The co-solvent Cremophor EL limits absorption of orally administered paclitaxel in cancer patients.

The purpose of this study was to investigate the effect of the co-solvents Cremophor EL and polysorbate 80 on the absorption of orally administered paclitaxel. 6 patients received in a randomized setting, one week apart oral paclitaxel 60 mg m(-2) dissolved in polysorbate 80 or Cremophor EL. For 3 patients the amount of Cremophor EL was 5 ml m(-2), for the other three 15 ml m(-2). Prior to paclitaxel administration patients received 15 mg kg(-1) oral cyclosporin A to enhance the oral absorption of the drug. Paclitaxel formulated in polysorbate 80 resulted in a significant increase in the maximal concentration (C(max)) and area under the concentration-time curve (AUC) of paclitaxel in comparison with the Cremophor EL formulations (P = 0.046 for both parameters). When formulated in Cremophor EL 15 ml m(-2), paclitaxel C(max) and AUC values were 0.10 +/- 0.06 microM and 1.29 +/- 0.99 microM h(-1), respectively, whereas these values were 0.31 +/- 0.06 microM and 2.61 +/- 1.54 microM h(-1), respectively, when formulated in polysorbate 80. Faecal data revealed a decrease in excretion of unchanged paclitaxel for the polysorbate 80 formulation compared to the Cremophor EL formulations. The amount of paclitaxel excreted in faeces was significantly correlated with the amount of Cremophor EL excreted in faeces (P = 0.019). When formulated in Cremophor EL 15 ml m(-2), paclitaxel excretion in faeces was 38.8 +/- 13.0% of the administered dose, whereas this value was 18.3 +/-15.5% for the polysorbate 80 formulation. The results show that the co-solvent Cremophor EL is an important factor limiting the absorption of orally administered paclitaxel from the intestinal lumen. They highlight the need for designing a better drug formulation in order to increase the usefulness of the oral route of paclitaxel

A phase I and pharmacokinetic study of bi-daily dosing of oral paclitaxel in combination with cyclosporin A.

PURPOSE: To investigate dose escalation of bi-daily (b.i.d.) oral paclitaxel in combination with cyclosporin A in order to improve and prolong the systemic exposure to paclitaxel and to explore the maximum tolerated dose and dose limiting toxicity (DLT) of this combination. PATIENTS AND METHODS: A total of 15 patients received during course 1 two doses of oral paclitaxel (2 x 60, 2 x 90, 2 x 120, or 2 x 160 mg/m2) 7 h apart in combination with 15 mg/kg of cyclosporin A, co-administered to enhance the absorption of paclitaxel. During subsequent courses, patients received 3-weekly intravenous paclitaxel at a dose of 175 mg/m2 as a 3-h infusion. RESULTS: Toxicities observed following b.i.d. dosing of oral paclitaxel were generally mild and included toxicities common to paclitaxel administration and mild gastrointestinal toxicities such as nausea, vomiting, and diarrhea, which occurred more often at the higher dose levels. Dose escalation of b.i.d. oral paclitaxel from 2 x 60 to 2 x 160 mg/m2 did not result in a significant increase in the area under the plasma concentration-time curve (AUC) of paclitaxel. The AUC after doses of 2 x 60, 90, 120, and 160 mg/m2 were 3.77 +/- 2.70, 4.57 +/- 2.43, 3.62 +/- 1.58, and 8.58 +/- 7.87 microM.h, respectively. The AUC achieved after intravenous administration of paclitaxel 175 mg/m2 was 17.95 +/- 3.94 microM.h. CONCLUSION: Dose increment of paclitaxel did not result in a significant additional increase in the AUC values of the drug. Dose escalation of the b.i.d. dosing regimen was therefore not continued up to DLT. As b.i.d. dosing appeared to result in higher AUC values compared with single-dose administration (data which we have published previously), we recommend b.i.d. dosing of oral paclitaxel for future studies. Although pharmacokinetic data are difficult to interpret, due to the limited number of patients at each dose level and the large interpatient variability, we recommend the dose level of 2 x 90 mg/m2 for further investigation, as this dose level showed the highest systemic exposure to paclitaxel combined with good safety.

Phase I clinical and pharmacokinetic study of PNU166945, a novel water-soluble polymer-conjugated prodrug of paclitaxel.

