Determination of trantinterol enantiomers in human plasma by high-performance liquid chromatography - tandem mass spectrometry using vancomycin chiral stationary phase and solid phase extraction and stereoselective pharmacokinetic application

A sensitive and enantioselective vancomycin chiral stationary phase high-performance liquid chromatography-tandem mass spectrometry method was developed for the determination of trantinterol enantiomers in human plasma. Baseline resolution was achieved using the vancomycin chiral stationary phase known as Chirobiotic V with polar ionic mobile phase consisting of acetonitrile-methanol (60:40, v/v) containing 0.01% ammonia and 0.02% acetic acid at a flow rate of 1.0 mL/min. Waters Oasis HLB C18 solid phase extraction cartridges were used in the sample preparation of trantinterol samples from plasma. The detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring mode via electrospray ionization. The calibration curve was linear in a concentration range from 0.0606 to 30.3 ng/mL in plasma, with the lower limit of quantification of 0.0606 ng/mL. The intra- and interday precision (relative standard deviation) values were within 9.7% and the accuracy (relative error) was from -6.6 to 7.2% at all quality control levels. The method was successfully applied to a study of stereoselective pharmacokinetics in human.

Separation and determination of clenbuterol by HPLC using a vancomycin chiral stationary phase

Enantiomers of clenbuterol were separated by a new HPLC method on a chiral column. Enantiomeric resolution was achieved on a vancomycyin macrocyclic antibiotic chiral stationary phase known as chirobiotic V with UV detection at 247 nm. The polar ionic mobile phase consisting of methanol-triethylamine-glacial acetic acid (100 + 0.05 + 0.025, v/v/v), was used at a flow rate of 1.0 mL/min. The method was validated for linearity, accuracy, precision, and robustness. Standard linear calibration curves were established for the R-(-) and S-(+) enantiomers over the range of 0.2-20 microg/mL, and an average recovery of 98.0% and a mean relative standard deviation of 1.5% were obtained at 5.0 microg/mL. The lower limit of detection was 0.05 microg/mL for each enantiomer. The mean recovery for R-(-) and S-(+)-clenbuterol enantiomers from plasma was 91.0-97.0% at 0.20-20 microg/mL. The method was successfully used to identify and quantify the clenbuterol enantiomers in human plasma.

High throughput screening of sub-ppb levels of basic drugs in equine plasma by liquid chromatography–tandem mass spectrometry

This paper describes a high throughput LC-MS-MS method for the screening of 75 basic drugs in equine plasma at sub-ppb levels. The test scope covers diversified classes of drugs including some alpha- and beta-blockers, alpha- and beta-agonists, antihypotensives, antihypertensives, analgesics, antiarrhythmics, antidepressants, antidiabetics, antipsychotics, antiulcers, anxiolytics, bronchodilators, CNS stimulants, decongestants, sedatives, tranquilizers and vasodilators. A plasma sample was first deproteinated by addition of trichloroacetic acid. Basic drugs were then extracted by solid-phase extraction (SPE) using a Bond Elut Certify cartridge, and analysed by LC-MS-MS in positive electrospray ionization (+ESI) and multiple reaction monitoring (MRM) mode. Liquid chromatography was performed using a short C(8) column (3.3 cm L x 2.1mm ID with 3 microm particles) to provide fast analysis time. The overall instrument turnaround time was 8 min, inclusive of post-run and equilibration time. No interference from the matrices at the expected retention times of the targeted masses was observed. Over 60% of the drugs studied gave limits of detection (LoD) at or below 25 pg/mL, with some LoDs reaching down to 0.5 pg/mL. The inter-day precision for the relative retention times ranged from 0.01 to 0.54%, and that for the relative peak area ratios (relative to the internal standard) ranged from 4 to 37%. The results indicated that the method has acceptable precision to be used on a day-to-day basis for qualitative identification.

[Determination of ambroxol and clenbuterol in human plasma by LC-MS/MS method]

Ambroxol and clenbuterol were extracted from human plasma samples by liquid-liquid extraction, ambroxol was separated on a Zorbax XDB-C18 column and detected by tandem mass spectrometry with an atmospheric pressure chemical ionization interface after oral administration of a compound preparation. Clenbuterol was separated on a Zorbax XDB-C8 column and detected by tandem mass spectrometry with an electrospray ionization interface. Diphenhydramine is used as the internal standard. The linear concentration ranges of the calibration curves for ambroxol and clenbuterol were 0.080 - 400 microg x L(-1) and 5.0 - 5 000 ng x L(-1), respectively. The lower limits of quantification were 0.080 microg x L(-1) for ambroxol and 5.0 ng x L(-1) for clenbuterol, individually. The inter-day and intra-day precision (RSD) across three validation run over the entire concentration range was below 7.5%, and the accuracy (RE) was within +/- 2.5% for both ambroxol and clenbuterol. The methods were used to determine the pharmacokinetic parameters of ambroxol and clenbuterol in human plasma after oral administration of a compound preparation containing 60 mg ambroxol hydrochloride and 40 microg clenbuterol hydrochloride. The method was proved to be highly sensitive, selective and suitable for the pharmacokinetic study of different compound preparations containing ambroxol and clenbuterol.

