Determination of piroximone in human plasma by high-performance liquid chromatography

A rapid and selective high-performance liquid chromatographic (HPLC) method using solid-phase extraction (SPE) for measuring piroximone in plasma samples has been developed. Human plasma and internal standard were pipetted onto a Bond Elut C18 extraction cartridge conditioned with methanol and water. Impurities and proteins were washed out with water. Piroximone and internal standard were eluted with methanol. After evaporation, the residue was dissolved in the mobile phase and the aliquot injected into the HPLC system. Piroximone and its related compounds were separated on a reversed phase C18 HPLC column maintained at 50 degrees C using a mobile phase consisting of phosphate buffer and methanol. Piroximone-N-oxide, piroximone, and internal standard were detected spectrophotometrically at 340 nm. The extraction recovery for piroximone was 94%. The within- and between-run coefficients of variation were < 3% in the concentration range of 320-5,000 ng/ml and < 17.5% at lower concentrations, e.g., 20 ng/ml. The limit of detection was 10 ng/ml.

Pharmacokinetic and pharmacodynamic studies following single and multiple doses of rolafagrel, a novel inhibitor of thromboxane synthase, in normal volunteers

The pharmacokinetics and pharmacodynamics of rolafagrel (FCE 22178), a novel thromboxane synthase inhibitor, were evaluated after single and multiple oral doses in eight healthy volunteers. After a single dose (400 mg), the drug was absorbed rapidly, peak plasma concentrations being attained within 2 h in all subjects. Elimination followed a biphasic course, with a rapid initial decline followed after 12-24 h by a late phase with a terminal half-life of about 10 h. About 100% of the administered dose could be recovered in urine within 72 h, mostly in conjugated form. During multiple dosing (400 mg t.i.d. for 5 days), steady-state conditions were approached on day 2 and AUC values over a dosing interval were similar to those observed after a single dose (72.3 vs 76.3 micrograms.ml-1.h). Pharmacokinetic parameters calculated after multiple doses were similar to those observed after a single dose (Cmax: 20.1 vs 18.2 micrograms.ml-1; tmax: 1.2 vs 1.1 h; terminal half-life: 10.9 vs 11.4 h; CL: 85.2 vs 70.4 ml.h-1.kg-1; V: 1.23 vs 1.24 l.kg-1). Platelet generation of thromboxane B2, the stable breakdown product of thromboxane A2, was inhibited by 85% at a plasma rolafagrel concentration of about 4 micrograms.ml-1, and only a small increase in inhibition was observed at higher concentrations.

Determination of DuP 128, an ACAT inhibitor and its sulphoxide and sulphone metabolites in human plasma by liquid chromatography

A sensitive and specific high-performance liquid chromatographic (HPLC) method with fluorescence detection was developed for the simultaneous determination of DuP 128 (N'-(2,4-difluorophenyl)-N-[5-(4,5-diphenyl-1H-imidazol-2-ylthio)p entyl]-N- hepthylurea), an ACAT inhibitor, its sulphone metabolite (XB277), and the separate determination of sulphoxide metabolite (XC164) in human plasma. After deproteinizing plasma samples with acetonitrile, the organic layer, created by adding approximately 0.25 g of NaCl, was removed, evaporated to dryness, and the residue then reconstituted with 400 microliters of acetonitrile. The acetonitrile layer was washed with 5 ml of hexane and then 50 microliters was injected into the HPLC. DuP 128 and XB277 were simultaneously quantified using a YMC basic column and fluorescence detection (lambda Ex = 270 nm and lambda Em = 385 nm). XC164 was quantified using a Waters microBondpack C18 reversed-phase column and fluorescence detection (lambda Ex = 270 nm and lambda Em = 365 nm). The relationship between the peak height and plasma concentrations best fit a power curve and showed an average correlation coefficient of > 0.99 over a concentration range of 1-200 ng ml-1 for DuP 128 and XC164 and 2.5-200 ng ml-1 for XB277. Good intraday and interday assay precisions (RSD < 10%) and accuracy (< 14%) for all three compounds were observed. The methods were sufficiently sensitive and selective to quantify plasma concentrations of DuP 128 and its sulphoxide and sulphone metabolites after oral administration of single or multiple dose(s) of > 350 mg of DuP 128 to healthy subjects.

