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Biomedical subjects

B Oosterhuis

Publications and source records attributed to B Oosterhuis.

At least 19 recordsLinked to original sources

Rational experimental design for bioanalytical methods validation. Illustration using an assay method for total captopril in plasma.

Generally, bioanalytical chromographic methods are validated according to a predefined programme and distinguish a pre-validation phase, a main validation phase and a follow-up validation phase. In this paper, a rational, total performance evaluation programme for chromatographic methods is presented. The design was developed in particular for the pre-validation and main validation phases. The entire experimental design can be performed within six analytical runs. The first run (pre-validation phase) is used to assess the validity of the expected concentration-response relationship (lack of fit, goodness of fit), to assess specificity of the method and to assess the stability of processed samples in the autosampler for 30 h (benchtop stability). The latter experiment is performed to justify overnight analyses. Following approval of the method after the pre-validation phase, the next five runs (main validation phase) are performed to evaluate method precision and accuracy, recovery, freezing and thawing stability and over-curve control/dilution. The design is nested, i.e., many experimental results are used for the evaluation of several performance characteristics. Analysis of variance (ANOVA) is used for the evaluation of lack of fit and goodness of fit, precision and accuracy, freezing and thawing stability and over-curve control/dilution. Regression analysis is used to evaluate benchtop stability. For over-curve control/dilution, additional to ANOVA, also a paired comparison is applied. As a consequence, the recommended design combines the performance of as few independent validation experiments as possible with modern statistical methods, resulting in optimum use of information. A demonstration of the entire validation programme is given for an HPLC method for the determination of total captopril in human plasma.

Calibration

The pharmacokinetics of three multiple dose regimens of chloroquine: implications for malaria chemoprophylaxis.

The pharmacokinetics of chloroquine were studied in healthy volunteers who received one of three different multiple-dose regimens for 3 weeks: once weekly 300 mg, twice weekly 200 mg and once daily 50 mg chloroquine. Plasma concentrations of chloroquine and metabolites were determined by h.p.l.c. with fluorescence detection. The concentration-time course was fitted to a multiple-dose pharmacokinetic model. Volume of distribution, elimination half-life and clearance were not different for the three regimens, ranging from 250-302 l kg-1, 374-479 h and 0.44-0.58 l h-1 kg-1 respectively. After the first week of all dosage regimens, peak and trough concentrations of chloroquine were above 16 micrograms l-1, sufficiently suppressive for chloroquine-sensitive P. falciparum strains. These data suggest that once daily chloroquine could be combined with proguanil in a single tablet and should improve compliance when given for malaria chemoprophylaxis.

Adult

Biopharmaceutic characteristics of a new extended-release theophylline formulation (Uni-Dur).

BACKGROUND: There is a close relationship between improvement in airway function and the plasma concentration of theophylline, as well as between rapidly rising plasma theophylline concentrations and increased frequency of undesired effects. Development of pharmaceutical formulations and prescribed dosage intervals for theophylline dosage forms should therefore be directed toward providing the most stable plasma concentrations attainable. OBJECTIVE: To characterize the steady-state biopharmaceutic profile of Uni-Dur following once-daily or twice-daily administration. METHODS: Twenty-four adult male volunteers with average theophylline clearance (3.0 and 5.5 L.h-1) received three treatments on separate occasions: Uni-Dur 800 mg once-daily, Uni-Dur 400 mg twice-daily, and Uniphyl 800 mg once-daily. Treatments were taken after a meal for five days with at least 1 week washout between treatment periods. Trough blood samples were collected prior to the AM dose on days 3, 4, and 5, and at specified intervals up to 48 hours after the AM dose on day 5 for subsequent determination of theophylline concentrations in plasma. RESULTS: The area under the plasma concentration-time curve (AUC; microgram.mL-1.h) for theophylline over 24 hours on day 5 was 187 for Uni-Dur 800 mg once-daily, 187 for Uni-Dur 400 mg twice-daily, and 172 for Uniphyl 800 mg once-daily; the peak plasma concentrations were 10.4, 9.4, and 11.0 micrograms.mL-1 and the trough concentrations were 5.5, 7.2, and 3.5 micrograms.mL-1, respectively; fluctuation index (peak minus trough divided by trough) was 78%, 16%, and 231%, respectively. No further accumulation of theophylline occurred after day 3. No serious nor severe adverse events were reported during any treatment. CONCLUSIONS: Uni-Dur is an extended-release formulation that provides stable plasma concentrations of theophylline over a 24-hour period with less fluctuation than observed with a once-daily reference formulation. In subjects with normal theophylline clearance, Uni-Dur administered twice-daily provided remarkably stable theophylline plasma concentrations over a 24-hour period. Absorption of theophylline from Uni-Dur was not affected by food, and no evidence of dose-dumping was observed. Uni-Dur should provide efficacious theophylline therapy with minimal adverse events in patients with symptoms of asthma and reversible bronchospasm associated with chronic bronchitis and emphysema.

