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.

Pharmacokinetics and biochemical efficacy after single and multiple oral administration of losartan, an orally active nonpeptide angiotensin II receptor antagonist, in humans

1. The pharmacokinetics and biochemical efficacy of losartan, an orally active nonpeptide angiotensin II (AII) receptor antagonist, were evaluated in healthy male volunteers after single and multiple oral administration. 2. Plasma and urinary concentrations of losartan and its active metabolite, E-3174, were determined by a specific high performance liquid chromatographic (h.p.l.c.) method. 3. Plasma concentrations of losartan were proportional to dose over the range of 25 to 200 mg and the terminal half-lives (t1/2,z) ranged from 1.5 to 2.5 h. The mean values of Cmax and AUC0-infinity increased in a dose-dependent manner. 4. Plasma concentrations of E-3174 were higher than those of losartan at all dose levels. The values of Cmax and AUC0-infinity for E-3174 were approximately 2 and 5-8 times higher than those for losartan, respectively. Also the value of t1/2,z was 2 times longer than that of losartan. 5. After multiple dosing for 7 days, the pharmacokinetics of losartan and E-3174 each did not change significantly between day 1 and day 7. 6. Plasma renin activity (PRA) and plasma concentrations of AII increased markedly at all dose levels. Plasma aldosterone levels were slightly reduced, but a similar decrease was also observed with placebo. 7. No clinically significant adverse reaction was observed in any of the volunteers during either study. Blood counts, routine laboratory tests, urine analyses, and electrocardiograms were also not modified by losartan. 8. Losartan appears to be a potent orally active angiotensin II antagonist with a relatively long duration of action.

Liquid chromatography-mass spectrometry for the determination of medetomidine and other anaesthetics in plasma

A liquid chromatographic-atmospheric pressure chemical ionization mass spectrometric method is presented for the simultaneous determination of medetomidine and other anaesthetic drugs in solutions and dog plasma. The drugs examined were flumazenil, butorphanol, atropine, ketamine, xylazine, medetomidine, atipamezole and midazolam. The separation was carried out on a reversed-phase column using methanol-0.1 M ammonium acetate (3:2) as eluent.

The time course of action of three differing doses of noberastine, a novel H1-receptor antagonist, on histamine-induced skin wheals and the relationship to plasma drug concentrations in normal human volunteers

1. The time course and magnitude of effect of the novel H1-receptor antagonist noberastine, structurally modified from astemizole to achieve a more rapid onset while retaining a good duration of action, has been investigated using histamine-induced skin wheals in healthy volunteers. 2. The pharmacokinetics and pharmacodynamics of three doses (10, 20 and 30 mg) have been studied in a double-blind, placebo controlled, randomised cross-over trial involving 12 healthy male volunteers. 3. All doses of noberastine caused inhibition of histamine-induced skin wheals, which were significantly different from placebo (P < 0.0001) when assessed as the area under the percent inhibition of the response vs time curves. 4. Following single dose administration of 10, 20 and 30 mg noberastine significant inhibition of histamine-induced skin wheals occurred and this effect persisted beyond 24 h. 5. At the higher (20 and 30 mg) doses studied significant inhibition of the histamine-induced skin wheal occurred by 1 h of dosing, whereas this did not occur until 2 h following the 10 mg dose. 6. An increase in plasma concentrations of noberastine was seen after administration of all doses, with mean (s.d.) concentrations of 4.14 (3.70), 8.38 (7.81) and 12.66 (11.82) ng ml-1 1 h following administration of 10, 20, and 30 mg respectively. 7. Visual analogue scale measurements of drowsiness identified no sedative effects above those of placebo at any of the dose levels. 8. We conclude that noberastine is an effective H1-receptor antagonist in the human as assessed by its effect on histamine-induced skin wheals.

Further arguments against 4-methylimidazole as causal factor in ammoniated forage toxicosis: experimental seed-hay poisoning in young lambs

4-methylimidazole (4-MeI) is up to now the main tremorogenic poison known to be present in ammoniated roughages. The concentration of 4-MeI is widely used as an indicator of the potential toxicity of individual batches of ammoniated straw and hay.