Blockade by intravenous losartan of AT1 angiotensin II receptors in rat brain, kidney and adrenals demonstrated by in vitro autoradiography

1. The in vivo inhibition of angiotensin II (AII) receptor binding in the rat brain, kidney and adrenal was investigated after intravenous administration of the AT1-selective AII receptor antagonist losartan. 2. Male Sprague-Dawley rats were administered intravenously either vehicle, or losartan at doses of 1, 3 or 10 mg/kg. Plasma samples were collected and tissues removed at 1, 2, 8 or 24 h after administration of the antagonist. The effects of losartan on AII receptor binding were assessed by quantitative in vitro autoradiography. 3. Losartan significantly increased plasma renin activity (PRA) by six-fold and nine-fold at doses of 1 and 10 mg/kg, respectively (P < 0.05). Plasma losartan concentrations rose from 0.83 micrograms/mL at 1 mg/kg to 46.5 micrograms/mL at 10 mg/kg 1 h after administration of the drug. Plasma renin activity returned to control, whilst losartan was undetectable 24 h after injection of the antagonist. 4. In the brain, losartan produced a dose-dependent inhibition of AII receptor binding to the brain structures which express exclusively, or predominantly, AT1 receptors both outside and within the blood brain barrier. By contrast, losartan did not affect binding to the nuclei which contain exclusively, or predominantly, AT2 receptors. 5. In the kidney, losartan blocked AII receptor binding to all anatomical sites in a dose-dependent manner. The inhibition peaked at 1 h and persisted beyond 24 h despite the fact that PRA had returned to control, and losartan was not detectable in the circulation. In the adrenal gland, where AT1 and AT2 receptors occur in both the cortex and medulla, losartan caused partial inhibition at both regions. 6. These results indicate that losartan, administered intravenously at these doses, and/or its active metabolites, partially penetrate the blood brain barrier to selectively inhibit central AT1 receptors, and exert selective and prolonged blockade at AT1 receptors in peripheral target tissues.

Pharmacokinetics and pharmacodynamics of intraspinal dexmedetomidine in sheep

INTRODUCTION

Epidural and spinal injection of alpha 2-adrenergic agonists causes analgesia and hypotension. For opioids, relative analgesic potency of epidural to intravenous administration decreases with increasing lipophilicity, but such pharmacodynamic studies have been performed with only one alpha 2-adrenergic agonist, clonidine, of moderate lipophilicity. This study examines antinociception, transfer to cerebrospinal fluid (CSF), and CSF pharmacokinetics in sheep of the selective alpha 2-adrenergic agonist dexmedetomidine, with lipophilicity 3.5 times greater than clonidine, and correlates CSF concentrations to hemodynamic effects.

METHODS

Six sheep with chronically implanted epidural, intrathecal, and vascular catheters received, on separate days, 100 micrograms dexmedetomidine intravenously, epidurally, or intrathecally. Cerebrospinal fluid and blood were sampled at specified intervals for dexmedetomidine assay. Pharmacokinetics of dexmedetomidine in CSF were determined using a NONMEM approach. Hemodynamic effects were measured and correlated to CSF concentrations. A second group of four sheep received intrathecal dexmedetomidine to define its time course for antinociception.

RESULTS

Intrathecal dexmedetomidine decreased blood pressure within 1 min, with a maximum reduction of -22 +/- 3%. Epidural injection decreased blood pressure with a slower onset (11 min) and to a lesser degree (-14 +/- 4%), whereas intravenous injection did not affect blood pressure (-8 +/- 6%). Dexmedetomidine absorption in CSF after epidural injection was rapid (Tmax = 5-20 min), although pharmacokinetic modeling suggested a biphasic absorption process. Only 22% of the injected dose was identified in the CSF. There was a delay of at least 30 min between peak CSF concentrations and time of maximal reduction in blood pressure. At times of identical CSF dexmedetomidine concentrations, blood pressure decreased more after epidural than after intrathecal administration. Intrathecal dexmedetomidine injection produced maximum antinociception within 20-30 min of injection.

CONCLUSIONS

These data support a primary spinal site of action for decreased blood pressure after intraspinal dexmedetomidine injection. Dexmedetomidine appears rapidly in CSF after epidural administration and decreases blood pressure. The relationship between CSF dexmedetomidine concentrations and drug effect may require more complex modeling tools than those used to relate plasma drug concentrations to effects of systemically administered opioids or neuromuscular blockers.

Dexmedetomidine decreases thiopental dose requirement and alters distribution pharmacokinetics

BACKGROUND

alpha 2-Adrenergic agonists such as dexmedetomidine can be used to reduce the dose requirement of intravenous and volatile anesthetics. Whereas dexmedetomidine and volatile anesthetics interact pharmacodynamically (reduction of MAC), the mechanism of interaction between dexmedetomidine and intravenous anesthetics is not known.

METHODS

Fourteen male ASA physical status 1 patients were randomly assigned to serve as control subjects (n = 7) or to be treated with dexmedetomidine (n = 7; 100, 30, and 6 ng.kg-1.min-1 for 10 min, 15 min, and thereafter, respectively). After 35 min, in all patients, thiopental (100 mg/min) was infused until burst suppression appeared in the raw tracing of the electroencephalogram. By using concentrations of thiopental in plasma and the electroencephalogram as a continuous pharmacologic effect measure, the apparent effect site concentrations for thiopental were estimated in both groups. Three-compartment pharmacokinetics were calculated for thiopental.

