Analysis of albuterol in human plasma based on immunoaffinity chromatographic clean-up combined with high-performance liquid chromatography with fluorimetric detection

Modulation of the Ca(2+) permeability of human endplate acetylcholine receptor-channel

In slow-channel congenital myasthenic syndrome, point mutations of the endplate acetylcholine receptor (AChR) prolong channel openings, leading to excessive Ca(2+) entry with ensuing endplate degeneration and myasthenic symptoms. The Ca(2+) permeability of the human endplate AChR-channel is quite high, and is further increased by two slow-channel mutations in its ɛ subunit, worsening the pathological cascade. To gain further support to the hypothesis that the ɛ subunit plays a crucial role in controlling Ca(2+) permeability of endplate AChR-channel, in this work we measured the fractional Ca(2+) current (P(f), i.e., the percentage of the total current carried by Ca(2+) ions) of a panel of AChR carrying slow-channel mutations in the α, β and ɛ subunits detected in patients (α(N217K), α(S226Y), α(C418W), β(V266A), β(V266M), ɛ(I257F), ɛ(V265A) and ɛ(L269F)). We confirm that only mutations in the ɛ subunit altered Ca(2+) permeability of AChR-channels, with ɛ(L269F) increasing P(f) (10% vs. 7% of wild type AChR) and ɛ(I257F) decreasing it (to 4.6%). We also found that, for ɛ(L269F)-AChR, the Ca(2+) permeability and ACh-induced cell death can be normalized by clinically relevant concentrations of salbutamol or verapamil, providing the first evidence that the Ca(2+) permeability of AChR-channels can be modulated and this treatment may provide protection against excitotoxic insults.

Validation of high-performance liquid chromatography assay for quantification of formoterol in urine samples after inhalation using UV detection technique

A novel high-performance liquid chromatography (HPLC) assay for the estimation of formoterol in urine samples was developed and validated. A solid phase extraction (SPE) using Oasis HLB was optimised to isolate formoterol from a urine matrix followed by HPLC with UV detection. This extraction procedure concentrated the final analyte forty times so that UV detection can be used to determine even a low concentration of formoterol in urine samples. The urinary assay was performed in accordance with FDA and ICH regulations for the validation of bioanalytical samples. The samples were injected onto a C18 Spherisorb (250 mm x 4.6 mm x 5 microm) analytical column maintained at 30 degrees C. The mobile phase consisted of 5 mM of potassium dihydrogen orthophosphate buffer (adjusted to pH 3 with ortho phosphoric acid):acetonitrile (ACN) (70:30, v/v), and the formoterol peak was detected at wavelength 214 nm. The extraction recovery of formoterol from the urine sample was >95%. The calibration curve was linear (r2=0.99) over formoterol concentrations ranging from 1.5 to 25 ng/mL (n=6). The method had an accuracy of >92% and intra and inter-day precision CV% of <3.9% and <2.2%, respectively, at three different concentrations low, medium and high (10, 15, 20 ng/mL). The limit of quantification (LOQ) for formoterol was found to be 1.50 ng/mL. The accuracy and precision at the LOQ level were 95% and %CV <3.7% (n=10), respectively. The method reported is simple, reliable, precise, and accurate and has the capacity to be used for determination of formoterol in urine samples.

Beta2-agonist extraction procedures for chromatographic analysis

Normally, different procedures were necessary to prepare sample matrices for chromatographic determination of beta2-agonists. The present review includes sampling, pre-treatment and extraction/purification for urine, plasma, liver, meat, feeds, hair and milk powder, as previous steps for chromatographic analysis of beta2-agonists. Six methodologies were especially revised for extraction/purification namely, liquid-liquid extraction, solid-phase extraction (SPE), matrix solid-phase dispersion, immunoaffinity chromatography, dialysis and supercritical fluid extraction. SPE was discussed in detail and five mechanisms were described: adsorption, apolar, polar, ion-exchange and mixed phase. A brief conclusion in this field was also outlined.

