity of the R-enantiomer. Thus there is a common enantiomeric profile for the skeletal muscle and bronchorelaxant activity of the compound.

Drug form selection in albuterol-containing metered-dose inhaler formulations and its impact on chemical and physical stability

New albuterol-containing metered-dose inhaler (MDI) formulations were under development to replace chlorofluorocarbon (CFC) propellants with more environmentally friendly hydrofluoroalkane (HFA) propellants. To achieve good chemical and physical stability of MDI formulations with HFA propellants, different drug forms were evaluated in model formulations (drug, oleic acid, and one of the following: P12/P11, P12/ethanol, P12, P134a/ethanol, P134a). The effects of drug form (base versus sulfate), propellant type (P12 versus P134a), and cosolvent type (P11 or ethanol versus none) on the chemical and physical stability were examined. The chemical stability of the formulations was determined by monitoring the percent drug remaining in the formulations using HPLC. The physical stability of the formulations was followed by visually assessing the suspension appearance, and by determining the mass median diameter (MMD) of the suspended particles using laser diffraction analysis. The drug form has a great impact on the chemical and physical stability of the formulations. The sulfate formulations were chemically stable up to 12 months when stored at 30 degrees C and 40 degrees C/85% relative humidity (RH). Poor chemical stability was observed for the base formulations, except for ethanol-free formulations (P12/P11, P12, and P134a) at 30 degrees C and a P134a formulation at 40 degrees C/85% RH. The chemical instability of albuterol base formulations at 30 degrees C correlates with its solubility. The presence of a cosolvent greatly improved the dispersion characteristics of both sulfate and base formulations. The sulfate formulations in the presence of a cosolvent (P12/P11, P12/ethanol, and P134a/ethanol) showed good physical stability when stored for up to 12 months at 30 degrees C and 40 degrees C/85% RH. The physical stability of the base formulations was not acceptable due to crystal growth/agglomeration in all formulations, except for the P12/P11 formulation. The physical instability of both sulfate and base formulations not only correlates with the drug solubility, but also with particle agglomeration. In conclusion, good chemical and physical stability of albuterol-containing suspension formulations can be achieved with the appropriate choice of drug form and formulation constituents.

Effect of single doses of S-salbutamol, R-salbutamol, racemic salbutamol, and placebo on the airway response to methacholine

BACKGROUND

Commercially available salbutamol is a racemic mixture consisting of equal amounts of the two enantiomers, R-salbutamol and S-salbutamol, felt to be active and inert, respectively.

METHODS

A double blind, randomised, four way, crossover study was performed in 12 well controlled asthmatic subjects (forced expiratory volume in one second (FEV1) > 70% predicted, no beta 2 agonists for > or = 4 weeks). Subjects were studied on four days at intervals of 48 hours to seven days. FEV1 was assessed before and both FEV1 and methacholine PC20 were measured 20 and 180 minutes after a single dose of nebulised racemic salbutamol 2.5 mg, R-salbutamol 1.25 mg, S-salbutamol 1.25 mg, and placebo.

RESULTS

Equivalent bronchodilation was seen for both R-salbutamol and racemic salbutamol (mean (SE) 12.4 (3.1)% and 12.0 (3.0)%, respectively, at 20 minutes and 5.9 (2.9)% and 5.2 (2.2)% at 180 minutes). The increase in FEV1 of 5.2 (0.9)% at 20 minutes and the decline in FEV1 of 2.9 (2.1)% at 180 minutes after S-salbutamol were not significantly different from the placebo response. Compared with placebo the methacholine PC20 after R-salbutamol and racemic salbutamol improved by 3.3 (95% CI 2.5 to 4.1) and 3.4 (95% CI 2.6 to 4.2) doubling doses, respectively, at 20 minutes and 1.2 (95% CI 0.6 to 1.8) and 1.0 (95% CI 0.2 to 1.8) doubling doses at 180 minutes. S-salbutamol resulted in an improvement of 0.9 (95% CI 0.3 to 1.5) doubling doses at 20 minutes and no change at 180 minutes. Restlessness (n = 11) and increased pulse were seen 20 minutes after racemic and R-salbutamol but not S-salbutamol or placebo, and not at 180 minutes. There were no other adverse events.

CONCLUSION

A single dose of 1.25 mg nebulised R-salbutamol produced equivalent bronchoprotection, bronchodilation, restlessness, and tachycardia as did 2.5 mg of racemic salbutamol. S-salbutamol 1.25 mg had a weak bronchoprotective effect; this could be because of a small amount of contamination with R-salbutamol or because S-salbutamol is an intrinsically weak beta 2 receptor stimulant.

