http://repub.eur.nl/res/aut/5749/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/40001/ 2013-02-15T00:00:00Z http://repub.eur.nl/res/pub/33890/ 2011-12-15T00:00:00Z In view of future pharmacokinetic studies, a highly sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous quantification of tamoxifen and three of its main phase I metabolites in human lithium heparinized plasma. The analytical method has been thoroughly validated in agreement with FDA recommendations. Plasma samples of 200μl were purified by liquid-liquid extraction with 1ml n-hexane/isopropanol, after deproteination through addition of 50μl acetone and 50μl deuterated internal standards in acetonitrile. Tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen were chromatographically separated on an Acquity UPLC®BEH C18 1.7μm 2.1mm×100mm column eluted at a flow-rate of 0.300ml/min on a gradient of 0.2mM ammonium formate and acetonitrile, both acidified with 0.1% formic acid. The overall run time of the method was 10min, with elution times of 2.9, 3.0, 4.1 and 4.2min for endoxifen, 4-hydroxy-tamoxifen, N-desmethyl-tamoxifen and tamoxifen, respectively. Tamoxifen and its metabolites were quantified by triple-quadrupole mass spectrometry in the positive ion electrospray ionization mode. The multiple reaction monitoring transitions were set at 372>72 (m/z) for tamoxifen, 358>58 (m/z) for N-desmethyl-tamoxifen, 388>72 (m/z) for 4-hydroxy-tamoxifen and 374>58 (m/z) for endoxifen. The analytical method was highly sensitive with the lower limit of quantification validated at 5.00nM for tamoxifen and N-desmethyl-tamoxifen and 0.500nM for 4-hydroxy-tamoxifen and endoxifen, which is equivalent to 1.86, 1.78, 0.194 and 0.187ng/ml for tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen, respectively. The method was also precise and accurate, with within-run and between-run precisions within 12.0% and accuracy ranging from 89.5 to 105.3%. The method has been applied to samples from a clinical study and cross-validated with a validated LC-MS/MS method in serum. http://repub.eur.nl/res/pub/34088/ 2011-04-01T00:00:00Z Background: Omeprazole is one of the most prescribed medications worldwide and within the class of proton pump inhibitors, it is most frequently associated with drug interactions. In vitro studies have shown that omeprazole can alter the function of metabolic enzymes and transporters that are involved in the metabolism of irinotecan, such as uridine diphosphate glucuronosyltransferase subfamily 1A1 (UGT1A1), cytochrome P-450 enzymes subfamily 3A (CYP3A) and ATP-binding cassette drug-transporter G2 (ABCG2). In this open-label cross-over study we investigated the effects of omeprazole on the pharmacokinetics and toxicities of irinotecan. Methods: Fourteen patients were treated with single agent irinotecan (600 mg i.v., 90 min) followed 3 weeks later by a second cycle with concurrent use of omeprazole 40 mg once daily, which was started 2 weeks prior to the second cycle. Plasma samples were obtained up to 55 h after infusion and analysed for irinotecan and its metabolites 7-ethyl-10- hydroxycampothecin (SN-38), SN-38-glucuronide (SN-38G), 7-ethyl-10-[4-(1- piperidino)-1-amino]-carbonyloxycamptothecin (NPC) and 7-ethyl-10-[4-N-(5- aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC) by high-performance liquid chromatography (HPLC). Non-compartmental modelling was performed. Toxicities were monitored during both cycles. Paired statistical tests were performed with SPSS. Results: The exposure to irinotecan and its metabolites was not significantly different between both cycles. Neither were there significant differences in the absolute nadir and percentage decrease of WBC and ANC, nor on the incidence and severity of neutropenia, febrile neutropenia, diarrhoea, nausea and vomiting when irinotecan was combined with omeprazole. Conclusion: Omeprazole 40 mg did not alter the pharmacokinetics and toxicities of irinotecan. This widely used drug can, therefore, be safely administered during a 3-weekly single agent irinotecan schedule. http://repub.eur.nl/res/pub/33926/ 2011-01-25T00:00:00Z A rapid and sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method has been developed and validated for the simultaneous quantitative determination of dextromethorphan (DM) and its metabolites dextrorphan (DX), 3-methoxymorphinan (3MM) and 3-hydroxymorphinan (3HM), in human lithium heparinized plasma. The extraction involved a simple liquid-liquid extraction with 1ml n-butylchloride from 200μl aliquots of plasma, after the addition of 20μl 4% (v/v) ammonium hydroxide and 100μl stable