Forward and Inverse Energy Cascade in Fluid Turbulence Adhere to Kolmogorov's Refined Similarity Hypothesis

We study fluctuations of the local energy cascade rate Φ_{ℓ} in turbulent flows at scales (ℓ) in the inertial range. According to the Kolmogorov refined similarity hypothesis (KRSH), relevant statistical properties of Φ_{ℓ} should depend on ε_{ℓ}, the viscous dissipation rate locally averaged over a sphere of size ℓ, rather than on the global average dissipation. However, the validity of KRSH applied to Φ_{ℓ} has not yet been tested from data. Conditional averages such as ⟨Φ_{ℓ}|ε_{ℓ}⟩ as well as of higher-order moments are measured from direct numerical simulations data, and results clearly adhere to the predictions from KRSH. Remarkably, the same is true when considering forward (Φ_{ℓ}>0) and inverse (Φ_{ℓ}<0) cascade events separately. Measured ratios of forward and inverse cascade probability densities conditioned on ε_{ℓ} also confirm the applicability of the KRSH to analysis of the fluctuation relation from nonequilibrium thermodynamics.

Oscillations Modulating Power Law Exponents in Isotropic Turbulence: Comparison of Experiments with Simulations

Inertial-range features of turbulence are investigated using data from experimental measurements of grid turbulence and direct numerical simulations of isotropic turbulence simulated in a periodic box, both at the Taylor-scale Reynolds number R_{λ}∼1000. In particular, oscillations modulating the power-law scaling in the inertial range are examined for structure functions up to sixth-order moments. The oscillations in exponent ratios decrease with increasing sample size in simulations, although in experiments they survive at a low value of 4 parts in 1000 even after massive averaging. The two datasets are consistent in their intermittent character but differ in small but observable respects. Neither the scaling exponents themselves nor all the viscous effects are consistently reproduced by existing models of intermittency.

Turbulence is an Ineffective Mixer when Schmidt Numbers Are Large

We solve the advection-diffusion equation for a stochastically stationary passive scalar θ, in conjunction with forced 3D Navier-Stokes equations, using direct numerical simulations in periodic domains of various sizes, the largest being 8192^{3}. The Taylor-scale Reynolds number varies in the range 140-650 and the Schmidt number Sc≡ν/D in the range 1-512, where ν is the kinematic viscosity of the fluid and D is the molecular diffusivity of θ. Our results show that turbulence becomes an ineffective mixer when Sc is large. First, the mean scalar dissipation rate ⟨χ⟩=2D⟨|∇θ|^{2}⟩, when suitably nondimensionalized, decreases as 1/logSc. Second, 1D cuts through the scalar field indicate increasing density of sharp fronts on larger scales, oscillating with large excursions leading to reduced mixing, and additionally suggesting weakening of scalar variance flux across the scales. The scaling exponents of the scalar structure functions in the inertial-convective range appear to saturate with respect to the moment order and the saturation exponent approaches unity as Sc increases, qualitatively consistent with 1D cuts of the scalar.

Small-Scale Isotropy and Ramp-Cliff Structures in Scalar Turbulence

Passive scalars advected by three-dimensional Navier-Stokes turbulence exhibit a fundamental anomaly in odd-order moments because of the characteristic ramp-cliff structures, violating small-scale isotropy. We use data from direct numerical simulations with grid resolution of up to 8192^{3} at high Péclet numbers to understand this anomaly as the scalar diffusivity, D, diminishes, or as the Schmidt number, Sc=ν/D, increases; here ν is the kinematic viscosity of the fluid. The microscale Reynolds number varies from 140 to 650 and Sc varies from 1 to 512. A simple model for the ramp-cliff structures is developed and shown to characterize the scalar derivative statistics very well. It accurately captures how the small-scale isotropy is restored in the large-Sc limit, and additionally suggests a possible correction to the Batchelor length scale as the relevant smallest scale in the scalar field.

Cancellation exponents in isotropic turbulence and magnetohydrodynamic turbulence

Small-scale characteristics of turbulence such as velocity gradients and vorticity fluctuate rapidly in magnitude and oscillate in sign. Much work exists on the characterization of magnitude variations, but far less on sign oscillations. While in homogeneous turbulence averages performed on large scales tend to zero because of the oscillatory character, those performed on increasingly smaller scales will vary with the averaging scale in some characteristic way. This characteristic variation at high Reynolds numbers is captured by the so-called cancellation exponent, which measures how local averages tend to cancel out as the averaging scale increases, in space or time. Past experimental work suggests that the exponents in turbulence depend on whether one considers quantities in full three-dimensional (3D) space or uses their one- or two-dimensional cuts. We compute cancellation exponents of vorticity and longitudinal as well as transverse velocity gradients in isotropic turbulence at Taylor-scale Reynolds numbers up to 1300 on 8192^{3} grids. The 2D cuts yield the same exponents as those for full 3D, while the 1D cuts yield smaller numbers, suggesting that the results in higher dimensions are more reliable. We make the case that the presence of vortical filaments in isotropic turbulence leads to this conclusion. This effect is particularly conspicuous in magnetohydrodynamic turbulence, where an increased degree of spatial coherence develops along the direction of an imposed magnetic field.

Steep Cliffs and Saturated Exponents in Three-Dimensional Scalar Turbulence

The intermittency of a passive scalar advected by three-dimensional Navier-Stokes turbulence at a Taylor-scale Reynolds number of 650 is studied using direct numerical simulations on a 4096^{3} grid; the Schmidt number is unity. By measuring scalar increment moments of high orders, while ensuring statistical convergence, we provide unambiguous evidence that the scaling exponents saturate to 1.2 for moment orders beyond about 12, indicating that scalar intermittency is dominated by the most singular shocklike cliffs in the scalar field. We show that the fractal dimension of the spatial support of steep cliffs is about 1.8, whose sum with the saturation exponent value of 1.2 adds up to the space dimension of 3, thus demonstrating a deep connection between the geometry and statistics in turbulent scalar mixing. The anomaly for the fourth and sixth order moments is comparable to that in the Kraichnan model for the roughness exponent of 4/3.

Reynolds number scaling of velocity increments in isotropic turbulence

Using the largest database of isotropic turbulence available to date, generated by the direct numerical simulation (DNS) of the Navier-Stokes equations on an 8192^{3} periodic box, we show that the longitudinal and transverse velocity increments scale identically in the inertial range. By examining the DNS data at several Reynolds numbers, we infer that the contradictory results of the past on the inertial-range universality are artifacts of low Reynolds number and residual anisotropy. We further show that both longitudinal and transverse velocity increments scale on locally averaged dissipation rate, just as postulated by Kolmogorov's refined similarity hypothesis, and that, in isotropic turbulence, a single independent scaling adequately describes fluid turbulence in the inertial range.