RESULTS

Dexmedetomidine reduced the thiopental dose requirement for electroencephalographic burst suppression by 30%. There was no difference in estimated thiopental effect site concentrations between dexmedetomidine and control patients, suggesting the absence of a major pharmacodynamic interaction. Dexmedetomidine significantly decreased distribution volumes (V2, V3, and Vdss) and distribution clearances (Cl12 and Cl13) of thiopental.

CONCLUSIONS

The thiopental dose-sparing effect of dexmedetomidine on the electroencephalogram is not the result of a pharmacodynamic interaction but rather can be explained by a dexmedetomidine-induced decrease in thiopental distribution volume and distribution clearances. Dexmedetomidine reduces thiopental distribution, most probably by decreasing cardiac output and regional blood flow.

Determination of alpidem, an imidazopyridine anxiolytic, and its metabolites by column-switching high-performance liquid chromatography with fluorescence detection

Alpidem, 6-chloro-2-(4-chlorophenyl)-N,N-dipropylimidazo[1,2-a]pyridine- 3-acetamide, is an anxiolytic imidazopyridine that undergoes a first-pass elimination after oral administration to humans; it is actively metabolized and three circulating metabolites have been identified in plasma due to N-dealkylation, oxidation or a combination of both processes. For the determination of the unchanged drug and its metabolites in human plasma, a column-switching HPLC method was developed. The method, based on solid-phase extraction (performed on-line), involves the automatic injection of plasma samples (200 microliters) on to a precolumn filled with C18 material, clean-up of the sample with water in order to remove protein and salts and transfer of the analytes to the analytical column (after valve switching) by means of the mobile phase. All the processes were performed in the presence of an internal standard, a compound chemically related to alpidem. During the analytical chromatography, the precolumn was flushed with different solvents and after regeneration with water, it was ready for further injections. The analytical column was a C8 type and the mobile phase was acetonitrile-methanol-phosphate buffer solution (45:15:45, v/v/v) at a flow-rate of 1.5 ml min-1. The column was connected to a fluorimetric detector operating at excitation and emission wavelengths of 255 and 423 nm, respectively. The limits of quantitation of alpidem and three metabolites were 2.5 and 1.5 ng ml-1, respectively, in human plasma.

The pharmacokinetics and pharmacodynamics of the angiotensin II receptor antagonist losartan potassium (DuP 753/MK 954) in the dog

The pharmacokinetics and plasma concentration-effect relationship for the nonpeptide angiotensin II (Ang II) receptor antagonist losartan potassium (losartan) have been determined with conscious and anesthetized dogs. The p.o. bioavailability of single doses of 5 to 20 mg/kg was low, 23 to 33%, and independent of the dose. Absorption was rapid, with peak plasma levels observed within 1 hr, and the Cmax and area under the concentration vs. time curve to infinity were proportional to the dose, P < .05. The elimination half-life, 108 to 153 min, was longer than that observed after a single i.v. dose, 41 min, and may reflect both continuous absorption and enterohepatic recirculation because the major route of excretion was via the bile. Single i.v. doses were eliminated rapidly, with a systemic plasma clearance of 22.2 ml/min/kg. When corrected for the blood:plasma distribution ratio, 0.66 to 0.72, the systemic clearance approximates hepatic blood flow, suggesting that clearance is primarily via hepatic metabolism and biliary excretion. Losartan was not distributed extensively to tissues; apparent volume of distribution at steady-state of 0.30 liters/kg and was highly but not extensively bound to plasma proteins; 2.7 to 2.9% unbound (free). The plasma concentration vs. blockade of exogenous Ang II-induced vasopressor response was also determined after a single 3-mg/kg i.v. dose of losartan with a sigmoidal Emax model. Blockade of the pressor response was rapid, 89% at 5 min, and declined to 11% at 240 min postdose. The relationship between concentration and effect was highly significant (r = 0.922, P < .01), with an IC50 (total) of 96 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitive determination of a novel bisphosphonate, YM529, in plasma, urine and bone by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method for the sensitive determination of 1-hydroxy-2-(imidazo[1,2-a]pyridin-3-yl)ethane-1, 1-bisphosphonic acid monohydrate (YM529) in plasma, urine and bone is described. Plasma obtained in high-dose animal studies is treated by method A, a simple method using 1 ml of plasma, which is based on deproteinization of plasma followed by coprecipitation of the drug with calcium phosphate and dissolution of the precipitate in EDTA. Plasma obtained in low-dose clinical studies is treated by method B, a more sensitive method using 4 ml of plasma, which is based on direct precipitation of the drug prior to the deproteinization in method A. Urine and bone samples are prepared by solid-phase extraction using a Sep-Pak C18 cartridge coupled with method A. The drug is separated with a reversed-phase column using a mobile phase at pH 7, and detected with a fluorescence detector following postcolumn alkalization of the mobile phase to enhance fluorescence intensity. The limit of determination is 0.2 ng/ml for method A and 0.05 ng/ml for method B in plasma, 0.05 ng/ml in urine, and 5 ng/g in bone.

