Pharmacokinetic and bioequivalence assessment of two formulations of tianeptine sodium in healthy male volunteers.

BACKGROUND: Tianeptine is widely used for controlling depressive symptoms. OBJECTIVE: The aim of this study was to evaluate the bioequivalence between the generic (test) formulation containing tianeptine sodium 12.5 mg and the branded (reference) formulation Stablon® with regard to their pharmacokinetic profiles. METHODS: A randomized, two-sequence, two-treatment crossover study was conducted in healthy male Korean volunteers. All of the enrolled subjects were allocated to one of two sequence groups. They were administered a tablet of the test or reference formulation and then administered the alternative formulation after a 7-day washout period. The blood samples were taken before dosing and at 0.33, 0.67, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, and 10 hours after dosing. The plasma concentrations of tianeptine were analyzed using high-performance liquid chromatography with tandem mass spectrometer. Tolerability was assessed throughout the study. RESULTS: The pharmacokinetic parameters were assessed in the 40 subjects who completed the study. The tianeptine C(max) for the test formulation was 283.13 ± 57.58 ng/mL (mean ± SD) and that for the reference formulation was 272.50 ± 59.00 ng/mL. The AUC(last) of tianeptine was 803.24 ± 180.94 ng×h/mL for the test formulation and 792.27 ± 180.93 ng×h/mL for the reference formulation. The geometric mean ratio (%) of the test to reference formulation was 104.04 (90% CI, 99.66 - 108.61) for C(max) and 101.30 (98.01 - 104.71) for AUC(last). Clinically significant adverse events were not reported during the study. CONCLUSION: The test and reference formulations of tianeptine were bioequivalent with regard to the pharmacokinetic parameters of Cmax and AUC(last). Both formulations were tolerated by all of the participants.

Pharmacokinetic evaluation of a novel benzopyridooxathiazepine derivative as a potential anticancer agent.

BACKGROUND/AIMS: The in vivo metabolic profile of a benzopyridooxathiazepine (BPT) derivative, a potent tubulin polymerization inhibitor with a promising in vitro activity, was investigated. METHODS: The quantification of the BPT derivative and the identification of metabolites in the plasma of Wistar rats after i.p. and oral administration of 10 mg/kg were performed by the HPLC-mass spectrometry method. RESULTS: Following a single i.p. dose of the BPT derivative, the plasma concentrations showed a biexponential decay (with a rapid decline) followed by a slow decay with a terminal half-life of 77.90 min. The area under the concentration-time curve from time 0 to infinity (AUC0-∞) was 18.90 µg/ml·min. After oral administration, the plasmatic concentrations reached a peak of 0.06 µg/ml at 35 min and then decayed with a half-life of 108 min. The AUC0-∞ was 10.25 µg/ml·min, representing 54.2% of the relative bioavailability. The compound was well distributed in the body, and its elimination seemed to be fast, regardless of the administration route. The major metabolic pathways were demethylation and hydroxylation reactions, both followed by conjugation with glucuronic acid. CONCLUSION: In rats, the BPT derivative is well distributed and undergoes extensive metabolism, leading to several metabolites. With promising in vitro activity and very good oral bioavailability, this compound seems to be an attractive candidate for further development as an anticancer agent.

Characteristics of quetiapine and 7-hydroxyquetiapine in hair roots and blood after a single dose of quetiapine.

This study investigated the kinetics of quetiapine and its metabolite 7-hydroxyquetiapine in guinea pig blood and hair roots during the whole time course of absorption and elimination after intragastric administration of three dosages (25 mg/kg, 50 mg/kg, 100 mg/kg). The mean maximum concentration (Cmax) values of quetiapine in the blood of the low-, medium- and high-dose groups were 334.4, 849.0, and 2751.1 ng/mL, respectively, and those of 7-hydroxyquetiapine were 75.6, 175.5, and 173.7 ng/mL, respectively. The corresponding mean Cmax values of quetiapine in hair roots were 2.0, 5.9, and 14.7 ng/mg, and those of 7-hydroxyquetiapine were 1.0, 1.8, and 6.4 ng/mg. The mean half-lives of quetiapine at the three dosages in blood were 3.8 h, 5.0 h, and 6.0 h, and those in hair roots were 48.2 h, 41.5 h, and 162.3 h; for 7-hydroxyquetiapine, the values were 2.9 h, 4.1 h, and 4.2 h in blood and 77.1 h, 103.6 h, and 385.9 h in hair roots. The levels of quetiapine in blood and hair roots were higher than those of 7-hydroxyquetiapine, and there were significant positive correlations (p<0.05) between the concentrations of quetiapine and 7-hydroxyquetiapine in hair roots and the respective doses within 24 h and 48 h. Quetiapine and 7-hydroxyquetiapine could still be detected in some guinea pigs even after 28 days, which means that drugs remain in the hair roots longer than in the blood. This finding shows that hair roots could be a good alternative or supplemental matrix to common biological samples such as blood and urine, as hair roots substantially extend the detection window from days to months. Moreover, quetiapine and 7-hydroxyquetiapine were detected within 15min after administration in hair roots, which also suggests that the drug enters the hair roots quickly. Therefore, hair root analysis may be a good choice to detect acute poisoning and single-dose administration if other matrices are unavailable or to provide complementary information for other matrices.