Abnormalities in left inferior frontal gyral thickness and parahippocampal gyral volume in young people at high genetic risk for bipolar disorder

BACKGROUND

Fronto-limbic structural brain abnormalities have been reported in patients with bipolar disorder (BD), but findings in individuals at increased genetic risk of developing BD have been inconsistent. We conducted a study in adolescents and young adults (12-30 years) comparing measures of fronto-limbic cortical and subcortical brain structure between individuals at increased familial risk of BD (at risk; AR), subjects with BD and controls (CON). We separately examined cortical volume, thickness and surface area as these have distinct neurodevelopmental origins and thus may reflect differential effects of genetic risk.

METHOD

We compared fronto-limbic measures of grey and white matter volume, cortical thickness and surface area in 72 unaffected-risk individuals with at least one first-degree relative with bipolar disorder (AR), 38 BD subjects and 72 participants with no family history of mental illness (CON).

RESULTS

The AR group had significantly reduced cortical thickness in the left pars orbitalis of the inferior frontal gyrus (IFG) compared with the CON group, and significantly increased left parahippocampal gyral volume compared with those with BD.

CONCLUSIONS

The finding of reduced cortical thickness of the left pars orbitalis in AR subjects is consistent with other evidence supporting the IFG as a key region associated with genetic liability for BD. The greater volume of the left parahippocampal gyrus in those at high risk is in line with some prior reports of regional increases in grey matter volume in at-risk subjects. Assessing multiple complementary morphometric measures may assist in the better understanding of abnormal developmental processes in BD.

Refined similarity hypothesis using three-dimensional local averages

The refined similarity hypotheses of Kolmogorov, regarded as an important ingredient of intermittent turbulence, has been tested in the past using one-dimensional data and plausible surrogates of energy dissipation. We employ data from direct numerical simulations, at the microscale Reynolds number R(λ)∼650, on a periodic box of 4096(3) grid points to test the hypotheses using three-dimensional averages. In particular, we study the small-scale properties of the stochastic variable V=Δu(r)/(rε(r))(1/3), where Δu(r) is the longitudinal velocity increment and ε(r) is the dissipation rate averaged over a three-dimensional volume of linear size r. We show that V is universal in the inertial subrange. In the dissipation range, the statistics of V are shown to depend solely on a local Reynolds number.

Universal intermittent properties of particle trajectories in highly turbulent flows

We present a collection of eight data sets from state-of-the-art experiments and numerical simulations on turbulent velocity statistics along particle trajectories obtained in different flows with Reynolds numbers in the range R{lambda}in[120:740]. Lagrangian structure functions from all data sets are found to collapse onto each other on a wide range of time lags, pointing towards the existence of a universal behavior, within present statistical convergence, and calling for a unified theoretical description. Parisi-Frisch multifractal theory, suitably extended to the dissipative scales and to the Lagrangian domain, is found to capture the intermittency of velocity statistics over the whole three decades of temporal scales investigated here.

Effect of administration route and length of exposure on pharmacokinetics and metabolism of diltiazem in dogs

The objective of this study was to systematically determine the pharmacokinetics and metabolism of diltiazem (DTZ) after a single i.v. dose, and after single and multiple oral (p.o.) doses. Four mongrel dogs (3 M, 1 F), aged 1-3 years, body weight 19-25 kg, were each given a single 30 mg dose of DTZ as a solution by i.v injection, the same dose orally from an immediate release tablet (Cardizem, Aventis Pharma, Canada, QC), and also t.i.d. for 10 doses. A 3-4 week washout period was allowed between each treatment. Blood samples (4 ml each) were obtained after each treatment from each animal via a cephalic vein at 0 (just before dosing), 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 6.0, 8.0, and 12.0 h post dose. Urine samples were collected for 24 h. The plasma samples were immediately separated by centrifugation and stored at -20 degrees C until analysis. The results showed that the bioavailability after a single p.o. dose of DTZ was 26+/-24%. Following a single i.v. dose, DTZ declined bi-exponentially with a terminal half-life (t1/2) of 4.2+/-1.7 h. N-Monodesmethyl DTZ (M(A)), deacetyl DTZ (M1), and deacetyl N-monodesmethyl DTZ (M2) were the major metabolites. Contrary to the results observed in clinical studies, there were no increase of plasma concentrations of DTZ after repeated doses (accumulation factor R = 0.94+/-0.51). Plasma concentrations of M1 decreased following repeated oral doses, accompanying by an increase of plasma concentrations of M2, although these changes were not statistically significant (p >0.05). This study cautions the use of mongrel dogs for direct extrapolation to humans, particularly for chronic pharmacokinetics studies of DTZ.

VEGF-2 (St Elizabeth's Medical Center)

St Elizabeth's Medical Center of Boston is developing VEGF gene therapy for the potential treatment of angina and diabetic neuropathy. The center is studying three isoforms of VEGF, although the expression of phVEGF165 has yielded the most positive results [312563]. VEGF-2 gene therapy augments perfusion of ischemic myocardium that contributes to improved clinical outcomes in patients with chronic myocardial ischemia as assessed by NOGA electromechanical mapping [390786]. Phase I trials demonstrated that gene transfer directly into the heart of the patient facilitates blood flow to the primary muscles of the heart, providing relief of angina [348564]. Reduced angina was reported by 28 out of 30 patients and tolerance of exercise increased from 240 to 410 s up to 180 days post-therapy [348632].

Determination of plasma concentrations of losartan in patients by HPLC using solid phase extraction and UV detection

PURPOSE

To establish a HPLC assay for plasma losartan and its active metabolite EXP3174 to facilitate clinical pharmacokinetic studies.

METHODS

the HPLC system consisted of a 250 x 2 mm i.d. C18 reversed phase column preceded by a 4 x 4 mm guard column, a UV detector set at 254 nm, and an integrator. The mobile phase was a mixture of 0.01 M ammonium phosphate: acetonitrile: methanol (6:3:1) containing 0.02 % sodium azide and 0.04% TEA, with pH adjusted to 3.2. The system was operated isocratically at ambient temperature at a flow rate of 0.3 ml/min. Losartan and its active metabolite EXP3174 were extracted from plasma using C2 bonded silica gel standard solid phase extraction.

RESULTS

recoveries of losartan and EXP3174 from plasma were greater than 70%. Using 0.5 ml of plasma sample, standard curves were linear from 10 to 300 ng/ml (r2 = 0.996 and 0.997 for losartan and EXP 3174, respectively). Sensitivity of the assay was < 10 ng/ml. Intra-and inter-assay variations were < 10 and 15%. respectively. The assay has been successfully applied to measuring plasma concentrations of losartan and EXP3174 in patients receiving a daily dose of losartan (50-100 mg).

CONCLUSION

The HPLC assay has adequate sensitivity, reproducibility, and specificity for clinical pharmacokinetic studies.

Technology evaluation: transgenic antithrombin III (rhAT-III), Genzyme Transgenics

AT-III LLC, a joint venture between Genzyme Transgenics (GTC) and Genzyme General, is developing transgenic recombinant human antithrombin III (rhAT-III) as a potential treatment for sepsis and other disorders involving thrombosis. It is in phase III clinical trials in the US and Europe as an anticoagulant in patients undergoing elective cardiac surgery such as cardiopulmonary bypass.

