Pharmacokinetics of 5-fluorouracil and its catabolites determined by 19F nuclear magnetic resonance spectroscopy for a patient on chronic hemodialysis

Removal rate of 5-fluorouracil and its metabolites in patients on hemodialysis: a report of two cases of colorectal cancer patients with end-stage renal failure

PURPOSE

Hyperammonemia is a serious adverse effect of 5-fluorouracil (5FU) administration. Hemodialysis can be used for its management, but detailed data on the concentrations and removal rate of 5FU and its metabolites during hemodialysis remain unclear. Here, we present two cases of hemodialysis patients with end-stage renal disease who received concurrent 5FU infusion.

METHODS

Blood samples were collected from the hemodialysis circuit before and after the dialyzer during day 2 hemodialysis sessions, and from the internal shunt just before and after day 4 hemodialysis sessions. The serum levels of 5FU and its metabolites-α-fluoro-β-alanine (FBAL) and monofluoroacetate (FA)-were measured using liquid chromatography-tandem mass spectrometry.

RESULTS

Seven sets of blood samples were collected for case 1; the removal rates (mean ± standard deviation) of 5FU and FBAL by the dialyzer were 81.2 ± 23.2% and 96.1 ± 8.6%, respectively (p < 0.001). Three sets of blood samples were collected for case 2; the removal rates of 5FU and FBAL were 81.7 ± 3.9% and 94.8 ± 2.7%, respectively (p = 0.03). Twenty-seven sets of blood samples were collected for case 1; reductions in blood FBAL and FA levels were 49.3 ± 8.8% (p < 0.001) and 64.2 ± 30.3% (p = 0.04), respectively. Bayesian estimation yielded similar results. Three sets of blood samples were collected for case 2; reductions in the blood FBAL and FA levels were 49.9 ± 6.9% and 50.6 ± 33.0%, respectively.

CONCLUSION

In this study, 5FU and its metabolite FBAL were directly removed from the blood by approximately 90% during hemodialysis, and the blood levels of FBAL and FA were reduced by approximately 50% with a single hemodialysis session.

Impact of renal impairment on dihydropyrimidine dehydrogenase (DPD) phenotyping

BACKGROUND

The chemotherapeutic agent 5-fluorouracil (5-FU) is catabolized by dihydropyrimidine dehydrogenase (DPD), the deficiency of which may lead to severe toxicity or death. Since 2019, DPD deficiency testing, based on uracilemia, is mandatory in France and recommended in Europe before initiating fluoropyrimidine-based regimens. However, it has been recently shown that renal impairment may impact uracil concentration and thus DPD phenotyping.

PATIENTS AND METHODS

The impact of renal function on uracilemia and DPD phenotype was studied on 3039 samples obtained from three French centers. We also explored the influence of dialysis and measured glomerular filtration rate (mGFR) on both parameters. Finally, using patients as their own controls, we assessed as to what extent modifications in renal function impacted uracilemia and DPD phenotyping.

RESULTS

We observed that uracilemia and DPD-deficient phenotypes increased concomitantly to the severity of renal impairment based on the estimated GFR, independently and more critically than hepatic function. This observation was confirmed with the mGFR. The risk of being classified 'DPD deficient' based on uracilemia was statistically higher in patients with renal impairment or dialyzed if uracilemia was measured before dialysis but not after. Indeed, the rate of DPD deficiency decreased from 86.4% before dialysis to 13.7% after. Moreover, for patients with transient renal impairment, the rate of DPD deficiency dropped dramatically from 83.3% to 16.7% when patients restored their renal function, especially in patients with an uracilemia close to 16 ng/ml.

CONCLUSIONS

DPD deficiency testing using uracilemia could be misleading in patients with renal impairment. When possible, uracilemia should be reassessed in case of transient renal impairment. For patients under dialysis, testing of DPD deficiency should be carried out on samples taken after dialysis. Hence, 5-FU therapeutic drug monitoring would be particularly helpful to guide dose adjustments in patients with elevated uracil and renal impairment.

