Pharmacokinetic Parameters Of Paclitaxel Research Articles

Pharmacokinetic Herb-Drug Interactions of Xiang-Sha-Liu-Jun-Zi-Tang and Paclitaxel in Male Sprague Dawley Rats and Its Influence on Enzyme Kinetics in Human Liver Microsomes.

Paclitaxel is a prescribed anticancer drug used to treat various cancers. It is a substrate of cytochrome P-450 (CYP-450) enzymes. Despite its efficacy, paclitaxel has severe side effects. Herbal medicines are commonly used to treat the side effects of chemotherapy. They can be administered before, during, and after chemotherapy. Xiang-Sha-Liu-Jun-Zi Tang (XSLJZT) is a herbal formula commonly used in breast cancer patients. The main purpose of this study was to assess the pharmacokinetic (PK) influence of XSLJZT on paclitaxel PK parameters, determine its effect on CYP-450 enzyme expression, and evaluate its effect on enzyme activity. Sprague Dawley rats were classified into pretreatment and co-treatment groups, where XSLJZT was pre-administered for 3, 5, and 7 days and co-administered 2 h before paclitaxel administration. The rat liver tissues and Hep-G2 cells were used to determine the effects of XSLJZT on CYP3A1/2 and CYP3A4 enzymes respectively. Western blot analysis was used to detect changes in the CYP3A1/2 and CYP3A4 enzymes expression. The influence of XSLJZT on enzyme activity was evaluated using human liver microsomes, and a liquid chromatography-tandem mass spectrometric system was developed to monitor paclitaxel levels in rat plasma. Results demonstrated that XSLJZT increased the area under the concentration versus time curve (AUC) for paclitaxel in pretreatment groups by 2-, 3-, and 4-fold after 3, 5, and 7 days, respectively. In contrast, no significant change in the AUC was observed in the co-treatment group. However, the half-life was prolonged in all groups from 17.11 min to a maximum of 37.56 min. XSLJZT inhibited CYP3A1/2 expression in the rat liver tissues and CYP3A4 enzymes in Hep-G2 cells in a time-dependent manner, with the highest inhibition observed after 7 days of pretreatment in rat liver tissues. In the enzyme kinetics study, XSLJZT inhibited enzyme activity in a competitive dose-dependent manner. In conclusion, there is a potential interaction between XSLJZT and paclitaxel at different co-treatment and pretreatment time points.

Intestinal P-glycoprotein inhibitors, benzoxanthone analogues.

The inhibitors of P-glycoprotein (P-gp) which limits an access of exogenous compounds in the luminal membrane of the intestine have been studied to enhance the intestinal P-gp-mediated absorption of anticancer drugs. Inhibition of the efflux pump by synthesized benzoxanthone derivatives was investigated in vitro and in vivo. MCF-7/ADR cell line was used for cytotoxicity assay and [3 H]-daunomycin (DNM) accumulation/efflux study. Eight benzoxanthone analogues were tested for their effects on DNM cytotoxicity. Among them, three analogues were selected for the accumulation/efflux and P-gp ATPase studies. Paclitaxel (PTX), a P-gp substrate anticancer drug, was orally administered to rats with/without compound 1 (8,10-bis(thiiran-2-ylmethoxy)-7H-benzo[c]xanthen-7-one). The pharmacokinetic parameters of PTX in the presence/absence of compound 1 were evaluated from the plasma concentration-time profiles. Compound 1 increased the DNA accumulation to 6.5-fold and decreased the DNM efflux to approximately 1/2 in the overexpressing P-gp cell line. Relative bioavailability (RB) of PTX in rats was significantly increased up to 3.2-fold by compound 1 (0.5 or 2 mg/kg). Benzoxanthone analogue, compound 1 is strongly suggested to be a promising inhibitor of P-gp to improve an oral absorption of compounds for cancer therapy.

Effects of Adamantyl Derivatives on Pharmacokinetic Behavior of Paclitaxel in Rats.

