Unit to unit variation of pesticide residues--options for acute dietary risk assessment.

Within the context of the current UK policy for those commodities where the potential variability of residues in individual commodity units is taken into account, a variability factor nu, which reflects the ratio of a high level residue in the individual commodity unit to the corresponding composite residue level, is used. Data gathered from supervised industry trials in which individual items were analysed following treatment, although limited, show that variability is typically lower than that reflected by the default factors currently used and that the range of variability is reproducible over the limited range of different a.i./crop/method of application combinations investigated. In order to improve the accuracy of the acute dietary exposure estimate, the European Crop Protection Association (ECPA) proposes the following alternative to the current Tier I approach. The residue level input from a 'hot' unit within the dietary risk assessment should be determined using the highest composite sample residue from supervised field trials and a generic variability factor (nu) determined experimentally from supervised trials. The variability factor itself should be calculated as the 95th percentile level of the residue level found in an individual unit (or single serving portion for large crops) divided by sample mean for data produced from supervised trials. This would improve the accuracy of the Tier I approach and allow attention to be focused on particular a.i./crop/method of application combinations where the NESTI > acute RfD (based on a Tier I assessment) and generation of individual unit residue data for the particular outlet or other mitigation may be appropriate.

Rapid multimethod for verification and determination of toxic pesticides in whole blood by means of capillary GC-MS.

A rapid and single multimethod was developed to determine substances of different pesticide classes in whole blood in the event of acute human intoxications, as required by EU Commission Directive 96/46. The method was validated by an in-house and an independent laboratory validation. Whole blood is hemolyzed and then deproteinized. After extraction of the supernatant, blood levels are determined by gas chromatography-mass spectrometry. The method, which can be performed within 120 min, covers 15 active substances (8 organophosphate pesticides, 2 carbamates, 3 pyrethroids, 1 azole, and 1 organochlorine pesticide) classified as toxic or very toxic. These compounds can be identified down to concentrations between 100 and 1000 ng/mL by comparison of their mass spectra to those in a commercial pesticide mass spectra library. Using the standard addition method, they can be quantitated down to concentrations between 30 and 200 ng/mL. These limits of quantitation are considered to be sufficient in comparison to respective LD50 values.

Determination of cefpirome (HR 810) in serum and urine.

Cefpirome (HR 810) is a new cephalosporin under clinical investigation. Specific and sensitive HPLC- and agar-diffusion methods were developed for the determination of serum- and urine concentrations. The methods are fully validated according to the IFCC Recommendations on Quality Control in Clinical Chemistry. In order to demonstrate the usefulness of both methods, pharmacokinetic profiles of cefpirome after 1 g i.v. administration to human volunteers are presented.

A new aspect of serum protein binding of tolbutamide.

Tolbutamide is known to bind highly to serum proteins. Quite different values have, however, been reported for binding, ranging from 80 to 99 percent. In this study, in vivo and in vitro binding of increasing concentrations of tolbutamide to human serum proteins were evaluated. In vitro studies were done serum from three healthy males and for in vivo studies serum samples from eight healthy males who had received 1,000 mg tolbutamide were used. Protein binding was determined by equilibrium dialysis, using DIANORM system. Tolbutamide concentrations were determined by HPLC method of Uihlein and Hack. The results suggest that there is an increase in percent tolbutamide bound with increasing concentrations of tolbutamide. Generally, an inverse relationship between the total concentration of a drug in serum and its bound fraction is observed. Our findings seem to be contrary to this, at least within the concentration range studied. There exist at least two binding sites on albumin with different affinities for tolbutamide and most probably, at low concentrations, the drug binds mainly to the high affinity sites, whereas at higher concentrations additional drug will bind to the lower affinity sites leading to the observed increase in fraction bound with concentration. In conclusion it may be said that serum protein binding is a much more complicated phenomenon than generally stated and that the normal observations are only true for some ideal compounds where only one site of adsorption has to be taken into account.