Intravenous administration of paclitaxel is hindered by poor water solubility of the drug. Currently, paclitaxel is dissolved in a mixture of ethanol and Cremophor EL; however, this formulation (Taxol) is associated with significant side effects, which are considered to be related to the pharmaceutical vehicle. A new polymer-conjugated derivative of paclitaxel, PNU166945, was investigated in a dose-finding phase I study to document toxicity and pharmacokinetics. A clinical phase I study was initiated in patients with refractory solid tumors. PNU16645 was administered as a 1-h infusion every 3 weeks at a starting dose of 80 mg/m(2), as paclitaxel equivalents. Pharmacokinetics of polymer-bound and released paclitaxel were determined during the first course. Twelve patients in total were enrolled in the study. The highest dose level was 196 mg/m(2), at which we did not observe any dose-limiting toxicities. Hematologic toxicity of PNU166945 was mild and dose independent. One patient developed a grade 3 neurotoxicity. A partial response was observed in one patient with advanced breast cancer. PNU166945 displayed a linear pharmacokinetic behavior for the bound fraction as well as for released paclitaxel. The study was discontinued prematurely due to severe neurotoxicity observed in additional rat studies. The presented phase I study with PNU166945, a water-soluble polymeric drug conjugate of paclitaxel, shows an alteration in pharmacokinetic behavior when paclitaxel is administered as a polymer-bound drug. Consequently, the safety profile may differ significantly from standard paclitaxel.

The effect of different doses of cyclosporin A on the systemic exposure of orally administered paclitaxel.

The objective of this study was to define the minimally effective dose of cyclosporin A (CsA) that would result in a maximal increase of the systemic exposure to oral paclitaxel. Six evaluable patients participated in this randomized cross-over study in which they received at two occasions two doses of 90 mg/m(2) oral paclitaxel 7 h apart in combination with 10 or 5 mg/kg CsA. Dose reduction of CsA from 10 to 5 mg/kg resulted in a statistically significant decrease in the area under the plasma concentration-time curve (AUC) and time above the threshold concentrations of 0.1 microM (T>0.1 microM) of oral paclitaxel. The mean (+/-SD) AUC and T>0.1 microM values of oral paclitaxel with CsA 10 mg/kg were 4.29+/-0.88 microM x h and 12.0+/-2.1 h, respectively. With CsA 5 mg/kg these values were 2.75+/-0.63 microM x h and 7.0+/-2.1 h, respectively (p=0.028 for both parameters). In conclusion, dose reduction of CsA from 10 to 5 mg/kg resulted in a significant decrease in the AUC and T>0.1 microM values of oral paclitaxel. Because CsA 10 mg/kg resulted in similar paclitaxel AUC and T>0.1 microM values compared to CsA 15 mg/kg (data which we have published previously), the minimally effective dose of CsA is determined at 10 mg/kg.

Coadministration of cyclosporine strongly enhances the oral bioavailability of docetaxel.

PURPOSE: Oral bioavailability of docetaxel is very low, which is, at least in part, due to its affinity for the intestinal drug efflux pump P-glycoprotein (P-gp). In addition, metabolism of docetaxel by cytochrome P450 (CYP) 3A4 in gut and liver may also contribute. The purpose of this study was to enhance the systemic exposure to oral docetaxel on coadministration of cyclosporine (CsA), an efficacious inhibitor of P-gp and substrate for CYP 3A4. PATIENTS AND METHODS: A proof-of-concept study was carried out in 14 patients with solid tumors. Patients received one course of oral docetaxel 75 mg/m(2) with or without a single oral dose of CsA 15 mg/kg. CsA preceded oral docetaxel by 30 minutes. During subsequent courses, patients received intravenous (IV) docetaxel 100 mg/m(2). RESULTS: The mean (+/- SD) area under the concentration-time curve (AUC) in patients who received oral docetaxel 75 mg/m(2) without CsA was 0.37 +/- 0.33 mg.h/L and 2.71 +/- 1.81 mg.h/L for the same oral docetaxel dose with CsA. The mean AUC of IV docetaxel 100 mg/m(2) was 4.41 +/- 2.10 mg.h/L. The absolute bioavailability of oral docetaxel was 8% +/- 6% without and 90% +/- 44% with CsA. The oral combination of docetaxel and CsA was well tolerated. CONCLUSION: Coadministration of oral CsA strongly enhanced the oral bioavailability of docetaxel. Interpatient variability in the systemic exposure after oral drug administration was of the same order as after IV administration. These data are promising and form the basis for the further development of a clinically useful oral formulation of docetaxel.

Co-administration of GF120918 significantly increases the systemic exposure to oral paclitaxel in cancer patients.

