Activation/Deactivation Free-Energy Profiles for the β2-Adrenergic Receptor: Ligand Modes of Action

We use enhanced-sampling simulations with an effective collective variable to study the activation of the β2-adrenergic receptor in the presence of ligands with different efficacy. The free-energy profiles are computed for the ligand-free (apo) receptor and binary (apo-receptor + G-protein α-subunit and receptor + ligand) and ternary complexes. The results are not only compatible with available experiments but also allow unprecedented structural insight into the nature of GPCR conformations along the activation pathway and their role in the activation mechanism. In particular, the simulations reveal an unexpected mode of action of partial agonists such as salmeterol and salbutamol that arises already in the binary complex without the G-protein. Specific differences in the polar interactions with residues in TM5, which are required to stabilize an optimal TM6 conformation that facilitates G-protein binding and receptor activation, play a major role in differentiating them from full agonists.

Development of an HPLC-MS/MS Method for Chiral Separation and Quantitation of (R)- and (S)-Salbutamol and Their Sulfoconjugated Metabolites in Urine to Investigate Stereoselective Sulfonation

The aim of this study was to develop and optimize a chiral HPLC-MS/MS method for quantitative analysis of (R)-/(S)-salbutamol and (R)-/(S)-salbutamol-4'-O-sulfate in human urine to allow for bioanalytical quantitation of the targeted analytes and investigations of stereoselectivity in the sulfonation pathway of human phase Ⅱ metabolism. For analytical method development, a systematic screening of columns and mobile phases to develop a separation via enantiomerically selective high performance liquid chromatography was performed. Electrospray ionization settings were optimized via multiple-step screening and a full factorial design-of-experiment. Both approaches were performed matrix-assisted and the predicted values were compared. The full factorial design was superior in terms of prediction power and knowledge generation. Performing a longitudinal excretion study in one healthy volunteer allowed for the calculation of excretion rates for all four targeted analytes. For this proof-of-concept, either racemic salbutamol or enantiopure levosalbutamol was administered perorally or via inhalation, respectively. A strong preference for sulfonation of (R)-salbutamol for inhalation and peroral application was found in in vivo experiments. In previous studies phenol sulfotransferase 1A3 was described to be mainly responsible for salbutamol sulfonation in humans. Thus, in vitro and in silico investigations of the stereoselectivity of sulfotransferase 1A3 complemented the study and confirmed these findings.

Temperature cycling-induced formation of crystalline coatings

The surface of particles is the hotspot of interaction with their environment and is therefore a major target for particle engineering. Particles with tailored coatings are greatly desired for a range of different applications. Amorphous coatings applied via film coating or microencapsulation have frequently been described in the pharmaceutical context and usually result in homogeneous surfaces. In the present study we have been exploring the feasibility of coating core particles with crystalline substances, a matter that has rarely been investigated. The expansion of the range of possible coating materials to include small organic molecules enables completely new product properties to be achieved. We present an approach based on temperature cycles performed in a tubular crystallizer to result in engineered crystalline coatings on excipient core particles. By manipulating the process settings and by the choice of coating substance we are able to tailor surface roughness, topography as well as surface chemistry. Benefits of our approach are demonstrated by using resulting particles as carriers in dry-powder-inhaler formulations. Depending on the resulting surface chemistry and surface roughness, coated carrier particles show varying fitness for delivering the model API salbutamol sulphate to the lung.

Uptake and Effects of the Beta-Adrenergic Agonist Salbutamol in Fish: Supporting Evidence for the Fish Plasma Model

The fish plasma model (FPM) predicts the fish blood plasma concentration of a pharmaceutical from the water concentration to which the fish is exposed and compares it with the human therapeutic plasma concentration (H_ther PC) with the postulate that no adverse toxic effects occur below the H_ther PC. The present study provides several lines of evidence supporting the FPM for the beta-adrenergic agonist salbutamol, a small cationic molecule at ambient pH. Salbutamol exhibited very low acute toxicity to early and adult life stages of fish. Biomass reduction in fish early life stages was the most sensitive apical endpoint, with no-observed-effect concentrations (NOECs) in the low mg/L range after continuous exposure for up to 120 d. Given that predicted and measured environmental concentrations are at least 1000-fold lower, the risk of salbutamol in freshwater is deemed very low. Increase in heart beat rate and decrease in total triglyceride content in fish also occurred at the low mg/L range and resembled effects known from humans. This finding supports the FPM assumption of conserved targets in fish with similar functionality. Plasma concentrations measured in adult and juvenile fish exposed to water concentrations at approximately the NOECs exceeded H_ther PC and even approached plasma concentrations toxic to humans. This result confirms for salbutamol the FPM hypothesis that no adverse (i.e., population-relevant) toxic effects occur in fish below the H_ther PC. Environ Toxicol Chem 2019;38:2509-2519. © 2019 SETAC.

Contrasting photoreactivity of β2-adrenoceptor agonists Salbutamol and Terbutaline in the presence of humic substances

The photodegradation reactions of two typical β2-adrenoceptor agonists, salbutamol (SAL) and terbutaline (TBL), alone, and in the presence of Aldrich humic acid (AHA) or Suwannee River fulvic acid (SRFA) were investigated by steady-state photolysis experiments, laser flash photolysis (LFP), kinetic modeling and quantum calculation. AHA and SRFA (2-20 mgC L^-1) accelerated the phototransformation of both SAL and TBL. For SAL, an inhibiting effect of oxygen on the photodegradation was observed that is fully consistent with the main involvement of excited triplet states of HS (³HS*). On the contrary, oxygen drastically enhanced the photodegradation of TBL showing that ³HS* were negligibly involved in the reaction. The involvement of singlet oxygen was also ruled out because of the low reaction rate constant measured between TBL and singlet oxygen. Quantum calculations were therefore performed to explore whether oxygenated radicals could through addition reactions explain the differences of reactivity of TBL and SAL in oxygen medium. Interestingly, calculations showed that in the presence of oxygen, the addition of phenoxyl on TBL led to the formation of adducts and to the loss of TBL while the same addition reaction on SAL partly regenerated the starting compound and at the end degraded SAL less efficiently. This study is of high relevance to understand the processes involved in SAL and TBL phototransformation and the photoreactivity of HS. Moreover, our findings suggest that TBL might be a promising probe molecule to delineate the role of oxygenated radicals.

Delivered Lung Dose and Aerodynamic Particle Size Distribution of Salbutamol Pressurized Metered Dose Inhaler After Living Under Patients' Realistic Retention Environments

Background: The impact of inhalers' postdispensing, real-life temperature and relative humidity (RH) environments on their delivered dose (DD) and aerodynamic particle size distribution (APSD) is usually overlooked. This work evaluated the salbutamol DD and APSD of Ventolin^® Evohaler^® (V) inhalers already been used and stored by respiratory patients. Methods: Adult patients, prescribed V for ≥3 months before study enrollment, were dispensed both new V to use and portable, handheld electronic temperature and RH data loggers to keep close to the given V before returning them both after 2-3 weeks. Patients' enrollment took place during summer (VS) and winter (VW) seasons. The returned V was then in vitro evaluated using the Next Generation Impactor, and compared with control V (VC) counterparts stored under 21°C and 46% RH. Results: The VS survived in fluctuating habitats of 21.2°C-40.4°C and 16.2%-63.2% RH, which significantly (p < 0.05) decreased the salbutamol DD from 80.4 to 70.5 μg compared with VC. This 12.3% DD reduction was accompanied with a decrease in the fine particle dose from 26.2 to 20.4 μg (p < 0.05), and an increase in the mass median aerodynamic diameter from 2.3 to 2.5 μm (p < 0.05). The VW and VC had equivalent DD and APSD. Conclusion: Patients using V are expected to receive smaller lung doses during the hot summer season compared with intentionally well-kept VC. To have equivalent lung deposition, V users should be advised to retain their inhalers around 20°C with minimal daily environmental fluctuations during summer times.