Paclitaxel (PTX) is one of the most frequently used anticancer agent for treating refractory ovarian cancer, metastatic breast cancer and non-small cell lung cancer. However, its oral administration is impeded by very low bioavailability (<5%) due to the Pglycopprotein (P-gp) efflux pump effect. This study investigated in vitro and in vivo P-gp inhibitory effects of adamantyl derivatives AC-603 and AC-786 in rats. Two adamantyl derivatives tested in this study increased the cytotoxicity of daunomycin (DNM) in P-gp overexpressed cell line by inhibiting P-gp efflux function. Pharmacokinetics of PTX with orally co-administered P-gp inhibitors were assessed in rats to improve PTX absorption. The pharmacokinetic parameters of PTX were determined in rats after intravenous (2 mg/kg) or oral (25 mg/kg) administration in the presence or absence of verapamil (a positive control), AC-603 or AC-786 (0.5 mg/kg or 5 mg/kg). Compared to control group (PTX alone), experimental groups (PTX with AC-603 or AC-786) significantly increased the area under the plasma concentration-time curve of PTX following oral administration by 1.7–2.2 fold. The volume of distribution and total clearance of PTX were decreased, while other parameters were not significantly changed. In conclusion, co-administration of AC-603 or AC-786 enhanced the relative bioavailability of orally administered PTX as compared to control.

Fentanyl Enhances Hepatotoxicity of Paclitaxel via Inhibition of CYP3A4 and ABCB1 Transport Activity in Mice.

Fentanyl, a potent opioid analgesic that is used to treat cancer pain, is commonly administered with paclitaxel in advanced tumors. However, the effect of fentanyl on the hepatotoxicity of paclitaxel and its potential mechanism of action is not well studied. The purpose of this study was to investigate the effect of fentanyl on the hepatotoxicity of paclitaxel and its potential mechanisms of action. Pharmacokinetic parameters of paclitaxel were tested using reversed phase high-performance liquid chromatography (RP-HPLC). Aspartate transaminase (AST), alanine aminotransferase (ALT), and mouse liver histopathology were examined. Moreover, the cytotoxicity of anti-carcinogens was examined using 1-(4, 5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), and the intracellular accumulation of doxorubicin and rhodamine 123 was detected by flow cytometry. Furthermore, the expression of ABCB1 and the activity of ABCB1 ATPase and CYP3A4 were also examined. In this study, the co-administration of fentanyl and paclitaxel prolonged the half-life (t1/2) of paclitaxel from 1.455 hours to 2.344 hours and decreased the clearance (CL) from 10.997 ml/h to 7.014 ml/h in mice. Fentanyl significantly increased the levels of ALT in mice to 88.2 U/L, which is more than 2-fold higher than the level detected in the control group, and it increased the histological damage in mouse livers. Furthermore, fentanyl enhanced the cytotoxicity of anti-carcinogens that are ABCB1 substrates and increased the accumulation of doxorubicin and rhodamine 123. Additionally, fentanyl stimulated ABCB1 ATPase activity and inhibited CYP3A4 activity in the liver microsomes of mice. Our study indicates that the obvious hepatotoxicity during this co-administration was due to the inhibition of CYP3A4 activity and ABCB1 transport activity. These findings suggested that the accumulation-induced hepatotoxicity of paclitaxel when it is combined with fentanyl should be avoided.

Abstract 5493: Genome-wide study of carboplatin and paclitaxel disposition in ovarian cancer patients

