Simple and fast LC-MS/MS method for quantification of terazosin in human plasma and application to bioequivalence study.

A simple, fast and sensitive LC-MS/MS method was developed to quantify terazosin in human plasma. The mobile phase consisted of acetonitrile-0.1% (v/v) formic acid (70:30, v/v). Prazosin was used as internal standard (IS). As deproteinization agent, acetonitrile produced a clean sample. A higher response intensity with more symmetrical peak was obtained using Agilent Poroshell 120 EC-C18 - Fast LC column (100 × 2.1mmID, 2.7 µm) compared with Kinetex XB-C18 (100 × 2.1 mm, 2.6 µm) column. The response of terazosin and IS were approximately two times in citrate phosphate dextrose (CPD) plasma compared with dipotassium ethylenediaminetetraacetic acid (K2EDTA) plasma. Plasma calibration curve was linear from 1.0 to 100.0 ng/mL, with coefficient of determination r2 ≥ 0.99. The within-run and between-run precision values (CV, %) were <5.2% and <7.8%, while accuracy values were 102.8-112.7% and 103.4-112.2%. The extended run accuracy was 98.6-102.8% and precision (CV, %) 4.3-10.4%. The recovery of analyte was >98% and IS >94%. Terazosin in plasma kept at benchtop was stable for 24 h, in autosampler tray for 48 h, in instrumentation room for 48 h, for 7 freeze-thaw cycles and in freezer for 140 days. Terazosin and IS stock standard solutions were stable for 140 days at room temperature and in the chiller. The high throughput method was successfully utilized to measure 935 samples in a bioequivalence study of terazosin.

Applications of shun shell column and nanocomposite sorbent for analysis of eleven anti-hypertensive in human plasma.

High-performance liquid chromatography (HPLC) and solid phase micro membrane tip extraction (SPMMTE) methods are developed for the simultaneous analysis of eleven cardiovascular drugs in human plasma. Iron nanoparticles were obtained by the green method, characterized by XRD, FT-IR, TEM, and EDS and utilized in SPMMTE for sample preparation. The mobile phase used was ammonium acetate buffer-methanol-acetonitrile (65:18:17) with a 1.0 mL/min flow rate at 260 nm detection. Column used was Sunshell C18 150 × 4.6 mm, 2.6 µm. The values of k, α, and Rs were ranged from 040 to109.22, 1.20 to 2.67 and 1.0 to 26.18. SPMMTE and HPLC methods were fast, reproducible, precise, robust, economic and rugged for analysis of methyldopa, hydrochlorothiazide, prazosin hydrochloride, furosemide, labetalol, propranolol, valsartan, losartan potassium, diltiazem, irbesartan and spironolactone in human plasma. The recoveries (%) of methyldopa, hydrochlorothiazide, prazosin hydrochloride, furosemide, labetalol, propranolol, valsartan, losartan potassium, diltiazem, irbesartan, and spironolactone were 91.0, 85.2, 92.3, 90.4, 90.1, 85.6, 86.6, 86.2, 85.1, 86.6, and 85.7, respectively. These results showed that SPMMTE and HPLC methods can be applied to test the described drugs in several matrices.

Magnetic-Dispersive Solid Phase Extraction Based on Graphene Oxide-Fe3O4 Nanocomposites Followed by High Performance Liquid Chromatography-Fluorescence for the Preconcentration and Determination of Terazosin Hydrochloride in Human Plasma.