Residues of Salbutamol and Identification of Its Metabolites in Beef Cattle

Salbutamol, a selective β₂-agonist, endangers the safety of animal products because of its illegal use in food animals. In this work, residues of salbutamol and its metabolites were investigated to select appropriate targets and marker residues for monitoring the illegal use of salbutamol. Ten metabolites of salbutamol were identified from plasma, urine, liver, and kidney samples; of these, six were newly identified. There were significant differences (P < 0.01) between the parent (nonconjugated) and total (conjugated + nonconjugated) salbutamol concentrations in plasma, urine, liver, and kidney tissues. Salbutamol residues in urine were relatively higher than those in plasma and other internal tissues during the dosing period and were rapidly eliminated from plasma, heart, spleen, and kidney tissues during the withdrawal time. Total salbutamol was identified as more preferable than parent salbutamol as a marker residue, and urine and eye tissues were found to be more suitable as targets for preslaughter and postslaughter monitoring of the illegal use of salbutamol in beef cattle.

Chiral liquid chromatography-mass spectrometry (LC-MS/MS) method development for the detection of salbutamol in urine samples

A sequential solid-phase extraction (SPE) method was developed and validated using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) for the detection and quantification of salbutamol enantiomers in porcine urine. Porcine urine samples were hydrolysed with β-glucuronidase/arylsulfatase from Helix pomatia and then subjected to a double solid-phase extraction (SPE) first using the Abs-Elut Nexus SPE and then followed by the Bond Elut Phenylboronic Acid (PBA) SPE. The salbutamol enantiomers were separated using the Astec CHIROBIOTIC™ T HPLC column (3.0mm×100mm; 5μm) maintained at 15°C with a 15min isocratic run at a flow rate of 0.4mL/min. The mobile phase constituted of 5mM ammonium formate in methanol. Salbutamol and salbutamol-tert-butyl-d9 (internal standard, IS) was monitored and quantified with the multiple reaction monitoring (MRM) mode. The method showed good linearity for the range of 0.1-10ng/mL with limit of quantification at 0.3ng/mL. Analysis of the QC samples showed intra- and inter-assay precisions to be less than 5.04%, and recovery ranging from 83.82 to 102.33%.

Drug permeation and cellular interaction of amino acid-coated drug combination powders for pulmonary delivery

The effect of three amino acid coatings (L-leucine, L-valine and L-phenylalanine) on particle integrity, aerosolization properties, cellular interaction, cytocompatibility, and drug permeation properties of drug combination powder particles (beclomethasone dipropionate and salbutamol sulphate) for dry powder inhalation (DPI) was investigated. Particles with crystalline L-leucine coating resulted in intact separated particles, with crystalline L-valine coating in slightly sintered particles and with amorphous L-phenylalanine coating in strongly fused particles. The permeation of beclomethasone dipropionate across a Calu-3 differentiated cell monolayer was increased when compared with its physical mixture. Drug crystal formation was also observed on the Calu-3 cell monolayer. The L-leucine coated particles were further investigated for cytocompatibility in three human pulmonary (Calu-3, A549 and BEAS-2B) and one human macrophage (THP-1) cell lines, where they showed excellent tolerability. The l-leucine coated particles were also examined for their ability to elicit reactive oxygen species in pulmonary BEAS-2B and macrophage THP-1 cell lines. The study showed the influence of the amino acid coatings for particle formation and performance and their feasibility for combination therapy for pulmonary delivery.

Ion activated in situ gel of gellan gum containing salbutamol sulphate for nasal administration

Nasal delivery is the promising approach for rapid onset of action and avoids the first pass metabolism. The main aim of present study was to develop a novel mucoadhesive in situ gel of salbutamol sulphate using gellan gum and hydroxylpropyl methyl cellulose (HPMC) for nasal administration. The formulations were prepared so as to have gelation at physiological ion content after nasal administration. Developed formulations were evaluated for gelation, viscosity, drug content, in vitro mucoadhesion, in vitro drug release study, ex vivo permeation, and histopathology. Formulations showed pH in the range of nasal cavity and optimum viscosity for nasal administration. The mucoadhesive force depends upon concentration of HPMC and drug release was found to be 97.34% in 11h. The histopathology did not detect any damage during ex vivo permeation studies. Hence, in situ gel system of gellan gum may be a promising approach for nasal delivery of salbutamol sulphate for therapeutic improvement.

[Spectroscopic Study of Salbutamol Molecularly Imprinted Polymers]

In order to solve the problem of on-site rapid detection of salbutamol residues in feed and animal products, and develop a new method of fast detection of salbutamol on the basis of the molecular imprinting technology, this article uses the salbutamol (SAL) working as template molecule, methacrylic acid (MAA) working as functional monomer. On this basis, a new type of core-shell type salbutamol molecularly imprinted polymers were prepared with colloidal gold particles as triggering core. Superficial characteristics of the MIPs and the related compounds were investigated by ultraviolet (UV) spectra and infrared (IR) spectra, Raman spectra, Scanning electron microscopy (SEM) respectively. The results indicated that a stable hydrogen bonding complex has been formed between the carboxyl groups of SAL and MA with a matching ratio of 1:1. The complex can be easily eluted by the reagent containing hydrogen bonding. The chemical binding constant K reaches -0.245 x 10⁶ L² · mol⁻². The possible binding sites of the hydrogen bonding was formed between the hydrogen atoms of -COOH in MA and the oxygen atoms of C==O in SAL. IR and Raman spectrum showed that, compared with MA, a significant red shift of -OH absorption peak was manifested in MIPs, which proved that SAL as template molecule occurred a specific bond between MA. Red shift of stretching vibration absorption peak of C==O was also detected in the un-eluted MIPs and obvious energy loss happened, which demonstrated a possible binding sites is SAL intramolecular of C==O atom of oxygen. If the hydrogen atoms of -COOH in MA wanted to generate hydrogen bond. However, the shapes of absorption peak of other functional groups including C==C, C==O, and -OH were very similar both in MIPs and NIPs. Specific cavities were formed after the template molecules in MIPs were removed. It was proved by the adsorption experiment that the specific sites in these cavities highly match with the chemical and space structure of SAL. Besides, colloidal gold type core-shell molecularly imprinted polymers have looser surface, more cavities in the surface compared with ordinary molecularly imprinted polymers, which increased the effective area of adsorption to target molecules. So it have better performance in adsorption. Based on the principle that these cavities can specificly recognize and combine with target molecule in the test sample, and the excellent ability of colloidal gold core-shell molecularly imprinted polymers, the development of novel methods for fast determination of SAL based on the molecular imprinting technology can be expected in the near future.

Poloxamer bioadhesive hydrogel for buccal drug delivery: Cytotoxicity and trans-epithelial permeability evaluations using TR146 human buccal epithelial cell line

A salbutamol sulfate (SS)-Poloxamer bioadhesive hydrogel specially developed for buccal administration was investigated by studying interactions with TR146 human buccal epithelium cells (i.e. cellular toxicity (i) and trans-epithelial SS diffusion (ii)). The assessment of cell viability (MTT, Alamar Blue), membrane integrity (Neutral Red), and apoptosis assay (Hoechst 33342), were performed and associated to Digital Holographic Microscopy analysis. After the treatment of 2h, SS solution induced drastic cellular alterations that were prevented by hydrogels in relation with the concentrations of poloxamer and xanthan gum. The formulation containing P407 19%/P188 1%/Satiaxane 0.1% showed the best tolerance after single and multiple administrations and significantly reduced the trans-epithelial permeability from 5.00±0.29 (×10(3)) (SS solution) to 1.83±0.22 cm/h. Digital Holographic Microscopy images in good agreement with the viability data confirmed the great interest of this direct technique. In conclusion, the proposed hydrogels represent a safe and efficient buccal drug delivery platform.

