Pharmacokinetics of mitomycin C in humans.

This paper describes an investigation into the pharmacokinetic behavior of mitomycin C (MMC) in 36 patients receiving either single-agent chemotherapy (10 to 20 mg/sq m), or a combination regimen including MMC (5 to 10 mg/sq m). A high-performance liquid chromatographic assay of MMC was applied for the analysis of plasma, urine, bile, and ascites fluid samples. The detection limit is 1 ng/ml sample. Most patients were given short-term i.v. infusion, although other methods of administration were used as well. Most plasma concentration-time curves fit a two-compartment model. Pharmacokinetic parameters revealed large interindividual variations. Median terminal half-lives in single-agent chemotherapy and combination chemotherapy were 50 and 42 min, respectively. The apparent volume of the central compartment was 7 liters/sq m in both groups. The volume of distribution was 22 liters/sq m in single-agent chemotherapy, and 25 litres/sq m in combination chemotherapy. Linear regression analysis of the area under the plasma concentration-time curve versus the dose did not produce any evidence that the pharmacokinetics was dose dependent. However, differences were observed between patients receiving MMC alone and those on combination chemotherapy, in particular with regard to the total body clearance: 18 liters/hr/sq m for single-agent chemotherapy and 28 liters/hr/sq m for combination chemotherapy. Urinary recovery was limited to a maximum of 15% of the administered dose. In one patient studied, MMC was found to be present in the bile. There is evidence for enterohepatic circulation of MMC, and MMC was also found to penetrate into the ascites fluid.

Penetration of VP 16-213 into cerebrospinal fluid after high-dose intravenous administration.

VP 16-213 in standard doses is active against a number of solid tumors. Its penetration into the cerebrospinal fluid (CSF) is very limited at these dose levels. In 10 patients treated with high-dose VP 16-213 (0.9-2.5 g/m2), CSF levels of up to 0.54 microgram/mL were detected. In two patients with central nervous system (CNS) metastases of small cell lung cancer (SCLC) a response was seen after 1.0 and 1.5 g/m2 intravenously. High-dose VP 16-213 can possibly play a role in the treatment of CNS metastases of SCLC. Its application in late intensification regimens as a form of prophylaxis of CNS metastases should be investigated.

Improved HPLC-ECD analysis of mitomycin C, porfiromycin, VP 16-213 and VM 26 by implantation of software filters.

In high performance liquid chromatography with electrochemical detection (HPLC/ECD) much attention has been paid to the performance of the applied detection system with respect to reliability and sensitivity. In general, insufficient attention has been paid to relatively easy to implant devices for improved collection and handling of detection signals. Four models of software filtering are studied and compared with hardware filtering. In the investigated chromatographic-electrochemical system, off-line parabolic filtering after on-line averaging of sixteen measurements proved to be the system of first choice, with respect to execution time, noise level, signal to noise ratio, peak height and resolution.

Handling of biological samples in the determination of the anti-neoplastic drug mitomycin C.

A study to ascertain suitable conditions for handling biological samples from patients, treated with the antibiotic mitomycin C (MMC), with the objective of improving the accuracy and reliability of the determination is described. Situations frequently occurring in medical practice are simulated to optimize procedures for reliable and reproducible sampling, sample treatment and determination of MMC. Continuation of drug partitioning in whole blood after sampling can be prevented by immediate cooling in ice before the separation of plasma from cells. The adjustment of the pH of urine samples is shown to be particularly important since a low urinary pH causes decomposition of MMC; moreover, it may decrease extraction recovery. Furthermore, long-term exposure of samples to daylight induces drug decomposition. Frozen storage of plasma and urine samples for periods greater than 3 weeks is to be avoided as this results in a considerable drop in MMC concentration. Repeated cycles of freezing and thawing are shown to have no effect upon the analytical results (6 cycles tested). The analysis of extracts of biological samples may take place up to at least 24 h after their preparation without measurable loss of analyte.