Effect of drug load and plate coating on the particle size distribution of a commercial albuterol metered dose inhaler (MDI) determined using the Andersen and Marple-Miller cascade impactors

PURPOSE

The purpose of this study is to investigate the effect of drug load, the coating of impactor stages, and the design of cascade impactors on albuterol MDIs particle size distribution measurements. The results of the investigation will be used to explain the "loading effect" recently reported.

METHODS

Particle size distribution parameters of a commercial albuterol MDI were measured using both Andersen (AI) and Marple-Miller (MMI) Cascade Impactors, where plates were either left uncoated or coated with silicone or glycerin. A previously validated HPLC-EC method was used for the assay of albuterol collected by the impactor and in single spray content determinations.

RESULTS

Coating impactor collection plates had an impact on measured MMAD and GSD values for single puff measurements but very little or no effect for the multi puff measurements. Due to particle bounce, the percent of albuterol fine particles deposited in the filter and impactor finer stages (< 1.10 microns in AI and < 1.25 microns in MMI) in uncoated single puff experiments was much higher in comparison to either coated single puff or multi-puff (coated and uncoated) measurements.

CONCLUSIONS

Evaluation of drug load and plate coating are necessary to determine whether observed particle size distributions are representative of the generated aerosol or are the result of particle bounce and reentrainment. In order to minimize particle bounce, especially for single puff determinations, it may be useful to apply a thin layer of a sticky coating agent to the surfaces of impactor plates.

Pharmacokinetics and extrapulmonary beta 2 adrenoceptor activity of nebulised racemic salbutamol and its R and S isomers in healthy volunteers

BACKGROUND

Racemic salbutamol remains one of the most commonly used bronchodilators in the treatment of reversible airways obstruction. Data from animal and human studies suggest that the S-isomer, whilst contributing no bronchodilator activity, may induce increased bronchial hyperreactivity and may explain the adverse effects of regular racemic salbutamol on asthmatic disease control. The purpose of this study was to evaluate the dose-response effects of racemic (+/-) salbutamol and its R(-) and S(+) isomers in terms of pharmacokinetics and pharmacodynamics at extrapulmonary beta 2 adrenoceptors when given by the inhaled route to healthy volunteers.

METHODS

Twelve healthy volunteers of mean age 20.6 years were studied in a double blind, placebo controlled, crossover design comparing cumulative doubling doses of nebulised R-salbutamol (R) and S-salbutamol (S) isomers (200 micrograms/400 micrograms/800 micrograms/1600 micrograms/3200 micrograms) and racemic salbutamol (RS) (400 micrograms/800 micrograms/1600 micrograms/3200 micrograms/6400 micrograms). Doses were administered at 20 minute intervals (t0/t20/t40/t60/t80) and measurements were made of extrapulmonary beta 2 responses as an increase in finger tremor and heart rate and fall in plasma potassium at baseline and each dose level (t0/t20/t40/t60/t80/t100). Plasma levels of salbutamol were measured at 15 minutes after each dose with a further sample at 30 minutes after the last dose (t110).

RESULTS

Pharmacodynamics showed dose related beta 2 responses for R-salbutamol and RS-salbutamol but not for the S isomer, and a plateau in response was not reached within the administered dose range. No differences in responses were found between R-salbutamol and RS-salbutamol when compared on a 1:2 microgram basis. The effects of the S isomer were indistinguishable from those of placebo. For all beta 2 responses there were differences between R-salbutamol and S-salbutamol (for t100 response as change from placebo); tremor (log units): R 0.74 vs S 0.03 (95% CI 0.39 to 1.03); fall in potassium (mmol/ 1): R 0.35 vs S -0.02 (95% CI 0.03 to 0.71). Pharmacokinetics showed consistently higher levels for S-salbutamol than R-salbutamol at 15 minutes after each dose, with R-salbutamol already being cleared and S-salbutamol reaching peak levels at 30 minutes after the last dose (at t110). There were higher plasma levels of R-salbutamol and S-salbutamol following administration of the respective isomers alone compared with their levels after administration of the racemate, suggesting an influence of each isomer on the clearance of the opposite isomer when given as a racemate.

CONCLUSIONS

The S-isomer of salbutamol has no detectable activity at extrapulmonary beta 2 adrenoceptors whilst exhibiting higher plasma levels than the R-isomer, in keeping with greater clearance of R-salbutamol than S-salbutamol. Inhalation of R-salbutamol and RS-salbutamol produced dose-related beta 2 responses which were equivalent when compared on a 1:2 microgram basis, despite higher plasma levels of R-salbutamol after administration of the R isomer than after administration of the racemate. Further dose ranging studies are required at steady state to evaluate the pharmacokinetics of R- and S-salbutamol and their relative effects on bronchial hyperreactivity when given on a regular basis to asthmatic subjects.