Production of Highly Charged Pharmaceutical Aerosols Using a New Aerosol Induction Charger

PURPOSE

Properly charged particles can be used for effective lung targeting of pharmaceutical aerosols. The objective of this study was to characterize the performance of a new induction charger that operates with a mesh nebulizer for the production of highly charged submicrometer aerosols to bypass the mouth-throat and deliver clinically relevant doses of medications to the lungs.

METHODS

Variables of interest included combinations of model drug (albuterol sulfate) and charging excipient (NaCl) as well as strength of the charging field (1-5 kV/cm). Aerosol charge and size were measured using a modified electrical low pressure impactor system combined with high performance liquid chromatography.

RESULTS

At the approximate mass median aerodynamic diameter (MMAD) of the aerosol (~0.4 μm), the induction charge on the particles was an order of magnitude above the field and diffusion charge limit. The nebulization rate was 439.3 ± 42.9 μl/min, which with a 0.1% w/v solution delivered 419.5 ± 34.2 μg of medication per minute. A new correlation was developed to predict particle charge produced by the induction charger.

CONCLUSIONS

The combination of the aerosol induction charger and predictive correlations will allow for the practical generation and control of charged submicrometer aerosols for targeting deposition within the lungs.

[Influence of CNTs on Photodegradation of Salbutamol in Water Environment]

The influence of CNTs on the photolysis of organic pollutant was investigated by studying the photodegradation kinetics of SAL under 1000 W Xenon lamp, in the presence of three kinds of CNTs (SCNT, MWNT-COOH, MWNT-OH). In addition, the interaction between CNTs and Fe3" was also investigated. The results showed that the photodegradation of salbutamol followed pseudo-first-order kinetics, which could be inhibited by all three kinds of CNTs through light screening effect. Formation of singlet oxygen was detected during the photolysis, using the molecular probe furfuryl alcohol. All three kinds of CNTs could absorb electrons through competition, i.e., inhibit SAL photodegradation by light screening effect; meanwhile, the CNTs could generate singlet oxygen through photoexcitation to promote the photodegradation reaction. Both mechanisms coexisted, and in most cases, the inhibition effect was dominant. In addition, CNTs could inactivate the photoactive substance Fe3 in the water body by electrostatic adsorption, and affect the photochemical behavior of organic pollutants in natural water body.

Reactivity of β-blockers/agonists with aqueous permanganate. Kinetics and transformation products of salbutamol

The possible oxidation of two β-blockers, atenolol and propranolol, and one β-agonist, salbutamol, with aqueous potassium permanganate (KMnO4) was investigated by liquid chromatography-quadrupole-time-of-flight-mass spectrometry (LC-QTOF-MS). Under strong oxidation conditions (2 mg L(-1) KMnO4, 24 h), only salbutamol did significantly react. In this way, the oxidation kinetics of salbutamol was further investigated at different concentrations of KMnO4, chloride, phosphate and sample pH by means of a full factorial experimental design. Depending on these factors, half-lives were in the range 1-144 min for drug and it was observed that KMnO4 concentration was the most significant factor, resulting in increased reaction rate as it is increased. Moreover, the reaction of salbutamol is also enhanced at basic pH and to a minor extent by the presence of phosphates, being both factors more relevant at low KMnO4 concentrations. The use of an accurate-mass LC-QTOF-MS system permitted the identification of a total of seven transformation products (TPs). The transformation path of the drug begins by the attack of KMnO4 on two double bonds of the aromatic ring of salbutamol via 3 + 2 and 2 + 2 addition reactions, which resulted in the ring opening and that continues with oxidative reactions to finally produce smaller size TPs, ending with tert-butyl-formamide, as the smallest TP identified. Reaction in real samples showed a slower and partial oxidation of the pharmaceutical, due to other competing water organic constituents, but still exceeding 60%. Moreover, the software predicted toxicity of TPs indicates that they are expected not to be more toxic than salbutamol, in contrast to the results obtained for the predicted toxicity of chlorination TPs, excepting predicted developmental toxicity.

Is the cellular uptake of respiratory aerosols delivered from different devices equivalent?

The study focuses on the application of a cell integrated modified Andersen Cascade Impactor (ACI) as an in vitro lung model for the evaluation of aerosols' behaviour of different formulation devices, containing the same active drug, specifically nebuliser, pressurised metered dose inhaler (pMDI) and dry powder inhaler (DPI). Deposition and transport profiles of the three different inhaled salbutamol sulphate (SS) formulations with clinically relevant doses were evaluated using a modified ACI coupled with the air interface Calu-3 bronchial cell model. Reproducible amounts of SS were deposited on Snapwells for the different formulations, with no significant difference in SS deposition found between the standard ACI plate and modified plate. The transport of SS aerosols produced from pMDI formulation had similar transport kinetics to nebulised SS but significantly higher compared to the DPI, which could have led to the differences in clinical outcomes. Furthermore, drug absorption of different inhaled formulation devices of the same aerodynamic fraction was found not to be equivalent due to their physical chemical properties upon aerosolisation. This study has established an in vitro platform for the evaluation of the different inhaled formulations in physiologically relevant pulmonary conditions.

Using gold nanoparticles as probe for detection of salmeterol xinafoate by resonance Rayleigh light scattering

The paper explores the method of determination of salmeterol xinafoate at nanogram level with gold nanoparticles (AuNPs) probe, to measure the intensity of resonance Rayleigh light scattering (RLS) by a common spectrofluorometer. The RLS intensity of salmeterol xinafoate was greatly enhanced by AuNPs, with the maximum scattering peak at 357 nm. The salmeterol xinafoate was determined basing on the binding of salmeterol xinafoate to AuNPs by electrostatic adsorption. Under the optimum conditions, the enhanced RLS intensity was directly proportional to the concentration of salmeterol xinafoate in the range of 0.054-6.038 μg mL(-1) with a good linear relationship (r=0.9928). The limit of detection (LOD) was 9.48 ng mL(-1). The interference tests were performed carefully. With the proposed method, the synthetic samples were analyzed satisfactorily, the recovery and RSD were 102.5-103.0% and 0.67-1.0% respectively.

Molecular insights into the dynamics of pharmacogenetically important N-terminal variants of the human β2-adrenergic receptor

The human β₂-adrenergic receptor (β₂AR), a member of the G-protein coupled receptor (GPCR) family, is expressed in bronchial smooth muscle cells. Upon activation by agonists, β₂AR causes bronchodilation and relief in asthma patients. The N-terminal polymorphism of β₂AR at the 16^th position, Arg16Gly, has warranted a lot of attention since it is linked to variations in response to albuterol (agonist) treatment. Although the β₂AR is one of the well-studied GPCRs, the N-terminus which harbors this mutation, is absent in all available experimental structures. The goal of this work was to study the molecular level differences between the N-terminal variants using structural modeling and atomistic molecular dynamics simulations. Our simulations reveal that the N-terminal region of the Arg variant shows greater dynamics than the Gly variant, leading to differential placement. Further, the position and dynamics of the N-terminal region, further, affects the ligand binding-site accessibility. Interestingly, long-range effects are also seen at the ligand binding site, which is marginally larger in the Gly as compared to the Arg variant resulting in the preferential docking of albuterol to the Gly variant. This study thus reveals key differences between the variants providing a molecular framework towards understanding the variable drug response in asthma patients.

The human β₂-adrenergic receptor (β₂AR) is an important member of the GPCR family and a mutation at the 16^th position, Arg16Gly, is commonly found in the population. This variation in asthma patients is linked to differential (good/bad) response to the drug albuterol, an agonist of the β₂AR. To date, the coordinates of the N-terminal residues harboring the 16^th position mutation have not been resolved. In our study we sought to glean insights into the dynamics of the variants that could address the differential response to albuterol. We used knowledge from class A GPCRs to build the N-terminal region of β₂AR variants in conjunction with the available structure of the inactive receptor. This was followed by atomistic simulations in triplicate totaling to a sampling of 6 µs. We observe that the N-terminal region of the Arg variant is more dynamic than the Gly variant. Amongst the various differences between the variants, we observe long-range effects at the binding site leading to preferential docking of albuterol to the Gly variant. Our work is a first step to unravel the molecular mechanism linking the Arg16Gly variation to the differential response to albuterol in asthma patients.