Highly sensitive assay for tiotropium, a quaternary ammonium, in human plasma by high-performance liquid chromatography/tandem mass spectrometry

Tiotropium bromide, a long-acting inhaled bronchodilator analogous to ipratropium bromide, is currently undergoing development for the treatment of chronic obstructive pulmonary disease. To evaluate its systemic absorption in humans, we have developed a rapid and sensitive method for its determination in human plasma based on high-performance liquid chromatography with tandem mass spectrometric detection (HPLC/MS/MS). Reversed-phase chromatography of tiotropium and the internal standard clenbuterol was carried out using acetonitrile/10 mM ammonium acetate (1% formic acid) 40:60 as mobile phase in a run time of 3.0 min. The sample preparation involved deproteination with acetonitrile, extraction into dichloromethane and back-extraction into hydrochloric acid. The assay was linear over the concentration range 0.500-50.0 pg/mL with intra- and inter-day precision (as relative standard deviation) both <or=7.34%. The method was successfully applied to a pharmacokinetic study of systemic absorption in healthy male volunteers given a single 18 microg inhaled dose.

Changes in lymphocyte glucocorticoid and beta-adrenergic receptors in veal calves treated with clenbuterol and steroid hormones for growth-promoting purposes*

In order to identify possible peripheral markers of illegal treatments with growth-promoting agents in veal calves, beta-adrenergic receptor (beta-AR) and glucocorticoid receptor (GR) concentrations were measured in lymphocytes of 12 male Friesian crossbred calves (six controls and six treated). The animals received a cocktail of anabolic and re-partitioning agents [17beta-oestradiol: 3 x 10 mg intramuscular (i.m.) doses at 17-day intervals; dexamethasone sodium phosphate: 4 mg/day for 6 days and 5 mg/day for six further days dissolved in milk; and clenbuterol: 20 microg/kg/day dissolved in milk for the last 40 days before slaughter]. Blood samples were collected by venipuncture at different time points and lymphocytes were isolated by density gradient centrifugation. Lymphocyte beta-AR and GR levels were measured by binding assays. Treatment with re-partitioning agents caused a significant down-regulation of lymphocyte beta-ARs 19 days after the beginning of clenbuterol administration and at day 55 (after dexamethasone withdrawal, just before slaughter). This phenomenon was partially reversed at day 50, after dexamethasone administration, at which time a significant decrease in GR concentrations also occurred. For both types of receptors, no significant changes in the dissociation constant values were observed at any time point. Lymphocytes express measurable concentrations of beta-ARs and GRs and the measurement of receptor levels highlights the fluctuation of receptor expression due to the dynamic interaction of the drugs used in combination. Lymphocyte receptor determination could therefore be included in a battery of biological assays to detect illegal treatments with anabolic agents in veal calves in the light of a multivariate approach.

Tissue distribution of clenbuterol in the horse

Plasma and tissue concentrations of clenbuterol (CLB) were determined following oral (p.o.) administration of 1.6 microg/kg twice daily (b.i.d.) for 2 weeks. Horses were administered the last dose on morning of day 15, killed at 0.25, 24, 48, and 72 h post-administration. At 0.25 h, the highest tissue concentrations of CLB were found in the liver (16.21 ng/g), lung (6.48 ng/g), left ventricle (4.99 ng/g), kidney (3.35 ng/g), bronchi (2.56 ng/g), right ventricle (2.08 ng/g), and eye fluids (1.09 ng/g) all of which were higher than that of plasma (1.10 ng/mL). The elimination half-lives (t(1/2k)) for CLB in tissues ranged from 21.2 to 56.3 h, the longest were in the eye fluids (56.9 h), spleen (21.2 h), cerebrum (27.1 h), cerebellum (21.5) and cecum (23.7 h). The t(1/2k) for plasma was 10.9 h. Tissue/plasma ratios of liver (14.7), lung (5.9), left ventricle (4.6), kidney (3.1), bronchi, (2.3) and right ventricle (1.9) were high at 0.25 h and remained elevated up to 72 h. Accumulation and sustained high concentration of CLB relative to plasma in these tissues contributed to the prolonged elimination and the ability to quantify CLB in plasma and urine for a prolonged period.

Pharmacokinetics and disposition of clenbuterol in the horse

The pharmacokinetics of clenbuterol (CLB) following a single intravenous (i.v.) and oral (p.o.) administration twice daily for 7 days were investigated in thoroughbred horses. The plasma concentrations of CLB following i.v. administration declined mono-exponentially with a median elimination half-life (t(1/2k)) of 9.2 h, area under the time-concentration curve (AUC) of 12.4 ng.h/mL, and a zero-time concentration of 1.04 ng/mL. Volume of distribution (V(d)) was 1616.0 mL/kg and plasma clearance (Cl) was 120.0 mL/h/kg. The terminal portion of the plasma curve following multiple p.o. administrations also declined mono-exponentially with a median elimination half-life (t(1/2k)) of 12.9 h, a Cl of 94.0 mL/h/kg and V(d) of 1574.7 mL/kg. Following the last p.o. administration the baseline plasma concentration was 537.5 +/- 268.4 and increased to 1302.6 +/- 925.0 pg/mL at 0.25 h, and declined to 18.9 +/- 7.4 pg/mL at 96 h. CLB was still quantifiable in urine at 288 h following the last administration (210.0 +/- 110 pg/mL). The difference between plasma and urinary concentrations of CLB was 100-fold irrespective of the route of administration. This 100-fold urine/plasma difference should be considered when the presence of CLB in urine is reported by equine forensic laboratories.