Transgenic antithrombin III (Genzyme)

ATIII LLC, a joint venture between Genzyme Transgenics (GTC) and Genzyme General, is developing transgenic recombinant human antithrombin III (rhAT-III) as a potential treatment for sepsis and other disorders involving thrombosis. It is in phase III clinical trials in the US and Europe as an anticoagulant in patients undergoing elective cardiac surgery requiring cardiopulmonary bypass (CPB). GTC has a license from Behringwerke (Hoechst Marion Roussel; now Aventis Pharma) to develop transgenic AT-III. Behringwerke retains exclusive worldwide marketing rights to the product, but has to purchase its entire supply of transgenic AT-III from GTC [156364]. In March 1997, GTC signed an agreement with SMIG, a joint venture formed by GTC and Sumitomo Metals, under which SMIG has the rights to develop rhAT-III in Asia in return for US dollar 4.4 million in additional funding for the continued transgenic development of rhAT-III. The dollar 4.4 million will be paid upon reaching certain milestones, which GTC expected to complete in 1997 [240202]. In December 1998, US-05843705 was issued covering rhAT-III production in transgenic goats [302263]. In January 2000, the results of the European phase III trial, which were significant in meeting the trial's primary endpoint of reduction in the use of fresh frozen plasma were reported. The trial was also significant in two of three secondary endpoints, maintenance of normal AT-III levels and changes in D-dimer and fibrin monomer [352041,353372]. Three phase III trials were initiated in the second quarter of 1998. Two identical trials, one in Europe and one in the US, evaluated the safety and efficacy of rhAT-III compared to placebo in restoring heparin sensitivity to heparin-resistant patients scheduled for elective cardiac surgery requiring CPB. The third trial, in both the US and Europe, will determine whether rhAT-III matches, at equivalent doses, the ability of plasma-derived AT-III to restore heparin sensitivity among heparin-resistant patients undergoing CPB [292235,292861]. Full enrollment onto the US trial was complete by the end of first quarter 2000 [363589], and the companies aim to complete trials and submit a filing by the end of 2000 [353372]. Clinical trials of the proteins in Japan were expected to begin in 1998 [286086].

A simple high-performance liquid chromatography assay for simultaneous measurement of adenosine, guanosine, and the oxypurine metabolites in plasma

To study the effect of pharmacologic agents on the biologic fate of adenosine, a reversed-phase high-performance liquid chromatography (HPLC) assay coupled with a solid-phase extraction (SPE) method was developed for simultaneous determination of plasma adenosine, hypoxanthine, xanthine, inosine, guanosine, and uric acid. The HPLC system consisted of a reversed phase C18 column, UV detector set at 254 nm, and a mobile phase composed of 0.01 M ammonium phosphate: methanol (9.5 : 0.5) vol/vol with the final pH adjusted to 3.9. The standard curves were linear between 0.1-2 microg/mL for all the analytes (except uric acid 50-400 microg/mL), with r2 > 0.99. The absolute recoveries were >60% and accuracy >85% in almost all cases. The limit of detection was <1 ng based on absolute injection of the analytes. The intraassay variations were <10% and interassay variations <15%. The presence of a wide range of medications in plasma samples did not interfere with the assay. The assay was applied successfully to measure plasma adenosine and the oxypurine metabolites in humans and rats. It was noted that plasma concentrations of adenosine and the oxypurine metabolites can vary considerably depending on the method of blood sample collection, and that species differences are apparent.

The spindle checkpoint in the dinoflagellate Crypthecodinium cohnii

Dinoflagellates are a major group of organisms with an extranuclear spindle. As the purpose of the spindle checkpoint is to ensure proper alignment of the chromosomes on the spindle, dinoflagellate cell cycle control may be compromised to accomodate the extranuclear spindle. In the present study, we demonstrated that nocodazole reversibly prolonged the G2 + M phase of the dinoflagellate cell cycle, in both metaphase and anaphase. The regulation of the spindle checkpoint involves the activation and inhibition of the anaphase promoting complex (APC), which in turn degrades specific cell cycle regulators in the metaphase to anaphase transition. In Crypthecodinium cohnii, nocodazole was also able to induce a prolongation of the degradation of mitotic cyclins and a delay in the inactivation of p13(suc1)-associated histone kinase activities. In addition, cell extracts prepared from C. cohnii in G1 phase and G2/M phase (or nocodazole treated) were able to activate and inhibit, respectively, the degradation of exogenous human cyclin B1 in vitro. The present study thus demonstrated the presence of the spindle checkpoint and APC-mediated cyclin degradation in dinoflagellates. This is discussed in relation to a possible role of the nuclear membrane in mitosis in dinoflagellates.

A simple high-performance liquid chromatography assay for simultaneous determination of plasma norepinephrine, epinephrine, dopamine and 3,4-dihydroxyphenyl acetic acid

A reversed-phase HPLC assay coupled with electrochemical detection for simultaneously measuring plasma levels of norepinephrine, epinephrine, dopamine, and 3,4-dihydroxyphenylacetic acid (DOPAC) was developed. Separation of the catecholamines and the internal standard isoproterenol was obtained by a mobile phase consisting of 7% methanol in 0.1 M citrate buffer containing 0.3 mM sodium ethylenediaminetetraacetic acid (EDTA), and 0.5 mM 1-octanesulfonic acid, operated under isocratic condition at a flow rate of 1.2 ml/min. The potential of the guard cell was set at +650 mV, the first electrode of the analytical cell at +100 mV and the second at + 350 mV. Using a signal-to-noise ratio of > 3, the minimum detection limit assessed by direct on column injection was < 10 pg for analyte. The assays were linear from basal concentrations to 400 ng/ml. The intra- and inter-assay variations were < 10 and 15%, respectively. The assay has been applied successfully to measure plasma concentrations of these catecholamines in humans, rabbits and rats.

Pharmacokinetics and hemodynamic effects of diltiazem in healthy volunteers: comparing resting with the effect of exercise

PURPOSE

To determine the steady-state plasma concentrations of diltiazem (DTZ) and hemodynamic effect in humans at rest and during exercise.

METHODS

Healthy volunteers (10 F, mean age 22, and 11 M, mean age 24) were recruited. Prior to receiving DTZ, each volunteer performed two 3-minute stages of treadmill exercise according to the Bruce protocol. Intra-arterial BP and ECG recordings were obtained before, during and immediately post exercise. Each volunteer then received DTZ 60 mg qid for one week. The same exercise protocol was repeated 1 h after the last dose. Steady-state plasma concentrations of DTZ were determined by a previously reported HPLC.