Plasma assay for the antineoplastic agent VP 16-213 (etoposide) using high-performance liquid chromatography with electrochemical detection.

A sensitive high-performance liquid chromatographic (HPLC) assay of the antineoplastic agent VP 16-213 (etoposide) in plasma is described. The system discriminates between the parent compound and possible metabolites, including the aglycone and the cis isomer. After extraction with 1,2-dichloroethane the drugs are chromatographed on a reversed-phase phenyl column with amperometric detection. Quantitative response is linear up to 250 ng/ml for 1 ml human plasma and up to 40.0 mug/ml for 0.1 ml human plasma. The detection limit is ca 2 ng/ml in plasma. Preliminary pharmacokinetic results show that the sensitivity and selectivity of the assay are adequate to establish plasma concentrations over 8-12 half-lives during elimination of the drug.

Post-column coulometric generation and cyclic voltammetric identification of the free radical of the antineoplastic agent etoposide (VP 16-213).

It has been suggested that etoposide can be transformed 'in vivo' into a radical intermediate, which may be involved in the irreversible binding of etoposide to microsomal proteins and in DNA damage. To investigate some physico-chemical properties, the on-line coulometric production of this free radical and its subsequent cyclic voltammetric detection is described. For the synthesis, a coulometric ESA Coulochem 5100A module, equipped with an ESA 5010 analytical cell, has been used. For its detection the computerized cyclic voltammetric detection system after HPLC controlled by an Apple IIe computer, using home-made software and a home-made glassy-carbon wall-jet detector, has been used. Application of a ramdisk allows storage of 68 cyclic voltammograms. In a methanol-phosphate buffer (pH=8) (40:60 w/w) containing mobile phase, the forward scan of the on-line cyclic voltammogram of etoposide shows two oxidation steps, caused by a double one-electron transfer. Post-column electrolysis at +500 mV versus the H(+)/H2 reference electrode results into total disappearance of the first oxidation step, whereas a reduction wave arises. The limiting current of this wave, and the remaining second oxidation wave, are of equal heights, indicating one-electron processes. Under these conditions, the half-life time of the product, and consequently the free radical, is 100 s, determined by stopped-flow analysis. Decreasing the pH of the buffer in the mobile phase to pH 2.2 results in merging of the two oxidation steps to a single two-electron transfer, disabling radical formation. Under physiological conditions ('in vivo') the established half-life time of the radical enables participation of the intermediate in metabolic processes.

Computerized cyclic voltammetric detection after HPLC of the antineoplastic agents etoposide, teniposide, adriamycin and its metabolite adriamycinol in urine samples.

A computerized electrochemical detection system for application after HPLC, provided with a cyclic voltammetric oxidative and reductive module, is described for the on-line qualitative determination of electroactive antineoplastic agents and metabolites in urine samples, collected from cancer patients, following intravenous administration.The application of two cyclic voltammetric detection modes provides an insight into both oxidative and reductive electrode reactions of compounds, passing the detector and the occurrence of (it)reversible chemical and electrochemical processes at the electrode surface. In this way, redox properties of drugs and metabolites characteristic of their molecular structure, can be established, which may provide information related to their (enzymatic) bioactivation.In the cyclic voltammetric mode, the system permits automatic detection of a compound in the cell, recording, storage and plotting of voltammograms and calculation of the retention times, the half-wave potentials and the peak potentials of each scan of all individual compounds. For routine use, storage of 68 voltammograms on-line is sufficient for the analysis of biological samples in clinical-pharmacological research. Special attention has been paid to automatic, multi-reference-point component detection.Based on their concentrations in urine, the oxidative cyclic voltammetric mode, using a glassy carbon electrode, permits the determination of etoposide and teniposide, whereas the reductive cyclic voltammetric mode, with a static mercury drop electrode, permits the determination of adriamycin and its metabolite adriamycinol.