Adult

Effect of diet on the single- and multiple-dose pharmacokinetics of sustained-release ketoprofen.

The indirect effect of diet on the single- and multiple-dose pharmacokinetics of sustained-release ketoprofen was studied in 16 healthy male volunteers. In an open, cross-over design, 200 mg ketoprofen was administered as a gastric-juice-resistant, sustained-release tablet once daily during two periods of 5 days. A low-calorie/low-fat diet (LCFD) was given in the first period and a high-calorie/high-fat diet (HCFD) in the second period. The first meal on each day was given 4 h after drug intake. Ketoprofen plasma concentrations were measured over 24 h after the first dose on day 1 and over 36 h after the final dose on day 5 of each period. On average, plasma concentrations of ketoprofen were higher with the LCFD than with the HCFD. With the HCFD there was a tendency to longer absorption-lag times on day 5. The maximum concentration and the area under the curve over one 24-h dosage period (AUC0-24) were significantly higher with the LCFD, both on day 1 and on day 5. For AUC0-24 the differences were on average 15% (day 1) and 24% (day 5). The same tendency was observed for the amount excreted in urine over 24 h (Ae), but the difference was only significant on day 1 (14%). The elimination rate constant (K beta) and the mean residence time were similar for the two diets, both on day 1 and on day 5. From these results, we conclude that there was an acute indirect effect of diet when a meal was had 4 h after intake of the medication.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral

Lack of pharmacokinetic interaction between vinpocetine and oxazepam.

The influence of multiple doses of vinpocetine (10 mg three times daily) on the steady state plasma concentrations of oxazepam (10 mg three times daily) was studied in 16 healthy subjects. The mean (+/- s.d.) AUC (ng ml-1h-1) of oxazepam over 24 h during combined treatment was 4716 +/- 2296 and for oxazepam treatment alone it was 4737 +/- 2448 (95% confidence intervals for ratio of means = 95.4-103.7%). The degree of plasma protein binding of oxazepam was 98.11 +/- 0.32% and was not affected by vinpocetine. Independent of vinpocentine treatment a significant diurnal change in the plasma binding of oxazepam was observed; the free drug fraction was 20% higher during the night than during the day. Cmax and AUC values based on total oxazepam in plasma were 10% lower during the night. The results indicate a lack of influence of vinpocetine on oxazepam kinetics. Diurnal changes in the plasma binding of oxazepam probably have no clinical consequences.

Adult

Hemodynamic effects of the new antiarrhythmic agent restacorin in patients with normal and decreased left ventricular function.

The hemodynamic and pharmacokinetic effects of the novel class 1c antiarrhythmic drug restacorin were investigated in two groups of patients. Group I consisted of 5 patients with normal left ventricular (LV) function, and group II consisted of 10 patients with mild heart failure [New York Heart Association (NYHA) II; mean LV ejection fraction 33 +/- 6%]. The study had an open label, baseline-controlled, single-dose design. Restacorin was infused in a total dosage of 1.2 mg/kg. In group I, the only significant change as compared with baseline findings was a 25% increase in right atrial pressure. In group II; cardiac output (CO), dP/dt, and stroke work index (SWI) decreased significantly (-18, -11, and -24%, respectively). In addition, a significant 32% increase was noted in pulmonary artery wedge pressure (PAWP), and a 27% increase occurred in systemic vascular resistance (SVR). No changes were observed in heart rate (HR) or mean arterial blood pressure (MAP). CO and SVR at baseline correlated with the average plasma concentrations (r = -0.65 and p = 0.009 and r = 0.56 and p = 0.028 respectively). Creatinine clearance was inversely correlated to the restacorin plasma concentration (r = -0.51, p = 0.05). The half-life (t1/2) elimination time of restacorin was 2.60 h for group I, and 4.06 h for group II. Clearance was 51.4 and 32.2 L.h-1, respectively. Restacorin appears to be well tolerated in patients with normal LV function. The drug is not recommended for use in patients with reduced LV function because of its moderate negative inotropic effect.