Clinical experience with angiotensin II receptor antagonists

This series of studies was designed to assess in normal volunteers the relationships between various doses (5, 10, 20, 40, 80, and 120 mg) of the orally active angiotensin II antagonist losartan (DuP 753, MK-954) and their inhibitory effect on the pressure response to a given bolus of angiotensin I or II. It was found that the maximal inhibitory effect was reached with a dose of 80 mg. The minimal dose necessary for maximal efficacy would therefore be expected to be between 40 and 80 mg. The effect lasted for more than 24 h and was related almost exclusively to the circulating levels of the active metabolite EXP3174. It remains to be demonstrated in hypertensive patients that the same dose relationship holds for the antihypertensive effect, but preliminary data already suggest that this is the case.

[A 13-week subacute oral toxicity study of 6-amidino-2-naphthyl 4-[(4,5-dihydro-1H-imidazol-2-yl) amino] benzoate dimethanesulfonate (FUT-187) in dogs

A subacute oral toxicity study of 6-amidino-2-naphthyl 4-[(4,5-dihydro-1H-imidazol-2-yl) amino] benzoate dimethanesulfonate (FUT-187), a new protease-inhibiting agent, was carried out in beagle dogs of both sexes. FUT-187 was administered to dogs at daily oral doses of 15, 50 and 150 mg/kg. Dogs in 150 mg/kg group were given twice a day in a.m. and p.m.. The results were as follows: 1. Changes of physical sign attributed to FUT-187, consisted of vomiting, diarrhea, salivation, decrease of locomotor activity, sedation and hyperemia of eye mucosa. These changes expect vomiting vanished within about 2 hours after treatment. One male given 150 mg/kg died on day 19 and two females given 150 mg/kg were sacrificed on day 55 and 67 due to deterioration of systemic conditions. 2. Body weight gain was suppressed in males given 150 mg/kg and females given 50 mg/kg or more. 3. In hematological examinations, some changes suggesting anemia or inflammation were observed in a few animals received 50 mg/kg or more 4. In serum biochemical examinations, dogs given 50 mg/kg or more had decrease of albumin, total protein, A/G ratio and total cholesterol, increase of GPT activity. In liver function test, decrease of function was observed in a few animals in 150 mg/kg group. These changes diminished by the end of recovery period. 5. In autopsy findings, ulcer formation and desquamation of mucosa in the digestive tract were observed in dead or sacrificed animals and survived animals given more than 50 mg/kg. In sacrificed animals, liver was yellow in color and intussusception was seen. 6. Plasma levels of intact FUT-187 and metabolites on the day 37 or 83 were higher than that on the first day of administration. 7. In histopathological examinations, ulcer formation, desquamation, degeneration and/or atrophy of mucosa in the digestive tract were observed in the animals from 50 mg/kg and 150 mg/kg groups. In addition, fatty deposition in hepatocytes was observed in one dead animal and two sacrificed animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of Intravenous Dexmedetomidine in Humans

Dexmedetomidine (DMED) is a novel clonidine-like compound known to have sedative, analgesic, and cardiovascular stabilizing qualities. DMED is a more highly selective alpha 2-adrenergic agonist than clonidine. This investigation examined the hemodynamic effects of four selected iv doses in consenting healthy male volunteers. In a randomized, double-blind, placebo-controlled trial subjects received 0 (n = 9), 0.25 (n = 6) 0.5 (n = 6), 1.0 (n = 6), or 2.0 (n = 10) micrograms/kg of DMED by infusion (2 min). ECG, heart rate (HR), arterial blood pressure (MABP), bioimpedance cardiac output (CO), and plasma catecholamines concentrations (CA) were monitored from 90 min before to 360 min after infusion. Plasma DMED concentrations were measured. DMED produced a maximum decrease in MABP at 60 min of 14%, 16%, 23%, and 27% for the 0.25, 0.5, 1.0, and 2.0 micrograms/kg groups, respectively (P < .05). At 330 min MABP remained below baseline by 8% and 17% at the two largest doses (P < .05). Both HR and CO decreased maximally by both 17% at 105 min. The two largest doses produced a transient (peak at 3 min lasting < 11 min) increased in MABP (16 +/- 2.5 and 24 +/- 10 mmHg, respectively; P < .05) with a concomitantly reduced CO (41%, 2 micrograms/kg; P < .05) and HR (22%, 2 micrograms/kg; P < .05), whereas systemic vascular resistance doubled. Even the lowest dose decreased CA immediately to values close to 20 pg/ml for 5 h. A 2-min iv infusion of DMED produced a transient increase in MABP and a longer lasting decrease in MABP and CA. These DMED doses were well tolerated in the healthy volunteers.