Successful management of hyperammonemia with hemodialysis on day 2 during 5-fluorouracil treatment in a patient with gastric cancer: a case report with 5-fluorouracil metabolite analyses

Purpose

Hyperammonemia is an important adverse event associated with 5-fluorouracil (5FU) from 5FU metabolite accumulation. We present a case of an advanced gastric cancer patient with chronic renal failure, who was treated with 5FU/leucovorin (LV) infusion chemotherapy (2-h infusion of LV and 5FU bolus followed by 46-h 5FU continuous infusion on day 1; repeated every 2 weeks) and developed hyperammonemia, with the aim of exploring an appropriate hemodialysis (HD) schedule to resolve its symptoms.

Methods

The blood concentrations of 5FU and its metabolites, α-fluoro-β-alanine (FBAL), and monofluoroacetate (FA) of a patient who had hyperammonemia from seven courses of palliative 5FU/LV therapy for gastric cancer were measured by liquid chromatography–mass spectrometry.

Results

On the third day of the first cycle, the patient presented with symptomatic hyperammonemia relieved by emergency HD. Thereafter, the 5FU dose was reduced; however, in cycles 2–4, the patient developed symptomatic hyperammonemia and underwent HD on day 3 for hyperammonemia management. In cycles 5–7, the timing of scheduled HD administration was changed from day 3 to day 2, preventing symptomatic hyperammonemia. The maximum ammonia and 5FU metabolite levels were significantly lower in cycles 5–7 than in cycles 2–4 (NH3 75 ± 38 vs 303 ± 119 μg/dL, FBAL 13.7 ± 2.5 vs 19.7 ± 2.0 μg/mL, FA 204.0 ± 91.6 vs 395.9 ± 12.6 ng/mL, mean ± standard deviation, all p < 0.05). After seven cycles, partial response was confirmed.

Conclusion

HD on day 2 instead of 3 may prevent hyperammonemia in 5FU/LV therapy.

Electronic supplementary material

The online version of this article (10.1007/s00280-020-04158-1) contains supplementary material, which is available to authorized users.

Anti-neoplastic agents for patients on peritoneal dialysis: A systematic review

BACKGROUND

There is no clear consensus on the administration of anti-neoplastic agents to patients on peritoneal dialysis. Dose adjustments to prevent serious adverse events are still not established. Thus, the aim of this study was to systematically review current evidence on the use of systemic oncology therapies in peritoneal dialysis.

METHODS

A systematic review was conducted using PubMed, Scopus, and Cochrane. All relevant data was collected, including clinical and pharmacokinetic parameters, with comparison to subjects with normal renal function.

RESULTS

Sixteen studies were included. All were case reports. Eighteen types of anti-cancer drugs were reviewed. Multiple adverse events and altered pharmacokinetics were reported.

CONCLUSION

Data concerning the use of anti-neoplastic drugs in patients on peritoneal dialysis are still sparse. The elimination of anti-cancer agents seems often altered in such patients, resulting in serious adverse events. Based on the available evidence, we suggest the need for dose adjustment of each drug.

Decreased Disposition of Anticancer Drugs Predominantly Eliminated via the Liver in Patients with Renal Failure

Background:

Evidence has revealed that renal impairment can affect the systemic exposure of drugs which are predominantly eliminated via the liver. The modulation of drug-metabolizing enzymes and transporters expressed in the liver and/or small intestine by diverse entities, including uremic toxins, in systemic circulation of patients with severe renal failure is considered as the cause of atypical pharmacokinetics, which sometimes induce undesirable adverse events that are especially critical for drugs with narrow therapeutic window such as anticancer drugs. A dosing strategy for anticancer drugs in these patients needs to be established.

Methods:

The effects of renal impairment on the systemic exposure and safety of anticancer drugs were summarized. The proposed mechanisms for the alterations in the pharmacokinetics of these anticancer drugs were also discussed.