Cefotaxime and desacetyl-cefotaxime blood levels in hepatic dysfunction.

Serum levels of cefotaxime and desacetyl-cefotaxime were studied in 18 patients with hepatic cirrhosis after an intravenous bolus injection of 2 g of cefotaxime. Blood levels were independent of the degree of hepatic dysfunction and did not differ from those reported in normal individuals.

Comparative bioavailability of two furosemide formulations in humans.

Twelve healthy male volunteers participated in a balanced crossover comparison of a brand-name and generic furosemide formulations. Each treatment was given as a single 40-mg tablet following an overnight fast. Furosemide concentrations in plasma and urine were determined up to 24 h after treatment; urine output and urinary sodium excretion were also measured. In comparison with the brand-name tablets, generic furosemide was significantly less bioavailable. Using a 95% confidence interval approach, generic furosemide gave up to 66% lower maximum furosemide plasma levels, up to 52% less area under the plasma level curve to infinite time, and up to 37% less urinary recovery of furosemide. Comparison of the effect of the two treatments was a less sensitive measurement of bioequivalence. Confidence intervals for differences in urinary output and sodium excretion over the period of maximum effect (0-4 h) were, however, asymmetrical, and pharmacodynamic differences between treatments were significant at the 10% level.

Kinetics and metabolism of nomifensine.

Metabolic and pharmacokinetic studies of nomifensine maleate, a tetrahydroisoquinoline derivative with antidepressant properties, are reviewed. Results of pharmacokinetic studies indicate that nomifensine has a short distribution phase and a large volume of distribution. It is rapidly metabolized to its N-glucuronide. Plasma levels of nomifensine-N-glucuronide are up to 100-fold higher than those of nomifensine, obviously because of a smaller volume of distribution. As nomifensine-N-glucuronide is extremely unstable and cleaved to nomifensine, determinations of nomifensine are easily falsified. It is therefore recommended only to determine the sum of nomifensine and its N-glucuronide (total nomifensine) in clinical trials. Kinetics of total nomifensine can best be described by the open two-compartment model: Maximum plasma levels are obtained 1-2 hours postadministration; mean elimination half-life is 2 hours. Excretion is almost entirely by the kidneys, with approximately 88% of an oral dose excreted within 24 hours.

[Cefotaxime and desacetylcefotaxime in cerebrospinal fluid of newborn and premature infants]. / Cefotaxim- und Desazetyl-Cefotaxim-Spiegel im Liquor cerebrospinalis von Neu- und Frühgeborenen.

On the occasion of clinically indicated lumbar of cisternal punctures in 19 newborn and premature babies treated with Cefotaxime 33 CSF-levels of Cefotaxime (CTX) and it's metabolite Desacetyl-Cefotaxime (D-CTX) were measured by means of HPLC. 6 of the 19 infants suffered from meningitis. The highest CTX-levels were found 2 to 4 hours after the last infusion of CTX (50 or 100 mg/kg within 20 min, each 12 hours). Patients with meningitis showed CTX-levels between 20 mg/l and less than 0.5 mg/l (limit of detection), those without meningitis between 11 mg/l and less than 0.5 mg/l. Because of the widely scattered CTX-levels any dependence from CTX-dosage or from degree of meningeal inflammation is not to be shown. With two exceptions D-CTX-levels ranged from 2 to 20 mg/l. Up to 9 1/2 hours after the last CTX-dose no clear decrease of the D-CTX-concentration in CSF may be seen. On the other hand, D-CTX-levels are also widely scattered. Nevertheless D-CTX apparently stays significantly longer in the CSF than CTX does. An influence of meningeal inflammation on the D-CTX-levels can not be observed. In E. coli- and in Klebsiella-spp. The geometrical means of MIC are found to range below 0.5 mg/l for CTX and below 2 mg/l for D-CTX. Therefore CTX might be recommended for treatment of meningitis caused by these germs. This recommendation may be supported by some reports about good clinical results, from our unit and from the literature as well.