Matrix effects in immunobiosensor determination of clenbuterol in urine and serum

The construction of immunochemical inhibition assays for beta-agonist and hormone residues have previously been described. In the present work the beta-agonist assay was further optimised for application to biological samples, using urine as the main model matrix. Matrix interferences with the antigen-antibody interaction and non-specific binding (NSB) of matrix components to the sensor surface were systematically studied. A full factorial design experiment was employed for evaluating the effects of assay buffer composition. In addition, the influence of antibody concentration and sample dilution on the matrix background was investigated. NSB from urine was highly affected by buffer pH and salt concentration, while buffer composition had little effect on matrix interferences with the antigen-antibody interaction. Ultra-filtration efficiently prevented NSB from urine and serum samples. Increased antibody dilution reduced the matrix background while sample dilution had an opposite effect.

Direct separation and quantitative determination of clenbuterol enantiomers by high performance liquid chromatography using an amide type chiral stationary phase

Enantiomers of clenbuterol were directly separated by a new high performance chromatographic method on Chirex 3005 column. Several parameters such as mobile phase composition, column temperature and flow rate were studied. Baseline enantioseparation was achieved, using the optimized mobile phase of n-hexane-1,2-dicholoethane-methanol (54:38:8, v/v/v) at 17 degrees C and 1.0 ml/min, with the separation factor (alpha) 1.43 and the resolution factor (R(S)) 1.81. The mechanism of separation was also discussed. Standard linear calibration cures were established for the R- and S-enantiomers, over the range of 26.1-1,045.8 and 5.7-229.6 nmol/ml, with the correlation coefficient of 0.9999 for both. The limits of detection were 0.47 and 1.04 nmol/ml for R- and S-enantiomers, respectively. Recovery and precision of the method were also evaluated, which had been successfully used to monitor and identify quantitatively the profile of the clenbuterol enantiomers in human serum.

Comparison of serum and urinary concentrations of clenbuterol with and without concomitant administration of furosemide in horses

Furosemide is frequently used to control or prevent exercise-induced pulmonary hemorrhage in performance horses. The bronchodilating agent clenbuterol is also commonly used as a treatment for inflammatory airway disease in performance horses. Use of both medications is regulated by many racing authorities. The effects of concomitant administration of furosemide and clenbuterol on the pharmacokinetics of clenbuterol have not been well characterized. A study was designed to evaluate the influence of furosemide on serum and urine concentrations of clenbuterol after oral administration of clenbuterol and intravenous administration of furosemide in horses. Results indicated that urinary concentrations of clenbuterol in horses treated concomitantly with furosemide and clenbuterol were increased, whereas serum concentrations of the drug were decreased. These effects persisted during the study period and varied among horses.

Distribution and muscle-sparing effects of clenbuterol in hindlimb-suspended rats

Based on their anabolic properties in skeletal muscles, beta-adrenergic agonists are of interest as potential countermeasures to microgravity-induced skeletal muscle atrophy. The levels of clenbuterol (Cb), a beta(2)-adrenergic agonist, in both plasma and skeletal muscle were higher in hindlimb-suspended rats than in their nonsuspended Cb-treated controls. Cb treatment was shown to help maintain the body weight in suspended rats, while reducing the amount of mesenteric fat. However, hindlimb suspension attenuated Cb's lipolytic effects. In skeletal muscle, the magnitude of response to unloading and Cb treatment followed a general regional pattern and was muscle and type specific. The highest magnitude of response to unloading was in predominantly slow-twitch muscles, and the least responsive were the predominately fast-twitch muscles.

Clenbuterol ingestion causing prolonged tachycardia, hypokalemia, and hypophosphatemia with confirmation by quantitative levels

BACKGROUND

Clenbuterol is a long acting beta2-adrenergic agonist used in the treatment of pulmonary disorders. Acute clenbuterol toxicity resembles that of other beta2-adrenergic agonists. Most previously reported cases of clenbuterol toxicity describe patients who ate livestock illicitly treated with clenbuterol.

CASE REPORT

We report a case of human clenbuterol toxicity confirmed and correlated with qualitative and quantitative serum clenbuterol assays. This poisoned patient, a 28-year-old woman, developed sustained sinus tachycardia at 140/min, hypokalemia (2.4 mEq/L, 2.4 mmol/L), hypophosphatemia (0.9 mg/dL, 0.29 mmol/L), and hypomagnesemia (1.52 mg/dL, 0.76 mmol/L) after ingesting a reportedly small quantity of clenbuterol. The patient received repeated doses of metoprolol to treat her cardiovascular stimulation and potassium chloride to treat her hypokalemia. She remained symptomatic for more than 20 hours after the ingestion. Analysis by enzyme-linked immunosorbent assay and liquid chromatography/mass spectrometry revealed a serum clenbuterol concentration of 2.93 mcg/L 3 hours after the ingestion and an undetectable serum concentration 20 hours after ingestion. It is noteworthy that at a serum concentration below the limit of detection by liquid chromatography/mass spectrometry, the patient remained symptomatic. Acute clenbuterol toxicity is rarely reported following illicit use in humans, and this is the first such case to provide confirmatory toxicological analysis.