The choice of jet nebulizer, nebulizing flow, and addition of albuterol affects the output of tobramycin aerosols

The use of inhaled antibiotics in the treatment of cystic fibrosis has become widespread despite controversy in the literature as to the appropriate dosing regimen and its effectiveness. This study compared two tobramycin (T) preparations (one with and one without the addition of albuterol) using two different jet nebulizers in order to determine if drug output would be affected. Using calibrated flows from a dry compressed gas source of 6 and 8 L/min as well as a specific compressor (Pulmo-Aide), the Hudson 1720 nebulizer was compared with the newer disposable Hudson 1730. The albuterol preparation used in this study was the Ventolin (albuterol) Respirator Solution (VRS). The nebulizers were charged with (1) 2 mL T (80 mg/2 mL) with 0.5 mL VRS (5 mg/mL) and normal saline solution to make the total nebulizer charge of 3 or 4 mL, or (2) 2 mL T and either 1 or 2 mL normal saline solution. A laser diffraction analyzer (Malvern 2600) was used to determine the aerosol particle size distribution. From the distribution, the respirable fraction, which is the fraction of aerosol that could enter and remain in the lungs, was calculated. For all solutions and each particular flow, the Hudson 1730 had a larger respirable fraction of T. The addition of VRS lowered the surface tension of the solution in the nebulizer and resulted in a greater output of T. This effect was most apparent for the 3-mL volume fills of the Hudson 1720. The greatest differences were between the 3-mL nebulizer charges of T using the Hudson 1720 driven by a flow of 6 L/min, which produced 8 mg of T in the respirable fraction, compared with 35 mg produced by the Hudson 1730 driven by a flow of 8 L/min. These results suggest that different nebulizers, different nebulizer solutions, and different techniques of nebulization may result in very different amounts of T aerosol output in the respirable fraction.

The development of a cascade impactor simulator based on adhesion force measurements to aid the development of dry powder inhalations

Adhesion and friction forces are the main physical factors determining the re-suspension of a micronized drug from carrier particles during inhalation. Hence, it appears useful to link adhesion and friction force measurements to the in vitro testing of dry powder inhalations, namely the assessment of the mass median aerodynamic diameter (MMAD) using an eight-stage Andersen cascade impactor. Interactive mixtures of micronized Salmeterol Xinafoate adhered to irrespirable lactose monohydrate carrier particles were used as model dosage forms. The adhesion force between the drug and carrier particles was assessed using a centrifuge technique, and the MMAD was determined under standardized working conditions using the Andersen-Cascade impactor (Mark II). A cascade impactor simulator (CIS), which is a computer program containing a re-suspension model to assess the amount of drug detached from the carrier particles during inhalation, was developed and validated using the experimental data. It could be shown, that the CIS provided a good estimate of the loss of drug due to adhesion to the carrier particles and the loss of drug on the cascade impactor walls. Small deviations between the theoretical and experimental mass median aerodynamic particle diameters however were found. These deviations were shown to be mainly due to the experimental error introduced by the cascade impactor, and that the error due to the experimental adhesion measurements is negligibly small. Hence, the CIS developed could be a useful tool in early development stages of dry powder inhalations to predict the in vitro aerodynamic performance of drug particles.

Gas chromatographic-mass spectrometric determination of beta 2-agonists in postmortem blood: application in forensic medicine

A solid-phase extraction procedure is described for the simultaneous determination of terbutaline, salbutamol and fenoterol in human postmortem whole blood, using gas chromatography-electron impact mass spectrometry. The limit of quantitation in 1 ml of blood was 1 ng/ml for all analytes. A linear response was observed over the concentration ranges tested, covering both low and high concentrations of each drug. The recoveries in postmortem blood were: terbutaline, 88%; salbutamol, 86%; fenoterol, 92%; orciprenaline (internal standard), 86%. Coefficients of variations for both intra-assay precision and inter-assay reproducibility ranged between 2.2 and 13.0% for all analytes. This method is sensitive and selective, and has been applied successfully to over 60 postmortem blood specimens.

Design and applications of a self-aligning liquid junction-electrospray interface for capillary electrophoresis-mass spectrometry

A simple self-aligning liquid junction-electrospray interface for coupling a capillary electrophoresis (CE) system to an atmospheric pressure ionization (API) mass spectrometer (CE-MS) was developed. In contrast to previous liquid junction interfaces, the self-aligning liquid junction interface simplifies the precise alignment of the CE capillary and the sprayer needle and uses a positive make-up flow. Several capillary CE-MS applications were run using both the self-aligning liquid junction interface and the widely used sheath flow interface for comparison purposes. The electrospray stability of the self-aligning liquid junction interface is consistently better even when non-volatile electrolyte solutions are used. At first, some band broadening was obtained with the self-aligning liquid junction interface. Experiments with different CE buffer systems suggested that this band broadening was caused by the materials used in constructing the interface. By using a more inert material for the sprayer needle, the self-aligning liquid junction exhibits excellent electrophoretic resolution, comparable sensitivity, and higher signal-to-noise ratios when run under the same conditions as the sheath flow interface.