High-performance liquid column and thin-layer chromatographic determination of human serum glibenclamide at therapeutic levels.

For glibenclamide bioavailability studies in serum, high-performance liquid column and thin-layer chromatographic methods were introduced. Both methods are specific, accurate and sensitive with detection limits of at least 5 ng of glibenclamide per ml of serum. Detection is performed in the ultraviolet at wavelengths of 200 nm for liquid chromatography or 300 nm for thin-layer chromatography. Serum levels determined by either method correlated well with those determined by an already existing radioimmunoassay. Some pharmacokinetic data were computed using a one-compartment open model.

Determination of plasma catecholamines by means of radioenzymatic labelling and high pressure liquid chromatographic separation.

0.05 ml plasma samples are incubated with 3H-S-adenosylmethionine and catechol-O-methyl-transferase. The resulting methodoxy derivatives are extracted, the extracts separated by high pressure liquid chromatography and the metanephrine fractions collected. Evaluation is performed by liquid scintillation counting of radioactivity in the respective fractions. The following performance criteria are presented: precision, accuracy, detectability (40 pg/ml for adrenaline and noradrenaline, 130 pg/ml for dopamine), linearity and day-by-day variation. Comparison with a standard method shows an excellent correlation for adrenaline and noradrenaline.

Quantitative determination of clobazam in serum and urine by gas chromatography, thin layer chromatography and fluorometry.

The procedures available for determination of clobazam (Frisium, Hoechst) are gas chromatography, fluorometry, and thin-layer chromatography. The study presents detailed descriptions of analytical procedures appropriate for routine determinations in serum and urine, and results from human trials. Moreover, the physicochemical properties of clobazam, viz., solubility, distribution, and protein binding are given.

Pharmacokinetics of single and multiple doses of clobazam in humans.

1. The pharmacokinetics of clobazam and its biotransformation product N-desmethylclobazam were investigated after single and multiple doses in normal subjects. 2. The relevant physicochemical properties of clobazam were measured and are presented. Different assay methods (radiochemical, fluorimetric and gas chromatographic) were applied and the results correlated. 3. After single doses the pharmacokinetic profile of clobazam includes time to peak levels 1--4 h after dosing, peak levels increasing linearly with the logarithm of dose, and terminal half-lives of about 18 hours. At least 87% of an oral dose is absorbed, as indicated by urinary recovery of labelled material. 4. In multiple-dose studies unchanged clobazam levelled off at minimum steady-state concentrations within one week of dosing. During 28 d of medication N-desmethylclobazam accumulated to near steady-state levels about eight times higher than those of the unchanged compound. 5. No pharmacokinetic interactions were discovered between clobazam and the antidepressant nomifensine.

Quantitative thin-layer and high-performance liquid chromatographic determination of the diuretic agent 2-chloro-5-[44-hydroxy-3-methyl-2-(methylimino)-4-thiazolidinyl]benzenesulphonamide hydrochloride in serum and urine.

Sensitive and specific thin-layer (TLC) and high-performance liquid chromatographic (HPLC) methods were developed for the determination of the diuretic agent 2-chloro-5-[4-hydroxy-3-methyl-2-(methylimino)-4-thiazolidinyl]benzenesulphonamide hydrochloride (HOE 740). HOE 740 can be determined in serum by HPLC. The detection is performed at a very short wavelength (202 nm), resulting in a detection limit of 10 ng/ml. By TLC only urine levels that are normally high can be determined directly (the detection limit is 70 ng/ml). For the determination of the lower serum levels it is necessary to convert the drug into its dehydration product, which has a higher absorbance and gives sufficient sensitivity (the detection limit is 10 ng/ml). Serum levels determined by the two methods correlate well. Some pharmacokinetic and excretion-kinetic data were computed using two-compartment open models.