Results:

Changes in pharmacokinetics and clinical response were reported in 9 out of 10 cytotoxic anticancer drugs investigated, although available information was limited and sometimes controversial. Systemic exposure of 3 out of 16 tyrosine kinase inhibitors was higher in patients with severe renal failure than that in patients with normal kidney function. An increase in systemic exposure of anticancer drugs in patients with renal impairment is likely to be observed for substrates of OATP1B1, despite the limited evidence.

Conclusion:

The molecular basis for the effect of uremia on non-renal drug elimination still needed to be clarified with further studies to generate generalizable concepts, which may provide insights into establishing better clinical usage of anticancer drugs, i.e. identifying patients at risk and dose adjustment.

[5-fluorouracil therapeutic drug monitoring: Update and recommendations of the STP-PT group of the SFPT and the GPCO-Unicancer]

Despite being 60-years old now, 5-FU remains the backbone of numerous regimen to treat a variety of solid tumors such as breast, head-and-neck and digestive cancers either in neo-adjuvant, adjuvant or metastatic settings. Standard 5-FU usually claims 15-40% of severe toxicities and up to 1% of toxic-death. Numerous studies show a stiff relationship between 5-FU exposure and toxicity or efficacy. In addition, 5-FU pharmacokinetics is highly variable between patients. Indeed, 80% of the 5-FU dose is catabolized in the liver by dihydropyrimidine dehydrogenase (DPD) into inactive compounds. It is now well established that DPD deficiency could lead to severe toxicities and, thus, require dose reduction in deficient patients. However, despite dosage adaptation based on DPD status, some patients may still experience under- or over-exposure, leading to inefficacy or major toxicity. The "Suivi thérapeutique pharmacologique et personnalisation des traitements" (STP-PT) group of the "Société française de pharmacologie et de thérapeutique" (SFPT) and the "Groupe de pharmacologie clinique oncologique" (GPCO)-Unicancer, based on the latest and most up-to-date literature data, recommend the implementation of 5-FU Therapeutic Drug Monitoring in order to ensure an adequate 5-FU exposure.

Safety of Regular-Dose Imatinib Therapy in Patients with Gastrointestinal Stromal Tumors Undergoing Dialysis

The number of cancer patients undergoing dialysis has been increasing, and the number of these patients on chemotherapy is also increasing. Imatinib is an effective and safe therapy for KIT-positive gastrointestinal stromal tumors (GIST), but the efficacy and safety of imatinib in dialysis patients remain unclear. Because clinical trials have not been conducted in this population, more investigations are required. We report on a 75-year-old Japanese man undergoing dialysis who presented with massive tarry stool from a duodenal GIST. The duodenal GIST was 14 cm in diameter with multiple liver and bone metastases. The patient underwent an urgent pancreaticoduodenectomy to achieve hemostasis. After surgery, he was administered imatinib 400 mg/day. No severe adverse event including myelosuppression, congestive heart failure, liver functional impairment, intestinal pneumonia, or Steven-Johnson syndrome occurred, and the liver metastasis remained stable for 4 months. During chemotherapy, hemodialysis continued three times per week without adverse events. We suggest that regular-dose imatinib is an effective and safe treatment in patients with GIST undergoing dialysis. In addition, we present a literature review of the effectiveness and safety of imatinib treatment in dialysis patients.

Antimicrobial dosing in acute renal replacement

Acute kidney injury (AKI) is a common problem in hospitalized patients and is associated with significant morbidity and mortality. Two large trials showed no benefit from increased doses of renal replacement therapy (RRT) despite previous clinical data suggesting that increased clearance from RRT has beneficial effects. Since infection is the leading cause of death in AKI, my group and others hypothesized that increased RRT antibiotic clearance might create a competing morbidity. The data from my group, as well as those of other groups, show that many patients are underdosed when routine "1 size fits all" antibiotic dosing is used in patients with AKI receiving continuous RRT (CRRT). Here, concepts of drug distribution and clearance in AKI are briefly discussed and then 1 antibiotic (piperacillin) is discussed in depth to illustrate the challenges in applying the medical literature to clinical practice. The fact that published data on drug dosing in AKI and dialysis reflect the evolution of practice patterns and often do not apply to present prescribing habits is also discussed. A more general approach to drug dosing facilitates situation-specific prescribing by the nephrologist and critical care specialist.