In the present study, a facile modified impregnation method was employed to synthesize superparamagnetic graphene oxide-Fe3O4 (GO-Fe3O4) nanocomposites. Based on the GO-Fe3O4 as adsorbent, a simple and fast magnetic-dispersive solid phase extraction followed by high performance liquid chromatography with fluorescence detection (M-dSPE-HPLC-FL) method was established and validated for the preconcentration and determination of terazosin hydrochloride (TRZ) in human plasma samples. The obtained nanomaterials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometry. Different parameters affecting the extraction efficiency, such as sample pH, amount of sorbent, extraction time, elution solvent and its volume and desorption time, were evaluated and optimized. The linearity of the proposed method was excellent over the range 0.3-50.0 ng mL-1 with an acceptable coefficient of determination (R2 = 0.9989). The limit of quantification and limit of detection were found to be 0.3 and 0.09 ng mL-1, respectively, and the preconcentration factor of 10 was achieved. Intra- and inter-day precision expressed as relative standard deviation (RSD %, n = 6) were between 2.2-3.8% and 4.7-6.4%, respectively. Accuracy, estimated by recovery assays, was 97.7-106.6% with RSD ≤ 5.2%. Ultimately, the applicability of the method was successfully confirmed by the extraction and determination of TRZ in human plasma samples.

A novel electrochemical sensor based on electrode modified with gold nanoparticles and molecularly imprinted polymer for rapid determination of trazosin.

A novel molecularly imprinted polymer sensor for fast and direct determination of trazosine (TR) was studied. The voltammetric sensor based on molecularly imprinted polymer (MIP) with disposable gold nanoparticles modified screen printed carbon electrode (MIP/AuNPs/SPCE) is developed for the determination of TR. Under the optimum conditions, the peak current of the sensor and TR concentration showed a good linear relationship over the range from 2.0 to 250.0 µM, with a low detection limit (S/N = 3) of 0.3 µM. The modified electrode demonstrated good electrocatalytic properties toward the oxidation of TR. This sensor selectively detected TR even in the presence of high concentration of similar compounds and MIP/AuNPs/SPCE was also confirmed successfully for the determination of TR in the various real samples including human blood serum, urine and trazosin tablet.

Micellar enhanced spectrofluorimetric approach for nanogram detection of certain α1 -blocker drugs: Application in pharmaceutical preparations and human plasma.

Alpha1-adrenergic-blocking drugs, namely; alfuzosin hydrochloride (ALF), doxazosin mesylate (DOX) and terazosin hydrochloride (TER) are effective as antihypertensive agents as well as in management of benign prostatic hypertrophy. In this study, a simple, very fast, highly sensitive and cheap technique was optimized for assay of these drugs in pure states and pharmaceutical tablets. The proposed method is dependent on enhancement of the native fluorescence of investigated drugs using the polyoxyethylene 50 stearate (POE50S) micellar system. The method showed excitation at 325, 340 and 250 nm for ALF, DOX and TER, respectively and an emission maxima at 382 nm. The fluorescence intensity-concentration charts of studied drugs were attained utilizing concentration ranges (2.0-60.0 ng mL-1 ) for DOX and (4.0-100.0 ng mL-1 ) for ALF and TER with quantitation limits 2.9, 1.6 and 2.5 ng mL-1 for ALF, DOX and TER, respectively. The suggested technique was approved according to International Council for Harmonisation (ICH) standards and the United States Food and Drug Administration (US FDA) bioanalytical method validation and has been effectively applied for assay of these medications in their dosage forms as well as for content uniformity test. The developed procedure was also efficiently applied for determination of these drugs in real human plasma with high accuracy.

Utility of Hantzsch reaction for development of highly sensitive spectrofluorimetric method for determination of alfuzosin and terazosin in bulk, dosage forms and human plasma.

A highly sensitive, cheap, simple and accurate spectrofluorimetric method has been developed and validated for the determination of alfuzosin hydrochloride and terazosin hydrochloride in their pharmaceutical dosage forms and in human plasma. The developed method is based on the reaction of the primary amine moiety in the studied drugs with acetylacetone and formaldehyde according to the Hantzsch reaction, producing yellow fluorescent products that can be measured spectrofluorimetrically at 480 nm after excitation at 415 nm. Different experimental parameters affecting the development and stability of the reaction products were carefully studied and optimized. The fluorescence-concentration plots of alfuzosin and terazosin were rectilinear over a concentration range of 70-900 ng ml-1 , with quantitation limits 27.1 and 32.2 ng ml-1 for alfuzosin and terazosin, respectively. The proposed method was validated according to ICH guidelines and successfully applied to the analysis of the investigated drugs in dosage forms, content uniformity test and spiked human plasma with high accuracy.

