M. T. Huizing

Pharmacokinetics of paclitaxel and metabolites in a randomized comparative study in platinum-pretreated ovarian cancer patients.

PURPOSE To investigate the pharmacokinetics and pharmacodynamics of paclitaxel in a randomized comparative study with four different treatment arms in patients with platinum-pretreated ovarian carcinoma. PATIENTS AND METHODS Eighteen patients were entered onto this study in which paclitaxel was administered at a high dose of 175 mg/m2 versus a low dose of 135 mg/m2 on a 3- or 24-hour infusion schedule. A solid-phase extraction technique for sample pretreatment followed by a reverse-phase high-performance liquid chromatographic (HPLC) assay was used for analysis of plasma. RESULTS Grade 3 neutropenia occurred in all four treatment arms. However, it was more severe on the 24-hour infusion schedule. Paclitaxel concentrations as low as 0.012 mumol/L were measured with the HPLC assay. With this low quantitation threshold, we found the plasma disappearance of paclitaxel to be triphasic, with half-lives t1/2(alpha), t1/2(beta), and t1/2(gamma) mean values for the different treatment arms of 0.19 hours (range, 0.01 to 0.4), 1.9 hours (range, 0.5 to 2.8), and 20.7 hours (range, 4 to 65), respectively. Eleven possible metabolites were found, of which three were identified as taxanes by on-line HPLC-photodiode array (PDA) detection. Investigation of pharmacodynamics shows no clear relationship between the pharmacokinetic parameters area under the plasma concentration time curve (AUC), area under the plasma concentration moment curve (AUMC), maximal plasma concentration (Cmax), clearance, and toxicity. However, a relationship was found between the duration of plasma concentrations above a threshold of 0.1 mumol/L with absolute neutrophil count (ANC) and white blood cell count (WBC). CONCLUSION Paclitaxel is metabolized, and putative metabolic products can be found in plasma of patients treated with the drug. Our results indicate that myelosuppression can be predicted by the measurement of the duration of plasma concentrations above the threshold of 0.1 mumol/L.

Taxanes: A New Class of Antitumor Agents

Taxanes belong to a new group of antineoplastic agents with a novel mechanism of action for a cytotoxic drug. They promote microtubule assembly and stabilize the microtubules. Paclitaxel, the first agent in this group to become available, was isolated from the Pacific yew, Taxus brevifolia, in 1971. In preclinical and clinical studies, paclitaxel and its semisynthetic analog docetaxel exhibit significant antitumor activity. This review deals with the physicochemical properties, pharmacology, and results of preclinical and clinical trials of the taxanes.

Cremophor EL causes (pseudo-) non-linear pharmacokinetics of paclitaxel in patients.

SummaryThe non-linear plasma pharmacokinetics of paclitaxel in patients has been well established, however, the exact underlying mechanism remains to be elucidated. We have previously shown that the non-linear plasma pharmacokinetics of paclitaxel in mice results from Cremophor EL. To investigate whether Cremophor EL also plays a role in the non-linear pharmacokinetics of paclitaxel in patients, we have established its pharmacokinetics in patients receiving paclitaxel by 3-, 24- or 96-h intravenous infusion. The pharmacokinetics of Cremophor EL itself was non-linear as the clearance (Cl) in the 3-h schedules was significantly lower than when using the longer 24- or 96-h infusions (Cl175–3 h = 42.8 ± 24.9 ml h–1 m–2; Cl175–24 h = 79.7 ± 24.3; P = 0.035 and Cl135–3 h = 44.1 ± 21.8 ml h–1 m–1; Cl140–96 h = 211.8 ± 32.0; P < 0.001). Consequently, the maximum plasma levels were much higher (0.62%) in the 3-h infusions than when using longer infusion durations. By using an in vitro equilibrium assay and determination in plasma ultrafiltrate we have established that the fraction of unbound paclitaxel in plasma is inversely related with the Cremophor EL level. Despite its relatively low molecular weight, no Cremophor EL was found in the ultrafiltrate fraction. Our results strongly suggest that entrapment of paclitaxel in plasma by Cremophor EL, probably by inclusion in micelles, is the cause of the apparent nonlinear plasma pharmacokinetics of paclitaxel. This mechanism of a (pseudo-)non-linearity contrasts previous postulations about saturable distribution and elimination kinetics and means that we must re-evaluate previous assumptions on pharmacokinetics–pharmacodynamics relationships.