Chronic administration of an alpha 2 adrenergic agonist desensitizes rats to the anesthetic effects of dexmedetomidine

alpha 2 adrenergic agonists are being administered perioperatively to facilitate the anesthetic management of the surgical patient. In some clinical settings, use of alpha 2 adrenergic agonists has been extended into the postoperative period to prolong the patients' sedative and stress-free state. We studied whether the administration of alpha 2 adrenergic agonists over an extended period of time would result in "desensitization" to the central actions of alpha 2 adrenergic agonists. Male Sprague-Dawley rats were administered dexmedetomidine, a highly selective alpha 2 adrenergic agonist, at rates varying between 1 and 10 micrograms.kg-1.h-1 via a chronically implanted SC osmotic pump. Spontaneous locomotor activity, tested in an open-field box, was significantly lower in both 3- and 10-micrograms.kg-1.h-1 treatment groups but returned to normal by the second or sixth day, respectively. The hypnotic response to dexmedetomidine IP was decreased in the 10-micrograms.kg-1.h-1 dose group from the second day, and by the fourth day in the 3-micrograms.kg-1.h-1 group. Recovery from the desensitized state was rapid and occurred on the third day after pump removal in the 3-micrograms.kg-1.h-1 group and by the fifth day after pump removal in the 10-micrograms.kg-1.h-1 dose group. By using a higher dose of dexmedetomidine IP (250 micrograms.kg in lieu of 100 micrograms/kg) at day 7 in "tolerant" rats, the hypnotic response could partially be "restored" towards normal. An attenuated hypnotic response could still be demonstrated even when dexmedetomidine was administered directly into the locus coeruleus (LC) in rats pretreated chronically with dexmedetomidine.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of the percutaneous absorption-enhancing effects of cyclodextrin derivatives in rats

2-Hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and 2,6-dimethyl-beta-cyclodextrin (D-beta-CyD) were studied for transdermal penetration enhancement of the cytochrome P450 inhibitor liarozole by an in vivo transdermal absorption rat model. The mode of action of penetration enhancement was investigated by differential scanning calorimetry (DSC). In-vivo, HP-beta-CyD, as a 20% aqueous solution, increased the absorption of liarozole approximately threefold and a 20% aqueous solution of D-beta-CyD decreased the percutaneous absorption of liarozole in blood by a factor of 0.6. However, pretreatment with D-beta-CyD (20%, 4 h) enhanced the transdermal absorption 9.4-fold. In the DSC experiments the thermal profile of human stratum corneum was practically unchanged after treatment with HP-beta-CyD, but treatment with D-beta-CyD revealed an interaction of D-beta-CyD with the protein and lipid fraction. Thus the results from DSC and those from the permeability experiments revealed that D-beta-CyD acts as a transdermal absorption enhancer by changing the stratum corneum barrier whereas HP-beta-CyD influences the partitioning behaviour of the drug in the skin.

Simultaneous screening and quantitation of alpidem, zolpidem, buspirone and benzodiazepines by dual-channel gas chromatography using electron-capture and nitrogen-phosphorus detection after solid-phase extraction

A rapid twin-column gas chromatographic (GC) method for simultaneous screening and determination of commonly prescribed benzodiazepines and other new anxiolytics from plasma is described. Identical fused-silica Ultra 2 (5% phenyl methyl silicone) columns were connected to nitrogen-phosphorus and electron-capture detectors. The drugs were isolated from 1 ml of plasma by solid-phase extraction (SPE) onto a C8 reversed-phase sorbent and recovered with 0.5% acetic acid in methanol. The eluate was reconstituted with isopropanol which was found suitable for on-column injection. Prazepam was used as internal standard. The method was found appropriate for the quantification in a single run of alpidem, alprazolam, buspirone, chlordiazepoxide, clobazam, clotiazepam, diazepam, estazolam, flunitrazepam, lorazepam, midazolam, oxazepam, tofisopam, triazolam, and zolpidem within 30 min. Limits of quantification allow toxicological or pharmacological determinations, except for buspirone: only toxic blood levels can be quantified by this method. This first SPE of imidazopyridines (alpidem and zolpidem) provides faster, more efficient and cheaper sample preparation than the traditional liquid-liquid procedure. This GC analysis of alpidem and zolpidem is also the first described procedure for simultaneous quantification of all different classes of anxiolytics.