Safety, Tolerability, Pharmacokinetic and Pharmacodynamic Evaluations Following Single Oral Doses of GSK2330672 in Healthy Japanese Volunteers.

GSK2330672 is an inhibitor of the ileal bile acid transporter, designed to have minimal systemic exposure, and is under development as a potential therapeutic for pruritus associated with primary biliary cholangitis and other cholestatic liver diseases. A phase 1, double-blind, placebo-controlled, 4-period crossover study was conducted to evaluate the safety, tolerability, and pharmacokinetic/pharmacodynamic characteristics of GSK2330672 in healthy Japanese participants. Sixteen healthy male participants received single oral doses of GSK2330672 (10-180 mg) or placebo in each period. No serious adverse events and no adverse events leading to study discontinuation or withdrawal were reported. Drug-related adverse events reported included gastrointestinal symptoms (mostly diarrhea) and positive fecal occult blood tests, and were all mild and resolved without any interventions. GSK2330672 was undetectable in the majority of participants' plasma. Pharmacodynamic observations included a tendency for total serum bile acids to reduce and for serum 7α-hydroxy-4-cholesten-3-one, a key intermediate of bile acid synthesis, to increase with increasing doses of GSK2330672. In the context of recently published indications of potential efficacy for cholestatic pruritus in non-Japanese populations, these data support further evaluations of GSK2330672 in Japanese patients.

Case Reports of Fatalities Involving Tianeptine in the United States.

Tianeptine is a tricyclic anti-depressant that is also known to have opioid receptor activity. We present two fatal cases of tianeptine intoxication in Texas in which tianeptine was used recreationally. The first case involved a 28-year-old white male found alone on the floor of his locked residence. He had a history of drug abuse but no other toxicological findings. The second case involved a 30-year-old white male found on the floor of the bathroom in his home. Drug paraphernalia and bags labeled as tianeptine powder were found at both scenes. In response to the first case, our laboratory developed a method for quantitation of tianeptine by LC-MS-MS. This method was then validated according to SWGTOX guidelines for specificity, calibration model, limit of detection, limit of quantitation, accuracy, precision, ion suppression, and carryover. This method was successfully used to determine tianeptine concentrations in postmortem blood in two cases. In these cases, tianeptine was measured at 2.0 mg/L and 8.4 mg/L. These represent the first known tianeptine fatalities in Texas and in the United States.

Effects of organic anion transporting polypeptide 1B1 haplotype on pharmacokinetics of pravastatin, valsartan, and temocapril.