[Management of chemotherapy in hemodialysis patients]

BACKGROUND

The increased incidence of cancer in dialysis patients has been discussed since the mid-70s. Consequently, oncologists, nephrologists and pharmacists are increasingly facing challenging situations of cytotoxic drug handling in dialysis patients. In dialysis patients, two main issues must be considered. First, renal function of hemodialysis (HD) patients is no longer functional. Therefore, these patients may necessitate drug dosage reduction, namely drug prescription, must be cautiously checked before administration with appropriate dosage adjustment whenever necessary to ensure efficacy while avoiding overdosage and related side effects. Secondly, drug clearance by dialysis must be taken into account for appropriate chemotherapy timing in order to avoid drug removal, which may result in a loss of efficacy.

METHODS

We reviewed the international literature on the pharmacokinetics, efficacy, tolerance and dosage adjustment of anticancer drugs used on hemodialysis cancer patients, using the key words: kidney, renal, dialysis, hemodialysis, end-stage renal disease and the name of each drug.

RESULTS

Only case reports and small series were found. 57.1% of the drugs need dosage adjustment and 64.3% should be administered after the dialysis session.

CONCLUSION

Cancer treatment in feasible in dialysis patients. Some drugs require dosage adaptation while others can be given as in patients with normal kidney function. These patients need coordinated care between oncologists, nephrologists and pharmacists to optimize drug delivery and logistics. Frailty scores, like in oncogeriatrics, should be built to optimally adapt cancer treatments in these dialysis patients.

A retrospective observational study on the use of capecitabine in patients with severe renal impairment (GFR <30 mL/min) and end stage renal disease on hemodialysis

Capecitabine (Xeloda) is an orally administered precursor of 5'deoxy-5-fluorouridine, which is a preferentially activated to 5-fluorouracil in tumors. It is used in the treatment of colorectal, gastric, and breast cancers. Based on a single Phase II trial, which included a total of 4 patients with severe renal impairment (GFR <30 mL/min), the manufacturer issued a 'Dear Doctor' letter contraindicating the use of capecitabine in these patients since a high rate of grade 3 and 4 adverse events were observed and because these patients tolerated shorter treatment durations.(1) We retrospectively studied 12 patients with a GFR <30 mL/min, including 2 patients with end stage renal disease on hemodialysis, who received capecitabine for mean duration of 7.1 months (1-26 months). The mean serum creatinine at the time of initiation of the drug was 2.63 mg/dL (1.8-6.4 mg/dL) and mean GFR was 20.9 mL/min (8-29 mL/min). Two patients remained on capecitabine after they progressed to end stage renal disease (ESRD) requiring hemodialysis (HD) for an additional 17 and 6 months, respectively. Most patients reported grade 1 and 2 adverse effects (AE), 2 patients reported grade 3 diarrhea and one patient died while on treatment with capecitabine. The starting dose ranged from 250 to 1000 mg/m(2), given twice daily at variable intervals. Dose modifications, with reductions of up to 50% of the starting dose, were made following reports of AEs. Serum tumor marker levels and/or follow up imaging studies were available on 9 patients. Response to capecitabine was documented in 4 patients, stable disease in 2, and disease progression in 3. We conclude that, with close monitoring of their clinical and chemical data, and with dose modification based on reported AEs, capecitabine can be safely administered to patients with severe renal impairment, including patients on hemodialysis.

Proposal for dosage adjustment and timing of chemotherapy in hemodialyzed patients

BACKGROUND

The increased incidence of malignancies in patients with chronic renal failure has been discussed since the mid-70s. On the other hand, the high frequency of chronic renal insufficiency among cancer patients has been recently assessed in the Insuffisance Rénale et Médicaments Anticancéreux Study which demonstrated a prevalence as high as 50%-60% of the patients for all stages of kidney disease. Furthermore, the incidence of end-stage renal disease is growing worldwide and so is the number of patients on chronic dialysis, hemodialysis (HD) for the large majority of them. As a result, the question of cytotoxic drug handling in those patients in terms of dosage adjustment and time of administration regarding the dialysis sessions needs to be addressed to optimize cytotoxic drug therapy in those patients.