labeled isotopic internal standards in acetonitrile. Chromatographic separations were achieved on an Aquity UPLC®BEH C181.7μm 2.1mm×100mm column eluted at a flow-rate of 0.250ml/min on a gradient of acetonitrile. The overall cycle time of the method was 7min, with elution times of 1.3min for DX and 3HM, 2.8min for 3MM and 2.9min for DM. The multiple reaction monitoring transitions were set at 272>215 (m/z), at 258>133 (m/z), at 258>213 (m/z) and at 244>157 (m/z) for DM, DX, 3MM and 3HM, respectively. The calibration curves were linear (r2≥0.995) over the range of 0.500-100nM with the lower limit of quantitation validated at 0.500nM for all compounds, which is equivalent to 136, 129, 129 and 122pg/ml for DM, DX, 3MM and 3HM, respectively. Extraction recoveries were constant, but ranged from 39% for DM to 83% for DX. The within-run and between-run precisions were within 11.6%, while the accuracy ranged from 92.7 to 110.6%. The applicability of the bioanalytical method was demonstrated and is currently implemented in a clinical trial to study DM as probe-drug for individualized tamoxifen treatment in breast cancer patients. http://repub.eur.nl/res/pub/31703/ 2011-01-15T00:00:00Z Purpose: Docetaxel pharmacokinetic (PK) parameters, notably clearance and exposure (AUC), are characterized by large interindividual variability. The purpose of this study was to evaluate the effect of PKguided [area under the plasma concentration versus time curve (AUC) targeted], individualized docetaxel dosing on interindividual variability in exposure. Experimental Design: A limited sampling strategy in combination with a validated population PK model, Bayesian analysis, and a predefined target AUC was used. Fifteen patients were treated for at least 2 courses with body surface area-based docetaxel and 15 with at least 1 course of PK-guided docetaxel dosing. Results: Interindividual variability (SD of ln AUC) was decreased by 35% (N = 15) after 1 PK-guided course; when all courses were evaluated, variability was decreased by 39% (P = 0.055). PK-guided dosing also decreased the interindividual variability of percentage decrease in white blood cell and absolute neutrophil counts by approximately 50%. Conclusions: Further research is required to determine whether the decrease in PK variability can contribute to a reduction in interindividual variability in efficacy and toxicity. http://repub.eur.nl/res/pub/28024/ 2010-03-11T00:00:00Z A rapid and sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method has been developed and validated for the quantitative determination of sunitinib and its n-desethyl metabolite SU12662, in 100 μl aliquots of human potassium EDTA plasma with deuterated sunitinib as internal standard. As sunitinib was found to be extremely sensitive to light causing rapid conversion of the Z (cis)-isomer to the E (trans)-isomer, the sample extraction and cleaning-up were performed under sodium-light and in amber vials. The extraction involved a simple liquid-liquid extraction with tert-butyl methyl ether. Chromatographic separations were achieved on an Aquity UPLC®BEH C181.7 μm, 2.1 mm × 50 mm column eluted at a flow rate of 0.250 ml/min on a gradient of acetonitrile. The overall cycle time of the method was 4 min, with elution times of 1.05, 1.43, 0.95, and 1.34 min, for the E (trans)- and Z (cis)-isomers of sunitinib and the E (trans)- and Z (cis)-isomers of SU12662, respectively. The multiple reaction monitoring transitions were set at 399 > 326 (m/z), at 371 > 283 (m/z) and at 409 > 326 (m/z) for sunitinib, SU12662 and the internal standard, respectively. The calibration curves were linear over the range of 0.200 to 50.0 ng/ml with the lower limit of quantitation validated at 0.200 ng/ml for both sunitinib and SU12662. The within-run and between-run precisions were within 11.7%, while the accuracy ranged from 90.5 to 106.8%. http://repub.eur.nl/res/pub/20201/ 2010-01-01T00:00:00Z Purpose: Response to anticancer therapy is believed to be directly related to the concentration of the anticancer drug in the tumor itself. Assessment of intra-tumor drug pharmacokinetics can be helpful to gain more insight into mechanisms involved in the (in)sensitivity of tumors to anticancer therapy. We explored the pharmacokinetics of 5-fluorouracil in both plasma and tumor tissue during a 5-day continuous infusion of 5-fluorouracil in patients with cancer. Sampling for measurement of 5-fluorouracil in tumor tissue was performed using microdialysis. Experimental design: In seven patients with an accessible (sub)cutaneous tumor treated with a continuous 5-fluorouracil