RESULTS

DTZ decreased resting DBP from 84 +/- 13 to 79 +/- 10 mmHg (p > 0.05), and HR from 89 +/- 11 to 82 +/- 13 bpm (p < 0.05). During exercise, an average of 32 and 10% increase in SBP and DBP, respectively, and a 47% increase of HR was found (p < 0.05). DTZ limited these increases to 21% for SBP, 5% for DBP, and 44% for HR (p < 0.05 for drug effect). Steady-state plasma DTZ concentrations were 141 +/- 56 ng/ml.

CONCLUSION

DTZ significantly decreased resting HR but not BP in health volunteers. It decreased both hemodynamic variables during exercise. Thus, the hemodynamic effects of diltiazem are more profound during exercise, and may be more useful surrogate markers for calcium antagonists and other cardiovascular agents in healthy volunteer studies.

Pharmacokinetics and hypotensive effect of diltiazem in rabbits after a single intravenous administration: effect of phenobarbital

Metabolism of the widely used calcium antagonist diltiazem (DTZ) is an important contributing factor to its therapeutic effects. In order to study the effects of CYP3A induction on the pharmacokinetics and haemodynamic effect of DTZ, it was administered as a single 5 mg/kg dose i.v. to two groups of New Zealand white rabbits (n = 6 in each group). Prior to the injection, one of the groups received phenobarbital 20 mg/kg s.c. two times a day for 3 days to ensure CYP3A induction, and the other received normal saline. A third group of animals (n = 6) received neither phenobarbital nor DTZ, and served as the control. Blood samples, systolic and diastolic blood pressure (SBP and DBP), and heart rate (HR) recordings were obtained from each rabbit up to 7 h, and urine samples for 48 h post-dose. Plasma concentrations of DTZ and its metabolites were determined by HPLC. The results showed that phenobarbital increased the Cl and Vdss of DTZ from 24 +/- 14 to 51 +/- 4.9 ml/min/kg and from 1.9 +/- 1.2 to 3.8 +/- 0.7 l/kg, respectively (p < 0.05). It also decreased the plasma concentrations of DTZ and all the measured metabolites in this study. Both phenobarbital and DTZ decreased SBP and DBP significantly without affecting the HR.

Pharmacokinetics and hypotensive effect of diltiazem in rabbits: comparison of diltiazem with its major metabolites

To assess the contribution of its metabolites to the antihypertensive effects of diltiazem, a previously established rabbit model has been used to compare the pharmacokinetics and haemodynamic effects of the drug with those of its major metabolites deacetyldiltiazem (M1) and deacetyl-N-monodemethyldiltiazem (M2). Diltiazem, M1 and M2 were administered separately to each animal (n = 5 or 6 per study group) as a single 5 mg kg(-1) intravenous dose. Blood samples, systolic and diastolic blood pressure (SBP and DBP) and heart rate were recorded for each rabbit up to 8 h, and urine samples were collected for 48 h post-dose. Plasma concentrations of diltiazem and its major metabolites were determined by HPLC. The results showed that systemic clearance (CL) and volume of distribution at steady state (Vdss) were smaller for diltiazem than for the metabolites. Diltiazem and the metabolites reduced both SBP and DBP, the effects of diltiazem being most potent. Their effects on heart rate were highly variable and not statistically different between treatment groups (P > 0.05). These results indicate that diltiazem is a more potent hypotensive agent than M1 or M2, possibly because of the higher plasma concentrations secondary to the smaller CL and Vdss of diltiazem compared with the metabolites. The effects of the metabolites might, however, be more sustained.

A simple high performance liquid chromatography assay for simultaneous determination of omeprazole and metronidazole in human plasma and gastric fluid

Antibiotics which are actively secreted into gastric fluid may be more efficacious in the eradication of Helicobacter pylori in peptic ulcer disease. Other agents used in the treatment of this disease such as omeprazole or other anti-secretory agents may alter the secretion and/or distribution characteristics of antibiotics. In order to test the applicability of these concepts to metronidazole, a sensitive and specific high performance liquid chromatography (HPLC) assay was developed to quantitate omeprazole in plasma, and metronidazole in plasma and gastric fluid. The HPLC system consisted of a multi-phase column combining anion exchange and reversed phase separation (OmniPac Pax-500, Dionex), and a variable wavelength UV detector set at 254 nm. The mobile phase was a mixture of 0.1 M sodium phosphate buffer:methanol:acetonitrile (60:20:20) with final pH adjusted to approximately 7.0. Metronidazole and omeprazole were extracted by adsorption onto a C2-bonded silica gel solid phase extraction column, and eluted with methanol. The extract was dried, reconstituted in a solution of acetyl salicylic acid (ASA), and then injected into the HPLC system. Under these conditions, metronidazole, omeprazole and ASA were well separated and recoveries in plasma were greater than 80%. Omeprazole could not be measured in gastric fluid because of rapid decomposition. Using 0.3 ml of sample, the assay sensitivity was less than 0.1 microgram ml-1 and linear up to 10 micrograms ml-1. Both intra- and inter-assay CV were greater than 15%. It was applied successfully in determining metronidazole concentrations in clinical samples of plasma and gastric fluid.

Pharmacokinetics and haemodynamic effect of deacetyl diltiazem (M1) in rabbits after a single intravenous administration

Deacetyl diltiazem (M1) is a major metabolite of the widely used calcium antagonist diltiazem (DTZ). In order to study the pharmacokinetic and haemodynamic effects of this metabolite, M1 was administered as a single 5 mg kg-1 dose intravenously (i.v.) to New Zealand white rabbits (n = 5) via a marginal ear vein. Blood samples, blood pressure (SBP and DBP), and heart rate (HR) recordings were obtained from each rabbit up to 8 h, and urine samples for 48 h post-dose. Plasma concentrations of M1 and its metabolites were determined by HPLC. The results showed that the only quantifiable basic metabolite in the plasma was deacetyl N-monodesmethyl DTZ (M2). The t1/2 and AUC of M1 and M2 were 2.1 +/- 0.5 and 3.0 +/- 1.1 h, and 1300 +/- 200 and 240 +/- 37 ng h mL-1, respectively. The Cl and Clr of M1 were 60 +/- 10 and 0.81 +/- 0.63 mL min-1 kg-1, respectively. M1 significantly decreased blood pressure (SBP and DBP) for up to 1 h post-dose (p < 0.05), but had no significant effect on the heart rate (P > 0.05). The Emax and EC50 as estimated by the inhibitory sigmoidal Emax model were 20 +/- 18% 620 +/- 310 ng mL-1, respectively for SBP; 20 +/- 8.3% and 420 +/- 160 ng mL-1 for DBP.