Suitability of CGP-12177 and CGP-26505 for quantitative imaging of beta-adrenoceptors

[3H]CGP-12177, a non-selective beta-adrenoceptor antagonist, and [3H]CGP-26505, a beta 1-selective beta-adrenoceptor antagonist, were intravenously administered to rats. 94-97% of the injected radioactivity disappeared from plasma with t1/2 0.2 and 0.5 min. Total/non-specific binding ratios of 5.4 and 6.9 (CGP-12177) or 2.0 and 2.8 (CGP-26505) were maintained in heart and lung from 10 to 40 min post-injection. Labelled plasma metabolites appeared after greater than 20 min (CGP-12177) or within 2 min (CGP-26505). No metabolites were found in the heart. CGP-12177 binds to blood cells, but CGP-26505 does not. CGP-12177 can be used for PET imaging of total (beta 1 and beta 2) adrenoceptors in the heart and lung of experimental animals, but CGP-26505 is less suitable for in vivo analysis of the beta 1-subpopulation.

Classifying antiarrhythmic actions: by facts or speculation

Classification of antiarrhythmic actions is reviewed in the context of the results of the Cardiac Arrhythmia Suppression Trials, CAST 1 and 2. Six criticisms of the classification recently published (The Sicilian Gambit) are discussed in detail. The alternative classification, when stripped of speculative elements, is shown to be similar to the original classification. Claims that the classification failed to predict the efficacy of antiarrhythmic drugs for the selection of appropriate therapy have been tested by an example. The antiarrhythmic actions of cibenzoline were classified in 1980. A detailed review of confirmatory experiments and clinical trials during the past decade shows that predictions made at the time agree with subsequent results. Classification of the effects drugs actually have on functioning cardiac tissues provides a rational basis for finding the preferred treatment for a particular arrhythmia in accordance with the diagnosis.

Determination of three metabolites of a new angiotensin-converting enzyme inhibitor, imidapril, in plasma and urine by gas chromatography-mass spectrometry using multiple ion detection

A specific and sensitive gas chromatographic-mass spectrometric method for the determination of three metabolites of the angiotensin-converting enzyme inhibitor, imidapril, in plasma and urine was developed. The metabolites were isolated from plasma and urine using a Bond Elut C18 solid-phase extraction cartridge. The isolated metabolites were converted to sensitive derivatives by pentafluorobenzyl bromide and heptafluoro-n-butyric acid anhydride. Following derivatization, the sample solutions were analysed by wide-bore column gas chromatography-mass spectrometry with multiple ion detection. The detection limits of the three metabolites were each 1 ng/ml in plasma and 5 ng/ml in urine. Analysis of the spiked plasma and urine samples demonstrated the good accuracy and precision of the method. This method was very useful for use in pharmacokinetic and bioavailability studies of the three metabolites of imidapril in humans.

High-performance liquid chromatographic determination of angiotensin II receptor antagonists in human plasma and urine. I. DuP 532 (L-694,492)

A sensitive reversed-phase high-performance liquid chromatographic method with ultraviolet detection was developed for the analysis of a new angiotensin II receptor antagonist, DuP 532 (L-694,492), in human plasma and urine. The analyte and internal standard are extracted from plasma and urine at a pH between 3.3 to 3.6 by liquid-liquid extraction and analyzed on a C6 column with ultraviolet detection at 254 nm. The mobile phase is composed of acetonitrile and phosphate buffer at pH 2.5. The limits of quantification are 6 and 7.5 ng/ml for plasma and urine, respectively.