Oral bioavailability of paclitaxel is very low, which is due to efficient transport of the drug by the intestinal drug efflux pump P-glycoprotein (P-gp). We have recently demonstrated that the oral bioavailability of paclitaxel can be increased at least 7-fold by co-administration of the P-gp blocker cyclosporin A (CsA). Now we tested the potent alternative orally applicable non-immunosuppressive P-gp blocker GF120918. Six patients received one course of oral paclitaxel of 120 mg/m(2)in combination with 1000 mg oral GF120918 (GG918, GW0918). Patients received intravenous (i.v.) paclitaxel 175 mg/m(2)as a 3-hour infusion during subsequent courses. The mean area under the plasma concentration-time curve (AUC) of paclitaxel after oral drug administration in combination with GF120918 was 3.27 +/- 1.67 microM x h. In our previously performed study of 120 mg/m(2)oral paclitaxel in combination with CsA the mean AUC of paclitaxel was 2.55 +/- 2.29 microM x h. After i.v. administration of paclitaxel the mean AUC was 15.92( )+/- 2.46 microM x h. The oral combination of paclitaxel with GF120918 was well tolerated. The increase in systemic exposure to paclitaxel in combination with GF120918 is of the same magnitude as in combination with CsA. GF120918 is a good and safe alternative for CsA and may enable chronic oral therapy with paclitaxel.

Phase I and pharmacokinetic study of oral paclitaxel.

PURPOSE: To investigate dose escalation of oral paclitaxel in combination with dose increment and scheduling of cyclosporine (CsA) to improve the systemic exposure to paclitaxel and to explore the maximum-tolerated dose (MTD) and dose-limiting toxicity (DLT). PATIENTS AND METHODS: A total of 53 patients received, on one occasion, oral paclitaxel in combination with CsA, coadministered to enhance the absorption of paclitaxel, and, on another occasion, intravenous paclitaxel at a dose of 175 mg/m(2) as a 3-hour infusion. RESULTS: The main toxicities observed after oral intake of paclitaxel were acute nausea and vomiting, which reached DLT at the dose level of 360 mg/m(2). Dose escalation of oral paclitaxel from 60 to 300 mg/m(2) resulted in significant but less than proportional increases in the plasma area under the concentration-time curve (AUC) of paclitaxel. The mean AUC values +/- SD after 60, 180, and 300 mg/m(2) of oral paclitaxel were 1.65 +/- 0.93, 3.33 +/- 2.39, and 3.46 +/- 1.37 micromol/L.h, respectively. Dose increment and scheduling of CsA did not result in a further increase in the AUC of paclitaxel. The AUC of intravenous paclitaxel was 15.39 +/- 3.26 micromol/L.h. CONCLUSION: The MTD of oral paclitaxel was 300 mg/m(2). However, because the pharmacokinetic data of oral paclitaxel, in particular at the highest doses applied, revealed nonlinear pharmacokinetics with only a moderate further increase of the AUC with doses up to 300 mg/m(2), the oral paclitaxel dose of 180 mg/m(2) in combination with 15 mg/kg oral CsA is considered most appropriate for further investigation. The safety of the oral combination at this dose level was good.

Metabolism and excretion of paclitaxel after oral administration in combination with cyclosporin A and after i.v. administration.

The objective of this study was to compare the quantitative excretion of paclitaxel and metabolites after i.v. and oral drug administration. Four patients received 300 mg/m2 paclitaxel orally 30 min after 15 mg/kg oral cyclosporin A, co-administered to enhance the uptake of paclitaxel. Three weeks later these and three other patients received 175 mg/m2 paclitaxel by i.v. infusion. Blood samples, urine and feces were collected up to 48-96 h after administration, and analyzed for paclitaxel and metabolites. The area under the plasma concentration-time curve of paclitaxel after i.v. administration (175 mg/m2) was 16.2 +/- 1.7 microM x h and after oral administration (300 mg/m2) 3.8 +/- 1.5 microM x h. Following i.v. infusion of paclitaxel, total fecal excretion was 56 +/- 25%, with the metabolite 6alpha-hydroxypaclitaxel being the main excretory product (37 +/- 18%). After oral administration of paclitaxel, total fecal excretion was 76 +/- 21%, of which paclitaxel accounted for 61 +/- 14%. In conclusion, after i.v. administration of paclitaxel, excretion occurs mainly in the feces with the metabolites as the major excretory products. Orally administered paclitaxel is also mainly excreted in feces but with the parent drug in highest amounts. We assume that this high amount of parent drug is due to incomplete absorption of orally administered paclitaxel from the gastrointestinal tract.