infusion, plasma and microdialysate samples from tumor and normal adipose tissue were collected over a period of 5 days. Results: For six patients, drug concentrations in both tumor tissue and plasma were available. Concentration-time curves of unbound 5-fluorouracil were lower in tumor tissue compared to the curves in plasma, but exposure ratios of tumor tissue versus plasma increased during the 5-day infusion period. The presence of circadian rhythmicity of 5-fluorouracil pharmacokinetics in the tumor itself was demonstrated as 5-fluorouracil concentrations in tumor extracellular fluid were higher during the night than during daytime. Conclusion: Microdialysis was successfully employed in patients with cancer during a continuous 5-day 5-fluorouracil infusion. Plasma and tumor pharmacokinetics of 5-fluorouracil differed substantially with increasing 5-fluorouracil concentrations in tumor over time, possibly resulting from a lowered interstitial fluid pressure by 5-fluorouracil itself. This microdialysis 5-fluorouracil model might be useful to monitor the effect of drug delivery modulating strategies in future studies. http://repub.eur.nl/res/pub/17162/ 2009-12-05T00:00:00Z A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantitative determination of RBG-286638, a novel multi-targeted protein kinase inhibitor, in 200 μl aliquots of human potassium EDTA plasma with deuterated RGB-286638 as internal standard. The sample extraction and cleaning-up involved a simple liquid-liquid extraction with 100 μl aliquots of acetonitrile and 1 ml aliquots of n-butylchloride. Urine was accurately 5- and 10-fold diluted in blank plasma prior to extraction. Chromatographic separations were achieved on a reversed phase C18 column eluted at a flow-rate of 0.250 ml/min on a gradient of 0.2 mM ammonium formate and acetonitrile both acidified with 0.1% formic acid. The overall cycle time of the method was 7 min, with RGB-286638 eluting at 1.9 min. The multiple reaction monitoring transitions were set at 546 > 402 (m/z), and 549 > 402 (m/z) for RGB-286638 and the internal standard, respectively. The calibration curves were linear over the range of 2.00 to 1000 ng/ml with the lower limit of quantitation validated at 2.00 ng/ml. The within-run and between-run precisions were within 7.90%, while the accuracy ranged from 92.2% to 99.7%. The method was successfully applied to samples derived from a clinical study. http://repub.eur.nl/res/pub/15940/ 2008-10-01T00:00:00Z Purpose: Administration of chemotherapy in patients with renal failure, treated with hemodialysis or continuous ambulatory peritoneal dialysis (CAPD) is still a challenge and literature data is scarce. Here we present a case study of a patient on CAPD, treated with weekly and three-weekly paclitaxel/ carboplatin for recurrent ovarian cancer. Experimental: During the first, second and ninth cycle of treatment, blood, urine and CAPD samples were collected for pharmacokinetic analysis of paclitaxel and total and unbound carboplatin-derived platinum. Results: Treatment was well tolerated by the patient. No excessive toxicity was observed and at the end of treatment she was in a complete remission. The plasma pharmacokinetics of paclitaxel were unaltered compared to historical data, with neglectable urinary and CAPD clearance. In contrast, the pharmacokinetics of carboplatin were altered, with doubled half-lives compared to patients with normal renal function. Of the administered carboplatin dose, up to 20% was cleared via the dialysate, while only up to 8% was cleared via the urine. Conclusion: Paclitaxel and carboplatin can be safely administered to patients with chronic renal failure on CAPD. For paclitaxel the generally applied dose can be administered, and although for carboplatin dose-adjustment is required due to the diminished renal function, the dose can be calculated using Calvert's formula. http://repub.eur.nl/res/pub/36171/ 2007-10-18T00:00:00Z Microdialysis is a novel and minimally invasive sampling technique, based on the diffusion of analytes from the interstitial compartment through a semi-permeable membrane, and enables direct assessment of tissue disposition and penetration of drugs. Variable antitumor responses may be associated with differences in tumor vascularity, capillary permeability or tumor interstitial pressure resulting in variable delivery of anticancer agents. In preparation of pharmacokinetic studies, aimed at measuring docetaxel concentrations in healthy and malignant tissues in vivo, in pre-clinical as well as clinical studies, in vitro recovery experiments were performed. In contrast