Unconjugated bilirubin elevation impairs the function and expression of breast cancer resistance protein (BCRP) at the blood-brain barrier in bile duct-ligated rats.

AIM: Liver failure is associated with dyshomeostasis of efflux transporters at the blood-brain barrier (BBB), which contributes to hepatic encephalopathy. In this study we examined whether breast cancer resistance protein (BCRP), a major efflux transporter at the BBB, was altered during liver failure in rats. METHODS: Rats underwent bile duct ligation (BDL) surgery, and then were sacrificed after intravenous injection of prazosin on d3, d7 and d14. The brains and blood samples were collected. BCRP function at the BBB was assessed by the brain-to-plasma prazosin concentration ratio; Evans Blue extravasation in the brain tissues was used as an indicator of BBB integrity. The protein levels of BCRP in the brain tissues were detected. Human cerebral microvessel endothelial cells (HCMEC/D3) and Madin-Darby canine kidney cells expressing human BCRP (MDCK-BCRP) were tested in vitro. In addition, hyperbilirubinemia (HB) was induced in rats by intravenous injection of unconjugated bilirubin (UCB). RESULTS: BDL rats exhibited progressive decline of liver function and HB from d3 to d14. In the brain tissues of BDL rats, both the function and protein levels of BCRP were progressively decreased, whereas the BBB integrity was intact. Furthermore, BDL rat serum significantly decreased BCRP function and protein levels in HCMEC/D3 cells. Among the abnormally altered components in BDL rat serum tested, UCB (10, 25 µmol/L) dose-dependently inhibit BCRP function and protein levels in HCMEC/D3 cells, whereas 3 bile acids (CDCA, UDCA and DCA) had no effect. Similar results were obtained in MDCK-BCRP cells and in the brains of HB rats. Correlation analysis revealed that UCB levels were negatively correlated with BCRP expression in the brain tissues of BDL rats and HB rats as well as in two types of cells tested in vitro. CONCLUSION: UCB elevation in BDL rats impairs the function and expression of BCRP at the BBB, thus contributing to hepatic encephalopathy.

Pharmacokinetics of terazosin enantiomers in healthy Chinese male subjects.

The purpose of this study was to elucidate the pharmacokinetics of terazosin enantiomers in healthy Chinese male subjects. After a single oral dose of 2-mg terazosin, the plasma concentrations of terazosin enantiomers were measured over the course of 48 h in 12 healthy subjects. The plasma concentrations of (+)-(R)-terazosin at all time points were higher than those of (-)-(S)-terazosin. The area under the plasma concentration-time curve (AUC(0-∞) ) and maximum plasma concentration of (+)-(R)-terazosin were significantly greater than those of the (-)-(S)-terazosin (P < 0.01, respectively). The R/S ratio of AUC(0-∞) of terazosin was 1.68. For the first time, it was proven that the pharmacokinetics of terazosin was stereoselective in healthy Chinese male subjects.

Direct analysis of dried blood spots utilizing desorption electrospray ionization (DESI) mass spectrometry.

A novel approach to the quantitative determination of xenobiotics in whole blood samples without sample preparation or chromatography is described. This method is based on direct analysis of microlitre volumes of blood which are spotted onto specialized paper cards and dried, with the resulting dried blood spots (DBS) analyzed directly via desorption electrospray ionization (DESI) mass spectrometry (MS). Using sitamaquine, terfenadine, and prazosin as model compounds with verapamil as a common internal standard, this methodology demonstrated detection of each compound down to 10 ng mL(-1) from DBS where standard calibration curves show linearity from 10-10,000 ng mL(-1) with r(2) > 0.99. Three (3) different untreated types of filter papers (Whatman 903 and 31ETF as well as Ahlstrom 237) and two (2) treated types of filter paper (Whatman FTA and FTA Elute) were examined and the effect of each surface on the recovery of each analyte was evaluated. The results show that the untreated papers provide the best substrates for DBS analysis by DESI. A more in depth study of the quantitation of sitamaquine on 31ETF paper stock provided bias and error measurements of less than 20%. The promising results shown in this study may have important implications in the areas of therapeutic drug monitoring (TDM), clinical and forensic toxicology, and pharmacology.