METHODS

We reviewed the international literature on the pharmacokinetics, efficacy, tolerance and dosage adjustment of cytotoxic drugs used to treat solid tumor patients and when available, specific literature on HD cancer patients.

RESULTS

From these data, dosing recommendations are given for the most prescribed cytotoxic drugs in clinical practice.

CONCLUSIONS

Dosage adjustments are often necessary in HD cancer patients. These adaptations have to be carefully carried out to optimize drug exposure, ensure efficacy and reduce the risk of side-effects.

Systemic anticancer therapy in gynecological cancer patients with renal dysfunction

Chronic kidney disease is a common occurrence in patients with gynecological cancer. Systemic anticancer treatment in such patients is a challenge for clinicians because of altered drug pharmacokinetics. For those drugs that are excreted mainly by the kidneys, decreased renal function may lead to increased systemic exposure and increased toxicity. Dose adjustment based on pharmacokinetic changes is required in this situation to avoid life-threatening toxicity. In this review, we summarize the nephrotoxicity and pharmacokinetic data of agents commonly used in systemic anticancer treatment of gynecological cancers and dose adjustment guidelines in the presence of impaired renal function. We review 17 medications that need dose adjustment (cisplatin, carboplatin, doxorubicin, epirubicin, cyclophosphamide, ifosfamide, topotecan, irinotecan, etoposide, capecitabine, bleomycin, methotrexate, actinomycin D, granulocyte-macrophage colony-stimulating factor, metoclopramide, cimetidine, and diphenhydramine) as well as 27 drugs that do not (paclitaxel, docetaxel, pegylated liposomal doxorubicin, gemcitabine, oxaliplatin, fluorouracil, vincristine, letrozole, anastrozole, tamoxifen, leuprorelin, megestrol, gefitinib, erlotinib, trastuzumab, leucovorin, granulocyte colony-stimulating factor, erythropoietin, ondansetron, granisetron, palonosetron, tropisetron, dolasetron, aprepitant, dexamethasone, lorazepam, and diazepam). We also review the formulae commonly used to estimate creatinine clearance, including Cockcroft-Gault, Chatelut, Jelliffe, Wright, and the Modification of Diet in Renal Disease study formulae.

How may anticancer chemotherapy with fluorouracil be individualised?

Fluorouracil is used clinically against various solid tumours. Both fluorouracil toxicity and pharmacokinetics vary highly within and between individuals. The reasons why doses are not individualised routinely are difficulties in defining, predicting and achieving an optimal fluorouracil exposure or dose because of a narrow therapeutic index, nonlinear pharmacokinetics, variabilities in administration rates and metabolism, and in targets like thymidylate synthase. To individualise fluorouracil administration before the first dose, assessment of the individual dihydropyrimidine dehydrogenase (DPD) activity may be useful, because this genetically highly polymorphic enzyme controls approximately 80% of fluorouracil elimination. A complete or partial loss of DPD activity in 0.1 and 3-5% of Caucasians, respectively, leads to increased fluorouracil exposure and toxicity. Several methods to assess DPD activity in patients have been proposed (genotyping, various phenotyping methods), but each of them has limitations, as has the fluorouracil test dose approach. To adapt exposure towards fluorouracil a priori, a combination of genotyping and phenotyping may yield better prediction of toxicity than one method alone. A prerequisite for dose adaptation is the definition of fluorouracil exposure ranges with sufficient therapeutic activity, but without serious toxicity. While an increased risk of leukopenia, diarrhoea, stomatitis, and hand-foot syndrome during continuous 5-day infusions was related to fluorouracil exposures above an area under the plasma concentration-time curve (AUC) threshold of 25-30 mg.h/L, tumour response was higher when an AUC of approximately 30 mg.h/L was achieved, illustrating the extremely narrow therapeutic window of fluorouracil. Pharmacokinetic target values are less clear for other regimens, including chronomodulated regimens, which yielded a superior clinically efficacy and tolerability in several trials. However, the monitoring of fluorouracil plasma concentrations seems principally useful for individual a posteriori dose adjustment. Whether an adaptation of the fluorouracil starting dose to the results of two DPD activity tests before fluorouracil administration a priori, and the adaptation of doses to fluorouracil exposure a posteriori is a reasonable approach to better prevent toxicity and increase efficacy, remains to be evaluated in randomised clinical studies comparing these strategies to routine clinical safety monitoring.