to published data, the recovery experiments suggest that docetaxel has a very low recovery as a result of non-specific binding to currently available microdialysis catheters. Here we discuss our findings with docetaxel in a historical perspective and we report on our experience using polysorbate 80 to eliminate the non-specific binding and its effects on the recovery of docetaxel. http://repub.eur.nl/res/pub/36125/ 2007-03-01T00:00:00Z Purpose: Aprepitant, a selective neurokinin-1 (NK-1) receptor antagonist approved for the treatment and prevention of emesis caused by moderately and highly emetogenic chemotherapy, is an inhibitor, inducer, and substrate of the cytochrome P450 3194 pathway. The CYP3A4 pathway is the major pathway of the metabolism of vinorelbine, a vinca alkaloid frequently used in combination with cisplatin. Therefore, we studied the potential interaction of the aprepitant 3-day antiemetic regimen on the pharmacokinetics of vinorelbine. Patients and methods: Fourteen patients with metastatic solid tumors were included in this open-label, balanced, 2-period crossover study. In treatment arm A, vinorelbine (25 mg/m2weekly) was administered alone, while in treatment arm B the same dose of vinorelbine was administered following the administration of the aprepitant antiemetic regimen on day 1 and alone on day 8. The antiemetic regimen of aprepitant was comprised of the following; on day 1:125 mg aprepitant, 12 mg dexamethasone, and 32 mg ondansetron; on days 2 and 3:80 mg aprepitant and 8 mg dexamethasone and on day 4:8 mg dexamethasone. Blood samples for vinorelbine pharmacokinetic analysis were collected over 96 h. Results: Two patients discontinued the study due to adverse events that were judged not to be drug-related. Complete pharmacokinetic data of vinorelbine administered alone and with the aprepitant antiemetic regimen were obtained in 12 patients. The mean plasma concentration profile of vinorelbine administered with aprepitant was identical to that following vinorelbine administered alone, with geometric mean vinorelbine plasma AUC ratios of treatment B day 1/treatment A day 1 and of treatment B day 8/treatment A day of 1.01 (0.93, 1.10) and 1.00 (0.92, 1.08), respectively. Conclusion: As the aprepitant antiemetic regimen has no detectable inhibitory or inductive effect on the pharmacokinetics of vinorelbine, aprepitant when added to a standard antiemetic regimen consisting of ondansetron and dexamethasone can be safely combined with vinorelbine at clinically recommended doses. http://repub.eur.nl/res/pub/14085/ 2006-09-18T00:00:00Z OBJECTIVE: Delayed-type diarrhea is a common side effect of irinotecan and is associated with a bacterial-mediated formation of the active irinotecan metabolite SN-38 from its glucuronide conjugate in the intestine. Based on a pilot study, we hypothesized that concomitant administration of the antibiotic neomycin would diminish exposure of the gut to SN-38 and ameliorate the incidence and severity of diarrhea. PATIENTS AND METHODS: Patients were treated with irinotecan in a multicenter, double-blind, randomized, placebo-controlled trial. Eligible patients received irinotecan (350 mg/m(2) once every 3 weeks) combined with neomycin (660 mg three times daily for three consecutive days, starting 2 days before chemotherapy) or combined with placebo. Blood samples were obtained for additional pharmacokinetic and pharmacogenetic analyses. RESULTS: Sixty-two patients were evaluable for the toxicity analysis. Baseline patient characteristics, systemic SN-38 exposure, and UGT1A1*28 genotype status (i.e., an additional TA repeat in the promoter region of uridine diphosphate-glucuronosyltransferase isoform 1A1) were similar in both arms. Although distribution, severity, and duration of delayed-type diarrhea did not differ significantly between arms, grade 3 diarrhea tended to be less frequent in the neomycin arm. The presence of at least one UGT1A1*28 allele was strongly related to the incidence of grade 2-3 diarrhea. In the neomycin arm, grade 2 nausea was significantly more common. CONCLUSION: Our results do not suggest a major role for neomycin as prophylaxis for irinotecan-induced delayed-type diarrhea. It is suggested that the UGT1A1*28 genotype status could be used as a screening tool for a priori prevention of irinotecan-induced delayed-type diarrhea. http://repub.eur.nl/res/pub/10375/ 2005-01-01T00:00:00Z PURPOSE: To assess the maximum-tolerated dose, toxicity, and pharmacokinetics of DE-310, a macromolecular prodrug of the topoisomerase I inhibitor exatecan (DX-8951f). in patients with advanced