Affinity Chromatography: A Review of Clinical Applications

Affinity chromatography is a type of liquid chromatography that makes use of biological-like interactions for the separation and specific analysis of sample components. This review describes the basic principles of affinity chromatography and examines its use in the testing of clinical samples, with an emphasis on HPLC-based methods. Some traditional applications of this approach include the use of boronate, lectin, protein A or protein G, and immunoaffinity supports for the direct quantification of solutes. Newer techniques that use antibody-based columns for on- or off-line sample extraction are examined in detail, as are methods that use affinity chromatography in combination with other analytical methods, such as reversed-phase liquid chromatography, gas chromatography, and capillary electrophoresis. Indirect analyte detection methods are also described in which immunoaffinity chromatography is used to perform flow-based immunoassays. Other applications that are reviewed include affinity-based chiral separations and the use of affinity chromatography for the study of drug or hormone interactions with binding proteins. Some areas of possible future developments are then considered, such as tandem affinity methods and the use of synthetic dyes, immobilized metal ions, molecular imprints, or aptamers as affinity ligands for clinical analytes.

Analytical methodology for enantiomers of salbutamol in human urine for application in doping control

Liquid chromatographic procedure with fluorimetric detection for chiral separation and quantification of salbutamol enantiomers in urine samples has been developed. The extraction of free salbutamol from urine has been considered using liquid-liquid and solid-phase procedures. The effect of pH, salting-out effect and organic solvent has been studied in liquid-liquid extraction from aqueous and urine samples. For solid-phase extraction, different mechanisms (polar, non-polar, cation-exchange and interactions with a polymeric phase) have been tested and the effect of the urine matrix on the extraction recoveries has been considered. Bond-Elut Certify extraction cartridges provided the best specificity and good recoveries for salbutamol in urine. The sample is acidified, applied to the preconditioned cartridges and, after a washing step, salbutamol enantiomers are eluted with a mixture of chloroform and 2-propanol (80:20, v/v) containing 2% ammonia. Atenolol is used as external standard. Enantioselective separation is accomplished with a Chirex 3022 stationary phase (urea type silica-bonded chiral phase) using a mobile phase containing hexane-dichloromethane-methanol-trifluoroacetic acid (250:218:31:1, v/v) and fluorimetric detection with excitation and emission wavelengths set at 230 and 309 nm, respectively. The method proposed is rapid, selective and sensitive, and seems to be useful to differentiate between an authorized and a prohibited use of the drug in doping control.

Survey of recent advances in analytical applications of immunoaffinity chromatography

Methods that use immunoaffinity chromatography (IAC) for sample preparation or detection are becoming increasingly popular as tools in the analysis of biological and nonbiological compounds. This paper presents an overview of immunoaffinity chromatography and examines some recent developments of this technique in analytical applications. The emphasis is placed on HPLC-based IAC methods or those that combine IAC with other instrumental techniques; however, novel approaches that employ low-performance IAC columns for chemical quantitation are also considered. Particular applications that are examined include (1) the use of IAC in the direct detection of analytes, (2) the extraction of samples by IAC prior to on- or off-line detection by other methods, (3) the use of IAC in chromatographic-based immunoassays, and (4) the development of postcolumn reactors based on IAC for the detection of analytes as they elute from other types of chromatographic columns. The advantages and limitations for each approach are considered. In addition, a summary is provided of reports in the literature that have used IAC for these various formats.

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.