Adolescent

A simple optical fiber device for quantitative fluorescence microscopy of single living cells.

A simple and relatively inexpensive system is described for obtaining quantitative fluorescence measurements on single living cells loaded with a fluorescent probe to study cell physiological processes. The light emitted from the fluorescent cells is captured by and transported through an optical fiber. After passage through appropriate filters the light is measured using a photomultiplier tube. The optical fiber is mounted in one of the microscope outlets. Signals derived from the photomultiplier are converted to voltage, amplified, and displayed on a recorder. In the excitation pathway a shutter control unit is mounted. With this control unit the period that the excitation pathway is 'opened' and 'closed' can be adjusted, to reduce cell damage and/or bleaching of the probe. This option allows time-lapse recording of experiments up to 1 h. We have used this set-up with a single and dual emission fluorescent probe to determine intracellular calcium concentrations and pH, respectively. In Fluo-3-loaded K562 target cells bound to natural killer cells, a temporary rise in [Ca2+]i was accompanied by bleb formation. The simple construction of this set-up is interchangeable between different types of fluorescence microscopes and can easily be combined with other microscopy techniques, e.g., patch clamp.

Calcium

Dose-dependent uricosuric effect of ambroxol.

Ambroxol is known to promote bronchial secretion and is used as an expectorant. Previous studies had suggested that high doses of ambroxol could reduce the plasma uric acid concentration. The present study was undertaken to confirm this finding, to determine its dose-response relationship and to identify the underlying mechanism of action. Using a placebo-controlled, double-blind parallel group design, 48 healthy male volunteers were randomly allocated to receive placebo b.d. and ambroxol 125 mg b.d., 250 mg b.d. or 500 mg b.d. (12 subjects per group). The subjects were hospitalised during a dietary run-in period of 3 days (Days -3 to -1) and a treatment period of 5 days (Days 1 to 5). On Day -1 (baseline) and Days 1 to 5, all urine was collected and blood samples were taken for the analysis of uric acid, creatinine, xanthine and ambroxol. The measurements were repeated four days after treatment had closed. Steady state plasma concentrations of ambroxol (trough levels) were reached after 2 or 3 days and were linearly related to dose. Ambroxol induced a significant, dose-dependent, reduction in plasma uric acid (250 mg b.d. about 20%; and at 500 mg b.d. about 30%). The diurnally fluctuating uric acid clearance was dose dependently increased and there was no notable effect on creatinine clearance. Plasma hypoxanthine levels were not affected by ambroxol. No severe adverse events were reported and no drug induced changes in the clinical laboratory values were observed. It is concluded that ambroxol has an uricosuric action following oral administration of higher doses (250 mg-500 mg b.d.) and it is well tolerated.

Adult

The effect of oxprenolol dosage time on its pharmacokinetics and haemodynamic effects during exercise in man.

We have studied the effect of dosage time of oxprenolol (Trasicor) on its pharmacokinetics and pharmacodynamics in six healthy volunteers. The drug effects measured were heart rate and systolic blood pressure during exercise. Oxprenolol was taken orally at 08.00 h, 14.00 h, 20.00 h, and 02.00 h in randomized order, with 1 week between successive doses. There were differences in the pharmacokinetics of oxprenolol for the ratio between the apparent volume of distribution and systemic availability (P = 0.04) and for elimination half-life (P = 0.006). Both were lowest after administration at 14.00 h (163 (77) l and 1.2 (0.6) h; mean (SD)) and highest after administration at 02.00 h (229 (100) l, and 1.7 (0.6) h). The systolic blood pressure during exercise before oxprenolol did not vary with dosage time, but heart rate during exercise before intake was lowest before dosage time 08.00 h and highest before dosage time 20.00 h (P = 0.03). The time-course of heart rate during exercise after oxprenolol was described by a model that incorporated the factors drug concentration and spontaneous diurnal variation. EC50 and Emax did not vary between dosage times. The spontaneous diurnal variation in heart rate during exercise was unaffected by oxprenolol, leading to an apparently greater effect of oxprenolol during the night than during the day.