solid tumors. EXPERIMENTAL DESIGN: Patients received DE-310 as a 3-hour infusion once every 2 weeks (dose, 1.0-2.0 mg/m(2)) or once every 6 weeks (dose, 6.0-9.0 mg/m(2)). Because pharmacokinetics revealed a drug terminal half-life exceeding the 2 weeks administration interval, the protocol was amended to a 6-week interval between administrations also based on available information from a parallel trial using an every 4 weeks schedule. Conjugated DX-8951 (the carrier-linked molecule), and the metabolites DX-8951 and glycyl-DX-8951 were assayed in various matrices up to 35 days post first and second dose. RESULTS: Twenty-seven patients were enrolled into the study and received a total of 86 administrations. Neutropenia and grade 3 thrombocytopenia, and grade 3 hepatotoxicity with veno-occlusive disease, were dose-limiting toxicities. Other hematologic and nonhematologic toxicities were mild to moderate and reversible. The apparent half-life of conjugated DX-8951, glycyl-DX-8951, and DX-8951 was 13 days. The area under the curve ratio for conjugated DX-8951 to DX-8951 was 600. No drug concentration was detectable in erythrocytes, skin, and saliva, although low levels of glycyl-DX-8951 and DX-8951 were detectable in tumor biopsies. One patient with metastatic adenocarcinoma of unknown primary achieved a histologically proven complete remission. One confirmed partial remission was observed in a patient with metastatic pancreatic cancer and disease stabilization was noted in 14 additional patients. CONCLUSIONS: The recommended phase II dose of DE-310 is 7.5 mg/m(2) given once every 6 weeks. The active moiety DX-8951 is released slowly from DE-310 and over an extended period, achieving the desired prolonged exposure to this topoisomerase I inhibitor. http://repub.eur.nl/res/pub/13543/ 2004-11-03T00:00:00Z BACKGROUND: Irinotecan is a topoisomerase I inhibitor that has been approved for use as a first- and second-line treatment for colorectal cancer. The response to irinotecan is variable, possibly because of interindividual variation in the expression of the enzymes that metabolize irinotecan, including cytochrome P450 3A4 (CYP3A4) and uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). We prospectively explored the relationships between CYP3A phenotype, as assessed by erythromycin metabolism and midazolam clearance, and the metabolism of irinotecan and its active metabolite SN-38. METHODS: Of the 30 white cancer patients, 27 received at least two treatments with irinotecan administered as one 90-minute infusion (dose, 600 mg) with 3 weeks between treatments, and three received only one treatment. Before the first and second treatments, patients underwent an erythromycin breath test and a midazolam clearance test as phenotyping probes for CYP3A4. Erythromycin metabolism was assessed as the area under the curve for the flux of radioactivity in exhaled CO2 within 40 minutes after administration of [N-methyl-14C]erythromycin. Midazolam and irinotecan were measured by high-performance liquid chromatography. Genomic DNA was isolated from blood and screened for genetic variants in CYP3A4 and UGT1A1. All statistical tests were two-sided. RESULTS: CYP3A4 activity varied sevenfold (range = 0.223%-1.53% of dose) among patients, whereas midazolam clearance varied fourfold (range = 262-1012 mL/min), although intraindividual variation was small. Erythromycin metabolism was not statistically significantly associated with irinotecan clearance (P = .090), whereas midazolam clearance was highly correlated with irinotecan clearance (r = .745, P<.001). In addition, the presence of a UGT1A1 variant with a (TA)7 repeat in the promoter (UGT1A1*28) was associated with increased exposure to SN-38 (435 ng x h/mL, 95% confidence interval [CI] = 339 to 531 ng x h/mL in patients who are homozygous for wild-type UGT1A1; 631 ng x h/mL, 95% CI = 499 to 762 ng . h/mL in heterozygous patients; and 1343 ng x h/mL, 95% CI = 0 to 4181 ng x h/mL in patients who are homozygous for UGT1A1*28) (P = .006). CONCLUSION: CYP3A4 phenotype, as assessed by midazolam clearance, is statistically significantly associated with irinotecan pharmacokinetics. Evaluation of midazolam clearance combined with UGT1A1*28 genotyping may assist with optimization of irinotecan chemotherapy. http://repub.eur.nl/res/pub/10327/ 2004-01-01T00:00:00Z PURPOSE: The purpose of our study was to determine the maximum-tolerated dose, dose-limiting toxicity, safety profile, and pharmacokinetics of the polyamine synthesis inhibitor SAM486A given in combination with 5-fluorouracil/leucovorin (5-FU/LV) in cancer patients. EXPERIMENTAL