Determination of SR 49059 in human plasma and urine by LC-APCI/MS/MS

Application of co-eluting structural analog internal standards for expanded linear dynamic range in liquid chromatography/electrospray mass spectrometry

Non-linear standard calibration curves occur frequently in liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS), necessitating the use of non-linear regression curve fitting or a reduction in assay dynamic range. Non-linearity can be minimized by the use of stable isotope internal standards, if the cause of curve bending is ionization saturation. Unfortunately, stable isotope internal standards can be difficult or expensive to synthesize. Structural analog internal standards, if sufficiently close to analytes both in chemical structures and HPLC retention times, may mimic the effect of stable isotope internal standards. Tentative experimental evidence supporting this concept is presented in this paper.

Placental transfer of SR49059 in the human dually perfused cotyledon in vitro

SR49059 is an antagonist of vasopressin V(1a)receptors currently developed as a tocolytic drug. We investigated the transplacental transfer of SR49059 in vitro using the single pass dually perfused human cotyledon model. Thirteen placentae were collected from normal term pregnancies immediately after delivery. The placental transfer of SR49059 was tested at steady state at three different concentrations (100 ng/ml, 200 ng/ml and 500 ng/ml) along with that of antipyrine 20 mg/l as a reference substance. Concentrations were assayed by liquid chromatography with UV (antipyrine) or mass spectrometry (SR49059) detection. At steady state, the mean+/-s.d. fetal transfer rate of SR49059 was 10.80+/-4.33 per cent, 9.34+/-4.41 per cent, and 11.78+/-3.26 per cent at 100 ng/ml, 200 ng/ml and 500 ng/ml, respectively. The corresponding clearance indices were 0.29+/-0.14, 0.25+/-0.08, and 0.31+/-0.06, respectively. The absence of saturation kinetics is consistent with a passive mechanism of transfer. Moderate amounts of SR49059 are transferred from the maternal to the fetal circulation. The clearance index of SR49059 appeared to be very similar to that of ritodrine, which is currently used as a tocolytic.

Determination of a beta(3)-agonist in human plasma by LC/MS/MS with semi-automated 48-well diatomaceous earth plate

Methods for the determination of a beta(3)-agonist (A) in human plasma were developed and compared based on high-performance liquid chromatography (HPLC) with tandem mass spectrometric (MS/MS) detection using a turbo ion spray (TIS) interface. Drug and internal standard were isolated from plasma by three sample preparation methods, liquid-liquid extraction, Chem Elut cartridges and 48-well diatomaceous earth plates, that successively improved sample throughput for LC/MS/MS. MS/MS detection was performed on a PE Sciex API 365 tandem mass spectrometer operated in positive ion mode and using multiple reaction monitoring (MRM). The precursor/product ion combinations of m/z 625/607 and 653/515 were used to quantify A and internal standard, respectively, after chromatographic separation of the analytes. Using liquid-liquid extraction and Chem Elut cartridges, the assay concentration range was 0.5-100 ng/ml. Using diatomaceous earth plates, the concentration range of the assay was extended to 0.5-200 ng/ml. For all three assays, the statistics for precision and accuracy is comparable. The assay accuracy ranged from 91-107% and intraday precision as measured by the coefficient of variation (CV) ranged 2-10%. The sample throughput was tripled when the diatomaceous earth plate method was compared with the original liquid-liquid extraction method.

Development and validation of a liquid chromatographic-tandem mass spectrometric method for the determination of pibutidine in human urine

A liquid chromatographic-tandem mass spectrometric method for the rapid quantitative determination of pibutidine, an H2-receptor antagonist, in human urine has been developed and validated over the concentration range 0.1-25.6 microg ml(-1). Urine samples were prepared based on a simple dilution with 0.05% acetic acid, followed by reversed-phase liquid chromatographic separation. Pibutidine and its internal standard (2H10-pibutidine) were ionized using an electrospray ionization interface and detected by tandem mass spectrometry in the selected reaction-monitoring mode. Completed validation demonstrated the method to be robust, accurate, precise and specific for the direct quantification of pibutidine in human urine. This method has enabled investigation of the urinary excretion of pibutidine following oral administration of pibutidine hydrochloride to healthy subjects.

Effects of the nonpeptide V(1) vasopressin receptor antagonist SR49059 in hypertensive patients

We assessed the clinical and pharmacological profile of the orally active V(1) vascular vasopressin (AVP) receptor nonpeptide antagonist SR49059 (SR) during the osmotic stimulation of AVP release in hypertensive patients. In a double-blind crossover-versus-placebo study, 24 untreated stage I or II essential hypertensive patients (12 whites and 12 blacks) received a single 300 mg oral dose of SR 2 hours before the stimulation of AVP secretion with a 5% hypertonic saline infusion. Hemodynamic, humoral, and hormonal parameters were monitored for up to 28 hours after drug administration. SR did not alter blood pressure or heart rate before the saline infusion and did not reduce the blood pressure increment induced by the hypertonic saline infusion. However, the blood pressure peak at the end of the hypertonic saline infusion was slightly lower in the presence of SR (P=0.04). Heart rate was significantly faster between 4 and 6 hours after SR administration (P=0.02). The rise in plasma sodium and osmolality triggered by the saline infusion was not modified by SR, but AVP release was slightly greater in the presence of SR (P<0.0003). AVP-induced aggregation of blood platelets in vitro was significantly reduced by SR, with a peak effect 2 hours after drug administration that coincided with the SR peak plasma concentration. Plasma renin activity and aldosterone before and after the saline infusion were not modified by SR. Urine volume and osmolality were not altered by SR administration. SR effects were similar in the 2 ethnic groups as well as in salt-sensitive versus salt-resistant patients. In a situation of AVP osmotic release and volume expansion in hypertensive patients, a single oral dose of the V(1) vascular AVP receptor nonpeptide antagonist SR49059, which is able to block AVP-induced platelet aggregation, exerts a transient vasodilation effect that is not associated with a sustained blood pressure reduction. SR49059 is a pure V(1) vascular receptor antagonist that is devoid of V(2) renal receptor actions.

Determination of TA-0201, a novel orally active non-peptide endothelin antagonist, in rat plasma and tissues by a liquid chromatography--electrospray ionization--tandem mass spectrometry system

N-[6-[2-[(5-bromo-2-pyrimidinyl)oxy]ethoxy]-5-(4-methylphenyl)-4-pyrimid inyl]-4-(2-hydroxy-1, 1-dimethylethyl) benzenesulfonamide sodium salt (TA-0201) is a novel orally active non-peptide antagonist for endothelin (ET) receptors. A sensitive and simultaneous determination method of TA-0201 and its major metabolites by liquid chromatography tandem mass spectrometry (LC--MS/MS) in a selected reaction monitoring mode using [2H6]TA-0201 as the internal standard was developed, and the plasma and tissue concentrations of TA-0201 and its major metabolites were determined in a pharmacokinetic study. The lower limit of determination of plasma TA-0201 concentrations by this method was 0.1 ng/0.5 ml, and the between- and within-run accuracy and precision were both less than 5.1%, in the calibration curve range of 0.1-50 ng/0.5 ml. This method was applied to determine the concentrations of TA-0201 and its metabolites in plasma and various target tissues, i.e. the heart, lung and kidney, after oral administration of TA-0201 (0.1 mg/kg(-1)) to male rats. TA-0201 and its major metabolite of a carboxylic acid form were detected in plasma and all the tissues 24 h after administration, their tissue concentrations being higher than those in plasma and still detectable at 72 h. Thus, this method could successfully be applied to study pharmacokinetic properties of TA-0201 in rats.