Adult

Electrophysiologic and pharmacokinetic profile of the new antiarrhythmic drug TYB-3823 in humans.

In an open-label study, electrophysiology and pharmacokinetics of TYB-3823, a new antiarrhythmic compound, were investigated. Sixteen patients underwent an electrophysiologic study before and after intravenous (i.v.) administration of TYB-3823. Two patients each received the following increasing doses: 0.2, 0.4, 0.8, and 1 mg/kg. Eight patients received 1.2-mg/kg. TYB-3823 concentrations followed a biexponential decrease with a terminal half-life (t1/2) of 3.88 +/- 0.87 h. Clearance was 47.2 +/- 18.5 L/h, and volume of distribution was 250 +/- 77 L. Dose-dependent pharmacokinetics were evident. Significant effects of TYB-3823 were apparent at doses > or = 0.8 mg/kg (n = 12), including increase in the AH and HV interval from 92 +/- 17 to 105 +/- 19 ms (p < 0.002) and 47 +/- 7 to 60 +/- 12 ms (p < 0.005), respectively. QRS duration was prolonged from 100 +/- 16 to 126 +/- 22 ms (p < 0.001), accompanied by an increase of the corrected QT interval from 425 +/- 28 to 465 +/- 37 ms (p < 0.002). The corrected JT interval remained unchanged, however, refractoriness did not change, but monophasic action potential duration (APD) tended to decrease. TYB-3823 appeared effective against reinduction of all arrhythmias observed during the control study [atrial fibrillation, atrioventricular (AV) nodal tachycardias]. TYB-3823 depresses conduction velocity significantly without prolonging refractoriness. Therefore, TYB-3823 may be classified as a class 1C antiarrhythmic. On the basis of the present results, additional class 1B activity cannot be excluded. TYB-3823 has antiarrhythmic properties, appears to be devoid of proarrhythmic effects, and is well tolerated.

Action Potentials

No influence of single intravenous doses of omeprazole on theophylline elimination kinetics.

The influence of single intravenous doses of omeprazole on the pharmacokinetics of intravenously administered theophylline was studied in eight healthy male volunteers. In a partially randomized three-period crossover design, an IV infusion of theophylline (400 mg over 30 min) was combined with IV omeprazole (either 40 mg over 2.5 min or 80 mg over 5 min) or with IV placebo (over 2.5 min). Theophylline and omeprazole plasma concentrations were measured over 24 hours after the start of the infusions and pharmacokinetic parameters were calculated. The theophylline plasma concentration-time profiles after omeprazole coadministration were virtually identical to the corresponding profile after placebo administration. For each of the pharmacokinetic parameters of theophylline, the 90% confidence intervals of the omeprazole coadministrations were within the 80 to 120% bioequivalence range with respect to the placebo coadministration. Omeprazole plasma concentrations indicated a biexponential decline in most subjects, with a more rapid elimination after the 40-mg than after the 80-mg dose (P less than .01). Doubling the dose caused an almost three-fold increase of AUC resulting in a difference in clearance (P less than .02), whereas the volume of distribution was similar. The results of this study indicate that the metabolism of theophylline is not affected by single intravenous doses of omeprazole. The nonlinear pharmacokinetics of omeprazole are ascribed to saturation of its main metabolizing enzyme, S-mephenytoin hydroxylase.

Adult

Unaltered ibuprofen-induced faecal blood loss upon coadministration of moclobemide.