Clenbuterol in the horse: confirmation and quantitation of serum clenbuterol by LC-MS-MS after oral and intratracheal administration

Clenbuterol is a beta2 agonist/antagonist bronchodilator, and its identification in post-race samples may lead to sanctions. The objective of this study was to develop a specific and highly sensitive serum quantitation method for clenbuterol that would allow effective regulatory control of this agent in horses. Therefore, clenbuterol-d9 was synthesized for use as an internal standard, an automated solid-phase extraction method was developed, and both were used in conjunction with a multiple reaction monitoring liquid chromatography-tandem mass spectrometry (LC-MS-MS) method to allow unequivocal identification and quantitation of clenbuterol in 2 mL of serum at concentrations as low as 10 pg/mL. Five horses were dosed with oral clenbuterol (0.8 microg/kg, BID) for 10 days, and serum was collected for 14 days thereafter. Serum clenbuterol showed mean trough concentrations of approximately 150 pg/mL. After the last dose on day 10, serum clenbuterol reached a peak of approximately 500 pg/mL and then declined with a half-life of approximately 7 h. Serum clenbuterol declined to 30 and 10 pg/mL at 48 and 72 h after dosing, respectively. By 96 h after dosing, the concentration was below 4 pg/mL, the limit of detection for this method. Compared with previous results obtained in parallel urinary experiments, the serum-based approach was more reliable and satisfactory for regulation of the use of clenbuterol. Clenbuterol (90 microg) was also administered intratracheally to five horses. Peak serum concentrations of approximately 230 pg/mL were detected 10 min after administration, dropping to approximately 50 pg/mL within 30 min and declining much more slowly thereafter. These observations suggest that intratracheal administration of clenbuterol shortly before race time can be detected with this serum test. Traditionally, equine drug testing has been dependent on urine testing because of the small volume of serum samples and the low concentrations of drugs found therein. Using LC-MS-MS testing, it is now possible to unequivocally identify and quantitate low concentrations (10 pg/mL) of drugs in serum. Based on the utility of this approach, the speed with which new tests can be developed, and the confidence with which the findings can be applied in the forensic situation, this approach offers considerable scientific and regulatory advantages over more traditional urine testing approaches.

Quantitative determination of clenbuterol enantiomers in human plasma by high-performance liquid chromatography using the macrocyclic antibiotic chiral stationary phase teicoplanin

We report a method for the high-performance liquid chromatographic (HPLC) chiral separation of racemic clenbuterol in human plasma. Human plasma was spiked with stock solutions of clenbuterol hydrochloride and practolol as the internal standard. Following a liquid-liquid extraction procedure with 10% (+/-)-2-butanol/isopropyl ether under alkaline conditions, the dried samples were reconstituted in methanol and chromatographed using a macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic T(trade mark) (teicoplanin). The mobile phase composition was methanol:acetonitrile (70:30, v/v), containing 0.3% (v/v) acetic acid and 0.2% (v/v) triethylamine. The resulting chromatogram achieved baseline separation for the clenbuterol enantiomers. Calibration curves (peak area ratio vs plasma concentration, n = 10) were constructed for the (-)-R-and (+)-S-clenbuterol enantiomers with a plasma concentration range of 0. 25-10 microM. The correlation coefficient (r) range was 0.99988-0. 99999 (mean = 0.99999). The lowest concentration measured was 0.25 microM. Inter- and intra-assay variation was determined for the lowest, medium and highest plasma concentration (0.25, 2 and 10 microM) by calculating the analytical recoveries with a range of 96-104%. The percentage recoveries for the clenbuterol enantiomers were 88.4-102% over the concentration range used. Detailed methodology is presented.

Solid phase extraction of clenbuterol from plasma using immunoaffinity followed by HPLC

An immuno-extraction column for clenbuterol has been prepared. Optimum conditions for the selective retention and elution of clenbuterol have been developed, based on a modification of our earlier work on morphine, chlortoluron and isoproturon. Clenbuterol could be retained on the immuno-column then eluted in one x one ml fraction using 50% methanol in phosphate buffered saline pH 2. On columns containing antisera (but not to clenbuterol) the clenbuterol was removed in the washing step. HPLC-UV determination gave clean traces. Day-to-day reproducibility was improved by precipitating the plasma proteins with acetonitrile.

Clenbuterol plasma pharmacokinetics in cattle

The pharmacokinetics of clenbuterol (Cb) were investigated to determine the extent to which analysis of plasma concentration can be used to discriminate between therapeutic and illicit growth promoting treatment of cattle. Analysis of plasma concentration enabled assessment of the extent of differences in pharmacokinetics between such dosing regimens. Cattle were treated with Cb using either a therapeutic (20 calves, 0.8 microgram Cb kg-1, twice daily in feed for 10 days), or growth promoting (30 calves, 10 micrograms Cb kg-1, twice daily by drench for 20 days) dosing regimens. Blood samples were collected by jugular venepuncture, and plasma Cb concentrations determined by direct enzyme immunoassay. To determine plasma pharmacokinetics, use of a two compartment model was applied to the data and revealed that steady state kinetics were reached after 3 and 5 days following initiation of therapeutic and growth promoting dosing regimens, respectively. Tolerance limit analysis of concentrations during the therapeutic regimen indicated that a plasma Cb concentration greater than 1.63 ng ml-1 would be indicative (p < 0.01) of a growth promoting dose.