Abstract Germline genetic variation can affect chemotherapeutic drug disposition, toxicity and efficacy. Identifying single nucleotide polymorphisms (SNPs) that influence chemotherapy disposition may help to personalize individual treatment. Compared to the traditional candidate gene approach, a genome-wide association study (GWAS) is unbiased but usually requires a large sample size. Since most cytotoxics have a short half-life and are given cyclically, multiple blood samples are therefore required to adequately define drug disposition and systemic exposure. This limits patient sample sizes in pharmacokinetic studies. The aim of this study was to identify SNPs that are associated with carboplatin and paclitaxel pharmacokinetic parameters using a GWAS approach in two small patient cohorts. Methods: Two independent pharmacokinetic cohorts were recruited in Australia (N = 61, both carboplatin and paclitaxel) and the Netherlands (N = 35, paclitaxel only). A total of 719,665 SNPs were genotyped using Illumina Human OmniExpress arrays. Linear regression was used to test the association between each SNP and the trait of interest, both unadjusted and adjusted for corresponding covariates using PLINK. We performed separate analysis within each population and then ran meta-analysis combining results from different populations weighted by sample sizes using METAL. Results: Carboplatin and paclitaxel disposition is a relative stable phenotype. The genomic control parameters in the test statistics for the adjusted carboplatin and paclitaxel analysis were 1.03 and 1.02 respectively, suggesting that there was little concern for population substructure or other artefacts. We identified highly significant SNPs in ABCC2 associated with carboplatin clearance (asymptotic p = 5.2 × 10−6, empirical p = 1.4 × 10−5 from 107 permutations) which are highly plausible pharmacogenomic markers given the known role of ABCC2 in carboplatin efflux. We also identified a novel SNP associated with paclitaxel disposition with genome wide significance in chromosome 1 (rs17130142, asymptotic p = 2.0 × 10−9, empirical p = 1.3× 10−7), in an intergenic region, neighboring PKN2. Conclusion: Although these findings requires a validation in a larger study, our work demonstrated that GWAS of chemotherapeutic drug disposition can be effective even when performed in a relative small sample number and can be adopted in drug development and treatment programs. Citation Format: Bo Gao, Yi Lu, Annemieke J.M. Nieuweboer, Hongmei Xu, Jonathan Beesley, Ingrid Boere, Anne-Joy M. de Graan, Peter de Bruijn, Howard Gurney, Catherine Kennedy, Yoke-Eng Chiew, Sharon E. Johnatty, Philip Beale, Michelle Harrison, Craig Luccarini, Alison M. Dunning, Ron H.J. Mathijssen, Paul Harnett, Rosemary L. Balleine, Georgia Chenevix-Trench, Stuart MacGregor, Anna deFazio. Genome-wide study of carboplatin and paclitaxel disposition in ovarian cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5493. doi:10.1158/1538-7445.AM2015-5493

Enhanced oral bioavailability and anti‐tumour effect of paclitaxel by 20(s)‐ginsenoside Rg3in vivo

The purpose of this study was to investigate the effect of paclitaxel in combination with 20(s)-ginsenoside Rg3 on its anti-tumour effect in nude mice. In the Caco-2 transport assay, the apparent permeability from the apical side to the basal side (P(app)) (A-B) and P(app) (B-A) of paclitaxel were measured when co-incubated with different concentrations of 20(s)-ginsenoside Rg3. The results indicated that the penetration of paclitaxel through the Caco-2 monolayer from the apical side to the basal side was facilitated by 20(s)-ginsenoside Rg3 in a concentration-dependent manner. Meanwhile, 20(s)-ginsenoside Rg3 inhibited P-glycoprotein (P-gp), and the maximum inhibition was achieved at 80 µM (p < 0.05). The pharmacokinetic parameters of paclitaxel after oral co-administration of paclitaxel (40 mg/kg) with various doses of 20(s)-ginsenoside Rg3 in rats were investigated by an in vivo pharmacokinetic experiment. The results showed that the AUC of paclitaxel co-administered with 20(s)-ginsenoside Rg3 was significantly higher (p < 0.001 at 10 mg/kg) compared with the control. The relative bioavailability (RB) % of paclitaxel with 20(s)-ginsenoside Rg3 was 3.4-fold (10 mg/kg) higher than that of the control. The effect of paclitaxel orally co-administered with 20(s)-ginsenoside Rg3 against human tumour MCF-7 xenografts in nude mice was also evaluated. Paclitaxel (20 mg/kg) co-administered with 20(s)-ginsenoside Rg3 (10 mg/kg) exhibited an effective anti-tumour activity with the relative tumor growth rate (T/C) values of 39.36% (p <0.05). The results showed that 20(s)-ginsenoside Rg3 enhanced the oral bioavailability of paclitaxel in rats and improved the anti-tumour activity in nude mice, indicating that oral co-administration of paclitaxel with 20(s)-ginsenoside Rg3 could provide an effective strategy in addition to the established i.v. route.