OBJECTIVE: Recent reports have shown that genetic polymorphisms in organic anion transporting polypeptide (OATP) 1B1 have an effect on the pharmacokinetics of drugs. However, the impact of OATP1B1*1b alleles, the frequency of which is high in all ethnicities, on the pharmacokinetics of substrate drugs is not known after complete separation of subjects with OATP1B1*1a and *1b. Furthermore, the correlation between the clearances of OATP1B1 substrate drugs in individuals has not been characterized. We investigated the effect of genetic polymorphism of OATP1B1, particularly the *1b allele, on the pharmacokinetics of 3 anionic drugs, pravastatin, valsartan, and temocapril, in Japanese subjects. METHODS: Twenty-three healthy Japanese volunteers were enrolled in a 3-period crossover study. In each period, after a single oral administration of pravastatin, valsartan, or temocapril, plasma and urine were collected for up to 24 hours. RESULTS: The area under the plasma concentration-time curve (AUC) of pravastatin in *1b/*1b carriers (47.4 +/- 19.9 ng.h/mL) was 65% of that in *1a/*1a carriers (73.2 +/- 23.5 ng.h/mL) (P = .049). Carriers of *1b/*15 (38.2 +/- 15.9 ng.h/mL) exhibited a 45% lower AUC than *1a/*15 carriers (69.2 +/- 23.4 ng.h/mL) (P = .024). In the case of valsartan we observed a similar trend as with pravastatin, although the difference was not statistically significant (9.01 +/- 3.33 microg.h/mL for *1b/*1b carriers versus 12.3 +/- 4.6 microg.h/mL for *1a/*1a carriers [P = .171] and 6.31 +/- 3.64 microg.h/mL for *1b/*15 carriers versus 9.40 +/- 4.34 microg.h/mL for *1a/*15 carriers [P = .213]). The AUC of temocapril also showed a similar trend (12.4 +/- 4.1 ng.h/mL for *1b/*1b carriers versus 18.5 +/- 7.7 ng.h/mL for *1a/*1a carriers [P = .061] and 16.4 +/- 5.0 ng.h/mL for *1b/*15 carriers versus 19.0 +/- 4.1 ng.h/mL for *1a/*15 carriers [P = .425]), whereas that of temocaprilat (active form of temocapril) was not significantly affected by the haplotype of OATP1B1. Interestingly, the AUC of valsartan and temocapril in each subject was significantly correlated with that of pravastatin (R = 0.630 and 0.602, P < .01). The renal clearance remained unchanged for each haplotype for all drugs. CONCLUSION: The major clearance mechanism of pravastatin, valsartan, and temocapril appears to be similar, and OATP1B1*1b is one of the determinant factors governing the interindividual variability in the pharmacokinetics of pravastatin and, possibly, valsartan and temocapril.

Endothelium-derived hydrogen peroxide accounts for the enhancing effect of an angiotensin-converting enzyme inhibitor on endothelium-derived hyperpolarizing factor-mediated responses in mice.

UNLABELLED: Background- We have recently identified that endothelium-derived hydrogen peroxide (H2O2) is an endothelium-derived hyperpolarizing factor (EDHF) in animals and humans, for which endothelial nitric oxide synthase (eNOS) is an important source. Angiotensin-converting enzyme (ACE) inhibitors are known to enhance EDHF-mediated responses. In this study, we examined whether endothelium-derived H2O2 accounts for the enhancing effect of an ACE inhibitor on EDHF-mediated responses and, if so, what mechanism is involved. METHODS AND RESULTS: Control and eNOS-/- mice were maintained with or without temocapril (10 mg/kg per day orally) for 4 weeks, and isometric tensions and membrane potentials of mesenteric arteries were recorded. In control mice, temocapril treatment significantly enhanced EDHF-mediated relaxations and hyperpolarizations to acetylcholine (n=8 each). Catalase, a specific scavenger of H2O2, abolished the beneficial effects of temocapril, although it did not affect endothelium-independent relaxations to sodium nitroprusside or NS1619, a direct opener of K(Ca) channels (n=6 each). Western blot analysis demonstrated that the temocapril treatment significantly upregulated the expression of eNOS. By contrast, this enhancing effect of temocapril was absent in eNOS-/- mice (n=6). CONCLUSIONS: These results indicate that endothelium-derived H2O2 accounts for the enhancing effect of temocapril on EDHF-mediated responses caused in part by eNOS upregulation, further supporting our H2O2 theory.

Determination of tianeptine in human plasma using high-performance liquid chromatography with fluorescence detection.

A new, selective and sensitive high-performance liquid chromatography (HPLC) method with fluorimetric detection was developed for the determination of tianeptine (TIA) in human plasma using solid phase extraction (SPE) procedures. The method is based on the derivatization of TIA with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in borate buffer of pH 8.5 to yield a yellow, fluorescent product. The HPLC separation was achieved on a Phenomenex C(18) column (250 mm x 4.6 mm) using a mobile phase of acetonitrile-10mM orthophosphoric acid (pH 2.5) (77:23, v/v) solvent system at 1 mL/min flow rate. Gabapentin (GA) was used as the internal standard. The fluorometric detector was operated at 458 nm (excitation) and 520 nm (emission). The assay was linear over the concentration range of 5-300 ng/mL. The detection limit (LOD) was found to be 2 ng/mL. The mean recovery was determined to be 88.6%. The proposed method was applied for pharmacokinetic study of 12.5mg TIA in a healthy volunteer.