In vitro studies on the behavior of salmeterol xinafoate and its interaction with calf thymus DNA by multi-spectroscopic techniques

The salmeterol xinafoate (SX) binding to calf thymus DNA in vitro was explored by fluorescence, resonance light scattering (RLS), UV-vis absorption, as well as viscometry, ionic strength effect and DNA melting techniques. It was found that SX could bind to DNA weakly, and the binding constants (Ka) were determined as 8.52×10(3), 8.31×10(3) and 6.14×10(3) L mol(-1) at 18, 28 and 38°C respectively. When bound to DNA, SX showed fluorescence quenching in the fluorescence spectra and hyperchromic effect in the absorption spectra. Stern-Volmer plots revealed that the quenching of fluorescence of SX by DNA was a static quenching. Furthermore, the relative viscosity and melting temperature of DNA solution were hardly influenced by SX, while the fluorescence intensity of SX-DNA was observed to decrease with the increasing ionic strength of system. Also, the binding constant between SX and double stranded DNA (dsDNA) was much weaker than that between SX and single stranded DNA (ssDNA). All these results suggested that the binding mode of SX to DNA should be groove binding. The obtained thermodynamic parameters indicated that electrostatic force might play a predominant role in SX binding to DNA. The quantum yield (φ) of SX was measured as 0.13 using comparative method. Based on the Förster resonance energy transfer theory (FRET), the binding distance (r0) between the acceptor and donor was calculated as 4.10 nm.

In situ cross-linked matrix tablets for sustained salbutamol sulfate release - formulation development by statistical optimization

BACKGROUND

The use of natural polymers in designing of matrix tablets for sustained-release drug delivery systems has received much attention.

OBJECTIVES

The study involves the development and optimization of in situ cross-linked matrix tablets for sustained salbutamol sulfate release.

MATERIAL AND METHODS

In situ cross-linked matrix tablets of salbutamol sulfate were prepared by direct compression and optimized by response surface methodology based on 32 factorial design. The influence on sodium alginate and a calcium salt (calcium carbonate) amounts in salbutamol sulfate matrix tablets on the properties like drug release and hardness of salbutamol sulfate sustained release matrix tablets were analyzed by response surface plots and corresponding contour plots. Drug contents, weight variations, hardness, and in vitro drug release with release kinetic analysis of these newly developed matrix tablets were also investigated.

RESULTS

All these in situ cross-linked salbutamol sulfate matrix tablets showed satisfactory drug contents, weight variations, hardness and prolonged sustained release of salbutamol sulfate over 6 h.

CONCLUSIONS

The developed salbutamol sulfate matrix tablets might be beneficial over the conventional tablets to decrease the dosing frequency and enhanced patient compliance.

Enantioselective disposition of (R/S)-albuterol in skeletal and cardiac muscle

Significant enhancement of skeletal muscle function has been observed with racemic albuterol (salbutamol). There is now general acceptance that the R-albuterol enantiomer elicits the pharmacological response, both in the lungs and extrapulmonary, while S-albuterol is pharmacologically inert. The objective of this study was to investigate the distribution of (R/S)-albuterol enantiomers into skeletal and cardiac muscle. Initially oral dosing was undertaken in neonatal mice administered a maximum tolerable dose of racemic albuterol. An in vivo infusion rat model was employed for the investigation of albuterol uptake into skeletal and cardiac muscle over 4 h. Tissue concentrations were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). From the oral dosing model, mean (±SD) levels of racemic albuterol after 5 days were 915 (±293) ng/mL in plasma, 2574 (±196) ng/g in muscle, and 53 (±6.6) ng/g in brain with enantioselective partitioning (muscle:plasma ratio of 5.7 and 1.7 for R- and S-albuterol, respectively). In the infusion model, enantioselective disposition was observed in skeletal muscle (muscle:plasma ratio of 1.2-1.7 and 0.6-0.7 for R- and S-albuterol, respectively) and in cardiac muscle (4.1 and 0.5, respectively). In conclusion, there is greater partitioning of active (R)-albuterol than inactive (S)-albuterol into both skeletal and cardiac muscle compared to plasma. These findings have relevance for albuterol sports doping, cardiac effects, and therapeutic use in muscle wasting diseases. Furthermore, the greater muscle partitioning of the active R-albuterol, and the availability of pure R-albuterol formulations highlight shortcomings in doping control measures using non-enantioselective assays.

Competitive interactions of ionic surfactants with salbutamol and bovine serum albumin: a molecular spectroscopy study with implications for salbutamol in food analysis

The effect of ionic surfactants, sodium dodecyl sulfate (SDS) and N-cetyl-N,N,N-trimethylammonium bromide (CTAB), on the interaction between β-agonist salbutamol (SAL) and bovine serum albumin (BSA) was investigated with the use of fluorescence spectroscopy (FLS) and chemometrics methods [multivariate curve resolution-alternating least-squares (MCR-ALS) and parallel factor analysis algorithm (PARAFAC)]. It was found that the binding constant of SAL to BSA in the presence of CTAB was much larger than that without this ligand. The ligand/BSA stoichiometry was 4:1, that is, (CTAB)4-BSA, and was 2:1 with the ligand, that is, (SAL)2-BSA. These results were obtained from the concentration profiles extracted by MCR-ALS for all three reactants. Quantitative information on the complex CTAB-BSA-SAL species was obtained with the resolution of the excitation-emission fluorescence three-way data matrices by PARAFAC. This research has implications for the analysis of SAL in food and might be performed in laboratories associated with organizations such as the U.S. Food and Drug Administration (FDA) and the International Olympic Committee (IOC).

Towards a more desirable dry powder inhaler formulation: large spray-dried mannitol microspheres outperform small microspheres

PURPOSE

To investigate, for the first time, the performance of a dry powder inhaler (DPI, Aerolizer(®)) in the case of a model drug (i.e. albuterol sulphate) formulated with spray dried mannitol carrier particles with homogeneous shape and solid-state form but different sizes.

METHODS

Spray dried mannitol (SDM) particles were characterized in terms of size, surface area, morphology, water content, solid-state, density and electrostatic charge by a novel approach. DPI formulations composed of SDM and albuterol sulphate (AS) were prepared and evaluated in terms of drug content homogeneity and in vitro aerosolization performance.

RESULTS

All SDM particles generated similar fine particle fractions of AS. Formulations consisting of larger SDM particles demonstrated better drug content homogeneity, reduced amounts of drug loss and reduced oropharyngeal deposition. Comparing different SDM products demonstrated that SDM powders with relatively poorer flowability, wider size distributions and higher charge density generated DPI formulations with poorer drug content homogeneity and deposited higher amount of drug on the inhaler, mouthpiece adaptor and throat. DPI formulation total desirability increased linearly with the mean diameter of SDM.

CONCLUSION

Particle shape and solid-state form of mannitol could dominate over carrier size, bulk density, flowability and charge in terms of determining the aerosolization behaviour of AS formulated with mannitol carrier, at least within the experimental protocols applied in the present study.