Probenecid markedly reduces urinary excretion of ethinylestradiol and trimethoprim slightly reduces urinary excretion of clenbuterol

This study investigated whether the illegal application of ethinylestradiol or clenbuterol in cattle as growth promotors may be concealed by co-treatment with drugs that affect urinary excretion. Therefore, six male veal calves were fed with ethinylestradiol and six different male veal calves were fed with clenbuterol for 13 days. Both groups received the growth promotors twice daily (days -2 to 11) with milk replacer. The calves receiving ethinylestradiol were additionally fed with probenecid on days 7-11, and the calves receiving clenbuterol were additionally fed with trimethoprim (days 7-11). During days 1-11 of the experiment, 24-h urine and blood samples (once daily) were collected and analyses for ethinylestradiol and clenbuterol by specific enzyme immunoassay. In four calves the average urinary excretion of ethinylestradiol during days 7-11 (co-treatment with probenecid) was only about 25% of their average urinary excretion of ethinylestradiol on days 1-6. In the other two calves of this group, the excretion of ethinylestradiol was reduced to 4% on days 7-11 compared with days 1-6. In these two calves several urine samples provided concentrations of ethinylestradiol around the limit of detection. As a consequence, there may be a chance of concealing ethinylestradiol application by co-treatment with probenecid. Co-treatment with trimethoprim led only to a slight reduction of urinary excretion of clenbuterol. The detection of clenbuterol in urine samples from calves which were co-treated with trimethoprim can thus not be prevented.

The potential of restricted access media columns as applied in coupled-column LC/LC-TSP/MS/MS for the high-speed determination of target compounds in serum. Application to the direct trace analysis of salbutamol and clenbuterol

This study investigated the potential of restricted access media (RAM) columns used as a first column in coupled-column LC hyphenated to thermospray tandem mass spectrometry (LC/LC-TSP/MS/MS) for the fast, selective, and sensitive determination of target drugs in serum samples. Because of their wide range in polarity, salbutamol and clenbuterol were chosen as model compounds and representatives of the class of beta 2-agonists. Three types of RAM columns were tested: (i) Pinkerton ISRP (internal surface reversed phase, 5 microns), (ii) SPS (semipermeable surface, 5 microns C18), and (iii) RP-18 ADS (alkyl-diol silica, 25 microns). A 3-micron C18 column (50 mm x 4.6 mm i.d.) was chosen as the second column. Tandem mass spectrometric detection was carried out in the selected reaction monitoring (one parent-->one daughter) mode. With regard to retention and, moreover, the peak elution volume of the analytes, the ISRP material was found to perform best: a 50-mm x 4.6-mm i.d. ISRP column in combination with a 100% aqueous buffer (pH of 7.0 +/- 0.2) allowed the injection of large volumes (up to 200 microL) of sample without additional band broadening of the analytes and provided sufficient preseparation between analytes and large-molecule serum constituents. Under the selected conditions, both analytes could be determined in serum samples up to a limit of quantification (LOQ) of 0.5 ng/mL, with a sample throughput of 7 and 5 h-1 for salbutamol and clenbuterol, respectively. Method validation was carried out by analyzing, in the course of several days, calf and human serum samples spiked with the analytes. In the case of salbutamol, the overall recovery from serum samples spiked at levels between 0.5 and 50 ppb (n = 33) was 103.4%, with a repeatability of 12.7% and reproducibility of 14.3%. The overall recovery for clenbuterol was 99.6% (n = 15, spiked level 0.5-5 ppb), with a repeatability of 15.2% and reproducibility of 16.4%. The adopted LC/LC-TSP/MS/ MS analyzer appeared to be very robust under the selected conditions, and, after the period of analysis involving the processing of more than 100 mL of serum, neither loss of chromatographic performance nor pressure increase of columns or of the interface was observed.

Effects of drugs which influence renal transport systems on the urinary excretion of the beta 2-adrenoceptor agonist clenbuterol and the anabolic steroids ethinylestradiol and methyltestosterone

The aim of this study was to determine whether the illegal application of clenbuterol, ethinylestradiol and methyltestosterone in cattle as growth promoters can be concealed by co-treatment with drugs that affect urinary excretion. Six male veal calves were fed with 0.8 micrograms clenbuterol kg-1 of body weight (BW), 3.5 micrograms ethinylestradiol kg-1 BW and 35 micrograms methyltestosterone kg-1 BW together twice daily for 28 days. At the eighth day of clenbuterol, ethinylestradiol and methyltestosterone treatment each calf was additionally fed either with probenecid, para-aminohippuric acid, trimethoprim, famotidine or cimetidine at three different doses which were increased in weekly intervals. During the treatment 24 h-urine and blood samples (once daily) were obtained and analysed for clenbuterol, ethinylestradiol and methyltestosterone by specific enzyme immunoassay. By high performance liquid chromatography/enzyme immunoassay it was determined whether these drugs or their metabolites interfered with the immunological detection of the growth promoters. Clenbuterol, ethinylestradiol and methyltestosterone could be detected in plasma and urine throughout the whole experiment. Co-treatment with probenecid led to a five-fold reduction in urinary excretion of ethinylestradiol and co-treatment with trimethoprim led to a three-fold reduction in urinary excretion of clenbuterol. None of the drugs reduced urinary excretion of the growth promoters to concentrations below the limit of detection. The detection of these three growth promoters in urine samples from calves which were co-treated with the drugs tested in this study can thus not be prevented.