Neuropharmacologic treatment of bronchial asthma with the antidepressant tianeptine: a double-blind, crossover placebo-controlled study.

Studies have shown the levels of free serotonin in plasma are increased in symptomatic patients with asthma. In addition, the concentration of free serotonin in symptomatic children with asthma correlates positively with clinical status and negatively with pulmonary function (forced expiratory volume in 1 second [FEV1]). Thus, reducing the concentration of free serotonin in plasma may be useful in treating children with asthma. We studied the effectiveness of tianeptine in treating these patients. Tianeptine is the only drug known to be able to reduce the level of free serotonin in plasma and to enhance the uptake by platelets. Sixty-nine of the 82 children with asthma initially enrolled participated in this study. Children were randomized to receive tianeptine or placebo or both in a double-blind crossover trial. The trial lasted 52 weeks. Tianeptine provoked a dramatic and sudden decrease of both clinical rating and free serotonin plasma levels and an increase in pulmonary function.

Tianeptine and its main metabolite pharmacokinetics in chronic alcoholism and cirrhosis.

The effect of chronic alcoholism (with or without associated moderate cirrhosis) on the disposition of the antidepressant tianeptine, which is devoid of substantial first-pass metabolism, was examined in 21 patients and 11 age-matched controls. Pharmacokinetic parameters for tianeptine and its C5 acid analogue metabolite (MC5 metabolite) were estimated by non-compartmental analysis. The area under the curve (AUC) for tianeptine, following a 12.5mg single oral dose, was decreased by 31% in chronic alcoholics and increased by only 14% in cirrhotics, compared to controls. These changes did not attain statistical significance. The trend of changes in the AUC for the MC5 metabolite was similar to that observed for the parent drug. No statistical difference was found in the terminal half-life for both tianeptine and its MC5 metabolite between patients and controls. On the basis of this study, it appears unnecessary to modify the proposed dosage regimen used in clinical trials (tianeptine sodium salt 12.5mg 3 times daily) in chronic alcoholics with or without associated moderate cirrhosis.

Pharmacokinetics of the antidepressant tianeptine at steady state in the elderly.

The pharmacokinetics of tianeptine, an antidepressant with an original serotoninergic neurochemical action, was investigated in elderly patients. Kinetic profiles were developed in 12 elderly patients (age range: 72-81 yr) after single (12.5 mg) dose and multiple oral dosages (12.5 mg tid for 17 days). Multiple dosing of tianeptine was well tolerated; no accumulation of the unchanged drug was observed. Tianeptine and its MC5 metabolite (C5 acid analogue of tianeptine) reached maximum plasma levels after 1.81 +/- .99 and 2.96 +/- 1.44 hr, respectively, with values of 353 +/- 198 and 81 +/- 20 ng/mL, respectively, after a single dose and of 405 +/- 202 and 175 +/- 85 ng/mL, respectively, after multiple dosing. Minimum plasma concentrations of tianeptine were about half those of its MC5 metabolite (68 +/- 41 and 121 +/- 64 ng/mL-1 on day 5), and for each compound, they were not statistically different from day 5 to day 18 of the chronic administration. This finding is compatible with the terminal half-lives that were observed after the single dose that was 2.8 +/- .9 hr for tianeptine and 12.3 +/- 7 hr for the MC5 metabolite. For both compounds, the area-under-the-plasma levels time curve at steady state was as predicted from the initial single dose that showed no deviation from linearity with time. The kinetics of tianeptine in elderly patients were similar to those reported for young adults. However, MC5 metabolite plasma levels were higher in elderly patients than in younger patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Tianeptine and its main metabolite. Disposition in chronic renal failure and haemodialysis.