DESIGN: Patients with advanced colorectal cancer were treated with 5-FU [bolus (400 mg/m(2)) followed by a 22-h infusion (600 mg/m(2))] and LV (200 mg/m(2)) and escalating doses of SAM486A, 1-3-h infusion daily for 3 days. Plasma sampling was performed to characterize the pharmacokinetics and pharmacodynamics of the combination RESULTS: Twenty-seven patients with metastatic colorectal cancer and 1 with pseudomyxoma peritonei were treated. Twenty-six patients received SAM486A in the combination at doses ranging from 25 to 150 mg/m(2)/day. Dose-limiting toxicity consisting of fatigue grade 3 was seen at 150 mg/m(2)/day. Other adverse events included neutropenia, hand and foot syndrome, nausea, vomiting, diarrhea, and constipation. Fifteen of 26 patients evaluable for best response according to the Southwest Oncology Group criteria achieved a partial response [8 (30%) of 26] or stable disease [9 (35%) of 26]. SAM486A did not influence the pharmacokinetics of 5-FU, and SAM486A clearance was similar to that when used as a single agent. CONCLUSIONS: The novel molecular agent SAM486A is tolerable and safe in combination with a standard 5-FU regimen in patients with advanced colorectal cancer. The dose of SAM486A recommended for additional studies with this combination is 125 mg/m(2)/day. A disease-directed evaluation of SAM486A using this regimen is warranted. http://repub.eur.nl/res/pub/9873/ 2002-01-01T00:00:00Z An additional chromatographic peak was observed in plasma samples of patients receiving NX 211, a liposomal formulation of the topoisomerase I inhibitor lurtotecan. We have isolated and purified this product by sequential solid-phase extractions, and we report its structure and cytotoxicity relative to lurtotecan and related agents. Nuclear magnetic resonance data indicate that cleavage of the piperazino moiety occurred at the N-C bond of the B-ring, yielding 7-methyl-10,11-ethylenedioxy-20(S)-camptothecin (MEC). Tests of the growth inhibition potential of MEC in seven human tumor cell lines showed that the compound was approximately 2-18-fold more cytotoxic than lurtotecan, topotecan, and 7-ethyl-10-hydroxy-20(S)-camptothecin (SN-38). Subsequently, we found that MEC was the product of rapid photolysis of lurtotecan, with the rate of degradation inversely proportional to NX 211 concentrations, and greatly depends on light intensity. Furthermore, MEC concentrations were found to increase significantly in plasma samples exposed to laboratory light but not in blood. MEC was not produced from NX 211 in the presence of human liver microsomes, suggesting that it is not a product of cytochrome P-450 metabolism. Using a validated analytical method, trace levels of MEC were quantitated in blood samples of two patients. These observations confirm that the precautions for protection from light currently specified for preparation and administration of NX 211 dose solutions are critical. Procedures to minimize formation of MEC, by the use of amber vials for NX 211 and by preparation of dilutions immediately before clinical use in a fashion completely protected from light, are now being routinely implemented. http://repub.eur.nl/res/pub/9960/ 2002-01-01T00:00:00Z St. John's wort (SJW), a widely used herbal product, has been implicated in drug interactions resulting from the induced expression of the cytochrome P450 CYP3A4 isoform. In this study, we determined the effect of SJW on the metabolism of irinotecan, a pro-drug of SN-38 and a known substrate for CYP3A4. Five cancer patients were treated with irinotecan (350 mg/m(2), intravenously) in the presence and absence of SJW (900 mg daily, orally for 18 days) in an unblinded, randomized crossover study design. The plasma levels of the active metabolite SN-38 decreased by 42% (95% confidence interval [CI] = 14% to 70%) following SJW cotreatment with 1.0 micro M x h (95% CI = 0.34 micro M x h to 1.7 micro M x h) versus 1.7 micro M x h (95% CI = 0.83 micro M x h to 2.6 micro M x h) (P =.033, two-sided paired Student's t test). Consequently, the degree of myelosuppression was substantially worse in the absence of SJW. These findings indicate that patients on irinotecan treatment should refrain from taking SJW because plasma levels of SN-38 were dramatically reduced, which may have a deleterious impact on treatment outcome. http://repub.eur.nl/res/pub/9635/ 2001-01-01T00:00:00Z This study was designed to evaluate irinotecan (CPT-11) disposition and pharmacodynamics in the presence and absence of the broad-spectrum antibiotic neomycin. Seven evaluable cancer patients experiencing diarrhea graded > or =2 