Enantioselective disposition of albuterol in humans

The study of enantioselective disposition of chiral drugs is important to provide a rationale of plasma concentration-effect relationships, which are often misleading when based on total drug concentration. It is also important when considering new dosage routes or formulations in order to optimize therapeutic plasma concentrations of the active enantiomer. Improvements in the sensitivity and selectivity of biological assays coupled with the developments in chiral analysis have made it possible to study the enantioselective disposition of drugs. Although valuable pharmacokinetic data were obtained for the beta 2-agonists by nonenantioselective methodology, more recent chiral studies have revealed the existence of extensive enantioselectivity in the disposition of these agents. The most significant features of the enantioselective disposition of albuterol are the relatively rapid plasma clearance and low bioavailability of the eutomer. Although this in itself does not necessarily justify the development of a single enantiomer formulation, the implications of the high levels of distomer after i.v. and oral dosing await clarification. Similarly, more work is required to elucidate the consequences of the major difference in disposition between albuterol and terbutaline in humans through both in vivo and in vitro studies of the mechanisms giving rise to this phenomenon. The enantioselective disposition of the other clinically used beta 2-agonists, such as fenoterol, formoterol, and salmeterol also needs to be characterized. The metabolism of the majority of beta 2-agonists is generally by conjugation to give one major metabolite. The situation is therefore uncomplicated by multiple metabolic pathways, which may differ in the extent and direction of their enantioselectivity. Many beta 2-agonists are excreted largely unchanged in the urine making studies of urinary excretion accessible without the requirement for very sensitive assays. The realization that the enantiomers of beta 2-agonists previously thought of as "inactive" may be associated with toxic effects is a further compelling reason to study the enantioselective pharmacokinetics of this class of drugs. In addition, the role of enantiomers in producing side effects, such as tremor and reduction in renal function, needs to be reassessed. The beta 2-agonists can be looked on as textbook examples of the inherent danger of ignoring chirality in the study of pharmacokinetics and pharmacodynamics. The growing body of information on the enantioselective disposition of beta 2-agonists in humans will enhance the rational use of these drugs in the future management of patients.

Selective extraction of beta-blockers from biological fluids by column-switching high-performance liquid chromatography using an internal-surface phenylboronic acid precolumn

A column-switching HPLC method using an internal-surface phenylboronic acid precolumn for the selective extraction of beta-blockers from biological fluids has been developed. Filtered urine and plasma samples (50 microliters) were injected onto the precolumn equilibrated with methanol-0.05 M disodium hydrogenphosphate (5:95, v/v). After the precolumn had been washed briefly, the selectively retained beta-blockers were eluted with methanol-0.05 M phosphate buffer (pH 2.0) and transferred to a reversed-phase analytical column, on which they were then separated. Even after exposure to at least 160 injections of non-treated urine and plasma samples, the retention efficiency of the precolumn was maintained with no increase in back pressure. Quantitative recoveries and good reproducibility were demonstrated with pindolol.

Plasma concentrations and effects of salbutamol administered orally to patients with cystic fibrosis

1. To test whether cystic fibrosis (CF) altered the kinetics and dynamics of oral salbutamol, 11 patients with CF (19-33 years old; five females; FEV1: 37 +/- 12% of predicted value) and 10 healthy volunteers (20-41 years old; five females; FEV1: 99 +/- 14% of predicted value) received orally 4 mg salbutamol. 2. The estimated pharmacokinetic parameters of salbutamol in patients with CF were identical to those in healthy subjects. For instance, peak plasma concentrations of salbutamol were 10.5 +/- 2.6 (mean +/- s.d.) and 10.2 +/- 2.9 ng ml-1 (NS), and the area under salbutamol plasma concentrations as a function of time (AUC (0, 7 h)) was 43.0 +/- 9.3 ng ml-1 h and 43.3 +/- 12.7 ng ml-1 h (NS) in CF patients and in healthy subjects, respectively. Since on a mg kg-1 dose basis, CF patients received a dose 28% greater than healthy subjects, this lack of differences implies a decrease in the amount of salbutamol absorbed, or alternatively, an increase in both clearance and volume of distribution of salbutamol. 3. Salbutamol did not elicit bronchodilation in CF patients, but increased heart rate from 77 +/- 2 to 103 +/- 3 beats min-1 (P < 0.05). 4. Salbutamol decreased plasma potassium concentrations from 4.5 +/- 0.1 to 3.8 +/- 0.1 mmol l-1 in the CF group (P < 0.05) and from 4.1 +/- 0.2 to 3.4 +/- 0.1 mmol l-1 in the controls (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Optimization of a column liquid chromatographic procedure for the determination of plasma salbutamol concentration