The disposition of the antidepressant tianeptine and its MC5 metabolite (pentanoic acid analogue of tianeptine) was studied following a single 12.5 mg oral dose of tianeptine sodium salt in 20 patients with chronic renal failure. In 12 patients (group I) having a creatinine clearance of less than 19 ml.min-1 the pharmacokinetics parameters for tianeptine and MC5 metabolite were determined and compared with those obtained in a matched control group (group II). The other 8 patients (group III) were functionally anephric and were studied during 1 dialysis to assess the haemodialysis clearances of tianeptine and MC5 metabolite. The comparison between groups I and II showed that renal failure did not appear to affect the disposition of parent tianeptine. However, the MC5 metabolite terminal half-life was found to be increased in renal patients compared to controls (14.2 +/- 9.3 h vs 4.9 +/- 1.7 h). Due to a large interindividual variability the difference did not reach a significant level (P = 0.054). According to the antidepressant activity of the MC5 metabolite in pharmacological tests, the sustained rise in its plasma level suggests that a reduced daily dose should be administered and 12.5 mg of tianeptine should be given twice daily to patients with chronic renal failure. In patients from group III elimination of the compounds by haemodialysis was found to be low. The dialysis clearances were 3.9 +/- 9.9 ml.min-1 and 19.2 +/- 8.6 ml.min-1 for tianeptine and its MC5 metabolite respectively. This low dialysability has 2 clinical implications. Firstly, patients currently undergoing haemodialysis and treated by tianeptine could be given the drug without taking dialysis into account. Secondly, haemodialysis does not appear to be an effective method for tianeptine elimination in cases of overdosage.

Lack of cardiovascular side effects of the new tricyclic antidepressant tianeptine. A double-blind, placebo-controlled study in young healthy volunteers.

In a double-blind, placebo-controlled, crossover study, the effects of therapeutic doses of the new tricyclic antidepressant tianeptine on cardiovascular function were closely monitored in 21 healthy volunteers during a 2-week treatment period. Blood pressure measurements, ECG recording, 24-h Holter monitoring, and echocardiography were carried out at 1-week intervals. Isotopic ventriculography was measured twice under each treatment. Tianeptine did not produce orthostatic hypotension or increase heart rate. No ECG changes could be observed and the cardiac conduction time remained unchanged. One subject presented with an increase in frequency of ventricular premature beats that could not be definitely attributed to the drug. Cardiac output assessed at rest and after a bicycle exercise stress test was not altered. The present study suggests that tianeptine is a tricyclic antidepressant endowed with less cardiac toxicity than classical tricyclic antidepressants.

Kinetic profiles of tianeptine and its MC5 metabolite in plasma, blood and brain after single and chronic intraperitoneal administration in the rat.

This study was conducted to determine kinetic profiles of the antidepressant tianeptine and its main metabolite (named MC5) in plasma, blood and brain after single (10 mg.kg-1) and chronic (10 mg.kg-1.day-1 and 2 x 10 mg.kg-1.day-1 for 15 days) intraperitoneal administration in Wistar rats. In plasma, tianeptine and MC5 reached a peak very quickly (5 and 15 min post administration respectively). Following the peak, disappearance of tianeptine was faster than that of MC5 with terminal half-lives close to 2.5 and 6.5 h respectively. During chronic treatment, accumulation of tianeptine was negligible, that of MC5 was slight as indicated by accumulation ratios equal to 1.28 (once daily administration) and 1.73 (twice daily administration). Tianeptine and MC5 rapidly appeared in brain tissue but at concentrations less than those observed in plasma. Peak concentrations of tianeptine in brain were higher than those of MC5. A very low penetration of tianeptine and MC5 into erythrocytes was observed.

Doping control analysis of emerging drugs in human plasma - identification of GW501516, S-107, JTV-519, and S-40503.

An important aspect of preventive doping research is the rapid implementation of tests for emerging drugs with potential for misuse into routine doping control assays. New therapeutics of different classes such as PPARdelta-agonists (e.g. GW501516), ryanodine-calstabin-complex stabilizers (e.g. S-107 and JTV-519), and selective androgen receptor modulators (SARMs, e.g. S-40503) are currently used for the treatment of particular medical conditions such as metabolic syndrome, cardiac arrhythmia, debilitating diseases and osteoporosis, respectively. Due to their being at an early stage of clinical trials and the limited availability of data on the metabolism and possible renal elimination of the active drugs, the development of protocols for doping control analyses of plasma specimens could be an option for the detection of the circulating agents. The mass spectrometric fragmentation of four emerging drug candidates (GW501516, S-107, JTV-519, and S-40503) was elucidated by positive electrospray ionization and collision-induced dissociation using a high resolution/high accuracy mass spectrometer. A screening and confirmation procedure was established based on liquid chromatography/tandem mass spectrometry requiring a volume of 100 microL of plasma. Proteins were precipitated using acetonitrile, the specimens were centrifuged and the supernatant analyzed using a triple-quadrupole mass spectrometer employing multiple reaction monitoring of diagnostic ion transitions. The method was validated with regard to specificity, limits of detection (0.4-8.3 ng/mL), recoveries (72-98%), intraday and interday precisions (12-21%), and ion suppression/enhancement effects.