Probenecid, sulfinpyrazone and pyrazinamide do not inhibit urinary excretion of the beta 2-adrenoceptor agonist clenbuterol in cattle

The objective of this study was to develop an analytical approach to determine whether the illegal application of clenbuterol in cattle as an anabolic agent can be concealed by co-treatment with substances that affect urinary excretion. Female veal calves were dosed orally with 0.8 microgram clenbuterol per kg of body weight twice daily for 28 days, as licensed for the therapeutic use which is registered in most European countries. On the eighth day of clenbuterol treatment each calf was additionally dosed orally either with probenecid, sulfinpyrazone or pyrazinamide at three different doses that were increased in weekly intervals. During the treatment blood and urine samples were obtained and analysed for clenbuterol by enzyme immunoassay and by high performance liquid chromatography/ enzyme immunoassay to determine whether these drugs or their metabolites interfered with the immunological detection of clenbuterol. Clenbuterol could be in plasma (approximately 200 pg ml-1) and urine (1-40 ng ml-1) 5 h after the initial intake and throughout the whole treatment. None of the drugs reduced urinary excretion of clenbuterol to concentrations below the limit of detection. There was no prevention of clenbuterol detection in urine samples from calves that were co-treated with the drugs tested in this study. Our results demonstrate the uselessness of applying these drugs in order to conceal the illegal use of clenbuterol in meat production.

Direct enantioselective separation of clenbuterol by chiral HPLC in biological fluids

An isocratic and simple high-performance liquid chromatographic method was developed for the direct resolution of the clenbuterol enantiomers. The method involved the use of a urea type chiral stationary phase (CSP) made of (S)-indoline-2-carboxylic acid and (R)-1-(alpha-napthyl) ethylamine known as the Chirex 3022 column. The stereochemical separation factor (alpha) obtained was 1.27 and the stereochemical resolution factor (Rs) was 4.2 when using a mobile phase composed of hexane:1,2-dichloroethane:ethanol/trifluoroacetic acid (80:10:10 by vol) at 23 degrees C. The (+)-R enantiomer eluted first, with a capacity factor (k'2) of 2.67 followed by (-)-S enantiomer with a capacity factor (k'1) of 3.38. As standard linear calibration curve was constructed over the range of 10 nmol/mL to 250 nmol/mL with a correlation coefficient of 0.999. The method is specific and sensitive with a lower limit of quantitation of 0.1 nmol. Data demonstrating recovery and precision of the assay are presented and the method has been used to monitor and identify quantitatively the profile of the enantiomers of clenbuterol in biological fluids.

Detection of clenbuterol (Ventipulmin) in the horse

An enzyme linked immunosorbent assay (ELISA) was developed to detect the beta 2-agonist clenbuterol in equine blood and urine. The antiserum was raised in rabbits, employing clenbuterol-diazo-BSA as antigen. Clenbuterol-diazo-horseradish peroxidase served as enzyme conjugate. The concentration of clenbuterol to decrease tracer binding by 50% (IC50 value) was found to be 27.50 +/- 4.20 pg/well (1.37 ng/ml). The antibody cross-reacted with salbutamol (30%), terbutaline (14%) and cimaterol (1%). Horse serum was used directly to screen for clenbuterol, while urine was employed diluted. Positive screening results were confirmed by means of two independent HPLC systems combined with off-line detection by the clenbuterol-ELISA. Salbutamol served as internal standard to ascertain relative retention of the drug. The detection limit of clenbuterol in serum and urine amounted to 0.04 ng/ml. In addition, GC/MS technique was applied to detect clenbuterol in urine samples by a newly developed derivatization method. Confirmation of intravenously given clenbuterol in serum of horses treated with Ventipulmin (0.8 microgram clenbuterol.HCl/kg) was achieved by HPLC/ELISA up to 24 h, in urine up to 96 h. After oral administration, the beta 2-agonist was detected in serum for 48 h and in urine for 75 h.

Tissue distribution and residues of clenbuterol, salbutamol, and terbutaline in tissues of treated broiler chickens

To examine the tissue distribution and residues after withdrawal of various beta-agonists (i.e., clenbuterol, salbutamol, and terbutaline) 160 1-d-old broiler chickens were assigned to four groups. During treatment (16 to 35 d), the birds were fed a control diet or a diet containing 1 ppm of clenbuterol, 10 ppm of salbutamol, or 10 ppm of terbutaline. After d 35 all groups received the control diet. Five birds of each group were then slaughtered and tissues were collected on d 0, 1, 2, 3, 7, 14, and 43 following withdrawal of beta-agonists from the feed. Extraction of beta-agonists from the tissues was carried out by a new method using hetero-bifunctional solid phase extraction. The amount of beta-agonists in the extracts was measured by an enzyme immunoassay (EIA). The highest concentrations of beta-agonists were found in feathers: 224 ng of clenbuterol/g, 1,140 ng of salbutamol/g, and 1,159 ng of terbutaline/g. Clenbuterol accumulated above plasma levels in all tissues that were investigated (liver, kidney, stomach, muscle, fat, feather, eye). Salbutamol was most concentrated in feather, eye, liver, and kidney; terbutaline accumulated only in feather, liver, and kidney. Overall, clenbuterol showed the highest accumulation in the tissues analyzed. A withdrawal period of greater than 2 wk was required for residues in edible tissues to decline below detectable levels.