Pharmacokinetics and haemodynamic effect of diltiazem in rats: effect of route of administration

Diltiazem is a calcium antagonist widely used for the treatment of angina and hypertension. Previous studies in patients have shown that the haemodynamic effects of diltiazem are greater after parenteral rather than oral administration. The rat has been used as an animal model to determine the effect of the route of administration on the pharmacokinetic and haemodynamic effects of diltiazem. The results showed that plasma concentrations of diltiazem were more than 10 times higher after the intra-arterial dose. The plasma concentrations of the major metabolites were also higher after intra-arterial administration, although only for deacetyl diltiazem (M1) did the difference reach statistical significance (P < 0.05). The haemodynamic effects (on blood pressure and heart rate) of diltiazem were considerably greater after intra-arterial administration; this was attributed mainly to the much higher plasma concentrations of diltiazem. The hypotensive and chronotropic effects of diltiazem were similar; Emax and EC50 for diastolic blood pressure were 72+/-19% and 4.4+/-5.9 microg mL(-1); for heart rate they were 77+/-32% and 10.0+/-11.7 microg mL(-1), respectively. The haemodynamic effects of diltiazem are much greater after intra-arterial administration, mainly because of the much higher plasma concentrations of the drug. The contribution by the metabolites would be minimal after this route of administration.

Pharmacokinetics and hypotensive effect of deacetyl N-monodesmethyl diltiazem (M2) in rabbits after a single intravenous administration

Deacetyl N-monodesmethyl diltiazem (M2) is a major metabolite of the widely used calcium antagonist diltiazem (DTZ). In order to study the pharmacokinetic and haemodynamic effects of this metabolite, M2 was administered as a single 5 mg/kg dose intravenously (i.v.) to New Zealand white rabbits (n = 5) via a marginal ear vein. Blood samples, blood pressure (SBP and DBP), and heart rate (HR) recordings were obtained from each rabbit up to 8 h, and urine samples for 48 h post-dose. Plasma concentrations of M2 were determined by HPLC. The results showed that there were no identifiable basic metabolites which could be quantified and characterized in the plasma. The apparent terminal t1/2 and AUC were 2.8 +/- 0.7 h and 2000 +/- 290 ng x h/ml, respectively. The Cl and Clr of M2 were 38 +/- 4.8 ml/min/kg and 0.57 +/- 0.23 ml/min/kg, respectively. M2 significantly decreased blood pressure (SBP and DBP) for up to 2 h post-dose (P < 0.05), but had no significant effect on the heart rate (P > 0.05). The Emax and EC50 as estimated by the inhibitory sigmoidal Emax model were 15 +/- 7% and 450 +/- 46 ng/ml, respectively, for SBP; 15 +/- 20% and 430 +/- 120 ng/ml for DBP.

Effect of diltiazem on plasma concentrations of oxypurines and uric acid

To determine the clinical effect of diltiazem on the metabolism of adenosine, and its importance in ischemic heart disease, arterial plasma concentrations of the purine metabolites were determined in 21 healthy volunteers (10 female and 11 male) and 19 patients with effort angina (8 female and 11 male) before, during, and immediately after standard treadmill exercise tests conducted before and after they had taken 60 mg diltiazem (Cardizem; Hoechst Marion Roussel, Laval, QC, Canada) four times a day for 1 week. The results showed that the cardiac patients had significantly lower mean plasma concentrations of uric acid (46.82 +/- 25.51 versus 95.47 +/- 35.41 micrograms/ml, p 0.05), inosine (0.25 +/- 0.19 versus 0.84 +/- 0.17 microgram/ml, p < 0.05), and hypoxanthine (0.28 +/- 0.35 versus 0.50 +/- 0.27 microgram/ml, p < 0.05). Diltiazem decreased the mean resting plasma concentrations of uric acid in patients (uric acid 43.47 +/- 22.26 versus 46.82 +/- 25.51 micrograms/ml, p < 0.05) and healthy volunteers (uric acid 85.68 +/- 26.71 versus 95.47 +/- 35.41 micrograms/ml, p < 0.05). There was no statistically significant change in the plasma concentrations of the purine metabolites during exercise (p < 0.05). Female subjects had significantly lower plasma concentrations of uric acid than males (patients, 34.87 +/- 26.93 versus 55.78 +/- 21.25 micrograms/ml; healthy volunteers, 84.79 +/- 32.07 versus 104.22 +/- 37.05 micrograms/ml; p < 0.05 for both). Results of the study suggest that normal therapeutic doses of diltiazem may modulate the metabolism of adenosine and that some of the purine metabolites may be useful markers for specific types of ischemic heart disease.

Effect of diltiazem on intraarterial blood pressure and heart rate during stress testing in patients with angina: a gender comparison study

The purpose of this study was to measure the blood pressure and electrocardiographic responses of a small, matched group of women (n = 8) and men (n = 9) who experienced typical, effort angina during an exercise on the treadmill (up to the second stage of a Bruce protocol). These responses were measured before and after therapy with diltiazem (60 mg four times daily for 1 week). Reports of previous studies have described significant gender differences in blood pressure responses to diltiazem in healthy volunteers tested with the same protocol. In contrast to the data in healthy individuals, gender differences in blood pressure responses to exercise before and after diltiazem administration were not observed. Results of analysis of pulse pressure responses to exercise were also similar in male and female patients with angina. A significant postexercise drop in blood pressure was observed, which was augmented by diltiazem. These data suggest that gender differences in drug action may be difficult to demonstrate in patients with vascular disease.

Sequence data for two large-subunit rRNA genes from an Asian strain of Alexandrium catenella

PCR generated two distinct products from a toxic isolate of Alexandrium catenella, which had been taken from Dai Ya Bay (southern China), by using primers for large-subunit rRNA. This pattern is distinct from published data for North American Alexandrium species. Sequences of the two products suggest that the smaller was generated by a deletion event. Single-cell PCR generated the same pattern, confirming that the two products were not the results from different individuals.

Effect of omeprazole on movement of intravenously administered metronidazole into gastric juice and its significance in treatment of Helicobacter pylori

Four healthy, Helicobacter-negative volunteers were studied to determine the effect of omeprazole on the movement of metronidazole across the gastric mucosa into the gastric lumen. Each received a 500-mg intravenous infusion of metronidazole and repeated serum, and gastric juice samples were obtained concomitantly over an 8-hr study via indwelling intravenous catheter and nasogastric tube. The same protocol was repeated following one week of oral omeprazole 20 mg twice daily. Metronidazole concentrations were measured by high-performance liquid chromatography. The results demonstrated that: metronidazole moves rapidly from serum into gastric juice; omeprazole causes a marked reduction in total metronidazole concentrations in gastric juice, completely accounted for by pH-related shifts in the proportion of ionized metronidazole, but does not alter concentrations of nonionized metronidazole, which remain above the MIC level against H. pylori; and even under conditions where no pH-related drug trapping occurs (pH > 4), concentrations of metronidazole were higher in gastric juice than in serum during most of the study, indicating that a special transport mechanism may be operational. The practical implication of this effect of omeprazole in combination therapy with metronidazole remains to be established.

