The measurement of d-fenfluramine and its metabolite, d-norfenfluramine in plasma and urine with an application of the method to pharmacokinetic studies.

1. A specific and sensitive gas chromatographic assay is described for the measurement of d-fenfluramine and its de-ethylated metabolite, d-norfenfluramine, in biological fluids, together with some data on its application to the oral pharmacokinetics of the drug. 2. The analytical method developed has advantages over the previously described methods since it uses nitrogen specific detection and, when applied routinely, enables smaller sample volumes to be used (typically 1 ml of plasma) with a shorter chromatography time and an improved sensitivity (minimum quantifiable level of 2.5 ng ml-1). 3. Peak plasma concentrations of 22 and 24 ng ml-1 of intact drug were reached at 4 h after an oral dose of 14C-d-fenfluramine hydrochloride (30 mg) given to two volunteers as part of a metabolism and disposition study. Subsequently, concentrations of intact drug declined monoexponentially with a half-life of approximately 13 h. Peak concentrations of 10 and 8 ng ml-1 of the metabolite, d-norfenfluramine, were reached after 4 and 6 h and were maintained as a plateau for a further 4-6 h. Assessment of the half-life of the metabolite could not be made because of lack of data on the terminal portion of the curves. 4. The urinary excretion of d-fenfluramine (6.0 and 10.6% of the dose) and d-norfenfluramine (5.8 and 8.8% of the dose) was low, indicating extensive metabolism of the parent drug.

A new method for the measurement of nitrosoureas in plasma: an h.p.l.c. procedure for the measurement of fotemustine kinetics.

1. An analytical method for a novel nitrosourea, fotemustine, has been developed using solid-phase extraction and h.p.l.c. with u.v. detection. As part of the development, different methods for stabilising fotemustine after sample collection have been investigated. The method has been successfully applied to pharmacokinetic studies in monkeys and man. 2. Providing plasma was separated immediately from blood and frozen within 3 min of collection, negligible degradation of fotemustine occurred. The samples could then be stored at -20 degrees C in the dark for up to six days particularly if thawing prior to analysis was accelerated using a 50 degrees C water-bath so that it was complete within 3 min. Equivalent results were also obtained with samples stabilised with 0.1 M citric acid immediately after the preparation of plasma. 3. The analytical method showed good precision with a within-day variation ranging between +/- 10.7% at the lowest concentration investigated (0.1 micrograms ml-1) to 2.0% at 50.0 micrograms ml-1. The accuracy of measurement was from 108.9% to 97.6% at 0.1 and 50.0 micrograms ml-1 respectively and the response was linear up to 50 micrograms ml-1. The minimum level of quantitation was 20 ng ml-1. 4. After a single intravenous bolus dose of [14C]fotemustine (100 mg m-2) to Cynomolgus monkeys, intact drug levels rapidly declined (t1/2 12.6 +/- 0.5 min) although the half-life of radioactivity (approx 100 h) was much longer. The plasma clearance of fotemustine was 225 +/- 63 ml min-1 with a volume of distribution based on area of 4.1 +/- 1.2 litres. 5. As with monkey, plasma levels of intact fotemustine in a patient given [14C]-drug as a 1 h constant rate intravenous infusion (approx. 100 mg m-2), declined rapidly but with a half-life of 23.2 min. Again, the half-life for total radioactivity was considerably longer (30.8 h). The plasma clearance was 1426 ml min-1 and the volume of distribution based on area was 47.71.

Measures of flow variability for great lakes tributaries.

Design of monitoring programs for load estimation is often hampered by the lack of existing chemical data from which to determine patterns of flux variance, which determine the sampling program requirements when loads are to be calculated using flux-dependent models like the Beale Ratio Estimator. In contrast, detailed flow data are generally available for the important tributaries. For pollutants from non-point sources there is often a correlation between flow and pollutant flux. Thus, measures of flow variability might be calibrated to flux variability for well-known watersheds, after which flow variability could be used as a proxy for flux variability to estimate sampling needs for tributaries for which adequate chemical observations are lacking.Three types of measures of flow variability were explored: ratio measures, which are of the form q x/qy, where q xis the flow corresponding to the percentile x, and y=100-x; spread measures, of the form (q x-qy)/qm, where q mis the median flow; and the coefficient of variation of the logs of flows. In the latter, flows are log transformed because flow distributions are often approximately log-normal. Three ratio measures were evaluated, based on the percentiles (10,90), (20,80), and (25,75). The analogous spread measures were also evaluated; the spread measure based on percentiles (25,75) is derived from the commonly used fourth spread of non-parametric statistics. The ratio measures and the spread measures are scale independent, and thus are measures only of the shape of the distribution. The coefficient of variation is also scale independent, but in log space.Values of these measures of flow variability for 120 Great Lakes tributaries are highly intercorrelated, although the relationship is often non-linear. The coefficient of variation of the log of the flows is also well correlated with the coefficient of variation of fluxes of suspended solids, total phosphorus, and chloride, for a smaller set of rivers where the existence of abundant chemical data allows comparison.Tributaries with abnormal distributions often show up as outliers when one measure of flow variability is plotted against another. Several examples are discussed.