The influence of moclobemide on ibuprofen-induced faecal blood loss was investigated in 24 volunteers. The subjects were randomly assigned to one of two groups and received from day 1 until day 14 either moclobemide 150 mg t.i.d. (group A) or placebo t.i.d. (group B). On days 8-14, when moclobemide concentrations in group A were at steady state, all volunteers additionally received ibuprofen (600 mg t.i.d). From day 15 to 21, all subjects received placebo alone. Faecal blood loss (FBL) was quantified daily by the 51Cr-labelled erythrocyte method. As expected for ibuprofen, a significant increase in FBL during the second week of the study was observed. There was no difference in FBL between the two treatment groups (moclobemide or placebo). Similar FBL values were observed in both groups (group A vs B): during the first week the FBL values were (mean +/- SD) 0.40 +/- 0.23 ml/day vs 0.55 +/- 0.53 ml/day on days 1-3 and 0.40 +/- 0.21 ml/day vs 0.37 +/- 0.13 ml/day on days 4-7. The increase in FBL during the second week was comparable in both groups, with and without moclobemide (days 8-10: 0.78 +/- 0.59 ml/day vs 0.80 +/- 0.58 ml/day; days 11-14: 1.49 +/- 0.95 ml/day vs 1.28 +/- 0.62 ml/day). A decline in FBL was observed during the third week under placebo in both groups, but baseline values were not reached during the observation period. Again there was no difference between the two groups (days 15-17: 0.91 +/- 0.52 ml/day vs 0.92 +/- 0.47 ml/day; days 18-21: 0.74 +/- 0.30 ml/day vs 0.68 +/- 0.48 ml/day). No statistically significant interaction was found between week and type of treatment, indicating that no significant influence of moclobemide on the ibuprofen-induced faecal blood loss occurred. No notable pharmacokinetic interaction between moclobemide and ibuprofen was observed. Moclobemide plasma concentration-time profiles with and without concomitantly administered ibuprofen were superimposable. The results demonstrate that the concomitant administration of ibuprofen and moclobemide to healthy volunteers does not result in a clinically significant interaction, either at the pharmacodynamic (faecal blood loss) or at the pharmacokinetic level.

Adult

Time-dependent effects of dexamethasone administration on the suppression of plasma hydrocortisone, assessed with a pharmacokinetic model.

The influence of the time of dexamethasone (DEX) administration (0.5 mg i.v.) on the suppression of plasma hydrocortisone (HC) was investigated in six healthy subjects, by comparing dosage times of 8 and 20 hr. To estimate HC production after DEX administration a pharmacokinetic model was developed and applied to the time course of plasma HC. This model was based on the assumption that HC production could be described as a continuous i.v. infusion, that stops and starts instantaneously. After DEX at 8 hr, HC production was reduced instantaneously to a minimum level and HC disappeared rapidly from plasma with an elimination half-life of 1.32 +/- 0.28 hr (mean +/- S.D.). Almost complete suppression of HC production lasted for 20 hr. The nocturnal increase in HC production at 20 hr after DEX administration was still attenuated compared to the preceding night. After DEX administration at 20 hr, plasma HC was lower than control for about 20 hr, but it was not reduced to the very low level observed after DEX dosage in the morning. Approximately 20 hr after dosage of DEX at 20 hr, HC production seemed to follow the normal diurnal variation of the control values again. To explain the difference in HC suppression by DEX at different dosage times, we constructed a curve describing the relationship between DEX concentration and suppression of the sudden increase in HC production during the night. This curve indicates that HC suppression by DEX could be completely dependent on DEX concentration, without a DEX independent circadian variation.

Adult

Kinetic-dynamic modeling of lymphocytopenia induced by the combined action of dexamethasone and hydrocortisone in humans, after inhalation and intravenous administration of dexamethasone.

Ten healthy male volunteers received 5 mg of dexamethasone sodium phosphate (DEX) i.v. and, on an other occasion, by way of nebulization. Plasma DEX and hydrocortisone (HC) concentrations as well as blood lymphocyte count (BLC) were monitored over 12 hr and at 24 to 28 hr after DEX administration. Bioavailability of DEX after inhalation was about 27% of DEX i.v. DEX-induced depletion of plasma HC could be predicted with a pharmacokinetic model. The reonset rate of HC-production was dependent of DEX dose. BLCs declined after DEX administration, reaching a minimum between 4- and 8-hr postdosing. The DEX- and HC-induced depression of BLC could be described by an integrated pharmacokinetic-pharmacodynamic competitive-interaction model that assumes that both agonists act on the same receptor. With this model the potency and efficacy of DEX and HC with respect to lymphocytopenia could be estimated simultaneously. The potency of DEX was 10 times greater than the potency of HC. The estimated efficacy suggests that HC is only a partial agonist; the maximal lymphocytopenic effect (Emax) of HC was estimated at 80% (27-99%) of the efficacy of DEX. Our results indicate that DEX should be preferred instead of HC in conditions in which the lymphocytopenic effect is the primary systemic corticosteroid treatment goal.