The Promotive Effects of Antioxidative Apigenin on the Bioavailability of Paclitaxel for Oral Delivery in Rats

This study was to investigate the effect of apigenin on the bioavailability of paclitaxel after oral and intravenous administration in rats. The effect of apigenin on P-glycoprotein (P-gp), cytochrome P450 (CYP)3A4 activity was evaluated. The pharmacokinetic parameters of paclitaxel were determined in rats after oral (40 mg/kg) or intravenous (5 mg/kg) administration of paclitaxel with apigenin (0.4, 2 and 8 mg/kg) to rats. Apigenin inhibited CYP3A4 activity with 50% inhibition concentration (IC50) of 1.8 μM. In addition, apigenin significantly inhibited P-gp activity. Compared to the control group, apigenin significantly increased the area under the plasma concentration-time curve (AUC, p<0.05 by 2 mg/kg, 59.0% higher; p<0.01 by 8 mg/kg, 87% higher) of oral paclitaxel. Apigenin also significantly (p<0.05 by 2 mg/kg, 37.2% higher; p<0.01 by 8 mg/kg, 59.3% higher) increased the peak plasma concentration (Cmax) of oral paclitaxel. Apigenin significantly increased the terminal half-life (t1/2, p<0.05 by 8 mg/kg, 34.5%) of oral paclitaxel. Consequently, the absolute bioavailability (A.B.) of paclitaxel was significantly (p<0.05 by 2 mg/kg, p<0.01 by 8 mg/kg) increased by apigenin compared to that in the control group, and the relative bioavailability (R.B.) of oral paclitaxel was increased by 1.14- to 1.87-fold. The pharmacokinetics of intravenous paclitaxel were not affected by the concurrent use of apigenin in contrast to the oral administration of paclitaxel. Accordingly, the enhanced oral bioavailability by apigenin may be mainly due to increased intestinal absorption caused via P-gp inhibition by apigenin rather than to reduced renal and hepatic elimination of paclitaxel. The increase in the oral bioavailability might be mainly attributed to enhanced absorption in the gastrointestinal tract via the inhibition of P-gp and reduced first-pass metabolism of paclitaxel via the inhibition of the CYP3A subfamily in the small intestine and/or in the liver by apigenin. It appears that the development of oral paclitaxel prepara- tions as a combination therapy is possible, which will be more convenient than the i.v. dosage form.

Effects of Silibinin, Inhibitor of CYP3A4 and P-Glycoprotein in vitro, on the Pharmacokinetics of Paclitaxel after Oral and Intravenous Administration in Rats

Silibinin, a flavonoid, is an inhibitor of P-glycoprotein (P-gp)-mediated efflux transporters, and its oxidative metabolism is catalyzed by CYP3A4. The purpose of this study was to investigate the effect of oral silibinin on the bioavailability and pharmacokinetics of orally and intravenously administered paclitaxel in rats. The pharmacokinetic parameters of paclitaxel were determined in rats after oral (40 mg/kg) or intravenous (4 mg/kg) administration in the presence and absence of silibinin (0.5, 2.5 or 10 mg/kg). The effect of silibinin on the P-gp as well as CYP3A4 activity was also evaluated. Silibinin inhibited CYP3A4 enzyme activity with an IC₅₀ of 1.8 µmol/l. In addition, silibinin significantly inhibited P-gp activity. Compared to the control group, silibinin significantly (p < 0.05 by 2.5 mg/kg, p < 0.01 by 10 mg/kg) increased the area under the plasma concentration-time curve (65.8–101.7% higher) of oral paclitaxel. Silibinin also significantly increased (p < 0.05 by 2.5 mg/kg, 31.0% higher; p < 0.01 by 10 mg/kg, 52.9% higher) the peak plasma concentration of paclitaxel. Consequently, the absolute bioavailability of paclitaxel was increased by silibinin compared to that in the control group, and the relative bioavailability of oral paclitaxel was increased 1.15- to 2.02-fold. The intravenous pharmacokinetics of paclitaxel were not affected by the concurrent use of silibinin in contrast to the oral administration of paclitaxel. Accordingly, the enhanced oral bioavailability in the presence of silibinin could mainly be due to the increased intestinal absorption of paclitaxel via P-gp inhibition.