after receiving CPT-11 alone (350 mg/m(2) i.v. once every 3 weeks) received the same dose combined with oral neomycin at 1000 mg three times per day (days -2 to 5) in the second course. Neomycin had no effect on the systemic exposure of CPT-11 and its major metabolites (P > or = 0.22). However, it changed fecal beta-glucuronidase activity from 7.03 +/- 1.76 microg/h/mg (phenolphthalein assay) to undetectable levels and decreased fecal concentrations of the pharmacologically active metabolite SN-38. Although neomycin had no significant effect on hematological toxicity (P > 0.05), diarrhea ameliorated in six of seven patients (P = 0.033). Our findings indicate that bacterial beta-glucuronidase plays a crucial role in CPT-11-induced diarrhea without affecting enterocycling and systemic SN-38 levels. http://repub.eur.nl/res/pub/9462/ 2000-01-01T00:00:00Z The clinical pharmacokinetic behavior of paclitaxel (Taxol) is distinctly nonlinear, with disproportional increases in systemic exposure with an increase in dose. We have recently shown that Cremophor EL, the formulation vehicle used for i.v. administration of paclitaxel, alters drug distribution as a result of micellar entrapment of paclitaxel, and we speculated that the free drug fraction (fu) is dependent on dose and time-varying concentrations of Cremophor EL in the central plasma compartment. To test this hypothesis, a reproducible equilibrium dialysis method has been developed for the measurement of paclitaxel fu in plasma. Equilibrium dialysis was performed at 37 degrees C in a humidified atmosphere of 5% CO(2) using 2.0-ml polypropylene test tubes. Experiments were carried out with 260-microliter aliquots of plasma containing a tracer amount of [G-(3)H]paclitaxel with high-specific activity against an equal volume of 0.01 M phosphate buffer (pH 7.4). Drug concentrations were measured by both reversed-phase HPLC and liquid scintillation counting. Using this method, fu has been measured in three patients receiving three consecutive 3-weekly courses of paclitaxel at dose levels of 135, 175, and 225 mg/m(2) and found to range between 0.036 and 0.079. The method was also used to define concentration-time profiles of unbound drug, estimated from the product of the total plasma concentration and fu. http://repub.eur.nl/res/pub/9463/ 2000-01-01T00:00:00Z The active metabolite of irinotecan (CPT-11), 7-ethyl-10-hydroxycamptothecin (SN-38), is either formed through enzymatic cleavage of CPT-11 by carboxyl esterases (CEs) or through cytochrome P-450 3A-mediated oxidation to 7-ethyl-10-[4-(1-piperidino)-1-amino] carbonyloxycamptothecin (NPC) and a subsequent conversion by CE. In the liver, SN-38 is glucuronidated (SN-38G) by UGT1A1, which also conjugates bilirubin. Fourteen patients were treated with 350 mg/m2 CPT-11, and we performed pharmacokinetic analysis during a 500-h collection period. The half-life and area under the plasma concentration-time curve of SN-38 were 47+/-7.9 h and 2.0+/-0.79 microM x h, respectively, both representing a 2-fold increase as compared with earlier reported estimates (A. Sparreboom et al, Clin. Cancer Res., 4: 2747-2754, 1998). As an explanation for this phenomenon, we noted substantial formation of SN-38 from CPT-11 and NPC by plasma CE, consistent with the low circulating levels of NPC observed. In addition, transport studies in Caco-2 monolayers indicated that nonglucuronidated SN-38 could cross the membrane from apical to basolateral, indicating the potential for recirculation processes that can prolong circulation times. Interestingly, individual levels of fecal beta-glucuronidase, which is known to mediate SN-38G hydrolysis, were not related to any of the SN-38 kinetic parameters (r = 0.09; P = 0.26), suggesting that interindividual variation in this enzyme is unimportant in explaining SN-38 pharmacokinetic variability. We have also found, in contrast to earlier data, that SN-38G/SN-38 plasma concentration ratios decrease over time from approximately 7 (up to 50 h) to approximately 1 (at 500 h). This decrease could be explained by the fact that glucuronidation of SN-38 and bilirubin is increasingly competitive at lower drug levels. In addition, no evidence was found for SN-38G transport through the Caco-2 cells. Our findings indicate that until now the circulation time of SN-38 has been underestimated. This is of crucial importance to our understanding of the clinical action of CPT-11 and for future pharmacokinetic/pharmacodynamic relationships. http://repub.eur.nl/res/pub/9074/ 1999-04-01T00:00:00Z We have determined the in vitro and in vivo cellular distribution of