Albuterol Enantiomers Research Articles

858 Cytokine, chemokine, and nitric oxide (NO) release in stimulated small airway epithelial cells (SAEC) treated with β2-agonist enantiomers of albuterol

858 Cytokine, chemokine, and nitric oxide (NO) release in stimulated small airway epithelial cells (SAEC) treated with β2-agonist enantiomers of albuterol

Pharmacokinetic and Pharmacodynamic Characteristics and Safety of Inhaled Albuterol Enantiomers in Healthy Volunteers

The pharmacokinetics and pharmacodynamics of inhaled albuterol given as single or multiple doses of racemate (RS-) or single enantiomers (R-, S-) were determined. In an open-label, three-way crossover, parallel-dose study, 1.25 and 5 mg of (R)- and (S)-albuterol and 2.5 and 10 mg of (RS)-albuterol were given via nebulization to 15 healthy volunteers. The pharmacokinetic parameters of each enantiomer were determined by noncompartmental and model-fitting analyses. Both (R)- and (S)-albuterol showed rapid absorption and biexponential decline, with half-lives (t1/2) averaging 4 and 6 hours, respectively. There were no differences in pharmacokinetics of (R)-albuterol when administered as (R)- or (RS)-albuterol at the 5-mg dose with equivalent relative bioavailability as seen from maximum concentration (Cmax) and area under the concentration-time curve (AUC). The same was true for (S)-albuterol at the 1.25-mg and 5-mg doses. The data from 5-mg doses were considered to be more reliable due to assay sensitivity limitations, and indicated equivalent absorption and disposition of the individual enantiomers. There was no evidence of in vivo racemization, and (R)-albuterol did not interconvert to (S)-albuterol. Plasma potassium, plasma glucose, heart rate, and QTc interval were used in linear and Emax models to assess responses relating to (R)-albuterol concentrations. The Emax for potassium change was 1.32 meq/L, with an EC50 of 0.59 and 0.94 ng/mL after administration of (R)- and (RS)-albuterol, respectively. The slopes and intercepts for glucose and heart rate changes were similar after administration of (R)- and (RS)-albuterol. No concentration-effect relationships were evident for QTc interval or for (S)-albuterol. The extrapulmonary responses of (R)-albuterol and adverse effects were similar for single R-enantiomer or the racemic mixture.

Effects of enantiomers of beta 2-agonists on ACh release and smooth muscle contraction in the trachea.

The beta 2-agonists currently used as bronchodilators are racemic mixtures of R- and S-enantiomers. In the present study, we examined the effects of enantiomers of the beta 2-agonists albuterol and formoterol on acetylcholine (ACh) release from equine trachealis parasympathetic nerves. ACh release was evoked by electrical field stimulation (20 V, 0.5 ms, 0.5 Hz) and measured by high-performance liquid chromatography coupled with electrochemical detection. We also tested the effects of enantiomers of albuterol and formoterol on equine tracheal smooth muscle (TSM) contraction in response to exogenous ACh. R- and RS-albuterol (10(-8) to 10(-5) M) and RR- and RR/SS-formoterol (10(-8) to 10(-5) M) augmented ACh release in a concentration-dependent manner. Beginning at 10(-6) M, SS-formoterol significantly increased ACh release, and at 10(-5) M, release increased by 71.9 +/- 8.7% over baseline. This effect was only observed, however, when the prejunctional muscarinic autoinhibitory effect of ACh was prevented with atropine. Both the RR- and SS-formoterol-induced increases in ACh release were abolished by the beta 2-antagonist ICI-118551 (3 x 10(-7) M). The effect of S-albuterol on ACh release was variable, and the mean increase induced by 10(-5) M was 30.8 +/- 16.1% in the presence of atropine. In the muscle tension study, R- and RS-albuterol and RR- and RR/SS-formoterol (10(-8) to 10(-5) M) but not the S-enantiomers inhibited TSM contraction. Even though R-enantiomers augment ACh release, they potently inhibit TSM contraction. Because racemic beta 2-agonists are bronchodilators on acute administration, the postjunctional spasmolytic effects of R-enantiomers predominate over the spasmogenic effect evoked via increased ACh release. The S-enantiomers, in contrast, do not inhibit TSM contraction and therefore would not contribute to the observed bronchodilation of the racemate. The S-enantiomers do prejunctionally facilitate ACh release when prejunctional muscarinic autoreceptors are dysfunctional, suggesting a potentially deleterious effect.

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.

A High Performance Liquid Chromatographic Method for the Determination of Albuterol Enantiomers in Human Serum Using Solid Phase Extraction and a Sumichiral-OA Chiral Stationary Phase

Abstract A chiral high performance liquid chromatographic method was developed for the simultaneous assay of S(+) and R(−) albuterol in human serum. The assay utilizes solid-phase extraction on a silica column as a sample clean-up step. The chiral separation was accomplished under isocratic conditions using a Sumichiral OA 4700 column and a mobile phase consisting of 350:410:40:2 v/v/v/v hexane/methylene chloride/absolute methanol/trifluoroacetic acid at a flow rate of 1.0 mL/min. The enantiomers were measured using fluorescence detection set at 228 nm excitation and an emission filter of >280nm. Racemic atenolol was used as internal standard. Drug to internal standard peak height ratios were linear over a 2–20 ng/mL range for each enantiomer. The limit of detection of each analyte was 2.0 ng/mL (S/N = 3). The lowest quantifiable level of each enantiomer was 3 ng/mL.

A high performance liquid chromatographic method for the determination of albuterol enantiomers in human serum using solid phase extraction and chemical derivatization.

A high performance liquid chromatographic method was developed for the simultaneous assay of R(-)- and S(+)-albuterol in human serum. The assay involves solid phase extraction as a sample clean-up step and derivatization of racemic albuterol to its diastereomeric thioureas with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl isothiocyanate. Chromatographic separation was accomplished under isocratic conditions using an octadecylsilane column and a mobile phase consisting of 29:71 acetonitrile:distilled water containing 0.1% triethylamine, pH 4.0 (adjusted with concentrated phosphoric acid) at a flow rate of 0.8 mL/min. The diastereomers were detected using a fluorescence detector set at 223 nm excitation and no emission filter. Racemic bamethane was used as internal standard. Drug to internal standard peak-height ratios were linear over a 2-20 ng/mL range for each enantiomer. The limit of detection of each analyte was 1.0 ng/mL (S/N = 3).