Mixing time effects on the dispersion performance of adhesive mixtures for inhalation

This paper deals with the effects of mixing time on the homogeneity and dispersion performance of adhesive mixtures for inhalation. Interactions between these effects and the carrier size fraction, the type of drug and the inhalation flow rate were studied. Furthermore, it was examined whether or not changes in the dispersion performance as a result of prolonged mixing can be explained with a balance of three processes that occur during mixing, knowing drug redistribution over the lactose carrier; (de-) agglomeration of the drug (and fine lactose) particles; and compression of the drug particles onto the carrier surface. For this purpose, mixtures containing salmeterol xinafoate or fluticasone propionate were mixed for different periods of time with a fine or coarse crystalline lactose carrier in a Turbula mixer. Drug detachment experiments were performed using a classifier based inhaler at different flow rates. Scanning electron microscopy and laser diffraction techniques were used to measure drug distribution and agglomeration, whereas changes in the apparent solubility were measured as a means to monitor the degree of mechanical stress imparted on the drug particles. No clear trend between mixing time and content uniformity was observed. Quantitative and qualitative interactions between the effect of mixing time on drug detachment and the type of drug, the carrier size fraction and the flow rate were measured, which could be explained with the three processes mentioned. Generally, prolonged mixing caused drug detachment to decrease, with the strongest decline occurring in the first 120 minutes of mixing. For the most cohesive drug (salmeterol) and the coarse carrier, agglomerate formation seemed to dominate the overall effect of mixing time at a low inhalation flow rate, causing drug detachment to increase with prolonged mixing. The optimal mixing time will thus depend on the formulation purpose and the choice for other, interacting variables.

Binding characteristics of salbutamol with DNA by spectral methods

Salbutamol interacting with deoxyribonucleic acid (DNA) was examined by fluorescence, UV absorption, viscosity measurements, and DNA melting techniques. The binding constants and binding sites were obtained at different temperatures by fluorescence quenching. The Stern-Volmer plots showed that the quenching of fluorescence of salbutamol by DNA was a static quenching. To probe the binding mode, various analytical methods were performed and the results were as follows: hyperchromic effect was shown in the absorption spectra of salbutamol upon addition of DNA; there was no appreciable increase in melting temperature of DNA when salbutamol was presented in DNA solution; the fluorescence intensity of salbutamol-DNA decrease with the increasing ionic strength; the relative viscosity of DNA did not change in the presence of salbutamol; the binding constant of salbutamol with double strand DNA (dsDNA) was much higher than that of it with single strand DNA (ssDNA). All these results indicated that the binding mode of salbutamol to DNA should be groove binding. The thermodynamic parameters suggested that hydrogen bond or van der Waals force might play an important role in salbutamol binding to DNA. According to the Förster energy transference theory, the binding distance between the acceptor and donor was 3.70 nm.

Formulation and in vitro evaluation of salbutamol sulphate in situ gelling nasal inserts

The aim of this study was to formulate salbutamol sulfate (SS), a model drug, as mucoadhesive in situ gelling inserts having a high potential as nasal drug delivery system bypassing the first-pass metabolism. In situ gelling inserts, each containing 1.4% SS and 2% gel-forming polymer, hydroxypropyl methylcellulose (HPMC), carboxymethylcellulose sodium (CMC Na), sodium alginate (AL), and chitosan (CH) were prepared. The inserts were investigated for their different physicochemical properties. The weight of inserts was 16-27 mg, drug content was 3.9-4.2 mg, thickness ranged between 15 and 28 μm and surface pH was 5-7. Cumulative drug released from the inserts exhibited extended release for more than 10 h following the decreasing order: CH>AL>CMC Na>HPMC. The drug release from CMC Na and AL inserts followed zero-order kinetics while HPMC and CH inserts exhibited non-Fickian diffusion mechanism. The inserts exhibited different water uptake (7-23%) with the smallest values for CH. Differential scanning calorimetry study pointed out possible interaction of SS and oppositely charged anionic polymers (CMC Na and AL). The mucoadhesive in situ gelling inserts exhibited satisfactory mucoadhesive and extended drug release characteristics. The inserts could be used for nasal delivery of SS over about 12 h; bypassing the hepatic first-pass metabolism without potential irritation.

Triggering effect of N-acetylglucosamine on retarded drug release from a lectin-anchored chitosan nanoparticles-in-microparticles system

The aim of this study was to investigate the use of N-acetylglucosamine (NAG) to accelerate drug release from a lectin-modified carrier. A wheat germ agglutinin (WGA)-anchored salmeterol xinafoate (SalX)-loaded nanoparticles-in-microparticles system (NiMS) was prepared with an ionotropic gelation technique combined with a spray drying method. The formulated microparticles were spherical, with diameters ranging mainly from 2 to 8 μm; the drug entrapment efficiency was >70% (w/w), and the loading capacity was approximately 8% (w/w). Drug release from WGA-SalX-NiMS, within the first 4h, was approximately 30% less than that from SalX-NiMS, indicating an effect of lectin-modification to retard drug release from the NiMS. Due to "sugar-lectin" interactions, drug release from WGA-SalX-NiMS was substantially increased after the addition of NAG to the release medium. However, no significant influence of NAG was observed on the drug release profile of SalX-NiMS without WGA anchorage. The characteristics of NAG-WGA interaction may provide valuable insights into the "triggering-effects" of specific sugars on drug release from lectin-anchored carriers. These results suggest that it is possible to control drug release from a lectin-anchored drug delivery system using a specific sugar, and that the designed novel WGA-SalX-NiMS may be a suitable formulation for chronotherapy of asthma.

[High-resolution THz spectra of six biological and pharmaceutical materials]

The temperature dependent vibrational spectra of,three biological and pharmaceutical sets, genistein and biochanin A, clenbuterol hydrochloride and salbutamol, as well as ginseng R2 and R3, in the range of 0.2-4.5 THz (6.6-150.0 cm(-)) are presented over the temperature range from 295 to 77 K Although there are only some minor difference in their molecular structures, the spectra of two samples in every group are quite differences in both absorption band positions and their relative intensities, and display strong linewidth narrowing and frequency blue-shift with cooling. Au 77 K, 13 highly resolved spectral features for biochanin A were obtained and the sensitivity of the experiment allows detection of amounts as small as 1.9 x 10(-5) mol of ginseng R3. Such high-resolution THz fingerprint spectra provide a rapid, nondestructive and reliable method for the identification of these pharmaceutical settings molecules.

Excimer formation in inclusion complexes of β-cyclodextrin with salbutamol, sotalol and atenolol: spectral and molecular modeling studies

The inclusion complexation behavior of salbutamol, sotalol and atenolol drugs with β-cyclodextrin (β-CD) were investigated by UV-visible, fluorometry, time resolved fluorescence, FT-IR, (1)H NMR, SEM and PM3 methods. The above drugs gave a single emission maximum in water where as dual emission in β-CD. In β-CD solutions the shorter wavelength fluorescence intensity was regularly decreased and longer wavelength fluorescence intensity increased. Addition of β-CD to aqueous solutions of drugs resulted into excimer emission. The excimer emission is concluded to be due to a 1:2 inclusion complex between β-CD and drug. Nanosecond time-resolved studies indicated that all drugs exhibited biexponential decay in solvents and triexponential decay in CD. Investigations of thermodynamic and electronic properties confirmed the stability of the inclusion complex.

Suitability of Gelucire 50/13 for controlled release formulation of salbutamol sulphate

Gelucire 50/13 (G50/13) was assessed to develop controlled release formulation of salbutamol sulphate (SBL) a highly water soluble drug by semisolid matrix filling capsule technique. Drug release profiles of SBL release by using G50/13 and its blends with other hydrophilic or hydrophobic materials were investigated. Lipid matrix formulations prepared with increasing amount of polymer showed a substantial decrease in release rate of the drug while increasing drug amount in fixed polymer concentration did not significantly affect the release profile. Polyethylene glycol 6000 caused an increased water uptake resulting in fast erosion of the matrix whereas cetostearyl alcohol and stearic acid caused retardation in drug release. These findings confirm that a considerable amount of Gelucire is required alone or in combination with hydrophobic substances in order to sustain the release profiles of water soluble drugs. More linear profile was obtained by using matrix comprising Gelucire/stearic acid blend in more than 85% that was comparable to standard, Ventolin SR tablet. The test formulation showed a significant decrease at pH 1.0 and the drug release rate increased at high stirring speed. Moreover, short term stability of controlled release test formulation indicated slight increase in dissolution rate at high temperature.