Pharmacokinetic study of loprinone hydrochloride, a new cardiotonic agent, in beagle dogs

Pharmacokinetic parameters and bioavailability of a new cardiotonic agent, loprinone hydrochloride, in beagle dogs were determined by measuring plasma levels of loprinone after intravenous bolus and oral administration. The plasma half-life after intravenous administration of loprinone varied among individuals over the range 2.65-15.40 h. The bioavailability after oral administration of loprinone as a solution was 37.1%. Effects of enterohepatic circulation on the time-course of plasma levels after intravenous administration of the drug were also studied in bile-duct-cannulated beagle dogs. The amounts of loprinone and its glucuronide excreted in bile during 8 h after administration were 25.4 and 8.6% of the dose, respectively, indicating the possibility of enterohepatic circulation. The plasma half-life in bile-duct-cannulated beagle dogs was 1.98 h. These results indicate that the variation in the half-life in beagle dogs resulted from enterohepatic circulation and that the true half-life is about 2 h. The relative bioavailability after oral administration of the drug as a powder in a capsule compared with a solution was 95.7%. In addition, the amounts of loprinone and its glucuronide excreted in bile, and the AUC of plasma level after infusion for 30 min into the portal vein in bile-duct-cannulated beagle dogs were similar to those after bolus intravenous administration. These results show that the low bioavailability reflects incomplete absorption.

Multiple dose pharmacokinetics and concentration effect relationship of the orally active renin inhibitor remikiren (Ro 42-5892) in hypertensive patients

1 Three double-blind, randomized, placebo controlled, multiple oral dose studies in patients with mild to moderate hypertension were performed to study tolerability, pharmacodynamics and pharmacokinetics of remikiren. Doses of 100-800 mg remikiren or placebo were given over 8 days to altogether 144 patient volunteers. In some cases (n = 46) single i.v. doses of 100 mg were administered 4 h after the last oral dose. Plasma remikiren concentrations, plasma renin activity and immunoreactive renin concentrations were measured. Pharmacokinetic parameters were estimated using model independent techniques and the concentration-effect relationship was evaluated using population pharmacometric methods. 2 In most patients no distinct absorption and disposition phase could be identified, since plasma concentrations fluctuated widely over a period of approximately 10 h. Peak plasma concentrations (Cmax) were achieved within 0.25-2 h postdose. Mean Cmax values (on the first and last day of oral treatment) were in the magnitude of 4-6 ng ml(-1) (200 mg), 23-27 ng ml(-1) (300 mg), 65-83 ng ml(-1) (600 mg) and 47-48 ng ml(-1) (800 mg). Cmax and AUC0-t values were clearly different for different doses within single studies. Intersubject variability in pharmacokinetic parameters was much higher than intrasubject variability. No drug accumulation in plasma was apparent. 3 Inhibition of the angiotensin I production rate correlated well with plasma drug concentrations according to the Emax-model. An IC50 value of 0.5 ng ml(-1) (0.8 nM) was estimated. No correlation between blood pressure changes on the last day of oral treatment and either plasma remikiren concentrations or plasma renin inhibition was found.

Cardiopulmonary and behavioral responses to computer-driven infusion of detomidine in standing horses

Cardiopulmonary and behavioral responses to detomidine, a potent alpha 2-adrenergic agonist, were determined at 4 plasma concentrations in standing horses. After instrumentation and baseline measurements in 7 horses (mean +/- SD for age and body weight, 6 +/- 2 years, and 531 +/- 48.5 kg, respectively), detomidine was infused to maintain 4 plasma concentrations: 2.1 +/- 0.5 (infusion 1), 7.2 +/- 3.5 (infusion 2), 19.1 +/- 5.1. (infusion 3), and 42.9 +/- 10 (infusion 4) ng/ml, by use of a computer-controlled infusion system. Detomidine caused concentration-dependent sedation and somnolence. These effects were profound during infusions 3 and 4, in which marked head ptosis developed and all horses leaned heavily on the bars of the restraining stocks. Heart rate and cardiac index decreased from baseline measurements (42 +/- 7 beats/min, 65 +/- 11 ml.kg of body weight-1.min-1) in linear relationship with the logarithm of plasma detomidine concentration (ie, heart rate = -4.7 [loge detomidine concentration] + 44.3, P < 0.01; cardiac index = -10.5 [loge detomidine concentration] + 73.6, P < 0.01). Second-degree atrioventricular block developed in 5 of 7 horses during infusion 3, and in 6 of 7 horses during infusion 4. Mean arterial blood pressure increased significantly from 118 +/- 11 mm of Hg at baseline to 146 +/- 27 mm of Hg at infusion 4. Similar responses were observed for mean pulmonary artery and right atrial pressures. Systemic vascular resistance (baseline, 182 +/- 28 mm of Hg.ml-1.min-1.kg-1) increased significantly during infusions 3 and 4 (to 294 +/- 79 and 380 +/- 58, respectively). (ABSTRACT TRUNCATED AT 250 WORDS)