Determination of 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid in human plasma by a simple and rapid high-performance liquid chromatography assay

In order to study the pharmacodynamic effects of drugs on dopamine and serotonin metabolism, a reversed-phase HPLC assay coupled with electrochemical detection (ECD) for measuring plasma concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) was developed. The system was operated isocratically using a mobile phase of aqueous 0.03 M KH2PO4 buffer containing 0.15 mM EDTA in methanol (8.75:1.25), with a final pH of 4.0. The flow rate was set at 1.5 mL/min, and potentials at +450 mV. Using a signal to noise ratio of > 3, the minimum detection limit assessed by direct on-column injection of a standard solution for DOPAC and 5-HIAA was < 1 pg. The assays were linear from basal concentrations (1-10 ng/mL) to 100 ng/mL. The intra- and interassay variations were < 10% and < 20%, respectively.

Steady-state plasma concentrations of diltiazem and its metabolites in patients and healthy volunteers

Diltiazem (DTZ) is a calcium antagonist widely used in the treatment of angina and hypertension. It is extensively metabolized in humans via N-demethylation, O-demethylation, deacetylation, and oxidative deamination, yielding a host of metabolites, some of which have potent pharmacological properties. After our initial identification of O-desmethyl DTZ (Mx) and N,O-didesmethyl DTZ (MB) as major metabolites of DTZ and our subsequent of identification of their chemical synthesis, an improved high-performance liquid chromatography assay was developed to determine the plasma concentrations of DTZ and seven of its major basic metabolites, including the previously unquantitated Mx and MB. The system consisted of a C18 analytical column protected by a C18 cartridge guard column and a variable wavelength ultraviolet detector set at 237 nm. The mobile phase was a mixture of methanol, 0.04 M ammonium acetate, and acetonitrile (38:36:26) containing 0.08% triethylamine, with final pH of the mobile phase adjusted to 7.5. The system was operated at room temperature isocratically at a flow rate of 1.2 ml/min. Using verapamil as an internal standard, DTZ and the basic metabolites in plasma were determined in young healthy volunteers (n = 21) and in patients with ischemic heart disease (n = 19) at steady state after repeated oral doses of 60 mg DTZ four times daily. Preliminary results show that steady-state plasma concentrations of DTZ and its metabolites were higher in the older patients than in young healthy subjects (p < 0.05).

Effect of phenobarbital pretreatment on the pharmacokinetics and metabolism of diltiazem in rats

In order to study the effect of cytochrome P-450 isozyme induction on the pharmacokinetics and metabolism of diltiazem (DTZ), male Sprague-Dawley rats weighing 300-600 g were randomly assigned to two groups. The enzyme induction group (n = 4) received phenobarbital 60 mg/kg i.p. once daily for 4 days, whereas the control group (n = 6) received normal saline for the same duration. Each rat then received a single oral dose of DTZ in solution (20 mg/kg). Blood samples (0.5 ml) were collected from each rat via an implanted polyethylene catheter (0.040" i.d.) in the right carotid artery at 0 (just before dosing), 0.25, 0.5, 1,2,3,4,6,8 and 10 h post-dose. Arterial plasma concentrations of DTZ and its metabolites M(A), M1, M2, M4 and M6 were determined by HPLC. Pharmacokinetics parameters were calculated using non-linear regression. The results showed that both mean Cmax and AUC of DTZ were lower (871.6 vs 79.8 ng/ml; 1171 vs 101.9 ng-h/ml), but the mean Cmax of the primary metabolites M1 and M(A) was higher after phenobarbital (M1 413.0 vs 648.9 ng/ml; M(A) 683.0 vs 814.8 ng/ml). The highest increase was seen in the mean Cmax and AUC of the secondary metabolite M2 (837.5 vs 2585.7 ng/ml; 3312.1 vs 13156.5 ng-h/ml). In contrast, plasma concentrations of the O-desmethylated metabolites M4 and M6 did not increase after phenobarbital. These results suggest that both deacetylation and N-demethylation of DTZ in rats are catalyzed by drug metabolizing enzymes inducible by phenobarbital.

Pharmacokinetics and metabolism of diltiazem in rats following a single intra-arterial or single oral dose

Diltiazem (DTZ) 20 mg/kg was given to male Sprague-Dawley rats either orally (p.o.) or intra-arterially (i.a.) over a 5 min period (n = 6 for each group). Plasma concentrations of DTZ and its major basic metabolites were determined by high performance liquid chromatography assay (HPLC) as previously described over a 10 h period. The major metabolites found in the rat plasma were M2, followed by M6, MA, M1, and then M4. The metabolite Mx was measurable only in some of the plasma samples, and MB was not detected in this species. The mean apparent half-life (t1/2) of the measurable metabolites were longer than the parent DTZ. The metabolism profiles were qualitatively similar between the two routes of administration. Quantitatively, however, the plasma concentrations of the metabolites were higher after the i.a. route. These results are in agreement with a previous study reported in rabbits, and suggest that deacetylation of DTZ and MA in the blood is extremely important in this species.

The effect of multiple doses of ranitidine on the pharmacokinetics and metabolism of diltiazem in dogs

In order to determine the potential pharmacokinetic drug interaction between ranitidine and diltiazem (DTZ), each of ten male beagle dogs, age 2.7-4.0 years, weight 13-16 kg, received a single oral dose of sustained release DTZ with and without previous multiple oral doses of ranitidine (150 mg bid for five doses). The dog was selected as the animal model because the pharmacokinetics and metabolism profiles of DTZ are similar to those in humans and because sustained release DTZ capsules can be administered with ease to this species. Following the oral dose of DTZ, blood samples (5 ml each) were obtained via a cephalic vein at 0 (just before dosing), 1, 2, 3, 4, 5, 6, 8, 12, 18, 24, 30, 36, and 48 h after the dose. Urine samples were collected for 48 h post dose. Plasma and urine concentrations of DTZ and its major metabolites N-monodesmethyl DTZ (MA), deacetyl DTZ (M1), and deacetyl N-monodesmethyl DTZ (M2) were determined by HPLC. Pharmacokinetic parameters were calculated by non-linear curve fitting, and the effect of ranitidine was evaluated by two-factor analysis of variance (ANOVA). Pre-treatment of the animals did not significantly alter the disposition of DTZ (p > 0.05). Similar to the results reported in clinical studies, there were large variations in the plasma and urine concentrations of DTZ and its major metabolites among the beagle dogs. The effect of ranitidine on the disposition of DTZ was highly variable.