Sustained activation of a G protein-coupled receptor via "anchored" agonist binding. Molecular localization of the salmeterol exosite within the 2-adrenergic receptor

An inherent therapeutic limitation of many G protein-coupled receptor agonists is a short duration of action due to rapid dissociation from receptors. Salmeterol is a modified beta-adrenergic receptor (betaAR) agonist that has a long duration of action at the beta2AR (but not the beta1AR) both in vitro and in vivo and that is persistent despite extensive washout of the agonist. It has been proposed that salmeterol binds not only to the active site of the beta2AR (localized to receptor transmembrane spanning domains (TMDs) 3 and 5) but also to another site (termed the "exosite") that anchors it to the receptor and provides for repetitive active-site binding events. To identify the location of this exosite, we used site-directed mutagenesis to replace beta2AR amino acids 149-173 (within TMD4) with beta1AR sequence. The resulting constructs were then expressed in COS-7 cells for radioligand binding studies. Using this approach, when this domain was replaced with the analogous beta1AR sequence, the ability of salmeterol to persist at the receptor under washout conditions was reduced by 67%. The results from more selective mutants (S-(149-166), S-(164-173), and S-(149-158)) indicated that a limited 10-amino acid region (beta2AR residues 149-158), localized at the interface of the cytoplasm and the transmembrane domain, contains a critical determinant for exosite binding. Whereas CHW cells stably expressing wild-type beta2AR displayed persistent salmeterol-promoted cAMP accumulation despite agonist washout, substitution of beta2AR residues 149-158 with beta1AR sequence resulted in a 56% attenuation of salmeterol-promoted cAMP accumulation under identical washout conditions. A reverse chimera was also studied, which consisted of a substitution of beta2AR residues 152-156 into the beta1AR. This substitution was found to confer exosite binding to the beta1AR. None of these mutations decreased the affinity of salmeterol for the receptor at the active site as assessed in competition binding studies. Anchored binding to this motif thus represents a novel mechanism by which agonists like salmeterol can repetitively activate receptors. Conceivably, with other G protein-coupled receptors that have similar motifs, anchored ligands can be designed to provide for long durations of action by this mechanism.

Electrostatic charge on a plastic spacer device influences the delivery of salbutamol

The aim of this study was to determine whether electrostatic charge on a plastic spacer decreases the delivery of salbutamol from a pressurized metered-dose inhaler (pMDI) and, if so, to find an optimal and practical treatment to remove the charge. Ten single actuations from a salbutamol pMDI were drawn through different Volumatic spacers at a constant flow of 60 L.min-1. The efficacies of different methods of removing charge were tested, including detergent coating of the spacers. A multistage liquid impinger was used to determine the particle size distribution of the output of the pMDI through the Volumatic spacers. The electrostatic charge on the inner surface of the spacers was measured both quantitatively with an electrometer, and qualitatively by the attraction of a thin strip of cellulose membrane to the wall of the spacer. Each experiment was repeated four times. Ionic detergent coating of the spacers removed the charge for at least 24 h. This resulted in an increase of 55-70% in small particle (< 6.8 microns) delivery compared to delivery from new spacers with high charge. We have demonstrated that electrostatic charge plays a major role in the delivery of salbutamol through plastic spacers. Adequate treatment with ionic detergent removes the charge and improves drug delivery.

Permeation behavior of salbutamol sulfate through hydrophilic and hydrophobic membranes embedded by thermo-responsive cholesteryl oleyl carbonate

PURPOSE

To investigate the suitability of hydrophilic or hydrophobic membranes for use as potential thermo-responsive drug delivery system.

METHODS

Liquid crystal was embedded in membranes using vacuum filtration method to control the penetration rate of salbutamol sulfate. Cholesteryl oleyl carbonate (COC) with smectic-cholesteric phase transition temperature near 18 degrees C was used as a model liquid crystal.

RESULTS

It indicates only hydrophilic salbutamol sulfate can penetrate through the hydrophilic membranes embedded with or without COC, in which the permeation is mainly governed by the adsorption of COC. However, the hydrophilic drug do not pass through the hydrophobic membranes even if not embedded with COC. The void volume of the membrane also influences the penetration of salbutamol sulfate. The higher thermo-response efficacy of the COC-embedded membranes can be explained not only by less permeability through matrix part of the membrane but also by higher thermal motion of the COC molecules due to above the phase transition temperature.

CONCLUSIONS

A COC-embedded membrane with rate-controlled and thermo-responsive function is easily prepared by vacuum filtration method. High reversibly thermo-responsive function can be achieved by choosing membrane and COC concentration properly.