Effect of carrier particle shape on dry powder inhaler performance

The aim of this study was to characterise the aerosolisation properties of salbutamol sulphate (SS) from dry powder inhaler (DPI) formulations containing different carrier products. The difference in the elongation ratio (ER) of the different carriers was highlighted. Different set of carriers, namely commercial mannitol (CM), commercial lactose (CL), cooling crystallised mannitol (CCM), acetone crystallised mannitol (ACM) and ethanol crystallised mannitol (ECM) were used and inspected in terms of size, shape, density, crystal form, flowability, and in vitro aerosolisation performance using Multi Stage Liquid Impinger (MSLI) and Aerolizer inhaler device. Solid-state and morphological characterization showed that CM product was in pure β-form having particles with smaller ER (CM: ER=1.62 ± 0.04) whereas ACM and ECM mannitol particles were in pure α form with higher ER (ACM: ER=4.83 ± 0.18, ECM: ER=5.89 ± 0.19). CCM product crystallised as mixtures of β-form and δ-form and showed the largest variability in terms of particle shape, size, and DPI performance. Linear relationships were established showing that carrier products with higher ER have smaller bulk density (D(b)), smaller tap density (D(t)), higher porosity (P), and poorer flow properties. In vitro aerosolisation assessments showed that the higher the ER of the carrier particles the greater the amounts of SS delivered to lower airway regions indicating enhanced DPI performance. Yet, DPI performance enhancement by increasing carrier ER reached a "limit" as increasing carrier ER from 4.83±0.18 (ACM) to 5.89±0.19 (ECM) did not significantly alter fine particle fraction (FPF) of SS. Also, carrier particles with higher ER were disadvantageous in terms of higher amounts of SS remained in inhaler device (drug loss) and deposited on throat. Linear relationship was established (r(2)=0.87) showing that the higher the carrier ER the lower the drug emission (EM) upon inhalation. Moreover, poorer flowability for carrier products with higher ER is disadvantageous in terms of DPI formulation dose metering and processing on handling scale. In conclusion, despite that using carrier particles with higher ER can considerably increase the amounts of drug delivered to lower airway regions; this enhancement is restricted to certain point. Also, other limitations should be taken into account including higher drug loss and poorer flowability.

Photophysical and photochemical properties of the pharmaceutical compound salbutamol in aqueous solutions

Salbutamol is a potent β(2)-adrenergic receptor agonist widely used in the treatment of bronchial asthma and chronic obstructive pulmonary disease. An increasing number of studies have detected salbutamol in natural water systems worldwide. Studies have shown that sunlight degrades salbutamol resulting in the formation of products; some showing higher toxicity to bacteria Vibrio fischeri than the parent compound. In this contribution, steady-state absorption and emission techniques, high-performance liquid chromatography, and transient absorption spectroscopy are used to investigate the photochemistry of salbutamol in aqueous buffer solutions at controlled pH values. Ground- and excited-state calculations that include solvent effects are performed to guide the interpretation of the experimental results. Salbutamol is sensitive to UVB light absorption in the pH range from 3 to 12, forming products that absorb light at longer wavelengths than the parent compound. Quantum yields of degradation reveal that the deprotonated species is 10-fold more photo-active than the protonated species. In line with this result, the fluorescence quantum yield of the protonated species is more than an order of magnitude higher than that of the deprotonated species. Transient absorption spectroscopy shows that population of the triplet state occurs with a rate constant of 7.1×10(8)s(-1) in the protonated species, while a rate constant of 1.7×10(10)s(-1) is measured for the deprotonated species. While degradation of the deprotonated species is not affected by the presence of molecular oxygen, a twofold increase in the photodegradation yield of the protonated species in air-saturated conditions is observed.

Vibrating-mesh nebulization of liposomes generated using an ethanol-based proliposome technology

This is the first study that evaluates the influence of the compartmental design of the micropump Aeroneb Go nebulizer and the viscosity of a proliposome hydration medium on vibrating-mesh aerosolization of liposomes. Ethanol-based proliposomes comprising soya phosphatidylcholine and cholesterol (1:1 mole ratio) were hydrated by using isotonic NaCl (0.9%) or sucrose (9.25%) solutions to generate liposomes that entrapped approximately 61% of the hydrophilic drug, salbutamol sulphate. Liposomes were aerosolized by the nebulizer to a two-stage impinger. For both formulations, the aerosol mass output was higher than the phospholipid output, indicating some accumulation of large liposomes or liposome aggregate within the nebulizer. Using NaCl (0.9%) solution as the dispersion medium, aerosol droplet size was much smaller and aerosol mass and phospholipid outputs were higher. This was attributed to the lower viscosity of the NaCl solution, resulting in a reduced retention of the aerosols in the "trap" of the nebulizer. For the entrapped salbutamol sulphate, although the "fine particle fraction" was relatively high (57.44%), size reduction of the liposomes during nebulization caused marked losses of the drug originally entrapped. Overall, liposomes generated from proliposomes when using this nebulizer showed high nebulization output and small droplet size. However, further work is required to reduce the losses of the originally entrapped drug from liposomes.

Asthma treatment through the beta receptor: lessons from animal models

Asthma is a significant health problem worldwide with a prevalence that continues to rise and for which there is no cure. Animal models have been used for decades to investigate the cause and cures of asthma, and while they do not always mimic many of the facets of this syndrome, mechanistic animal studies are still nevertheless very useful. Animal studies with beta-agonists suggest much broader and perhaps more important roles for beta-agonists since beta-agonists reduce aspects of inflammation and may affect structural remodeling. Studies using enantiomers of beta-agonists provide a confusing picture of the degree and mechanism of the deleterious effects of racemic mixtures and/or the S-enantiomer or other classes of beta-agonists. Neural mechanisms are implicated. The future holds a promise of even more insight into the mechanisms of the acute and chronic role of the beta-adrenoceptor, asthma therapeutics, in particular, beta-agonists that will lead to a better understanding of the pathogenesis and treatment of asthma.

Design, synthesis and in vitro evaluation of (R)-4-(2-(tert-butylamino)-1-hydroxyethyl)-2-(hydroxymethyl)phenyl hydrogen phenylboronate: a novel salbutamol derivative with high intrinsic efficacy on the β2 adrenoceptor

We tested a set of boron containing arylethanolamine derivatives on the human and guinea pig β(2) adrenoceptor (β(2)AR) 3-D structures by docking methodology. The compound with the highest affinity based on docking analysis, (R)-4-(2-(tert-butylamino)-1-hydroxyethyl)-2-(hydroxymethyl)phenyl hydrogen phenylboronate (boronterol) was synthesized, characterized and tested in guinea pig tracheal rings at basal tone and with histamine-induced contractions. Boronterol was at least eightfold more potent than salbutamol as a smooth muscle relaxant drug (judged by the EC(50) values) and showed a similar maximal relaxant effect as isoproterenol. ICI118,551 showed competitive antagonism on the relaxing effect of boronterol. These results suggest the β(2)AR agonist action of boronterol.