Pharmacokinetics of paclitaxel and carboplatin in a dose-escalating and dose-sequencing study in patients with non-small-cell lung cancer. The European Cancer Centre.

PURPOSE To investigate the pharmacokinetics and pharmacodynamics of paclitaxel (P) and carboplatin (C) in a sequence-finding and dose-escalating study in untreated non-small-cell lung cancer (NSCLC) patients. PATIENTS AND METHODS Fifty-five chemotherapy-naive patients with NSCLC were entered onto the pharmacokinetic part of a large phase I trial in which P was administered as a 3-hour infusion at dosages of 100 to 250 mg/m2, and C over 30 minutes at dosages of 300 to 400 mg/m2. Patients were randomized for the sequence of administration, first C followed by P or vice versa. Each patient received the alternate sequence during the second and subsequent courses. RESULTS The most important hematologic toxicity encountered-was neutropenia. Hematologic toxicity was not dependent on the sequence in which P and C were administered, but there was cumulative neutropenia. Nonhematologic toxicities consisted mainly of vomiting, myalgia, and arthralgia. No sequence-dependent pharmacokinetic interactions for the P area under the concentration-time curve (P-AUC), maximal plasma concentration (P-Cmax), or time above a threshold concentration of 0.1 mumol/L (P-T > or = 0.1 mumol/L) were observed. However, there was a significant difference for the metabolite 6 alpha-hydroxypaclitaxel AUC (6OHP-AUC). Higher 6OHP-AUCs were observed when C was administered before P. The mean plasma ultrafiltrate AUC of C (CpUF-AUC) at the dosage of 300 mg/m2 for the sequence C-->P was 3.52 mg/mL.min (range, 1.94 to 5.83) and 3.62 mg/mL.min for the sequence P-->C (range, 1.91 to 5.01), which is not significantly different (P = .55). Of 45 assessable patients, there were five major responders (three complete responders and two partial responders). Four of five responses occurred at dosages above dose level 4 (P 175 mg/m2 + C 300 mg/m2). The median survival duration was best correlated with the P dose (4.8 months for doses < 175 mg/m2 v 7.9 months for doses > or = 175 mg/m2, P = .07; P-T > or = 0.1 mumol/L, 4.8 months for < 15 hours v 8.2 months for > or = 15 hours, P = .06). CONCLUSION There was no pharmacokinetic-sequence interaction between C and P in this study. A clear dose-response relation with respect to response rate and survival was observed. The pharmacokinetic parameter P-T > or = 0.1 mumol/L was related to improved survival in this study.

High-performance liquid chromatographic procedure for the quantitative determination of paclitaxel (Taxol) in human plasma.

An isocratic high-performance liquid chromatographic method has been developed and validated for the quantitative determination of paclitaxel (Taxol), a novel antimitotic, anticancer agent, in human plasma. The analysis required 0.5 ml of plasma, and was accomplished by detection of the UV absorbance of paclitaxel at 227 nm following extraction and concentration. The method involved extraction of paclitaxel from plasma, buffered with 0.5 ml of 0.2 M ammonium acetate (pH 5.0), onto 1-ml cyano Bond Elut columns. The eluent was evaporated under nitrogen and low heat, and reconstituted with the mobile phase, acetonitrile-methanol-water (4:1:5, v/v/v) containing 0.01 M ammonium acetate (pH 5.0). The samples were chromatographed on a reversed-phase octyl 5 microns column. The retention time of paclitaxel was 10 min. The validated quantitation range of the method was 10-1000 ng/ml (0.012-1.17 microM) of paclitaxel in plasma. Standard curve correlation coefficients of 0.995 or greater were obtained during validation experiments and analysis of clinical study samples. The observed recovery for paclitaxel was 83%. Epitaxol, a biologically active stereoisomer, and baccatin III, a degradation product, were also chromatographically separated from taxol by this assay. The method was applied to samples from a clinical study of paclitaxel in cancer patients, providing a pharmacokinetic profiling of paclitaxel.