Analysis of clenbuterol in human plasma using liquid chromatography/atmospheric-pressure chemical-ionization mass spectrometry

Clenbuterol is a beta-agonist drug used illegally as a growth stimulant in meat-producing animals and human athletes. The analysis of clenbuterol in spiked human plasma was performed using on-line liquid chromatography/atmospheric-pressure chemical-ionization mass spectrometry (LC/APCI-MS) using a conventional bore LC column (flow rate = 1.0 mL/min). At low sampling cone voltages, the mass spectrum was predominantly the [M+H]+ ion but diagnostic fragment ions were formed upon incremental increases in sampling cone voltage. The detection limit (signal-to-noise ratio of 3) using selected-ion monitoring of the [M+H]+ ion was 0.1 ng on-column (10 ppb). This is a 50-fold better sensitivity of detection than that previously reported for an on-line thermospray LC/MS method. The extraction procedures were not optimized for maximum sensitivity and the lack of interferences suggests that much lower detection limits for clenbuterol in plasma are attainable.

The pharmacokinetics and residues of clenbuterol in veal calves

Seven female Brown Swiss calves were used to study the pharmacokinetics of clenbuterol after an effective anabolic dosage of 5 micrograms/kg of BW was given twice daily for 3 wk. Analyses of clenbuterol concentrations in different tissues was done by enzyme immunoassay (EIA). Tissue samples were taken from three calves on the last day of administration and from two more after 3.5 or 14 d of clenbuterol withdrawal. The rate of clenbuterol elimination was dependent on time and tissue. Clenbuterol concentrations in the lung dropped from a mean of 76 ng/g to a level of less than .08 ng/g after 14 d, whereas in the liver the clenbuterol concentrations decreased from 46 ng/g to .6 ng/g within 14 d of withdrawal. Highest levels were always found in the eye: 118 ng/g, 57.5 ng/g, and 15.1 ng/g after 0, 3.5, and 14 d of withdrawal, respectively. These data reveal that different compartments contribute to the elimination of clenbuterol; therefore, concentrations in urine do not follow first order kinetics. An initial rapid decline in the concentration of clenbuterol in urine with a half-life of 10 h is followed by a slower elimination with a half-life of about 2.5 d. Treatments using the anabolic dose of 5 micrograms/kg of BW require longer withdrawal times than the therapeutic dose (.8 micrograms/kg BW).

High-performance liquid chromatographic determination of clenbuterol and cimaterol using post-column derivatization

A general high-performance liquid chromatographic method for the simultaneous and rapid determination of cimaterol and clenbuterol is described. Solid samples, such as animal tissues, faeces and feeding-stuffs, are extracted with dilute acid saturated with ethyl acetate. The resulting extracts or liquid samples, such as urine, plasma, blood and bile, are purified via Chem Elut columns. Separation is achieved by ion-pair chromatography on a Nova-Pak C18 column, and highly specific detection is obtained with an adapted version of the post-column derivatization described previously for the determination of clenbuterol in urine and animal tissues. Detection limits for liquids and solids are 0.1 ng/ml and 0.2 ng/g, respectively. The results are in complete agreement with analysis by high-performance thin-layer chromatography and gas chromatography-mass spectrometry, applied for confirmation after the same sample pretreatment. With this simple method, complete analysis of a liquid sample needs about 30 min and, even without an automatic sampler, 40 samples can be completely analysed in one day. This method has been used on a routine scale for nearly two years.

Determination of clenbuterol in bovine plasma and tissues by gas chromatography-negative-ion chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for the determination of clenbuterol in bovine plasma and tissues. Clenbuterol and the internal standard [2H9]clenbuterol were measured by gas chromatography-negative-ion chemical ionization mass spectrometry with methane as the reagent gas. Bovine tissues including muscle, liver, heart, kidney, lung, suet, brain, spinal cord and thymus were ground in a buffer of pH 7 and then extracted using ethyl acetate. After two subsequent purification steps, the cleaned-up organic extract was derivatized with pentafluoropropionic anhydride. The mass spectrometer was set to monitor the abundant ions m/z 368 and 377 of the perfluoroacyl derivatives. This assay was performed with 1 ml of plasma or 0.2 g of tissue. The feasibility of this method was demonstrated by the determination of clenbuterol residues as the femtomole level in a variety of tissues.