Docking studies on a refined human beta(2) adrenoceptor model yield theoretical affinity values in function with experimental values for R-ligands, but not for S-antagonists

G-protein coupled receptors (GPCR) belong to the largest group of membrane proteins involved in signal transduction. These receptors are implicated in diverse physiological and pathological events. The human beta(2) adrenergic receptor (hbeta(2)AR) is one of the few GPCRs whose 3-D structures are available on the Protein Data Bank. Because there is great interest by drug developers for hbeta(2)AR as a target, it is necessary to study its ligand-recognition process at the atomic level. The hbeta(2)AR can recognize both R/S enantiomeric ligands, R-agonists result in a greater activation than do S-agonists (eutomers and distomers for activation, respectively), according to experimental results. In this work is reported the ligand recognition on a refined hbeta(2)AR-structure of a set of well-known R/S-ligands by means of docking studies. Data obtained in silico were analyzed and compared with those reported in vitro. The theoretical affinity values were reproduced for agonists, but not for antagonist (or inverse agonists). However, theoretical data for R-antagonists are in function to experimental data. The theoretical results confirm the role of amino acids previously reported by mutagenesis studies due to their important roles in drug affinity and stereoselectivity.

Formulations generated from ethanol-based proliposomes for delivery via medical nebulizers

Multilamellar and oligolamellar liposomes were produced from ethanol-based soya phosphatidylcholine proliposome formulations by addition of isotonic sodium chloride or sucrose solutions. The resultant liposomes entrapped up to 62% of available salbutamol sulfate compared with only 1.23% entrapped by conventionally prepared liposomes. Formulations were aerosolized using an air-jet nebulizer (Pari LC Plus) or a vibrating-mesh nebulizer (Aeroneb Pro small mesh, Aeroneb Pro large mesh, or Omron NE U22). All vibrating-mesh nebulizers produced aerosol droplets having larger volume median diameter (VMD) and narrower size distribution than the air-jet nebulizer. The choice of liposome dispersion medium had little effect on the performance of the Pari nebulizer. However, for the Aeroneb Pro small mesh and Omron NE U22, the use of sucrose solution tended to increase droplet VMD, and reduce aerosol mass and phospholipid outputs from the nebulizers. For the Aeroneb Pro large mesh, sucrose solution increased the VMD of nebulized droplets, increased phospholipid output and produced no effect on aerosol mass output. The Omron NE U22 nebulizer produced the highest mass output (approx. 100%) regardless of formulation, and the delivery rates were much higher for the NaCl-dispersed liposomes compared with sucrose-dispersed formulation. Nebulization produced considerable loss of entrapped drug from liposomes and this was accompanied by vesicle size reduction. Drug loss tended to be less for the vibrating-mesh nebulizers than the jet nebulizer. The large aperture size mesh (8μm) Aeroneb Pro nebulizer increased the proportion of entrapped drug delivered to the lower stage of a twin impinger. This study has demonstrated that liposomes generated from proliposome formulations can be aerosolized in small droplets using air-jet or vibrating-mesh nebulizers. In contrast to the jet nebulizer, the performance of the vibrating-mesh nebulizers was greatly dependent on formulation. The high phospholipid output produced by the nebulizers employed suggests that both air-jet and vibrating-mesh nebulization may provide the potential of delivering liposome-entrapped or solubilized hydrophobic drugs to the airways.

Molecular mechanisms for the persistent bronchodilatory effect of the beta 2-adrenoceptor agonist salmeterol

BACKGROUND

Beta(2)-adrenoceptor agonists are effective bronchodilators. In vitro studies demonstrated long-lasting airway smooth muscle relaxation by salmeterol after washout, the quick disappearance of this effect in presence of antagonists and its recovery after antagonist removal. Current explanations invoke salmeterol accumulation in the membrane ('diffusion microkinetic' model) or the existence of salmeterol-binding 'exosites'. An alternative model based on 'rebinding' of a dissociated ligand to the receptor molecules also produces an apparent decrease in the ligand's dissociation rate in the absence of competing ligands. PURPOSE AND APPROACH: Computer-assisted simulations were performed to follow the receptor-occupation by a salmeterol-like ligand and a competing ligand as a function of time. The aptness of the models to describe the above in vitro findings was evaluated.

KEY RESULTS

The 'diffusion microkinetic' model is sufficient to explain a long-lasting beta(2)-adrenoceptor stimulation and reassertion as long as the membrane harbors a high concentration of the agonist. At lower concentration, 'rebinding' and, in second place, 'exosite' binding are likely to become operational.

CONCLUSIONS AND IMPLICATIONS

The 'rebinding' and 'exosite' binding mechanisms take place at a sub-cellular/molecular scale. Pending their demonstration by experiments on appropriate, simple models such as intact cells or membranes thereof, these mechanisms remain hypothetical in the case of salmeterol. Airway smooth muscle contraction could also be governed by additional mechanisms that are particular to this macroscopic approach.

Electrospray encapsulation of hydrophilic and hydrophobic drugs in poly(L-lactic acid) nanoparticles

An electrospray method is developed for preparation of beclomethasone-dipropionate- and salbutamol-sulfate-loaded biodegradable poly(L-lactic acid) nanoparticles. Different set-up parameters for electrospraying are examined on particle size, and preparation conditions are optimized for producing spherical-drug-loaded nanoscale particles by controllable processing parameters. Polylactide (PLA)-drug nanoparticles with average diameters of around 200 nm are achieved in a stable cone-jet mode with a flow rate of 4 microL min(-1), polymer concentration of 1%, and ammonium hydroxide content of 0.05%. Morphology and size of the drug-polymer nanoparticles are analyzed by scanning electron microscopy and transmission electron microscopy. Changes in the crystallinity of the PLA polymer and the model drugs are detected by X-ray powder diffraction, and the absence of molecular interactions are confirmed by thermal analyses. The results indicate clearly that electrospraying is a potential method for producing polymeric nanoparticles and for encapsulating both hydrophilic and hydrophobic drugs efficiently into the nanoparticles.

A comparative study of various microencapsulation techniques: effect of polymer viscosity on microcapsule characteristics

It is a comparative study of salbutamol sulphate-ethylcellulose microcapsules prepared by three different microencapsulation techniques i.e. coacervation thermal change, solvent evaporation and coacervation non-solvent addition by adjusting the ratio of salbutamol sulphate to ethylcellulose. In vitro release profiles of microcapsules were studied using USP XXIV dissolution apparatus-I in 450 ml double distilled water maintained at 37 degrees C at 50 rpm. Scanning electron microscopic results indicated that all microcapsules were aggregated, whitish and irregular in shape with good entrapment efficiency (86.34 to 97.83), production yield (87.91+/-1.34 to 98.33+/-1.37) and flow properties. Initial burst effect was observed in the drug release behavior from all microcapsules. A slight increase in actual drug loading but profound increase in mean diameter of microcapsules was observed with the increase in the viscosity of ethylcellulose. UV and FTIR spectroscopy, x-ray diffractometry and thermal analysis verified the absence of any strong chemical interaction between drugs and polymer. The drug release from all the formulations followed anomalous diffusion mechanism and was best fit to Higuchi's kinetic model. The results suggest coacervation thermal change as an appropriate approach to develop slow-release multi-unit oral dosage form of salbutamol sulphate suggesting at least twice administration in every 24 hours.

Ru(III)-catalyzed oxidation of pyridoxine and albuterol in pharmaceuticals

Ru(III) complexes with coordinated amide were synthesized and characterized by elemental, IR, mass, electronic, ESR spectral analysis, magnetic and conductance measurements and octahedral structures have been proposed. These complexes were used as catalysts for the oxidation of pyridoxine and albuterol in pharmaceuticals in presence of hydrogen peroxide. The role of co-oxidant and the effect of reaction time on the yields of oxidation products which were spectrophotometrically determined by condensing them with sulfanilic acid in acid medium were investigated. Structures of the oxidation products were established with the help of IR and NMR spectral analysis.