Phase I and pharmacologic study of the combination paclitaxel and carboplatin as first-line chemotherapy in stage III and IV ovarian cancer.

PURPOSE To determine the maximum-tolerated dose for the combination paclitaxel and carboplatin administered every 4 weeks and to gain more insight into the pharmacokinetics and pharmacodynamics of this combination in previously untreated ovarian cancer patients. PATIENTS AND METHODS Thirty-five chemotherapy-naive patients with suboptimally debulked stage III (tumor masses > 3 cm) and stage IV ovarian cancer were entered onto this phase I trial in which paclitaxel was administered as a 3-hour intravenous (IV) infusion at dosages of 125 to 225 mg/m2 immediately followed by carboplatin over 30 minutes at dosages of 300 to 600 mg/m2. A total of six courses was planned, followed by a second-look laparoscopy/laparotomy. Patients with a response and/or minimal residual disease at second-look laparoscopy received three additional courses. Twenty-six patients participated in the pharmacokinetic part of the study. RESULTS The most important hematologic toxicity encountered was neutropenia. Neutropenia was more pronounced for the higher dose levels (DLs) and was cumulative. Thrombocytopenia was mild in the first eight DLs, but increased during the treatment courses. Nonhematologic toxicities consisted mainly of vomiting, neuropathy, fatigue, rash, pruritus, myalgia, and arthralgia. Dose-limiting toxicities (DLTs) in this trial were neutropenic fever, thrombocytopenia that required platelet transfusions, and cumulative neuropathy. Of 33 patients assessable for response, 26 major responders (78%, 20 complete response [CR] and six partial response [PR]) were documented. The maximal concentration (Cmax) of paclitaxel and the area under the concentration-time curve (AUC) were not different from the historical data for paclitaxel as a single agent. Retrospective analysis using a modified Calvert formula showed that the measured carboplatin AUCs in plasma ultrafiltrate (pUF) were 30% +/- 3.4% less than the calculated carboplatin AUC. Neutropenia was more pronounced than could be expected on the basis of the historical times above a threshold concentration greater than 0.1 mumol/L (T > or = 0.1 mumol/L) or 0.05 mumol/L (T > or = 0.05 mumol/L), and thrombocytopenia was less than could be expected from historical sigmoidal Emax models. CONCLUSION The combination of paclitaxel 200 mg/ m2 and carboplatin 550 mg/m2 every 4 weeks is a well-tolerated treatment modality. The paclitaxel-carboplatin combination is highly active in stage III (bulky) and stage IV ovarian cancer. No indications for a pharmacokinetic drug-drug interaction between carboplatin and paclitaxel were found.

Pharmacokinetics and metabolism of docetaxel administered as a 1-h intravenous infusion.

Abstract Docetaxel, a taxane antitumor agent, was administered to 24 patients by a 1-h intravenous infusion at a dose level of 100 mg/m2 with pharmacokinetic monitoring. The plasma concentration-versus-time data were fitted with a three-compartment model. The mean area under the curve (AUC) for docetaxel was 3.1 ± 0.9 h · mg/l and the clearance was 34.8 ± 9.3 l/h per m2. There was considerable interpatient pharmacokinetic variability. In 33% of the patient population, metabolites were detected in plasma samples collected 5–30 min after the end of the infusion. The cyclized oxazolidinedione metabolite M4 was most frequently present and was detected in 8 out of 24 patients with maximal concentrations between 0.022 and 0.23 mg/l. Logistic regression analysis was performed to predict M4 docetaxel metabolism. In the final model, alanine aminotransferase and alkaline phosphatase levels were the strongest predictors. No relationship was found between M4 metabolism and percentage decrease in neutrophil count in this study. Three patients with high M4 concentrations in plasma during course 1 suffered from most pronounced fluid retention (grade 2–3) after two to five courses.