Pharmacokinetics of chlorpromazine and key metabolites

A study was carried out in 11 healthy young men to investigate the pharmacokinetics of chlorpromazine (CPZ) after a bolus intravenous (i.v.) dose (10 mg) and three single oral doses (25, 50 and 100 mg), with a washout period of two weeks between doses. Plasma levels of CPZ, CPZ N-oxide (CPZNO), CPZ sulfoxide (CPZSO) and both free and conjugated 7-hydroxy-CPZ (7-HOCPZ) were measured by extraction radioimmunoassays. CPZ exhibited multicompartmental pharmacokinetics in most subjects. There was wide between-subject variability in half life (11.05 h), volume of distribution (1215 l), volume of distribution at steady state (642 l) and mean residence time (8.88 h), whereas systemic clearance was somewhat less variable (76.6 l.h-1). All metabolites were present in measurable concentrations in the plasma of 9 of 11 subjects after i.v. CPZ, whereas free 7-HOCPZ was not detected in the other 2 individuals. With the exception of CPZNO, the biological half lives of the primary metabolites were longer than the half life of CPZ. After oral administration, the percentage of CPZ reaching the systemic circulation intact (F%) was very low (4-38%) and dose dependent. Moreover, both within-subject and between-subject variances were very high. The maximum plasma concentration (Cmax) and area under the plasma concentration versus time curve extrapolated to infinite time (AUC) showed evidence of nonlinearity, whereas half life did not appear to be dose dependent. These data suggest that the high degree of variability in the pharmacokinetics of CPZ is a result of extensive first pass metabolism rather than variation in half life.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte adenosine transport. A rapid screening test for cardiovascular drugs

An erythrocyte (RBC) model based on whole blood was used to investigate the effect of cardiovascular drugs on the uptake of adenosine in vitro. Fresh whole blood obtained from healthy volunteers was allowed to equilibrate with various concentrations (5-1000 microM) of a tested agent. (2-3H)-Adenosine was used as a substrate, and the reaction was terminated after 2 sec of incubation at room temperature by rapid addition of a "Stopping Solution" which was a mixture of erythro-9-(2-hydroxy-3-nonyl)adenine, dipyridamole, and EDTA. The mixture was centrifuged (1760 g, 4 degrees C, 10 min), and the radioactivity of an aliquot of the supernatant was determined by a scintillation counter. The results showed that dipyridamole was the most potent agent tested (IC50 = 0.2 microM). Amongst the calcium antagonists studied, isradipine was most potent, followed by verapamil, clentiazem, diltiazem, and then nifedipine. The racemates of two metabolites of diltiazem, MX and MB, were more potent than the parent drug. The antiarrhythmic agents, amiodarone and sotalol, the two new lipid peroxidation inhibitors, U-74389F and U-78517F, and the anxiolytic agent, alprazolam, were as active as verapamil. The beta-receptor antagonist propranolol and the angiotensin converting enzyme (ACE) inhibitor, enalapril, were practically inactive. In addition, the model was stereoselective such that the S(-)-enantiomer of verapamil was considerably more potent than the R(+)-antipote, whereas d(+)-sotalol was practically inactive compared to racemic sotalol.

Pharmacokinetics and metabolism of diltiazem in healthy males and females following a single oral dose

Plasma concentrations and urinary excretion of DTZ and its metabolites were determined in 20 healthy volunteers (10 males and 10 females) after they had each been given a single oral 90 mg dose of DTZ. DTZ and six of its metabolites which included N-monodesmethyl DTZ (MA), deacetyl DTZ (M1), deacetyl N-monodesmethyl DTZ (M2), deacetyl O-desmethyl DTZ (M4) and deacetyl DTZ N-oxide (M1NO) and deacetyl N,O-didesmethyl DTZ (M6), were determined by a sensitive and specific HPLC assay. The major metabolites measurable in the plasma of all the volunteers were MA, M1, and M2. The terminal half-lives (t1/2) of M1 and M2 were considerably longer than those of DTZ and MA. Less than 5% of the dose was excreted as unchanged DTZ in the urine over the 24 h period. The major urinary metabolite was MA, followed by M6, M2, and then M1. Except for the urinary excretion of M4 there were no statistically significant differences in any of the pharmacokinetic parameters between the males and the females. The mean 24 h urinary recovery of M4 was higher in the males than in the females (P < 0.05). However there were large inter-individual variations in the plasma concentrations and urinary excretion of DTZ and its metabolites with some parameters differing by more than 20-fold. In addition, O-desmethyl DTZ (Mx) and N,O-didesmethyl DTZ (MB) were identified as two other major urinary metabolites.

Synthesis, characterization, and Ca2+ antagonistic activity of diltiazem metabolites

Diltiazem is a calcium antagonist widely used in the treatment of angina and hypertension. The contributions of metabolites of diltiazem to the vasorelaxant effects of diltiazem were investigated. The synthesis and spectroscopic characterization of eight major cis-diltiazem metabolites are described. Three of the compounds--N, O-didemethylated metabolite (21), O-demethylated metabolite (22), and diltiazem N-oxide (27)--have been recently reported and have not previously been synthesized. The identities of all eight synthetic metabolites have been verified with samples obtained from human urine using combined LC-MS/MS. The Ca2+ antagonistic activities of diltiazem and its metabolites (except 27) were studied on hamster aorta preparations depolarized with KCl. The order of potencies (IC50 +/- SE, microM) is as follows: diltiazem (0.98 +/- 0.47) greater than 17 (2.46 +/- 0.38) greater than or equal to 23 (3.27 +/- 1.02) greater than 26 (20.2 +/- 10.5) greater than 22 (40.4 +/- 15.4) greater than or equal to 25 (45.5 +/- 18.1) greater than 21 (112.2 +/- 33.2) greater than or equal to 24 (126.7 +/- 24.2). Structure-activity relationships are also discussed.

Effect of diltiazem and its metabolites on the uptake of adenosine in blood: an in-vitro investigation

Using whole blood from man and rabbits, the effect of diltiazem, its metabolites, and other calcium antagonists on the uptake of adenosine has been described. The uptake and metabolism of adenosine was extremely rapid with a half-life in plasma of less than 30 s. Adenosine is rapidly and extensively metabolized to hypoxanthine. Metabolites of diltiazem, deacetyl diltiazem and deacetyl O-desmethyl diltiazem were considerably more potent than the parent drug. Diltiazem was one-tenth as active as verapamil, but more active than nifedipine or amlodipine. Dipyridamole was the most potent uptake-inhibitor tested (IC50 less than 1 microM), whereas the angiotensin converting enzyme inhibitor enalapril was virtually devoid of any inhibitory activities (IC50 greater than 1000 microM). The results obtained from both man and rabbit were similar.

A reliable technique for chronic carotid arterial catheterization in the rat

A reliable and simple method for cannulating the carotid artery of rats is described. The rat was anesthetized with halothane. The right carotid artery located between the omohyoideus and sternohyoideus muscles was exposed through a 2-cm ventral neck incision. The catheter was made of Silastic tubing and a monofilament line, which served as an obturator and internal support. The line was then filled with a viscous mixture of heparin, polyvinylpyrrolidinone and normal saline to prevent the formation of blood clots. The catheter was advanced through the carotid artery towards the heart by a predetermined distance (15-20 mm) depending on the size of the rat. The catheter was well tolerated by the rats and the success rate was 95%. Its patency lasted for at least 7 days postsurgery without any special maintenance care. With the described method one would be able to perform repetitive blood sampling and arterial blood pressure measurements in unanesthetized and unrestrained rats for prolonged period after catheterization.