Administration, Inhalation

A combined single and multiple dose pharmacokinetic study of oral isosorbide-5-mononitrate in healthy volunteers.

Pharmacokinetics of 20 mg isosorbide-5-mononitrate (IS-5-MN) after single and multiple administration of two different tablet formulations were investigated in twelve healthy human subjects using an open, randomized, two-way crossover experimental design. Pentacard 20 mg tablets were compared with Ismo 20 mg tablets. After single-dose administration, both preparations caused a rapid increase in IS-5-MN plasma levels with the peak plasma concentration occurring between 0.5 and 1.5 h. For both formulations, the mean plasma half-life was found to be approximately 5 h after a single dose. In steady state during multiple dosing (t.i.d. at 8 h dosing intervals), a reduced elimination rate was observed. In line with this observation, the area under the plasma concentration-time curve (AUC) for one 8 h dosing interval during multiple dosing was higher than the extrapolated AUC after a single dose. Based on statistical evaluation of the various relevant pharmacokinetic parameters calculated from the plasma concentrations occurring after single and multiple dosing, the tablet formulations are judged to be bioequivalent.

Administration, Oral

Clinical pharmacokinetics and tolerability of alpidem in healthy subjects given increasing single doses.

In a double-blind, placebo-controlled, cross-over experiment in 21 healthy male volunteers, aged 19 to 27 y, the pharmacokinetics and tolerance of the new anxiolytic drug alpidem (SL80.0342) and its three major metabolites were studied after single doses of 25, 50, 100 and 200 mg. Plasma concentrations of alpidem (in 20 subjects) and metabolites (in 6 subjects) were measured by HPLC over a period of 54 h after dosing. Cmax, tmax and AUC(0-54) and, when possible, t1/2 were determined for alpidem and metabolites and the dose linearity of the parameters was investigated. The time to peak of alpidem was dose independent in most subjects and was short (1-4 h); the mean values at the four dosing levels were 1.9, 1.7, 1.6 and 1.8 h. The peak concentration increased with the dose, the mean values being 17, 34, 88 and 115 ng.ml-1, respectively. In 50% of the subjects Cmax tended to stabilize between the 100 and 200 mg dose. Dose linearity was also present for the AUC, which plateaued between the 100 and 200 mg dose in only 3 out of 20 subjects; the mean AUC was 119, 281, 669 and 1117 ng.ml-1.h, respectively. The apparent half-life of elimination appeared to be dose independent, mean values at the increasing dosing levels being 18.7, 19.9, 18.1, and 17.9 h. A similar relationship between the kinetics parameters and dose of the alpidem was observed for the metabolites SL83.0912, SL80.0522 and SL83.0725. The formation of metabolites was not saturated as their AUCs relative to corresponding alpidem AUCs were not dose related.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

The influence of age on the pharmacokinetics of the antiepileptic agent oxcarbazepine.

The disposition of oxcarbazepine was studied in 12 young and 12 elderly healthy male and 12 young and 12 elderly healthy female volunteers, with emphasis on the influence of age. Oxcarbazepine was administered as a single dose of either 300 mg (men) or 600 mg (women), followed by multiple-dose (300 mg) administration twice a day for 7 days (men) or 6 days (women). Semilogarithmic plasma concentration-time curves showed an increasing decline at decreasing concentrations. Accumulation of the pharmacologically active metabolite monohydroxycarbamazepine was found to be more than one would anticipate on the basis of linear and unchanged pharmacokinetics. Saturation did not seem to occur at the level of renal excretion. No apparent differences between male and female volunteers were observed. A significant higher maximum concentration, higher area under the curve parameters, and a lower elimination rate constant were observed in the elderly. These observations are in line with a smaller renal clearance of monohydroxycarbamazepine in the elderly group. In a clinical situation, these age-related differences are not likely to have important implications. In general, treatment with oxcarbazepine was well tolerated.

Adolescent