Continuous α2-adrenoceptor blockade by atipamezole decreases neocortical high-voltage spindle activity in rats

The present study investigates the effects of a subchronic continuous infusion of atipamezole, a potent and selective alpha 2-adrenoceptor antagonist, on neocortical high-voltage spindle (HVS) activity in rats. Six days' subcutaneous infusion of atipamezole (0.125 mg/kg per h) with osmotic minipumps decreased HVS activity significantly. The HVS activity-decreasing effect of atipamezole persisted at the same level throughout the infusion. A single subthreshold dose of an alpha 2-adrenoceptor agonist, guanfacine (0.001 mg/kg i.p.), did not affect HVS activity either before or after the continuous atipamezole treatment. The central alpha 2-adrenoceptor blocking effect of atipamezole (0.1 mg/kg per h s.c.) was confirmed to be at the same level after one, three or seven days' infusion, as assessed by measuring the antagonism of detomidine-induced mydriasis in the rat. The serum concentration of atipamezole (0.1 mg/kg per h s.c.) increased slightly from day 3 (37 +/- 11 ng/ml) to day 7 (45 +/- 4 ng/ml). In conclusion, the results of the study suggest that the suppressant effects of atipamezole on neocortical high-voltage spindle activity are preserved during subchronic continuous treatment. In addition, alpha 2-adrenoceptor blockade, as measured in the rat mydriasis model, persists at the same level during subchronic infusion.

Effect of dexmedetomidine, an alpha 2-adrenergic agonist, in the isolated heart

Dexmedetomidine (DM) was studied in the isolated dog heart in the form of a Starling heart-lung preparation, (HLP). Hearts were subjected to increased loading by (a) increasing cardiac output, and (b) increasing systemic resistance. Results are depicted by cardiac function curves, prepared by plotting left atrial pressure against either systemic cardiac output or mean arterial pressure. DM, given in divided doses up to 44 micrograms, had no effect on heart rate or cardiac function, nor did injection of 0.5 mg of atipamezole, a selective alpha 2-antagonist. Additional injections of very large doses of DM, up to 4,444 micrograms, caused an increase in heart rate and a leftward shift of the function curves, ie, positive chronotropic and inotropic effects. Plasma catecholamine levels increased markedly between the 444 micrograms and the 4,444 micrograms cumulative doses of DM. Administration of 1 mg of prazosin had no effect, but 1 mg of propranolol returned the rate to baseline and markedly shifted function curves to the right and depressed their slopes. Thus, whereas low doses (corresponding to between 1 and 30 micrograms/kg in intact animals) of DM, given acutely IV, have been shown to depress cardiac function in intact and denervated dogs, this effect is not due to a direct effect on the myocardium. High doses, far beyond doses maximally effective in intact animals and man, release catecholamines from cardiac stores. Plasma DM levels after low doses in the HLP were between 1 to 10 times those seen in intact animals and human volunteers after the usual doses given clinically for their central effects. Because DM caused no myocardial depressant effect in the isolated, blood-perfused canine HLP, decreases in cardiac function seen after this drug is given to intact and autonomically denervated dogs must be due to factor(s) other than a direct action on the myocardium.

Quantitative determination of a new anticonvulsant (CGS 18416A) in human plasma using capillary gas chromatography/mass spectrometry

An analytical method has been developed for the determination of a new antiepileptic drug, CGS 18416A, in human plasma. CGS 18416A is a new anticonvulsant representative of a novel class of water-soluble agents being developed for the treatment of epilepsy. Preclinical trials indicate sustained efficacy at relatively low oral doses, indicating a need for a sensitive assay. The method is based on capillary gas chromatography/mass spectrometry and utilizes stable isotope-labelled CGS 18416A as the internal standard. Samples (1 mL) are acidified, then washed with pentane/ethyl acetate, followed by liquid/liquid extraction at pH 11 with pentane/ethyl acetate. Extracts are then concentrated and analysed directly by gas chromatography/mass spectrometry. Separation is accomplished on a thick film methylsilicone capillary column. Mass spectrometry was carried out under positive ion ammonia Cl conditions with selected ion monitoring of the protonated molecular ions (m/z = 248 and 252) for CGS 18416A and the 13CD3-CGS 18416A, respectively. Specificity was demonstrated by the lack of interfering peaks at the retention time of CGS 18416A and the internal standard. Recovery and reproducibility assessments indicate good accuracy and precision over the validated concentration range of 0.2-51 ng/mL. The limit of quantification is 0.2 ng/mL and the method has sufficient sensitivity to support clinical trials. This is illustrated with an example of quantification in a normal volunteer following oral dosing.