Carbogen breathing differentially enhances blood plasma volume and 5-fluorouracil uptake in two murine colon tumor models with a distinct vascular structure

For the systemic treatment of colorectal cancer, 5-fluorouracil (FU)-based chemotherapy is the standard. However, only a subset of patients responds to chemotherapy. Breathing of carbogen (95% O2 and 5% CO2) may increase the uptake of FU through changes in tumor physiology. This study aims to monitor in animal models in vivo the effects of carbogen breathing on tumor blood plasma volume, pH, and energy status, and on FU uptake and metabolism in two colon tumor models C38 and C26a, which differ in their vascular structure and hypoxic status. Phosphorus-31 magnetic resonance spectroscopy (MRS) was used to assess tumor pH and energy status, and fluorine-19 MRS was used to follow FU uptake and metabolism. Advanced magnetic resonance imaging methods using ultrasmall particles of iron oxide were performed to assess blood plasma volume. The results showed that carbogen breathing significantly decreased extracellular pH and increased tumor blood plasma volume and FU uptake in tumors. These effects were most significant in the C38 tumor line, which has the largest relative vascular area. In the C26a tumor line, carbogen breathing increased tumor growth delay by FU. In this study, carbogen breathing also enhanced systemic toxicity by FU.

Fluorine nuclear magnetic resonance spectroscopy of human biofluids in the field of metabolic studies of anticancer and antifungal fluoropyrimidine drugs

Fluorine-19 nuclear magnetic resonance (19F NMR) spectroscopy provides a highly specific tool for the detection, identification and quantification of fluorine-containing drugs and their metabolites in biofluids. The value and difficulties encountered in investigations on drug metabolism are first discussed. Then the metabolism of three fluoropyrimidines in clinical use, 5-fluorouracil, 5-fluorocytosine and capecitabine are reported. Besides the parent drug and the already known fluorinated metabolites, 12 new metabolites were identified for the first time with 19F NMR in human biofluids. Nine of them can only be observed with this technique: fluoride ion, N-carboxy-alpha-fluoro-beta-alanine, alpha-fluoro-beta-alanine conjugate with deoxycholic acid, 2-fluoro-3-hydroxypropanoic acid, fluoroacetic acid, O2-beta-glucuronide of fluorocytosine, fluoroacetaldehyde hydrate and its adduct with urea, fluoromalonic acid semi-aldehyde adducts with urea. This emphasizes the high analytical potential of 19F NMR for the furtherance in the understanding of fluoropyrimidine catabolic pathways. 19F NMR should also play a role in the therapeutic monitoring of FU and its prodrugs in specific groups of patients, e.g. hemodialyzed patients or patients with deficiency in FU catabolic enzymes.