Stability of diltiazem and its metabolites in plasma during storage

Diltiazem (DTZ) is a calcium antagonist widely used in the treatment of angina and related heart diseases. It is extensively metabolized into a host of metabolites, some of which have potent pharmacological activities. Previous work has shown that DTZ and its major metabolite N-desmethyl-DTZ (MA) were unstable and readily decomposed to deacetyl-DTZ (M1) and deacetyl N-desmethyl-DTZ (M2), respectively. This report describes the stability of DTZ and its metabolites in plasma samples stored at -20 and -70 degrees C for different periods up to 12 weeks. The results indicate that in those samples obtained from volunteers who received DTZ, no deterioration of DTZ or MA occurred up to 8 weeks, but considerable deterioration of DTZ to M1 and MA to M2 (p less than 0.01) occurred after 12 weeks. However, in samples prepared by adding DTZ and its metabolites to outdated plasma (spiked plasma), deterioration of DTZ occurred after 4-6 weeks of storage, but there were no concomitant increases in concentrations of M1 or M2. Thus, it appears that decomposition of DTZ and MA was affected by the nature of the plasma materials, but the reason for the differences in analyte stability observed between volunteers' and spiked plasma is not known. Also, it appeared that DTZ and its metabolites in plasma samples stored at -70 degrees C may be more stable than those at -20 degrees C, although further studies are required to substantiate this observation. On the basis of these results, plasma samples obtained from patients or volunteers receiving DTZ should be analyzed within 8 weeks when the samples are stored frozen at -20 degrees C.

Pharmacokinetics and metabolism of diltiazem in rabbits after a single intravenous or single oral administration

Diltiazem (DTZ) 5 mg/kg was given to rabbits either orally (n = 5) or intravenously (n = 6). Plasma concentrations and urinary excretion of DTZ and its metabolites were determined by a high performance liquid chromatography assay (HPLC) for 12 and 48 h post dose, respectively. The results showed that the metabolism and disposition of DTZ in rabbits was similar to that of humans, mean absolute bioavailability (F) of DTZ was approximately 30% and the systemic clearance was 64.0 ml/min/kg. The metabolism of DTZ between the two routes of administration was quantitatively different in that higher plasma concentrations of the metabolites were observed after the intravenous dose. This could be a result of incomplete oral absorption, higher clearance of DTZ and the metabolites during the first pass through the liver (i.e. higher sequential first pass effect), and/or extrahepatic metabolism. On the basis of the plasma concentration-time profiles and urinary excretion of DTZ and its metabolites, it is concluded that the rabbit is a suitable animal model to investigate the kinetics and metabolism of DTZ.

Liquid chromatography assay for amlodipine: chemical stability and pharmacokinetics in rabbits

Amlodipine is a long acting dihydropyridine calcium antagonist recently introduced for the treatment of angina and hypertension. In order to document its stability in vitro and to develop a pharmacokinetic model in rabbits, a new reversed-phase liquid chromatography (LC) assay with UV detection was developed. The method utilized a C18 column (250 x 4.6 mm i.d.) with a mobile phase composed of a mixture of methanol 0.04 M ammonium acetate-acetonitrile (38:38:24, v/v/v) containing 0.02% triethylamine (final pH 7.1). Under these conditions, the retention times of amlodipine and the internal standard desipramine were 10.6 and 12.9 min, respectively. Using 1 ml of plasma, sensitivity of the assay was 2.5 ng ml-1 at which the RSD was 11%. The standard curve was linear from 2.5 to 100 ng ml-1 (r2 = 0.990), and the mean RSD at this concentration range was 6.8%. The pharmacokinetic model was developed in rabbits which provides results similar to those in dogs, but at less expense. The assay was also applied to a stability study comparing amlodipine and nifedipine in pH 3 and pH 7 ammonium acetate buffers and in methanol. Amlodipine was considerably more stable than nifedipine under all conditions. Finally the assay was applied to a pharmacokinetic study in rabbits (n = 6) after a single 1 mg kg-1 intravenous dose. The mean half-life (t1/2) of amlodipine was 6.5 h, the systemic clearance (CL) was 4.8 l h-1 kg-1 and the apparent volume of distribution at steady state (Vdss) was 30.2 l kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Species comparison of pharmacokinetics and metabolism of diltiazem in humans, dogs, rabbits, and rats

Diltiazem (DTZ) is a calcium antagonist widely used in the treatment of angina and related heart diseases. It is extensively metabolized into a host of metabolites, some of which have potent pharmacological activities. In this study, the pharmacokinetics and metabolism of DTZ was investigated in humans, dogs, rabbits, and rats after each species (n = 4 or 5) was given a single oral dose of DTZ. After the drug administration, blood and urine samples were collected for 12 and 48 hrs, respectively. DTZ and six of its metabolites were quantitated in our laboratory by HPLC. The results indicated that, in humans, the major metabolites in plasma were N-monodesmethyl diltiazem (MA), deacetyl diltiazem (M1), and deacetyl N-monodesmethyl diltiazem (M2). These metabolites were also detected in the plasma of dogs, rabbits, and rats. However, there were quantitative differences. For example, in the humans and dogs, MA was the most abundant metabolite in plasma, while M1 and M2 were most prominent in the rabbits and rats, respectively, and M2 was a relatively minor metabolite in dog plasma. Less than 5% of the dose was recovered as unchanged DTZ in the urine of all the tested species. The most abundant metabolites in urine appeared to be MA and deacetyl N,O-didesmethyl diltiazem, although there were considerable inter- and intra-species variations. Two additional metabolites were detected in the urine of the humans, dogs, and rabbits, but not in the rats. They were tentatively identified as O-desmethyl diltiazem and N-O-didesmethyl diltiazem, using electron impact and ammonia chemical ionization mass spectrometry.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic assay of diltiazem and six of its metabolites in plasma: application to a pharmacokinetic study in healthy volunteers

A sensitive and specific reversed-phase high-performance liquid chromatographic assay for simultaneous determination of plasma concentrations of diltiazem and six of its metabolites known to occur in humans is reported. Using 2 mL of plasma, the lower limit of quantitation of the assay was less than 10 ng/mL of diltiazem and each of the metabolites, with coefficients of variation of less than 10%. The assay was successfully applied to determine the kinetics of diltiazem and its major metabolites in four healthy volunteers after each received a single 90-mg oral dose of diltiazem. In addition to the previously reported two major metabolites in humans, deacetyl diltiazem (M1) and N-monodemethyl diltiazem (MA), another previously unreported major metabolite, deacetyl N-monodemethyl diltiazem (M2), was present at comparable concentrations to M1 and MA in all four volunteers. In addition, another metabolite, deacetyl diltiazem N-oxide (M1-NO), which was previously found most abundant in urine, was also estimated in the plasma of two volunteers. Two other known human metabolites, deacetyl O-demethyl diltiazem (M4) and deacetyl N,O-didimethyl diltiazem (M6), were not detected in any of the four study subjects. The average maximum plasma concentrations of M1, M2, MA, and M1-NO were 10, 15, 26, and 13%, respectively, of the mean maximum diltiazem concentrations.