Quantitative determination of zetidoline, a new antipsychotic agent, in human blood plasma and saliva using capillary gas chromatograph-mass spectrometry

A specific and sensitive assay is described. Zetidoline is extracted with ethyl ether from 1 ml of plasma or saliva added with the internal standard. The extract is carefully purified and injected into a gas chromatography-mass spectrometry system equipped with a crosslinked capillary column and operated in single ion monitoring mode by electron impact. Quantitative response is linear in the range 2-50 ng/ml. The detection limit is 1 ng/ml.

Determination of carnosine and other biogenic imidazoles in equine plasma by isocratic reversed-phase ion-pair high-performance liquid chromatography

The isocratic reversed-phase ion-pair high-performance liquid chromatographic technique presented provides a sensitive, rapid and reproducible analytical method for the selective determination of carnosine and other biogenic imidazoles in equine plasma. Plasma was deproteinized with 5-sulphosalicylic acid and the compounds of interest were isolated by sorbent extraction on Bond Elut PRS cartridges. Recoveries were 97-105% and the lowest limits of detection were 58.3-80.1 nM. All compounds of interest were well resolved within a maximum retention time of 9.2 min. The mean equine plasma carnosine level determined by this method was 11.31 microM. Comparative determinations were made in canine and human plasma. Carnosine was not detected in human plasma. Concentrations of imidazole in canine plasma are reported here for the first time.

Determination of moxonidine (BDF 5895) in plasma by gas chromatography-negative ion chemical ionization mass spectrometry

For the measurement of the pharmacokinetic behaviour of moxonidine, 4-chloro-5-(2-imidazolin-2-yl-amino)-6-methoxy-2-methylpyrimidine, an extremely sensitive analytical method was needed. The GC-MS method developed is specific and reliably detects moxonidine plasma levels down to 40 pg ml-1. Using negative ion chemical ionization (NICI) the M- fragment of the ditrifluoromethyl benzamide derivative of moxonidine (m/z 721) and the [M-HCl]- fragment of the ditrifluoromethyl benzamide derivative of clonidine (internal standard, m/z 673) were monitored in the selected ion monitoring mode, ensuring a specific and sensitive detection of the compounds. The validation process carried out included assay precision, repeatability, linearity, accuracy, stability and estimation of the detection and determination limits. The plasma-level time-curves and pharmacokinetic parameters from two volunteers after oral administration of 0.2 mg moxonidine are presented and demonstrate the practicability of the method in, for example, clinical studies.

Hemodynamic effects of cibenzoline on normal myocardium and after pretreatment with DL-sotalol

The circulatory and myocardial effects of cibenzoline were investigated in 78 open-chest rats during and after a 7-min intravenous (i.v.) infusion. Measurements were performed in the intact circulation, and myocardial function was also examined by isovolumic registrations independent of circulatory changes. In the first part of the study, the dose-dependent effects of cibenzoline were investigated (2, 4, and 8 mg/kg vs. NaCl controls). Cibenzoline caused a dose-dependent decrease in heart rate (HR) (-16, -34, -37% vs. preinfusion values), mean aortic blood pressure (AoPm) (-8, -20, -30%), cardiac output (CO) (-6, -29, -39%), and dP/dtmax (+1, -21, -59%). The isovolumic peak left ventricular systolic BP (LVSBP) (-6, -6, -17%) and peak dP/dtmax (-8, -18, -54%) were also reduced. In the second part of the study, we examined the effects of 2 mg cibenzoline/kg after pretreatment with 2 mg DL-sotalol/kg: HR was -22% AoPm was -12%, CO was -29%, dP/dtmax was -40%, isovolumic LV pressure (LVP) was -12%, and peak dP/dtmax was -41%. Cibenzoline caused dose-dependent bradycardia, which cannot be explained by beta-adrenoceptor blockade. The auxotonic and isovolumic measurements indicate that cibenzoline possesses a dose-dependent negative inotropic effect: 2 mg cibenzoline/kg caused only a slight decrease in myocardial performance, but this effect was aggravated after pretreatment with DL-sotalol. Cibenzoline also increased peripheral resistance. The observed combination of negative inotropism and vasoconstriction caused by cibenzoline should be taken into consideration especially in patients with reduced LV function. This is of particular importance if cibenzoline is combined with DL-sotalol.