Renal actions of the selective angiotensin AT2 receptor ligands CGP 42112B and PD 123319 in the sodium-depleted rat

The purpose of this study was to investigate the renal actions of the new selective angiotensin AT2 receptor ligands, CGP 42112B and PD 123319, in comparison to those of the AT1 receptor antagonist losartan, in the sodium-depleted, anesthetized rat. Losartan (1, 3 and 10 mg/kg i.v.) produced a dose-dependent decrease in blood pressure and renal vascular resistance that was statistically significant. Effective renal blood flow tended to increase in response to all doses of losartan while glomerular filtration rate either did not change or decreased, leading to a significant fall in filtration fraction. Losartan did not induce significant changes in urine volume, urinary sodium excretion, urinary potassium excretion or free water formation. The selective AT2 receptor ligand CGP 42112B at infusion rates of 1-100 micrograms/kg per min i.v. had no significant effect on blood pressure or any measured parameter of renal function. However, when infused at 1000 micrograms/kg per min i.v., CGP 42112B did not affect blood pressure, but significantly increased effective renal blood flow, glomerular filtration rate, urinary sodium excretion, urinary potassium excretion and free water formation, while significantly decreasing renal vascular resistance. The selective AT2 receptor ligand PD 123319 at infusion rates between 1 and 100 micrograms/kg per min i.v. also had no significant effect on blood pressure or on any measured parameter of renal function. However, at an infusion rate of 1000 micrograms/kg per min i.v., PD 123319 tended to increase renal vascular resistance, urinary sodium excretion, urinary potassium excretion and free water formation, and to decrease effective renal blood flow, although none of these changes reached a level of statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical capture of free-ranging cattle: immobilization with xylazine or medetomidine, and reversal with atipamezole

Twenty-nine free-ranging Norwegian cattle were captured with xylazine (n = 20) or medetomidine (n = 9) using a tranquilizing gun, and the time from darting to recumbency (induction time) was recorded. Twenty-eight animals were given atipamezole IV 15-100 min after darting, and the effects of the antagonist were evaluated. Blood samples (n = 19) for haematology and serum chemistry were collected within 10 min after immobilization was induced. Xylazine (0.55 +/- 0.18 mg/kg; mean +/- SD; n = 18) or medetomidine-HCl (0.039 +/- 0.10 mg/kg; n = 8) induced complete immobilization after a single darting with sternal or lateral recumbency, the induction times being 9.6 +/- 3.8 and 12.0 +/- 6.8 min, respectively. No difference in the clinical effects of the two drugs was observed. Rapid reversal was achieved with 0.057 +/- 0.017 and 0.077 +/- 0.019 mg/kg of atipamezole-HCl in xylazine- and medetomidine-treated animals, respectively. All the animals stood within 2 min after IV administration of the antagonist. Seven animals showed signs of excitement shortly after reversal, but these side-effects were of brief duration. Heavy resedation with relapse into recumbency was seen 3-4 h after reversal in two cows captured with xylazine, while moderate resedation was observed in two medetomidine-treated animals 2 h after reversal. Except for the plasma glucose concentration, which was elevated in both xylazine- and medetomidine-treated animals, the mean values of the haematological and plasma chemical parameters were within the reference ranges established for Norwegian cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic determination of a potent AII receptor antagonist (DMP 811) in plasma

An HPLC assay for DMP 811, 4-ethyl-2-propyl-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imi dazole-5- carboxylic acid (I) in rat and dog plasma has been developed. Compound I was isolated from plasma using a liquid-liquid back extraction procedure. The extraction recovery was greater than 81%. Separation of I from endogenous components in plasma was achieved on an E. Merck C8 column using a mobile phase of 0.05 M ammonium acetate, brought to pH 3.75 with acetic acid, and acetonitrile (78:22, v/v). The eluent was monitored by fluorescence with excitation and emission set at 235 and 370 nm, respectively. The assay was linear from 2 to 2000 ng/ml. Inter- and intra-day coefficients of variation for the rat-plasma assay ranged from 0.9 to 5.2% (5-2000 ng/ml) and 2.7 to 16.5% (2-2000 ng/ml), respectively. The respective coefficients of variation for the dog-plasma assay were 1.9 to 5.6% and 1.2 to 14.0%. The percent differences from the accuracy results were 12% or less. Using 0.5 ml of plasma for extraction, the minimum quantifiable limit was 2 ng/ml. This method has been used to quantify plasma levels of I in rats or dogs following 3-10 mg/kg i.v. or p.o. doses.