Albuterol metered dose inhaler performance under hyperbaric pressures

The weight change per actuation and aerosol particle size and number delivered by albuterol metered dose inhalers (MDIs) were measured in a multiplace hyperbaric chamber at pressures ranging from one atmosphere absolute (1 ATA, 0 feet of seawater, fsw, 101 kPa) to three ATA (66 fsw, 304 kPa). Weight change per actuation by CFC (chlorofluorocarbon) and long canister HFA (hydrofluoroalkane) powered MDIs was 13 +/- 1% and 12 +/- 1% less, respectively, at 3 ATA compared to 1 ATA. However, weight change per actuation by short canister HFA MDIs was not significantly changed with pressure. The geometric mean diameters of nano particles from the CFC and short canister HFA MDIs decreased from 50 nm at 0 fsw to 32 nm at 66 fsw whereas the long canister HFA aerosol diameters were not affected. The numbers of nanometer size particles delivered at 66 fsw were only 4-7% of those delivered at 0 fsw for the CFC and long canister HFA MDIs whereas for the short canister MDIs it was 26%. We conclude that the weight change per actuation of albuterol and the sizes and numbers of aerosol particles emitted from albuterol MDIs actuated in a hyperbaric environment vary by canister type.

Chemical and physical compatibility of levalbuterol inhalation solution concentrate mixed with budesonide, ipratropium bromide, cromolyn sodium, or acetylcysteine sodium

BACKGROUND

Medications are frequently combined in the nebulizer cup, so it is important to determine their chemical and physical compatibility.

OBJECTIVE

To determine the chemical and physical compatibility of levalbuterol with ipratropium bromide, cromolyn sodium, acetylcysteine sodium, and budesonide.

METHODS

We mixed one dose of levalbuterol inhalation solution concentrate (1.25 mg/0.5 mL) with one dose of ipratropium bromide (0.5 mg/2.5 mL), cromolyn sodium (20 mg/2 mL), acetylcysteine sodium (1,000 mg/5 mL), or budesonide (0.5 mg/2 mL). Immediately after mixing the 2 drugs (time zero [T(0)]), and again after 30 min at room temperature (T(30)), we visually inspected the admixtures, measured their pH, and conducted high-pressure liquid chromatography (HPLC).

RESULTS

There was no evidence of physical incompatibility with these drugs combinations. With all the admixtures, both drugs were chemically stable for at least 30-min. Admixture pH had not changed significantly at T(30). Drug recovery was 93.2-102.6% of the initial or control values.

CONCLUSIONS

The 2-drug admixtures we studied were compatible for at least 30 min at room temperature.

Detection and assessment of co-association in inhalable drug particles using aerosol time-of-flight mass spectrometry

Aerosol Time-of-Flight Mass Spectrometry (AToFMS) was used to examine co-association between two inhaled drugs, fluticasone propionate (FP) and salmeterol xinofoate (SX), in fine aerosolised particles emitted from Seretide(R)/Advair(R) inhaled combination products. Principal Component Analysis (PCA) was used to identify fragmentation patterns indicative of either pure or co-associated particles (particles containing both drugs). A third component of the particles emitted from dry powder inhalers (DPIs), lactose, gave only a very weak mass spectral signal and no interpretable data was acquired for this compound; however, it was not found to interfere with the detection of the two drug substances. High levels of co-association were found in the emitted doses from both pressurised metered dose inhaler (pMDI) and dry powder inhaler (DPI) products.

Influence of Impactor Operating Flow Rate on Particle Size Distribution of Four Jet Nebulizers

When a nebulizer is evaluated by the Andersen Cascade Impactor (ACI), the flow rate is generally maintained at 28.3 L/min, as recommended by the manufacturer. However, the nebulizer flow rate that a patient inhales is only around 18 L/min. Because the drive flow of a nebulizer is approximately 6-8 L/min, the nebulized drug is mixed with outside air when delivered. Evaluating impactor performance at the 28.3 L/min flow rate is less than ideal because an additional 10 L/min of outside air is mixed with the drug, thereby affecting the drug size distribution and dose before inhalation and deposition in the human lung. In this study we operated the ACI at an 18.0 L/min flow rate to test whether the effect of the changing ambient humidity was being exaggerated by the 28.3 L/min flow rate. The study was carried out at three different relative humidity levels and two different impactor flow rates with four commercially available nebulizers. The mass median aerodynamic diameter (MMAD) and the geometric standard deviation (GSD) of the droplets were found to increase when the impactor was operated at a flow rate of 18 L/min compared to that of 28.3 L/min. The higher MMAD and GSD could cause the patient to inhale less of the drug than expected if the nebulizer was evaluated by the ACI at the operating flow rate of 28.3 L/min.

Quantifying the Degree of Disorder in Micronized Salbutamol Sulfate Using Moisture Sorption Analysis

Salbutamol sulfate is often micronized for use in dry powder inhalers. Therefore, it is of high interest to quantify the amorphous amount. It was investigated whether moisture sorption is able to measure the amorphous content of salbutamol sulfate. Different mixtures of amorphous and crystalline salbutamol sulfate were analyzed by moisture sorption. The amorphous material was obtained by spray drying. The measurement results were used to plot a calibration curve, which was used to quantify the amorphous amount in micronized salbutamol sulfate.

The Effect of Relative Humidity on Electrostatic Charge Decay of Drugs and Excipient Used in Dry Powder Inhaler Formulation

Electrostatic forces arising from charge accumulation on drug and excipient powders cause agglomeration and adhesion of particles to solid surfaces and problems during the manufacture and use of many pharmaceutical dosage forms, including dry powder inhalers (DPIs). The ability of materials to dissipate the acquired charge is therefore important and the aim of this work was to investigate the charge decay of salbutamol sulfate, ipratropium bromide monohydrate and alpha-lactose monohydrate. Differences in tri-phasic charge decay rates of the three materials in the order ipratropium bromide > lactose > salbutamol sulfate were demonstrated after corona charging and all materials showed an increased decay rate as the relative humidity was increased up to 86%. Preformulation knowledge of charge accumulation and decay in such materials will contribute to formulation, manufacture and performance of pharmaceutical dosage forms in general, and in particular DPIs.

The Use of Organic Vapor Sorption to Determine Low Levels of Amorphous Content in Processed Pharmaceutical Powders

Organic dynamic vapor sorption (organic-DVS) was used to characterize amorphous content in known amorphous-crystalline mixtures of lactose and salbutamol sulfate. N-octane was chosen as an apolar probe and measurements were carried out by exposing mixtures of each sample to partial pressures 0-90% p/p(0). A linear relationship between amorphous content and n-octane partial pressure was observed for both lactose and salbutamol sulfate with R(2) values of 0.992 and 0.999, respectively. In addition, the influence of sequential mechanical processing in a ball mill on the amorphous content in crystalline lactose was investigated. Cumulative milling times resulted in an exponential increase in amorphous content (using the linear relationship obtained for lactose), with a maximum amorphous content of 14% being induced after 60 min milling. In comparison, analysis of the 60 min mill time samples after exposure to 85% relative humidity suggested 0.00% amorphous content.

Combination particles containing salmeterol xinafoate and fluticasone propionate: Formulation and aerodynamic assessment

A precipitation process is used to produce combined particles consisting of two antiasthmatic drugs: salmeterol xinafoate and fluticasone propionate. To control the crystallisation of these particles, a micromixer is used to mix solvent and antisolvent flow. To produce particles in the respirable range, crystal growth inhibitors are added to the antisolvent flow. The obtained suspension is spray-dried afterwards to get a dry powder which can be further processed into inhalation drug products. It is found that a combination of polysorbate 80 and hydroxypropylmethyl cellulose (HPMC) represents the best excipient combination. It is supposed that the smaller molecule polysorbate rapidly stabilises the particle surface and with this inhibits crystal growth, whereas HPMC is observed to produce spherical particles during the spray-drying process acting as lubricant and dispersion-modifier. The processed particles show a needlelike habit and, therefore, tend to form aggregates. When dispersed from an inhaler device, they are only moderately disaggregated. The deposition of the single drugs salmeterol xinafoate and fluticasone propionate on the stages of the NGI shows a very uniform distribution, indicating that both drugs are evenly dispensed, with an FPF of about 22% for the combined particles which corresponds to the deposition of the marketed product.