Determination of metoclopramide in human plasma by LC-ESI-MS and its application to bioequivalance studies.

An LC-MS method for the determination of metoclopramide in human plasma was developed and validated. Sample preparation involved extraction with ethyl acetate. Chromatographic separation was performed on a Thermo Hypersil-Hypurity C18 (150 mm x 2.1 mm, 5 microm) with the mobile phase consisting of 40 mM ammonium acetate-methanol-acetonitrile. A single-quadrupole mass spectrometer with an electrospray interface was operated in the selected-ion monitoring mode to detect the [M+H]+ ions at m/z 300 for metoclopramide and at m/z 384 for the internal standard (prazosin). The method was validated over 0.78-50.00 ng mL(-1) for metoclopramide. The recovery was 67.8-83.1%, and the limit of quantitation (LOQ) detection was 0.78 ng mL(-1) for metoclopramide. The intra- and inter-day precision of the method at three concentrations was 5.0-13.6% with accuracy of 99.2-104.0%. Stability of compounds was established in a battery of stability studies. The method was successfully applied to bioequivalence studies of metoclopramide hydrochloride tablets to obtain the pharmacokinetic parameters.

Fluorescent quantification of terazosin hydrochloride content in human plasma and tablets using second-order calibration based on both parallel factor analysis and alternating penalty trilinear decomposition.

Two second-order calibration methods based on the parallel factor analysis (PARAFAC) and the alternating penalty trilinear decomposition (APTLD) method, have been utilized for the direct determination of terazosin hydrochloride (THD) in human plasma samples, coupled with the excitation-emission matrix fluorescence spectroscopy. Meanwhile, the two algorithms combing with the standard addition procedures have been applied for the determination of terazosin hydrochloride in tablets and the results were validated by the high-performance liquid chromatography with fluorescence detection. These second-order calibrations all adequately exploited the second-order advantages. For human plasma samples, the average recoveries by the PARAFAC and APTLD algorithms with the factor number of 2 (N=2) were 100.4+/-2.7% and 99.2+/-2.4%, respectively. The accuracy of two algorithms was also evaluated through elliptical joint confidence region (EJCR) tests and t-test. It was found that both algorithms could give accurate results, and only the performance of APTLD was slightly better than that of PARAFAC. Figures of merit, such as sensitivity (SEN), selectivity (SEL) and limit of detection (LOD) were also calculated to compare the performances of the two strategies. For tablets, the average concentrations of THD in tablet were 63.5 and 63.2 ng mL(-1) by using the PARAFAC and APTLD algorithms, respectively. The accuracy was evaluated by t-test and both algorithms could give accurate results, too.

Quantification of [11C]GB67 binding to cardiac alpha1-adrenoceptors with positron emission tomography: validation in pigs.