A circulating substance cross-reacting with antiimidazoline antibodies. Detection in serum in relation to essential hypertension

It has been shown in various mammal species that clonidine, a well known centrally acting hypotensive agent, acts through the activation of imidazoline receptors (IRs) in the nucleus reticularis lateralis (NRL) of the brainstem. Specific binding sites sensitive to imidazolines and insensitive to catecholamines have been detected in rat and bovine, as well as human brains. An endogenous ligand, other than catecholamines, should exist for these IRs. Such a ligand could play a role in the pathophysiology of human essential hypertension. Therefore, we developed two RIAs with polyclonal and monoclonal anticlonidine antibodies. These antibodies presented specificity spectra similar to that of the IRs: they bound imidazolines and not catecholamines at all. These RIAs were used to detect imidazoline-like immunoreactivity in the human serum. Immunoreactive substance was measured in 26 normotensive subjects' sera, and specificity of interaction between antibodies and sera was verified. None of the known endogenous substances tested so far were able to interact with the two antibodies. Immunoreactivity in 32 essential hypertensive patients' sera proved higher in approximately 30% of cases. Values of immunoreactivity positively correlated with the mean arterial pressure values. This study demonstrates the existence of an "imidazoline-like" immunoreactive substance in the human serum with high levels in some hypertensive patients.

Highly sensitive determination of imidapril, a new angiotensin I-converting enzyme inhibitor, and its active metabolite in human plasma and urine using high-performance liquid chromatography with fluorescent labelling reagent

A method for the simultaneous determination of imidapril and its active metabolite in human plasma and urine has been developed using high-performance liquid chromatography with a fluorescent labelling reagent, 9-anthryldiazomethane. Imidapril and its active metabolite were extracted from human plasma and urine using a solid-phase extraction cartridge (Bond Elut C18). Two compounds in the eluate were derivatized with 9-anthryldiazomethane and purified with a solid-phase extraction cartridge (Bond Elut SI). The derivatives were analysed using high-performance liquid chromatography with fluorometry. The detection limits of imidapril and its active metabolite were 0.2 ng/ml in plasma and 10 ng/ml in urine. This method could be applied to the pharmacokinetic study of imidapril.

High-performance liquid chromatographic assay with diode-array detection for toxicological screening of zopiclone, zolpidem, suriclone and alpidem in human plasma

A high-performance liquid chromatographic assay with diode-array detection has been developed for the toxicological screening of the newly developed non-benzodiazepine hypnotics and anxiolytics zopiclone, zolpidem, suriclone and alpidem. After single-step liquid-liquid extraction of plasma at pH 9.5 using chloroform-2-propanol-n-heptane (60:14:26, v/v), the substances are separated on a Nova-Pak C18 4-microns column (300 mm x 3.9 mm, I.D.), with methanol-tetrahydrofuran-pH 2.6 phosphate buffer (65:5:30, v/v) as the mobile phase (flow-rate 0.8 ml/min). Full ultraviolet spectra from 200 to 400 nm are recorded on-line during the entire analysis and may be automatically compared to spectra stored in a library. The retention times of the four drugs are 4.05 min (zopiclone), 4.66 min (zolpidem), 6.74 min (suriclone) and 10.97 min (alpidem). The analysis is performed in 15 min. The method is simple, rapid and highly specific. It is the first assay to be described for convenient screening of cyclopyrrolones and imidazopyridines.

Effects of an orally active renin inhibitor, Ro 42-5892, in patients with essential hypertension

Ro 42-5892 (Ro) is a new renin inhibitor that has been shown to be an orally effective compound in primates and in the first exploratory studies in humans. However, no firm conclusions could be drawn from the human trials and therefore the present study was designed to evaluate the antihypertensive efficacy of the compound in a double-blind, placebo-controlled trial. After a 3 week wash-out period and a 1 week single-blind placebo period, 24 patients were randomized to receive once daily orally either placebo or 600 mg Ro 42-5892 (N = 12/group) for 8 days. On the last day of treatment, an intravenous infusion of placebo or 100 mg Ro was given in a double-blind fashion, 4 h after the oral administration. Blood pressure (BP), heart rate (HR), plasma renin activity (PRA), immunoreactive renin (IRR), and plasma Ro levels were measured repeatedly on the first and last days of treatment. After the first oral intake of Ro, sitting diastolic BP dropped significantly from 30 min to 24 h post-dose when compared to placebo (-10.2 +/- 1.2 mm Hg v - 0.4 +/- 2.0 mm Hg at peak and -6.9 +/- 1.8 mm Hg v 1.7 +/- 0.9 mm Hg at trough; P < .01 respectively). The trough effects of Ro and placebo after the 7th and 8th doses were -5.1 +/- 1.6 mm Hg v -0.2 +/- 1.0 mm Hg; P < .05 and -5.4 +/- 1.3 mm Hg v 2.3 +/- 1.2 mm Hg; P < .01, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer-controlled infusion of intravenous dexmedetomidine hydrochloride in adult human volunteers

BACKGROUND

This investigation extended the pharmacokinetic analysis of our previous study, of intravenous dexmedetomidine in 10 healthy male volunteers, and prospectively tested the resulting compartmental pharmacokinetics in an additional six subjects using a computer-controlled infusion pump (CCIP) to target four different plasma concentrations of dexmedetomidine for 30 min at each concentration.