Determination of clenbuterol and mabuterol in equine plasma by ion-pair liquid chromatography with electrochemical detection. Chromatographic and electrochemical characteristics

A method for the routine determination of the beta-adrenergic drugs clenbuterol and mabuterol in equine plasma has been developed. The drugs were isolated from alkalinized plasma by liquid-liquid extraction. The organic phase was evaporated to dryness and the residue was dissolved in the mobile phase prior to injection. The recoveries were 98% and 95% for clenbuterol and mabuterol, respectively. The drugs were separated by reversed-phase high-performance liquid chromatography and quantitated by a use of a coulometric detector set at +0.75 V vs. the internal reference electrode. The influence of pH and amounts of organic modifier and ion-pairing agent on the retention times was investigated. The relationship between peak current and concentration was linear up to 1 microgram/ml for both compounds. The limits of detection were 0.5 ng/ml for clenbuterol and 2 ng/ml for mabuterol with a signal-to-noise ratio of 3. A brief discussion of the electrochemistry of the compounds is given.

[Comparative study of the tissue distribution of two beta-mimetics: clenbuterol and salbutamol in the dog]

Especially because of their physico-chemical properties, and in particular of their lipo-solubility, it was interesting to compare the tissue distribution of two beta 2 sympathomimetics: the clenbuterol and the salbutamol. The study was realised after a direct intravenous administration of clenbuterol chlorhydrate (5 micrograms/kg) and one of salbutamol sulfate (50 micrograms/kg) given to a dog. In a first time, the determination by mass-spectrometry of the two drugs in the plasma allows the pharmacokinetic study in dogs. After a three days wash out, this same experience was repeated. The animals are sacrificed and the assays of the two beta 2 sympathomimetics were effected in lung, bronchial, muscle, heart and brain tissue samples. The tissue distribution was different for clenbuterol and salbutamol and had to be considered as factors of selectivity in the sympathomimetic beta 2 activity. Nervous central diffusion of clenbuterol is higher than salbutamol but cardiac distribution is very important for salbutamol.

Enzyme immunoassay for mabuterol, a selective beta 2-adrenergic stimulant in the trachea

A sensitive double antibody and heterologous enzyme immunoassay for mabuterol was established. For competitive reactions, antibody raised against diazotized mabuterol-human serum albumin was incubated with a mixture of diazotized mabuterol analog (RC-1) labeled with beta-D-galactosidase and standard or sample. Free and antibody-bound enzyme hapten were separated using anti-rabbit IgG immobilized on polystyrene balls. Activity of the enzyme on the solid phase was fluorometrically determined. The present immunoassay allows detection of 0.5 to 100 pg/tube of mabuterol. Pharmacokinetic behavior of this agent in human plasma and urine was studied after a single oral administration (50 micrograms). The maximum level was achieved after 2-3 hrs with approximately 280 pg mabuterol /ml of plasma and the half life of mabuterol was estimated to be 19.5 hrs. Cumulative amount of mabuterol in the first 72 hrs urine was 64.3 +/- 13.2% of the administered dose.

Pharmacokinetics of plasma and urine clenbuterol in man, rat, and rabbit

Therapeutic dose (20, 40 and 80 micrograms/man) of clenbuterol hydrochloride, a beta 2-adrenergic stimulant, was orally administered to healthy volunteers, and the unmetabolized drug in plasma and urine was determined by enzyme immunoassay. The plasma levels of clenbuterol reached the maximum value of 0.1, 0.2 and 0.35 ng/ml, respectively, in a dose-dependent manner within 2.5 h, which lasted for over 6 h after the administration. The half-life of clenbuterol in plasma was estimated to be about 35 h. When the drug was orally administered repeatedly to men twice a day, the plasma level reached the plateau within 4 d after the initial administration. At that time, the plasma levels of the unchanged form were 0.2 to 0.3 ng/ml and 0.5 to 0.6 ng/ml at doses of 20 and 40 micrograms/man, respectively. The bound ratio of the drug to plasma protein was estimated to be 89-98% at a single administration of 80 micrograms of the drug. The cumulative urinary excretion of unchanged compound corresponded to about 20% of the administered dose as measured at 72 h following a single oral administration. When clenbuterol hydrochloride was orally administered to rats at a dose of 2 micrograms/kg, the plasma level reached the maximum at about 1 h after the administration. In rabbits, the plasma concentrations reached the maximum value of about 0.2 and 0.8 ng/ml within 2 h following administration of clenbuterol hydrochloride at doses of 0.5 and 2 micrograms/kg, respectively. The half-life of clenbuterol in plasma was about 30 h in rats and about 9 h in rabbits.

Enzyme immunoassay for clenbuterol, an beta 2-adrenergic stimulant

A sensitive double antibody and heterologous enzyme immunoassay for the quantitation of clenbuterol is established. Specific antiserum to this agent was raised in rabbits by immunization with diazotized clenbuterol and human serum albumin conjugate. For competitive reactions, antibody was incubated with a mixture of diazotized clenbuterol analog (NA 1141) labelled with beta-D-galactosidase and unlabelled standard or sample clenbuterol. The antibody-bound enzyme hapten was separated from free hapten by anti-rabbit IgG immobilized to a polystyrene ball. Activity of the enzyme on the solid phase was fluorometrically determined. The assay system made it possible to ascertain values as low as 0.5 pg /tube of clenbuterol. By use of this assay method, the time course of plasma levels of clenbuterol was examined after a single oral administration (20 micrograms) to 3 healthy volunteers. It was shown that the maximum level was achieved after 2-3 hr with approximately 10 ng clenbuterol/dl of plasma.