A reversed-phase column liquid chromatographic procedure with fluorescence detection for the determination of salbutamol in plasma is described. A l-ml aliquot of the sample, after the addition of bamethan as the internal standard, is passed through a Bond Elut silica extraction column. The column is selectively washed to remove neutral, acidic, and weakly basic compounds. The desired compounds are eluted with a l-ml aliquot of methanol. The eluate is evaporated under vacuum at ambient temperature and the residue is reconstituted in 40 microliters of the mobile phase which contains octanesulfonic acid as the ion-pairing reagent. The entire extract is injected onto a 150 x 4.6 mm I.D. column packed with 5-micron octylsilica particles. Peaks are detected with a fluorescence detector (excitation wavelength = 275 nm, emission wavelength = 310 nm). In the resulting chromatogram, salbutamol and the internal standard give sharp peaks that are well resolved from the extraneous peaks. The procedure allows the quantitation of salbutamol down to 0.2 ng/ml.

Immunoaffinity isolation of the sulfate conjugate of 4'-hydroxypropranolol from plasma

Selective extraction of sulfate conjugates of basic drugs from biological matrices has been difficult because of their highly polar nature. Immunoaffinity isolation may be the best solution to this analytical problem. This was tested for a model compound, the metabolite 4'-hydroxypropranolol sulfate (HOPS), which was effectively extracted from plasma by a column containing antibodies to the parent drug propranolol. The specificity was very high, giving little interference from the biological material in subsequent high-performance liquid chromatographic analysis with fluorometric detection. The method for HOPS was highly reproducible and provided a sensitivity of 1 ng/ml plasma. The technique was applied to measurements of HOPS in plasma after therapeutic doses of propranolol as well as to the individual enantiomers after chiral derivatization.

Measurement of terbutaline and salbutamol in plasma by high performance liquid chromatography with fluorescence detection

A method is described for the determination of terbutaline and salbutamol in plasma from patients given maximal therapy for brittle asthma. The analytes were isolated by solid phase extraction on alkali-treated Bond-Elut, unmodified, silica columns and measured by high performance liquid chromatography with fluorescence detection (excitation wavelength 200 nm). The limits of detection for a 1 mL sample containing salbutamol and terbutaline were 1 microgram/L and 2.5 micrograms/L, respectively. The intra-assay precision (CV) for samples containing 25 micrograms/L was 3.6 and 5.0% respectively. This method was applied to the measurement of terbutaline in samples from patients given continuous infusions of the drug to assess whether this treatment might result in toxicity.

Immunoaffinity-chromatography purification of salbutamol in liver and HPLC-fluorometric detection at trace residue level

A method combining immunoaffinity-chromatography (IAC) and high-performance liquid chromatography (HPLC) for the analysis of Salbutamol in liver with a low quantification limit of 1 micrograms/kg has been developed. Salbutamol was extracted with 0.01 mol/L HCl and purified by IAC. The samples were analysed on a liquid chromatograph fitted with a C18 mu-Bondapak column. A fluorometer was used for the detection of salbutamol. Recoveries of 67-80% could be obtained.

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).

Drug residue analysis using immunoaffinity chromatography

The background and applicability of immunoaffinity chromatographic separations and clean-up to drug residue analysis of agricultural commodities is discussed. The uses of antibody specificity for separation and concentration of drug residues are presented. Examples of immunoaffinity chromatography for the determination of residues of (1) nortestosterone and methyl testosterone in swine muscle, urine and bile; (2) chloramphenicol in swine tissue, eggs and milk; (3) clenbuterol in calf urine; (4) zeranol and beta-zearalanolin in calf urine: (5) diethylstilbestrol, dienestrol and hexestrol in calf urine are presented. Further, examples of the successful coupling of immunoaffinity separations with other chromatographic techniques such as gas chromatography and high-performance liquid chromatography are presented.