[The solutibility of local anaesthetics in cerebrospinal fluid and the dependency of the process on the hydrogene ion concentration (author's transl)]. / Löslichkeit von Lokalanaesthetika im Liquor cerebrospinalis und ihre Abhängigkeit von der Wasserstoffionenkonzentration.

Reports on in vitro precipitation of local anesthetics suggested the possibility of a damaging effect on nervous tissue with spinal anesthesia. The present assays showed that the solubility of local anesthetics in aqueous media decreases with rising pH-levels. The partial pressure of CO2 determines the pH-level of the cerebrospinal fluid, the level ranging at about 7.35 + 0.011 (95% range: 7.327-7.371). The solubilities calculated for a pH of 7.371 (at 37 degrees C) are as follows: Bupivacaine.HCl 0.83+/-0.10 mh/ml Carticaine.HCl 27 +/-2.8 mg/ml Lidocaine.HCl 24 +/-1.3 mg/ml Mepivacaine.HCl 14.8 +/- 0.2 mg/ml Tetracaine.HCl 1.4 +/- 0.12 mg/ml.

Quantitative determination of tiamenidine hydrochloride in human serum using gas chromatography mass spectrometry.

A method has been developed for the blood level determination of the antihypertensive agent tiamenidine hydrochloride. The serum samples are mixed with deuterium labelled tiamenidine hydrochloride as an internal standard and extracted with methylene chloride. The extracts are derivatized with heptafluorobutyric acid anhydride and analysed by means of gas chromatography mass spectrometry using the selected ion monitoring technique to measure the molecular ion intensities of the bis-heptafluorobutyryl derivatives of tiamenidine hydrochloride and of the internal standard. Using 5 ml serum, the limit of detection is 0.2 ng ml-1 with an accuracy of +/- 0.17 ng (Syx of the calibration curve).

Kinetic interaction of nomifensine with a 1, 5-benzodiazepine (clobazam).

1. Among the numerous possibilities of drug interactions, pharmacokinetic interactions may cause mutual changes in absorption, distribution, metabolism and elimination of either drug. In the present study this approach was used to investigate pertinent effects of nomifensine and clobazam. 2. Ten normal subjects participated in an intra-individual comparison of nomifensin 75 mg alone and in combination with clobazam 15 and 30 mg. The study design was carried out according to a Latin square in double-blind conditions. One-week wash-out periods were used between the trial days. Serum levels of nomifensine were measured by radioimmunoassay (RIA) and of original clobazam by gas chromatography (GC). Classical criteria for bioavailability (peak serum levels, time of peak, area under the serum level time curve) and the half-life of elimination from the serum were used for retrieval of pharmacokinetic information. 3. Results showed no relevant differences in the criteria mentioned above, after administration of each drug alone or in combination. Therefore, extrapolations were made to multiple dose kinetics based on assumptions derived from practical therapy. They showed comprehensive agreement with therapeutic results in depressed patients. 4. The use of the classical criteria for bioavailability, in addition to the calculation of the half-time of elimination from serum, provides sufficient information for the decision whether pharmacokinetic drug interaction is present or absent. There was no such interaction after single doses of nomifensine or clobazam.

High performance liquid chromatography in research of pharmacokinetics and metabolism.

High performance liquid chromatography in connection with monochromatic UV-detection has proved to be a powerful tool for separation and quantitative determination of drugs and their metabolites in body fluids. Serum samples from volunteers medicated with the psychotropic drugs fosazepam and nomifensine are analysed by this method. Separation times are less than 5 min; the detection limits are within the range of 30-50 ng/ml serum. The reliability of the method is discussed: The results are compared to those from the same serum samples obtained by measurement of total radioactivity and by quantitative mass spectrometry in order to confirm the accuracy of the method. Examples of the pharmacokinetic profile of the two drugs and their metabolites in serum are presented, based on analysis by the methods described.