Pharmacokinetic analysis of a combined chemoendocrine treatment with paclitaxel and toremifene for metastatic breast cancer

Multidrug resistance protein could be a target for improving the efficacy of paclitaxel (PXL). Toremifene (TOR) may moderate P-gp-related drug resistance in vitro. Some P-gp moderators may change the pharmacokinetic parameters of PXL in vivo. A pharmacokinetic (PK) study in metastatic breast cancer patients (MBC) was conducted to determine the safety and efficacy of PXL and TOR. Fifteen patients received 80 mg/m(2) PXL (i.v.) weekly and 120 mg/body TOR (p.o.) daily. For the pharmacokinetic study, PXL was administered on days 1, 8, 15, 32, and 39; TOR was given from day 18 to the end of study. On days 1, 8, 15, 18, 32, and 39, blood samples were collected from the patients who received either PXL alone or PXL + TOR, and these were analyzed by high-performance liquid chromatography. Among the 15 patients enrolled in the study, one showed a partial response, and eight had a stable disease. TOR caused no specific adverse events that were greater than grade 3, and its toxicity profile in combination with PXL was similar to that of PXL monotherapy. The PK profile of PXL was similar with or without TOR. The PK parameters of PXL indicated no inter- or intra-patient variability in previously treated patients with MBC. No increased PXL toxicity was observed. The PK profile of combined PXL and TOR was similar to that of PXL monotherapy. The addition of TOR to PXL in previously treated patients with MBC appears safe.

CYP2C8 haplotype structures and their influence on pharmacokinetics of paclitaxel in a Japanese population

CYP2C8 is known to metabolize various drugs including an anticancer drug paclitaxel. Although large interindividual differences in CYP2C8 enzymatic activity and several nonsynonymous variations were reported, neither haplotype structures nor their associations with pharmacokinetic parameters of paclitaxel were reported. Haplotype structures of the CYP2C8 gene were inferred by an expectation-maximization based program using 40 genetic variations detected in 437 Japanese patients, which included cancer patients. Associations of the haplotypes and paclitaxel pharmacokinetic parameters were analyzed for 199 paclitaxel-administered cancer patients. Relatively strong linkage disequilibriums were observed throughout the CYP2C8 gene. We estimated 40 haplotypes without an amino-acid change and nine haplotypes with amino acid changes. The 40 haplotypes were classified into six groups based on network analysis. The patients with heterozygous *IG group haplotypes harboring several intronic variations showed a 2.5-fold higher median area under concentration-time curve of C3'-p-hydroxy-paclitaxel and a 1.6-fold higher median value of C3'-p-hydroxy-paclitaxel/paclitaxel area under concentration-time curve ratio than patients bearing no *IG group haplotypes (P<0.001 for both comparisons by Mann-Whitney U-test). No statistically significant differences, however, were observed between patients with and without the *IG group (haplotypes) in clearance and area under concentration-time curve of paclitaxel, area under concentration-time curve of 6alpha-hydroxy-paclitaxel and 6alpha-, C3'-p-dihydroxy-paclitaxel, and area under concentration-time curve ratio of 6alpha-hydroxy-paclitaxel/paclitaxel. CYP2C8*IG group haplotypes were associated with increased area under concentration-time curve of C3'-p-hydroxy-paclitaxel and area under concentration-time curve ratio of C3'-p-hydroxy-paclitaxel/paclitaxel. Thus, *IG group haplotypes might be associated with reduced CYP2C8 activity, possibly through its reduced protein levels.