Isolation, purification, and biological activity of mono- and dihydroxylated paclitaxel metabolites from human feces

Three metabolites of the cytotoxic drug paclitaxel (Taxol) were isolated and purified from the feces of cancer patients receiving the agent as an intravenous infusion. The procedures involved sample homogenization in water followed by liquid-liquid extraction with diethyl ether and high-performance liquid chromatography (HPLC). Approximately 1–3.5 mg of each metabolite was obtained from 100 g of feces. As judged from the chromatographic traces of analytical HPLC with ultraviolet (UV) detection at 227 nm, the purity of each compound was >97%. On-line photodiode-array detection demonstrated that the UV spectrum of the isolated compounds closely resembles that of the parent drug. Mass spectrometry provided evidence that these metabolites are mono- and dihydroxy-substituted derivatives, namely, 6α-hydroxypaclitaxel, 3′-p-hydroxypaclitaxel, and 6α,3′-p-dihydroxypaclitaxel. The two 6α-hydroxy-substituted metabolites were shown to have lost their cytotoxicity in in vitro clonogenic assays using the A2780 human ovarian carcinoma and the CC531 rat colon-carcinoma tumor cell lines. In addition, the metabolites showed reduced myelotoxic effects as compared with paclitaxel in an in vitro hemopoietic progenitor toxicity assay. Our procedure for the isolation and purification of paclitaxel metabolites in milligram quantities should be useful for testing the biological activities of these compounds and for the preparation of calibration standards essential for pharmockinetics studies.

Hypersensitivity Reactions to the Taxanes Paclitaxel and Docetaxel

SummaryPaclitaxel and docetaxel are taxane derivatives with a significant antitumour activity. For both drugs, a high incidence of hypersensitivity reactions (HSRs) has been observed during the initial clinical development. However, current pretreatment regimens, consisting of corticosteroids and antihistamines, have led to a substantial decrease in major HSRs. In this study, we describe a case series of 9 out of a total of 415 patients from eight different taxane studies who received either paclitaxel or docetaxel and experienced severe HSRs, despite the use of premedication. Five of these 9 patients had allergies or atopy. We observed an increase in blood pressure during the HSR in 5 patients, whereas a decrease was anticipated. Retreatments, with additional corticosteroids, antihistamines and in some cases a lower infusion rate, were performed successfully in 7 patients. One of these patients was given, after two courses with HSR symptoms, sodium cromoglycate as prophylaxis, after which she received four successive courses without symptoms of HSR.In conclusion, premedication given before taxane infusions did not guarantee prevention of HSRs. We observed that these reactions did not resemble anaphylactic reactions in that there were unexpected increases in blood pressure. Retreatments were possible in most cases after appropriate measures were taken.

Determination of polyoxyethyleneglycerol triricinoleate 35 (Cremophor EL) in plasma by pre-column derivatization and reversed-phase high-performance liquid chromatography

A sensitive and selective reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of polyoxyethyleneglycerol triricinoleate 35 (Cremophor EL; CrEL), which requires only microvolumes (20 microliters) of plasma, has been developed and validated. The procedure is based on saponification of CrEL in alcoholic KOH, followed by extraction of the released fatty acid ricinoleic acid with chloroform and derivatization with 1-naphthylamine. Margaric acid was used as the internal standard. The products are separated using an HPLC system consisting of an analytical column packed with Spherisorb ODS-1 material and a mobile phase of methanol-acetonitrile-10 mM potassium phosphate buffer pH 7.0 (72:13:15, v/v). Detection was executed by UV absorption at 280 nm. The lower limit of quantitation and the lower limit of detection in plasma are 0.01 and 0.005% (v/v) of CrEL, respectively. The percentage deviation and precision of the procedure, over the validated concentration range of 0.01 to 1.0% (v/v) of CrEL in plasma, are < or = 8.0% and < or = 6.6%, respectively. Compared to the previously described bioassay, the presented HPLC method possesses superior sensitivity and reliability. Preliminary pharmacokinetic studies of CrEL in mice and patients receiving paclitaxel formulated in CrEL have demonstrated the applicability of the presented assay.