Effect of Hemodialysis on the Metabolic Clearance of 5-Fluorouracil in a Patient With End-Stage Renal Failure

A 64-year-old man on chronic hemodialysis for end-stage renal disease developed peritoneal carcinomatosis, and palliative chemotherapy with fluorouracil was started. The drug was administered (325 mg/m as IV bolus, at 2 PM) on 2 separate occasions, ie, 1 hour after dialysis and 2 days later, 49 hours after dialysis. The time course of the fluorouracil plasma concentration was determined, and the main pharmacokinetic parameters were calculated. The slope of the monoexponential decay of plasma concentration was significantly greater 1 hour (0.161 minutes) than 49 hours after dialysis (0.127 minutes), and plasma clearance was correspondingly higher (1.78 L/min versus 1.46 L/min). The volume of distribution did not change (11.1 L versus 11.5 L). Because fluorouracil is minimally excreted by the renal route (about 10% of the dose) and is almost entirely metabolized by dihydropyrimidine dehydrogenase (DPD), it is suggested that plasma factors that accumulate during the interdialytic period and are removed by dialysis may inhibit DPD activity and, consequently, fluorouracil metabolic clearance.

Fluorine-19 or phosphorus-31 NMR spectroscopy: A suitable analytical technique for quantitative in vitro metabolic studies of fluorinated or phosphorylated drugs

Fluorine-19 or phosphorus-31 NMR (19F NMR or 31P NMR) spectroscopy provides a highly specific tool for identification of fluorine- or phosphorus-containing drugs and their metabolites in biological media as well as a suitable analytical technique for their absolute quantification. This article focuses on the application of in vitro 19F or 31P NMR to the quantitative metabolic studies of some fluoropyrimidine or oxazaphosphorine drugs in clinical use. The first part presents an overview of the advantages (non-destructive and non-selective direct quantitative study of the biological matrices) and limitations (expensive cost of the spectrometers, limited mass or concentration sensitivity) of NMR spectroscopy. The second part deals with the criteria to be considered for successful quantification by NMR (uniform excitation over the entire spectral width of the spectrum, resonance signals properly characterised by taking into account T1 values and avoiding NOE enhancements, optimisation of the data processing, choice of a suitable standard reference). The third and fourth parts report some examples of quantification of 5-fluorouracil, its prodrug capecitabine, 5-fluorocytosine and their metabolites in bulk solutions (biofluids, tissue extracts, perfusates and culture media) and heterogeneous media (excised tissues and packed intact cells) as well as cyclophosphamide and ifosfamide in biofluids. These two parts emphasise the high potential of in vitro 19F or 31P NMR for absolute quantification, in a single run, of all the fluorine- or phosphorus-containing species in the matrices analysed. The limit of quantification in bulk solutions is 1-3 microM for 19F NMR and approximately 10 microM for 31P NMR. In heterogeneous media analysed with 19F NMR, it is 2-5 nmol in excised tissues and cell pellets.

Monitoring fluoropyrimidine metabolism in solid tumors with in vivo (19)F magnetic resonance spectroscopy

(19)Fluorine magnetic resonance spectroscopy ((19)F MRS) offers unique possibilities for monitoring the pharmacokinetics of fluoropyrimidines in vivo in tumors and normal tissue in a non-invasive way, both in animals and in patients. This method may therefore be useful for predicting response to fluoropyrimidine-based therapy with or without the effects of modulating agents, and this may be of value for the individualization of anticancer therapy and the strategic development of new anticancer drugs. (19)F MRS has been very valuable in elucidating the basic aspects of fluoropyrimidine metabolism, especially in animal studies. Studies in humans have indicated its clinical potential, but widespread application has been hampered by the relatively low detection sensitivity of the method. The recent introduction of clinical MR scanners with magnetic fields above 1.5 T may stimulate increased clinical use of (19)F MRS.

Effect of haemodialysis on the pharmacokinetics of antineoplastic drugs

Since renal failure itself creates an immunocompromised situation, malignant tumours in haemodialysis patients are increasing due to the prolonged lifespan of these patients. In treating these patients with anticancer agents, dosage reduction is often recommended to avoid adverse drug reactions, particularly for drugs with extensive renal excretion. On the other hand, if an anticancer drug is removed significantly by haemodialysis, dosage increase would be required to ensure adequate therapeutic efficacy. We address in this review the clinical pharmacokinetic aspects of antineoplastic therapy, and the application of pharmacokinetic principles to the adjustment of dosage of anticancer agents in haemodialysis patients.