INTRODUCTION: An increase in human cardiac alpha(1)-adrenoceptor (alpha(1)-AR) density is associated with various diseases such as myocardial ischemia, congestive heart failure, hypertrophic cardiomyopathy and hypertension. Positron emission tomography (PET) with an appropriate radioligand offers the possibility of imaging receptor function in the normal and diseased heart. [(11)C]GB67, an analogue of prazosin, has been shown in rats to have potential as a PET ligand with high selectivity to alpha(1)-AR. However, alpha(1)-AR density is up to ten times higher in rat heart compared to that in man. The aim of the present preclinical study was to extend the previous evaluation to a large mammal heart, where the alpha(1)-AR density is comparable to man, and to validate a method for quantification before PET studies in man. METHODS: Seven [(11)C]GB67 PET studies, with weight-adjusted target dose of either 5.29 MBq kg(-1) (pilot, test-retest and baseline-predose studies) or 8.22 MBq kg(-1) (baseline-displacement studies), were performed in four anaesthetised pigs (39.5 +/- 3.9 kg). Total myocardial volume of distribution (V (T)) was estimated under different pharmacological conditions using compartmental analysis with a radiolabelled metabolite-corrected arterial plasma input function. A maximum possible blocking dose of 0.12 mumol kg(-1) of unlabeled GB67 was given 20 min before [(11)C]GB67 administration in the predose study and 45 min after administration of [(11)C]GB67 in the displacement study. In addition, [(15)O]CO (3,000 MBq) and [(15)O]H(2)O, with weight adjusted target dose of 10.57 MBq kg(-1), were also administered for estimation of blood volume recovery (RC) of the left ventricular cavity and myocardial perfusion (MBF), respectively. RESULTS: [(11)C]GB67 V (T) values (in ml cm(-3)) were estimated to be 24.2 +/- 5.5 (range, 17.3-31.3), 10.1 (predose) and 11.6 (displacement). MBF did not differ within each pig, including between baseline and predose conditions. Predose and displacement studies showed that specific binding of [(11)C]GB67 to myocardial alpha(1)-ARs accounts for approximately 50% of V (T). CONCLUSION: The present study offers a methodology for using [(11)C]GB67 as a radioligand to quantify human myocardial alpha(1)-ARs in clinical PET studies.

Metabolism of prazosin in rat and characterization of metabolites in plasma, urine, faeces, brain and bile using liquid chromatography/mass spectrometry (LC/MS).

1. Prazosin, 2-[4-(2-furanoyl)-piperazin-1-yl]-4-amino-6,7-dimethoxyquinazoline, is an antihypertensive agent that has been used safely since 1976 and is currently being investigated for the treatment of post-traumatic stress disorder. The in vivo metabolism of prazosin in rat was first reported in 1977, although at the time analytical techniques were not as sophisticated, nor were the mass spectrometers as sensitive, as today. Recently, the in vitro metabolism of prazosin in rat liver microsomes and cryopreserved hepatocytes was investigated using liquid chromatography/mass spectrometry (LC/MS), which revealed new metabolic pathways. 2. In the present work, rat in vivo metabolism was reinvestigated using a quadrupole time-of-flight mass spectrometer coupled with ultra-performance liquid chromatography, or chip-based nanoflow electrospray ionization, with the aim of identifying metabolites revealed by the in vitro studies and any new metabolites. 3. It is reported that prazosin was metabolized in rats to produce the metabolites observed in vitro. In addition, new phase I metabolites, M18, M20 and M21, were formed and conjugation with glucose or taurine formed the new phase II metabolites, M16 and M19, respectively. 4. Evidence for bioactivation of prazosin included detection of ring-opened metabolites (M4 and M7) and a cysteinyl-glycine conjugate (M17). Further support to the structure of the ring-opened metabolite M7 was obtained by nuclear magnetic resonance (NMR) experiments on M7 isolated from urine.

Pharmacokinetic and pharmacodynamic modelling of arterial haemodynamic effects of terazosin in healthy volunteers.