METHODS

A three-compartment mamillary pharmacokinetic model best described the intravenous dexmedetomidine concentration versus time profile following the 5 min intravenous infusion of 2 micrograms/kg in our previous study. Nonlinear regression was performed using both two-stage and pooled data techniques to determine the population pharmacokinetics. The pooled technique allowed covariates, such as weight, age, and height of the subjects, to be incorporated into the nonlinear regression to test the hypothesis that these additional covariates would reduce the residual error between the measured concentrations and the predicted values.

RESULTS

The addition of age, weight, lean body mass, and body surface area as covariates of the pharmacokinetic parameters did not improve the predictive value of the model. However, the model was improved when subject height was a covariate of the volume in the central compartment. The residual error in the pharmacokinetic model was markedly lower with the pooled versus the two-stage approach. The following pharmacokinetic values were obtained from the pooled analysis of the zero-order dexmedetomidine infusion: V1 = 8.05, V2 = 12.4, V3 = 175 (L), Cl1 = (0.0101*height [cm]) -1.33, Cl2 = 2.05, and Cl3 = 2.0 (L/min). Prospective evaluation of the pooled pharmacokinetic parameters using a computer-controlled infusion in six healthy volunteers showed the precision (average [(absolute error)/measured concentration]) of the CCIP to be 31.5% and the bias (average [error/measured concentration]) to be -22.4%. A pooled regression of the combined CCIP and zero-order data confirmed that the covariate, height (cm), was related in linear fashion to Cl1. A striking nonlinearity of dexmedetomidine pharmacokinetics related to concentration was observed during the CCIP infusion. The final pharmacokinetic values for the entire data set were: V1 = 7.99, V2 = 13.8, V3 = 187 (L), Cl1 = (0.00791*height [cm]) -0.927, Cl2 = 2.26, and Cl3 = 1.99 (L/min).

CONCLUSIONS

Pharmacokinetics of dexmedetomidine are best described by a three-compartment model. Addition of age, weight, lean body mass, and body surface area do not improve the predictive value of the model. Additional improvement in CCIP accuracy for dexmedetomidine infusions would require magnification modification of the model based on the targeted concentration.

Rapid determination of a new angiotensin-converting enzyme inhibitor, imidapril, and its active metabolite in human plasma by negative-ion desorption chemical ionization-tandem mass spectrometry (MS/MS)

A very rapid and highly sensitive method using desorption chemical ionization (DCI)-tandem mass spectrometry (MS/MS) with selected reaction monitoring is reported for the simultaneous determination of imidapril and its active metabolite (M1) in human plasma. Imidapril and M1 in plasma were extracted by a C18 solid phase extraction cartridge after deproteinization, and derivatized with pentafluorobenzyl bromide. One microliter of prepared sample was applied to the DCI filament and analyzed by DCI/MS/MS within a few minutes. The limits of determination of imidapril and M1 were 0.2 and 0.5 ng/ml in human plasma, respectively. The features of this method make it appropriate for use in pharmacokinetic studies with human plasma after oral administration of imidapril.

A phase I dose-ranging safety and pharmacokinetics study of a novel oral thromboxane synthase inhibitor, FCE 22, 178

A 100- to 3200-mg dose range of FCE 22,178 was studied in this phase I single-dose escalation safety/kinetics study. After oral administration, a rapid drug absorptive phase and a biexponential disposition profile were observed. Mean estimates of the terminal elimination half-life of FCE 22,178, over the doses studied, ranged from 7.6 to 14.4 hours. A disproportionate increase in both maximum peak plasma concentration (Cmax) and area under the curve (AUC0-infinity) was noticed for doses higher than 400 mg. Mean estimates of systemic clearance (CLs/F) over the 100- to 400-mg doses were 0.053 to 0.064 L/hour/kg, and were significantly higher for the three higher dose levels. This nonlinearity appears to be related to the changes in oral bioavailability. Estimates of distribution volume (Vd, lambda z/F) for FCE 22,178 increased from 0.75 L/kg at the 100-mg dose to 3.00 L/kg at the 3200-mg dose, and renal clearance (CLr) also increased with dose. Both observations may be related to an increase in free fraction of FCE 22,178 at higher doses. Urinary excretion of unchanged drug averaged < 10% for all dose levels. The urinary excretion of the glucuronide metabolite (M1) averaged 41 to 70% for doses up to 400 mg, but diminished to 13% at the 3200-mg dose. The disposition of M1 appeared to be formation-rate limited. In addition, the ratio of the formation to the disposition clearance for M1 was relatively stable and apparently dose independent. No drug-related adverse experiences were observed over the studied dose range after single doses at FCE 22,178.