In vitro and in vivo metabolism of VP 16-213 in the rat.

A high-performance liquid chromatographic procedure utilizing u.v. and radioactivity detection was employed to examine the metabolism of the epipodophyllotoxin derivative VP 16-213 by the rat in vivo and in liver extracts and subcellular fractions. VP 16-213 has been shown to be metabolized extensively by rat liver homogenates and rat liver microsomes, with the formation of one major metabolite. The metabolite formed in vitro was the only metabolite present in plasma samples of rats treated with i.p. injections of VP 16-213. Based on its chromatographic and solubility characteristics, the metabolite is probably a cis- or trans-hydroxy acid derivative. The liver is involved in the metabolism of VP 16-213, and the localization of the enzyme(s) responsible for the formation of the major metabolite is in the microsomal fraction.

Electrolytically labeled [99mTc]MDP: chromatographic pattern, stability and biodistribution in rats.

The labeling of methylene diphosphonate with 99mTc is possible after reduction of pertechnetate by means of controlled potential electrolysis. This results in a [99mTc]MDP complex which differs slightly from 99mTc(Sn)-MDP in paper and gel chromatography. The scintigraphic images of both preparations are comparable in quality. Biodistribution in rats shows a higher bone uptake for the 99mTc(Sn)-MDP complex, whereas [99mTc]MDP shows a higher uptake in the gastric wall.

Pharmacokinetics of high dose etoposide (VP 16-213).

This paper describes the pharmacokinetics of etoposide in cancer patients after high dose administration (up to 3.5 g/m2). High performance liquid chromatography with electrochemical detection was used to determine etoposide, cis etoposide and the glucuronide of etoposide in plasma, bile, cerebro-spinal fluid, urine, saliva and ascites, the detection limit being 2 ng etoposide/ml plasma. The plasma concentration time curve shows a tri-phasic decay. The terminal phase is very slow. It was concluded that etoposide is strongly bound in the peripheral compartment. The volume of the central compartment varied from 7.4 to 20.1 l and the steady state volume of distribution from 3.1 to 7.8 l/m2. Relatively high concentrations of etoposide were found in saliva, bile, ascites and urine and low concentrations in cerebro-spinal fluid. The total body clearance varied from 12.0 to 26.8 ml/min/m2, and 26.2 to 53.4% was excreted as unchanged etoposide into the urine and 8.3 to 17.3% as glucuronide into the urine. Very low amounts of the trans hydroxy acid of etoposide and the cis etoposide were detected in the urine. Glucuronides were found in urine and duodenal fluid but not in plasma.

Pharmacokinetic evaluation of increasing dosages of etoposide in a chronic hemodialysis patient.

A chronic hemodialysis patient was treated for small cell lung cancer with a combination therapy consisting of doxorubicin, cyclophosphamide, and etoposide. The dose of etoposide was increased to normal in five steps because of the possible accumulation and higher plasma peak levels due to terminal renal failure. In order to study this phenomenon, plasma, urine, and dialysate levels of etoposide were determined during five treatment courses with a high-performance liquid chromatographic method combined with electrochemical detection; this proved that the pharmacokinetic curves for etoposide fit a two-compartment model. Peak plasma levels were 7.96, 10.84, 18.24, 21.0, and 24.0 micrograms/ml for dosages of etoposide of 75, 100, 150, 200, and 250 mg, respectively. No accumulation occurred, half-life times of the elimination phase were between 8.7 and 23.0 hours, apparent distribution volumes of the central compartment were between 9.2 and 14.5 L, and the total-body clearances were between 2.1 and 2.8 L/hour. Thus, pharmacokinetic parameters were comparable with those obtained in patients with normal renal function. Hemodialysis did not disturb the exponential decay of plasma etoposide concentration during the elimination phase. No etoposide was found in the dialysate and only minimal etoposide was recovered from the urine. The data presented here indicate that renal clearance is not indispensable for eliminating etoposide.