Coadministration of oral cyclosporin A enables oral therapy with paclitaxel.

i.v. paclitaxel is inconvenient and associated with significant and poorly predictable side effects largely due to the pharmaceutical vehicle Cremophor EL. Oral administration may be attractive because it may circumvent the use of Cremophor EL. However, paclitaxel, as well as many other commonly applied drugs, has poor bioavailability caused by high affinity for the mdrl P-glycoprotein drug efflux pump, which is abundantly present in the gastrointestinal tract. Consequently, inhibition of P-glycoprotein by oral cyclosporin A (CsA) should increase systemic exposure of oral paclitaxel to therapeutic levels. A proof-of-concept study was carried out in 14 patients with solid tumors. Patients received one course of oral paclitaxel of 60 mg/m2 with or without 15 mg/kg CsA and with i.v. paclitaxel in subsequent courses. The pharmacokinetics of paclitaxel and its major metabolites were determined during the first two courses. In addition, levels of CsA, Cremophor EL, and ethanol were measured. Bioavailability of oral paclitaxel in combination with CsA was 8-fold higher than after oral paclitaxel alone (P<0.001). Therapeutic concentrations were achieved on average during 7.4 h, which is comparable with an equivalent i.v. dose. The oral combination was well tolerated and did not induce gastrointestinal toxicity or myelosuppression. Cremophor EL plasma levels after oral drug administration were undetectable. In conclusion, coadministration of oral CsA increased the systemic exposure of oral paclitaxel from negligible to therapeutic levels. The combination enables treatment with oral paclitaxel. Undetectable Cremophor EL levels after oral administration may have a very beneficial influence on the safety of the treatment with oral paclitaxel.

Pharmacokinetics of paclitaxel administered as a 3-hour or 96-hour infusion.

AIM: To investigate the pharmacokinetics of paclitaxel (Paxene) administered to patients with advanced breast or ovarian cancer and to document safety and anti-tumour activity in this study population. PATIENTS AND METHODS: Patients with advanced breast or ovarian cancer were accrued to two clinical studies. Paclitaxel (Paxene) was administered as a 3-h 175 mg m-2 or as a 96-h 140 mg m-2(105 mg m-2 in the presence of liver metastases) infusion. Patients not responding to the 3-h schedule were permitted to cross-over to the 96-h schedule. The data were compared to those of five patients who were previously treated with paclitaxel administered as Taxol (140 mg m-296-h infusion) at our Institute. RESULTS: Fourteen patients with breast cancer and five ovarian cancer patients were entered into this study. Seven patients received the 3-h regimen, and 12 were assigned to the 96-h schedule. Five patients originally treated with the 3-h schedule, crossed over to the 96-h arm. For the 3-h 175 mg m-2 dose, the area under the plasma concentration vs time curve (AUC) was (mean+/-SD) 16.9+/-4.8 h x micromol x l-1, whereas the AUCs were 5.5+/-1.2 and 4.3+/-0.9 h x micromol x l-1 for the 96-h 140 mg m-2 and 105 mg m-2 doses, respectively. The clearance of paclitaxel was independent of the dose in the 96-h group, indicating linear pharmacokinetics. Pharmacokinetics of Paxene (96-h 140 mg m-2) were not significantly different from the kinetics after Taxol (96-h 140 mg m-2) administration.

Phase I and pharmacologic study of weekly doxorubicin and 1 h infusional paclitaxel in patients with advanced breast cancer.

Doxorubicin and paclitaxel both display strong antitumor activity in the treatment of breast cancer. The optimal schedule of this combination, however, remains undefined. In this phase I and pharmacologic study, we administered weekly 12 mg/m2 doxorubicin as a bolus infusion immediately followed by a 1 h 80 mg/m2 paclitaxel infusion to patients with metastatic breast cancer. A total of 119 weekly courses were delivered to seven patients. Grade IV neutropenia was observed in two patients at the first dose level, thus already defining the maximum tolerated dose. Pronounced non-hematologic toxicities were mild neuropathy (grade I: 39%) and stomatitis (grade I: 19%, grade II: 8%). No signs of cardiac toxicity were observed with this dose schedule. Three partial responses were achieved in this group of heavily pretreated patients. The pharmacokinetics of paclitaxel, doxorubicin and Cremophor EL with this schedule were analyzed. Overall, the schedule was well tolerated and combined with its preliminary response rate justifies further evaluation in phase II studies.

Determination of 3'-amino-3'-deoxythymidine, a cytotoxic metabolite of 3'-azido-3'-deoxythymidine, in human plasma by ion-pair high-performance liquid chromatography.

A sensitive high-performance liquid chromatographic assay has been developed to determine the levels of 3'-amino-3'-deoxythymidine (AMT), a cytotoxic metabolite of 3'-azido-3'-deoxy-thymidine (AZT, zidovudine), in human plasma. The sample pretreatment involved solid-phase extraction using cation-exchange extraction columns. Chromatography was carried out on a C8 column, using a mobile phase of methanol-0.01 M ammonium acetate (pH 5)-0.25 M sodium dioctylsulfosuccinate (60:40:4, v/v/v) and ultraviolet detection at 265 nm. The method has been validated, and stability tests under various conditions have been performed. The lower limit of quantitation is 5 ng/ml (using 500-microliters human plasma samples). The bioanalytical assay has been used for the determination of AMT in patients with AIDS who used AZT.