OBJECTIVE: This study aimed to investigate, in healthy volunteers, the relationship between the plasma concentrations of the alpha(1)-adrenoceptor antagonist terazosin and its effects on arterial blood pressure after a single oral administration of terazosin 2 mg. M ethods: Twenty-four healthy volunteers participated in this study. Pharmacokinetic and pharmacodynamic modeling were performed subject by subject. First, plasma concentrations were fitted according to a one-compartment model with first-order absorption and monoexponential elimination. Then the maximum drug-induced decrease (E(max)) effect compartment-model was developed to describe the pharmacodynamic relationships between systolic and diastolic blood pressure and plasma concentrations using the pharmacokinetic parameters that were previously estimated. RESULTS: For systolic blood pressure, E(max) was 29.9 +/- 10.6 mmHg. The corresponding value for decrease in diastolic blood pressure was 39.7 +/- 8.6 mmHg. The effects of terazosin on systolic and diastolic blood pressure could be quantified by an inhibitory E(max) effect compartment model. The obtained first-order rate constant values (0.40 +/- 0.006 h(-)(1) for systolic blood pressure and 0.47 +/- 0.012 h(-)(1) for diastolic blood pressure) were consistent with the rapid development of pharmacological effect. EC(50) (concentration of terazosin that induces an effect at 50% of E(max) values) values were similar for systolic (29.9 +/- 4.3 microg/L) and diastolic (28.7 +/- 4.0 microg/L) blood pressure. A decrease in diastolic blood pressure was the most sensitive response after oral administration of a single dose of terazosin. CONCLUSION: The direct haemodynamic effects of terazosin can be characterized by an E(max) effect compartment model.

Prediction of alpha1-adrenoceptor occupancy in the human prostate from plasma concentrations of silodosin, tamsulosin and terazosin to treat urinary obstruction in benign prostatic hyperplasia.

Alpha1-adrenoceptor antagonists are clinically useful for the improvement of urinary obstruction due to benign prostatic hyperplasia (BPH), and their therapeutic effects are mediated through the blockade of prostatic alpha(1)-adrenoceptors. The present study was undertaken to predict the magnitude and duration of alpha(1)-adrenoceptor occupancy in the human prostate after oral alpha(1)-adrenoceptor antagonists. Prostatic alpha(1)-adrenoceptor-binding parameters of silodosin were estimated by measuring specific [(3)H]prazosin binding in rat prostate after oral administration of this drug. The plasma concentration of silodosin after oral administration in rats and healthy volunteers was measured using a high-performance liquid chromatographic method. The alpha(1)-adrenoceptor-binding affinities (K(i)) of silodosin, tamsulosin, and terazosin in the human prostate and plasma concentrations of tamsulosin and terazosin were obtained from the literature. Using the alpha(1)-adrenoceptor binding parameters of silodosin in rat prostate, alpha(1)-adrenoceptor occupancy in the human prostate was estimated to be around 60-70% at 1-6 h after oral administration of silodosin at doses of 3.0, 8.1, and 16.1 micromol. Thereafter, the receptor occupancy was periodically decreased, to 24% (8.1 micromol) and 54% (16.1 micromol) 24 h later. A similar magnitude and time course of alpha(1)-adrenoceptor occupancy by silodosin in the human prostate were estimated using alpha(1)-adrenoceptor-binding affinities (K(i)) in the human prostate. Despite about two orders of differences in the plasma unbound concentrations after clinically effective oral dosages of silodosin, tamsulosin, and terazosin, there was a comparable magnitude of prostatic alpha(1)-adrenoceptor occupancy by these drugs. In conclusion, the prediction of alpha(1)-adrenoceptor occupancy in the human prostate by alpha(1)-adrenoceptor antagonists may provide the rationale for the optimum dosage regimen of these drugs in the therapy of BPH.

[Analysis of 37 drugs in whole blood by HPLC after solid phase extraction].

OBJECTIVE: To develop a specific, sensitive, reproducible SPE-HPLC method for the determination of 37 drugs in whole blood. METHODS: With the doxapram as internal standard, Oasis column was used to extract drugs from whole blood. Two kinds of mobile phases were used in this study. Separations were achieved by a LiChrospher 100 RP-C18 (250 mm x 4.0 mm x 5 microm) column kept at 50 degrees C, the DAD detector was set at 230 nm and 250 nm. RESULTS: The limit of detection were 1-30 ng/mL. The method showed excellent linearity and the linear correlation coefficient was > or =0.997 98. The relative standard deviation for between-day and within-day assay were <10%. CONCLUSION: The method is effective, simple, reliable and has been used in real cases.

Attenuation of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy)-induced rhabdomyolysis with alpha1- plus beta3-adrenoreceptor antagonists.