Planned complex suicide: an unusual case.

We report an unusual case of planned complex suicide. The victim was a woman aged 67 years, who was found dead in her bath in a state of advanced putrefaction. A plugged-in hairdryer was submerged in the water and the electrical fuses in the room had short-circuited. A kitchen knife lay below the body of the victim, whose left forearm bore incisions suggestive of wrist-cutting. At autopsy, no sign suggesting electrocution could be observed because of the advanced state of putrefaction of the body. Toxicological analysis revealed massive ingestion of tianeptine (blood concentration 15.5 mg/L). Although the exact cause of death could not be determined because of the state of the corpse, meticulous examination of the scene and information obtained from the victim's relatives led to the conclusion of suicide.

Quantitative determination of BMS186716, a thiol compound, in dog plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after formation of the methyl acrylate adduct.

As it is extremely unstable in blood, the thiol compound BMS186716 was stabilized by the addition of methyl acrylate (MA) to blood samples. The blood samples were then kept in ice for 10-15 min for completion of the Michael addition reaction to occur between the thiol group of BMS186716 and MA, after which the plasma was separated by centrifugation under refrigeration. For sample analysis, the standard and quality control samples were prepared by spiking blank plasma with the BMS186716-MA adduct. After addition of the internal standard, BMS 188035-MA, each sample was acidified with HCI and then extracted with methyl tert.-butyl ether. Each reconstituted extract was injected into a high-performance liquid chromatography-positive ion electrospray ionization mass spectrometric system. The electrospray condition was chosen to enhance the [M+NH4]+ signal at the expense of the [M+H]+ signal. Monitoring the [M+NH4]+ signal, a lower limit of quantitation of 2.5 ng/ml was achieved, with 0.5 ml plasma. We have thus shown that a sulfhydryl compound (BMS186716) in blood can successfully be stabilized by reacting it with MA and that the adduct produced is adequately stable in blood and plasma to allow the development of a rugged quantitative bioanalytical method.

Ion-pair extraction and high-performance liquid chromatographic determination of tianeptine and its metabolites in human plasma, urine and tissues.

An isocratic reversed-phase ion-pair liquid chromatographic method for the determination of tianeptine and its two main metabolites in plasma, urine and tissues, using an internal standard, is reported. The influence of two stationary phases on the retention of the drugs was studied. The drugs were extracted as ion pairs, using a heptane-octanol-tetraheptylammonium bromide mixture (98:2:0.5, v/v/w) as extraction solvent. This extraction procedure yielded plasma drug recoveries of greater than 60% and allowed UV detection at 220 nm without interference from endogenous components of plasma, urine or tissues. Linear standard curves up to 1.00 micrograms/ml and drug determination down to 0.01 microgram/ml were observed. This method has been successfully applied to the analysis of human plasma and urine samples and of encephales from tianeptine-dosed rats.

LC/MS/MS determination of omapatrilat, a sulfhydryl-containing vasopeptidase inhibitor, and its sulfhydryl- and thioether-containing metabolites in human plasma.

Omapatrilat, the most clinically advanced member of a new class of cardiovascular agents, vasopeptidase inhibitors, is under development at Bristol-Myers Squibb Pharmaceutical Research Institute for the treatment of hypertension and heart failure. An electrospray LC/MS/MS method has been developed and validated for the simultaneous determination of omapatrilat and its four metabolites in human plasma. Since omapatrilat and two of the metabolites are sulfhydryl-containing compounds, methyl acrylate was used to stabilize these compounds in human blood and plasma samples. Methyl acrylate reacted instantly with the sulfhydryl group to form a derivative that was stable in blood and plasma. Extraction of the analytes from plasma samples was achieved by semiautomated liquid-liquid extraction, where a robotic liquid handler performed the liquid-transferring steps. The mass spectrometer was operated in the negative ion selected-reaction-monitoring mode. The calibration curve ranges were 0.5-250 ng/mL for omapatrilat and one metabolite and 2.0-250 ng/mL for the other three metabolites.