Irreversible inhibition of thromboxane (TX) A2 synthesis by Y-20811, a selective TX synthetase inhibitor

As Y-20811, sodium (+-)-4-[alpha-hydroxy-5-(1-imidazolyl)-2-methylbenzyl]-3,5-dimethylb+ ++ enzoic acid, has been reported to inhibit serum thromboxane (TX) A2 production with a long duration of action, its mechanism of action was investigated. When [3H]Y-20811 (3 mg/kg) was administered orally to rats, the peak platelet concentration of Y-20811 was obtained 1 hr after the administration, and the T1/2 was 43 hr. The peak plasma concentration of Y-20811 was also obtained 1 hr after administration, but the elimination of Y-20811 from plasma was faster (T1/2 alpha = 1.5 hr, T1/2 beta = 15 hr) than that observed in platelets. Serum TXA2 (estimated as TXB2) production was inhibited significantly from 1 to 72 hr after the oral administration of unlabeled Y-20811 (3 mg/kg), which temporally resembled the change of the platelet Y-20811 concentration. In platelet-rich plasma, [3H]Y-20811 completely inhibited TXA2 production at about 1500 pg/10(9) platelets, and the IC50 level was about 600 pg/10(9) platelets, which was similar to values obtained in ex vivo studies. In addition, inhibition of TXA2 production by Y-20811 still remained after washing the drug-pretreated microsomes, whereas that of dazoxiben completely disappeared. A similar irreversible inhibition of TXA2 production was observed with aspirin. These results suggest that Y-20811 may firmly combine with platelet TX synthetase and may irreversibly inhibit TXA2 production.

Simultaneous determination of a novel angiotensin II receptor blocking agent, losartan, and its metabolite in human plasma and urine by high-performance liquid chromatography

A sensitive and selective high-performance liquid chromatographic method for the simultaneous determination of a new angiotensin II receptor blocking agent, losartan (DuP 753, MK-954, I), and its active metabolite, EXP3174 (II), in human plasma or urine is described. The two analytes and internal standard are extracted from plasma and urine at pH 2.5 by liquid-liquid extraction and analyzed on a cyano column with ultraviolet detection at 254 nm. The mobile phase is composed of acetonitrile and phosphate buffer at pH 2.5. The limit of quantification for both compounds in plasma is 5 ng/ml. The limit in urine is 20 and 10 ng/ml for I and II, respectively. The assay described has been successfully applied to samples from pharmacokinetic studies.

Hemodynamic and neurohumoral effects of moxonidine in patients with essential hypertension

The hemodynamic and neurohumoral effects of a single oral dose (0.4 mg) of the novel centrally acting antihypertensive agent moxonidine were investigated over 4 hours in ten patients with essential hypertension (WHO I-II). Pulmonary pressure indices and cardiac output were determined both at rest and during ergometric exercise by means of Swan-Ganz catheterization. Blood pressure was measured by sphygmomanometry and in the brachial artery. Moxonidine induced a significant fall in blood pressure over the 4-hour observation period from 176/105 mmHg to 158/95 mmHg (p less than 0.01), accompanied by a decrease in systemic vascular resistance from 1695 to 1427 dyn.sec/cm5 (p less than 0.01). Cardiac output remained unchanged, while heart rate increased slightly from 69 to 75 beats/min (p less than 0.01). No significant changes were recorded for either pulmonary artery pressure or pulmonary vascular resistance. Plasma levels of noradrenaline (337 vs. 224 pg/ml) and renin (2.6 vs 2.0 ng/ml/hr) activity fell significantly after moxonidine (p less than 0.05), both at rest and during exercise. Although aldosterone plasma levels fell slightly, level of angiotensin II and ANF remained unchanged. Moxonidine has favorable effects on hemodynamics and the neurohumoral system in patients with essential hypertension and is well tolerated at the dose administered.