the antineoplastic agent paclitaxel (Taxol) in human blood and the influence of Cremophor EL (CrEL), the vehicle used for i.v. drug administration. In the absence of CrEL, the blood:plasma concentration ratio was 1.07+/-0.004 (mean+/-SD). The addition of CrEL at concentrations corresponding to peak plasma levels achieved after the administration of paclitaxel (175 mg/m2 i.v. over a 3-h period; ie., 0.50%) resulted in a significant decrease in the concentration ratio (0.690+/-0.005; P < 0.05). Kinetic experiments revealed that this effect was caused by reduced erythrocyte uptake of paclitaxel by polyoxyethyleneglycerol triricinoleate, the major compound present in CrEL. Using equilibrium dialysis, it was shown that the affinity of paclitaxel for tested matrices was (in decreasing order) CrEL > plasma > human serum albumin, with CrEL present at or above the critical micellar concentration (approximately 0.01%). Our findings in the present study demonstrate a profound alteration of paclitaxel accumulation in erythrocytes caused by a trapping of the compound in CrEL micelles, thereby reducing the free drug fraction available for cellular partitioning. It is proposed that the nonlinearity of paclitaxel plasma disposition in patients reported previously should be reevaluated prospectively by measuring the free drug fractions and whole blood:plasma concentration ratios. http://repub.eur.nl/res/pub/9158/ 1999-01-01T00:00:00Z In this study, 11 patients with solid tumors were randomized to receive irinotecan (CPT-11; 200 mg/m2) as a 90-min i.v. infusion, immediately followed by cisplatin (CDDP; 80 mg/m2) as a 3-h i.v. infusion in the first course and the reversed sequence in the second course or vice versa. No significant differences in any toxicity were observed between the treatment schedules (decrease in absolute neutrophil count, 74.7 +/- 18.3 versus 80.3 +/- 18.0%; P = 0.41). CPT-11 lactone clearance was similar to single agent data and not significantly different between study courses (60.4 +/- 17.1 versus 65.5 +/- 16.3 liter/h/m2; P = 0.66). The kinetic profiles of the major CPT-11 metabolites SN-38, SN-38 glucuronide, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidinolcarbonyloxycamptothecine (APC), and 7-ethyl-10-[4-N-(1-piperidino)-1-amino]carbonyloxycamptothecine (NPC) were also sequence independent (P > or = 0.20). In addition, CPT-11 had no influence on the clearance of nonprotein-bound CDDP (40.8 +/- 16.7 versus 50.3 +/- 18.6 liter/h/m2; P = 0.08) and the platinum DNA-adduct formation in peripheral leukocytes in either sequence (1.94 +/- 2.20 versus 2.42 +/- 1.62 pg Pt/microg DNA; P = 0.41). These data indicate that the toxicity of the combination CPT-11 and CDDP is schedule independent and that there is no mutual pharmacokinetic interaction. http://repub.eur.nl/res/pub/9184/ 1999-01-01T00:00:00Z In the present work, we studied the pharmacokinetics and metabolic disposition of [G-(3)H]paclitaxel in a female patient with recurrent ovarian cancer and severe renal impairment (creatinine clearance: approximately 20 ml/min) due to chronic hypertension and prior cisplatin treatment. During six 3-weekly courses of paclitaxel at a dose level of 157.5 mg/m(2) (viz. a 10% dose reduction), the renal function remained stable. Pharmacokinetic evaluation revealed a reproducible and surprisingly high paclitaxel area under the plasma concentration-time curve of 26.0 +/- 1.11 microM.h (mean +/- S.D.; n = 6; c.v. = 4.29%), and a terminal disposition half-life of approximately 29 h. Both parameters are substantially increased ( approximately 1.5-fold) when compared with kinetic data obtained from patients with normal renal function. The cumulative urinary excretion of the parent drug was consistently low and averaged 1.58 +/- 0.417% (+/- S.D.) of the dose. Total fecal excretion (measured in one course) was 52.9% of the delivered radioactivity, and mainly comprised known mono- and dihydroxylated metabolites, with unchanged paclitaxel accounting for only 6.18%. The plasma area under the plasma concentration-time curve of the paclitaxel vehicle Cremophor EL, which can profoundly alter the kinetics of paclitaxel, was 114.9 +/- 5.39 microl.h/ml, and not different from historic data in patients with normal or mild renal dysfunction. Urinary excretion of Cremophor EL was less than 0.1% of the total amount administered. These data indicate that the substantial increase in systemic exposure of the patient to paclitaxel relates to decreased renal metabolism and/or urinary elimination of polar radioactive species, most likely lacking an intact taxane ring fragment.