1. Studies were designed to examine the effects of alpha(1) (alpha(1)AR)- plus beta(3)-adrenoreceptor (beta(3)AR) antagonists on 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy)-induced hyperthermia and measures of rhabdomyolysis (creatine kinase (CK)) and renal function (blood urea nitrogen (BUN) and serum creatinine (sCr)) in male Sprague-Dawley rats. 2. MDMA (40 mg x kg(-1), s.c.) induced a rapid and robust increase in rectal temperature, which was significantly attenuated by pretreatment with the alpha(1)AR antagonist prazosin (100 microg x kg(-1), i.p.) plus the beta(3)AR antagonist SR59230A (5 mg x kg(-1), i.p.). 3. CK levels significantly increased (peaking at 4 h) after MDMA treatment and were blocked by the combination of prazosin plus SR59230A. 4. At 4 h after MDMA treatment, BUN and sCr levels were also significantly increased and could be prevented by this combination of alpha(1)AR- plus beta(3)AR-antagonists. 5. The results from this study suggest that alpha(1)AR and beta(3)AR play a critical role in the etiology of MDMA-mediated hyperthermia and subsequent rhabdomyolysis.

High-performance liquid chromatographic analysis and pharmacokinetics of terazosin in healthy volunteers.

A high-performance liquid chromatographic (HPLC) analysis of terazosin in 1 ml of human plasma was developed using prazosin as an internal standard. The plasma sample was extracted with dichloromethane and ethylether and a 100-microl aliquot was injected onto the reversed-phase column. The mobile phase, 0.02 M sodium phosphate buffer:acetonitrile:tetrahydrofuran = 720:220:60 (v/v/v), was run at a flow rate of 0.8 ml/min and the column effluent was monitored using a florescence detector set at 370 and 250 nm for the emission and excitation wave numbers, respectively. The retention times for terazosin and prazosin were approximately 6.4 and 9.8 min, respectively, and the coefficients of variation of terazosin were generally low, below 6.4%. The present HPLC method was successful for the pharmacokinetic study of terazosin in healthy volunteers. Following oral administration of terazosin, 2 mg, to 20 healthy male volunteers, the area under the plasma concentration-time curve from time zero to time infinity was 421 +/- 71.8 ng h/ml and terminal half-life was 9.83 +/- 1.29 h.

Improved high-performance liquid chromatographic analysis of terazosin in human plasma.

A simple, sensitive and reproducible high-performance liquid chromatography (HPLC) method was developed for the determination of terazosin in human plasma. The method involves a one-step single solvent extraction procedure using dichloromethane with a 0.25 ml plasma sample. Recovery values were all greater than 90% over the concentration range 0.25-100 ng/ml. Terazosin was found to adsorb to glass or plastic tubes, but this could be circumvented by using disposable plastic tubes. Also, rinsing the injector port with methanol after each injection helped to prevent any carry-over effect. The internal standard, prazosin, did not exhibit this problem. The method has a quantification limit of 0.25 ng/ml. The within- and between-day coefficient of variation and accuracy values were all less than 7% over the concentration range 0.25-100 ng/ml and hence the method is suitable for use in pharmacokinetic studies of terazosin.

Pharmacodynamics of S-2150, a simultaneous calcium-blocking and alpha1-inhibiting antihypertensive drug, in rats.

The in-vivo pharmacodynamics of S-2150, a newly developed dual-blocking type antihypertensive drug, was evaluated following intravenous infusion to rats. Previous in-vitro studies showed that the drug has two distinct mechanisms of antihypertensive effect--calcium-channel blocking activity and alpha1-adrenoceptor antagonism--which could be explained by a combination of two different pharmacodynamic models. The present in-vivo study showed that S-2150 also displays a complex pharmacodynamic profile (as measured by the decrease in mean blood pressure), which could be described by a combination of two sigmoid Emax models independently connected with the central compartment and the effect compartment. These results suggested that the dual-blocking mechanism of S-2150, which has been observed in in-vitro experiments, was also evaluated by the pharmacodynamic analysis of in-vivo experimental data.