Salbutamol disposition and dynamics in conscious rabbits: influence of the route of administration and of the dose

This study assessed the influence of dose and route of administration on salbutamol kinetics and hypokaliemic effect. Salbutamol plasma kinetics were studied in a first group of 6 rabbits who received 60, 800, and 60 micrograms/kg by the intravenous (iv), oral (po), and intratracheal (it) routes, respectively, at 1-week intervals. A second group of 6 rabbits received 120, 2400, and 120 micrograms/kg of salbutamol by the same three routes. Multiple blood samples were withdrawn to assay salbutamol and potassium. Following iv salbutamol (60 micrograms/kg), total plasma clearance was 82 +/- 5 ml/min per kg, apparent volume of distribution was 5.0 +/- 0.5 l/kg, and terminal half-life was 41 +/- 2 min. Similar values were estimated when 120 micrograms/kg of salbutamol was administered iv or was given po or it. The bioavailability of po and it salbutamol was approximately 1 and 20%, respectively. For the first group, the maximal decrease in plasma potassium elicited by salbutamol was 0.80 +/- 0.19, 0.48 +/- 0.22, and 0.78 +/- 0.46 mmol/l, and for the second group, maximal decrement was 1.31 +/- 0.37, 0.70 +/- 0.24, and 0.84 +/- 0.17 mmol/l for the iv, po, and it routes, respectively. Compared to salbutamol peak plasma concentrations, maximal decrease in plasma potassium appeared between 60 and 108 min later for the iv route, 90 and 25 min later for po and it routes, and for this reason, the hypokaliemic effect was not associated to salbutamol plasma concentrations. The hypokaliemic effect was dependent upon the route, e.g., po > it > iv.(ABSTRACT TRUNCATED AT 250 WORDS)

A competitive enzyme immunoassay for albuterol: its application for the drug screening in urine

A competitive enzyme immunoassay using purified monoclonal IgG1 and an alkaline phosphatase-albuterol derivative has been developed for the quantification of albuterol in urine. The calibration curve obtained in optimal incubation conditions is characterized by a minimum detectable level of 26 fmol/well and a working range from 52 fmol to 4,2 pmol/well. This method allows the precise and accurate quantification of albuterol in horse urine without any clean up or extraction step. Moreover the definition of its specificity shows a cross-reactivity of the antibody with the glucurono-/sulfo-conjugates of albuterol. This property is particularly interesting for the screening of urinary albuterol residues in meat producing animals.

Immunoaffinity chromatography, its applicability and limitations in multi-residue analysis of anabolizing and doping agents

The use of (multi-)immunoaffinity chromatography in residue analysis is discussed. After an introduction to the immunochemical background an overview of applications is given. A distinction is made between the following methods: (1) single-antibody, single-analyte procedures; (2) single-antibody, multi-analyte procedures; (3) multi-antibody, multi-analyte procedures. It is concluded that immunoaffinity chromatography is superior to most other techniques for sample preparation and extract clean-up. Its advantages in multi-residue procedures are most clear when compared with e.g. high-performance liquid chromatography. In combination with gas chromatography-low-resolution mass spectrometry, very effective multi-residue methods are possible. Most frequently they concern screening procedures which can fulfill the identification criteria for reference methods. It is concluded that the use of (multi-)immunoaffinity chromatography will proliferate further in the 1990s. However, its future viability is highly dependent on the interest of commercial firms and on the involvement of the EC Community Bureau of Reference in manufacturing and supplying the necessary materials.

Radioimmunoassay for albuterol using a monoclonal antibody: application for direct quantification in horse urine

A monoclonal antibody was synthesized in mouse against the O-(3-carboxypropionyl) derivative of albuterol linked to bovine serum albumin. Isotyping of this material revealed the IgG1 class characterized by an affinity constant of 1.03 nM-1 and a density of sites of 0.55 nM. This antibody was found specific as its cross-reactivity to structurally related molecules was less than 1% except for clenbuterol (75%). A radioimmunoassay was set up with culture supernatant (final dilution 1/1000) and [3H] albuterol. The calibration curve was characterized by a maximum binding of 28%, an ED50 of 1.15 pmol per tube, the detection limit was 28.8 fmol/tube and the linearity of the response was up to 39.8 pmol/tube. This RIA method has been used for direct quantitation of albuterol in horse urine without any clean-up or extraction step.