Pharmacokinetic study of a combination chemo-endocrine treatment of paclitaxel and toremifene

13017 Background: The mechanism of paclitaxel (PXL) resistance has been investigated. P-glycoprotein (P-gp) on cell membrane could be an important target for improving efficacy of PXL. Toremifene (TOR) may moderate P-gp-related drug resistance in vitro. To determine safety and efficacy of PXL and TOR, we conducted a pharmacokinetic study for a combination chemo-endocrine treatment of PXL plus TOR for metastatic breast cancer. Methods: Patients with metastatic breast cancer, who were previously treated with a standard chemotherapy without PXL, were eligible. Patients received PXL 80 mg/m2(i.v.) weekly on days 1, 8, and 15 in a cycle. Concurrently, toremifene 120mg/body (p.o.) was given dairy from day 1–28 in a cycle. For pharmacokinetic study, single agent of PXL was initially administrated on day 1, 8, and 15. From day 18, TOR 120mg/body was given dairy. On day 22, PXL administration in second cycle was skipped. On day 32, blood samples were collected from the patients received PXL 80 mg/m2 + TOR 120 mg/day/body. Samples were analyzed by HPLC (Unisil Q 5CN). Response was evaluated by WHO criteria and adverse events were evaluated by NCI•CTC Ver.2. Results: Nineteen patients were enrolled. Out of 19, 15 patients had measurable disease, and 1 partial response, 8 stable disease, and 6 progressive disease were observed. The addition of TOR caused in no specific adverse events more than grade 3 and toxic profile in combination was similar that in PXL monotherapy. Pharmacokinetic profile of PXL was similar with/without TOR. In addition, Cmax of TOR was 1.85±0.71 mg/mL. Tmax was 2.9±1.8 hr were observed. AUC0–8 of TOR was not affected in the presence of PXL. AUC0- 8 of TOR-1, metabolite of TOR, also demonstrated the similar pharmacokinetic profile. Pharmacokinetic parameters of PXL did not reveal intra-patient variability in previously treated metastatic breast cancer patients. Conclusions: Pharmacokinetic profile in a combination of PXL and TOR was similar that in PXL monotherapy. The addition of TOR to PXL for previously treated metastatic breast cancer patients might be safety. No significant financial relationships to disclose.

Pharmacokinetics and safety of bevacizumab administered in combination with cisplatin and paclitaxel in cynomolgus monkeys

Bevacizumab is the first anti-angiogenic monoclonal antibody approved for use in combination with chemotherapy for treatment of a variety of solid tumors. The objective of this study was to evaluate the safety of bevacizumab when administered concomitantly with paclitaxel and cisplatin to cynomolgus monkeys, and to assess the pharmacokinetic and safety interactions between bevacizumab and the two chemotherapeutic agents. Twenty male cynomolgus monkeys (Macaca fasicularis) were randomized to one of four treatment groups: vehicle, bevacizumab alone, cisplatin alone, and the combination of cisplatin and bevacizumab. Blood collection over serial time points allowed determination of the pharmacokinetic parameters of paclitaxel and bevacizumab and the maximum concentration (C (max)) for cisplatin. Drug concentrations were determined by graphite-furnace atomic absorption, high performance liquid chromatography, and enzyme-linked immunosorbent assay methods, for cisplatin, paclitaxel, and bevacizumab, respectively. AUC0-t values for bevacizumab when administered alone or in combination with chemotherapy were 6,747 +/- 1,872 and 7,366 +/- 1,599 microg/ml x day, respectively. AUC0-t values for paclitaxel with or without concomitantly administered bevacizumab were 10.9 +/- 2.9 and 10.3 +/- 3.7 microg/ml x day, respectively. No alterations in the C (max) of bevacizumab, paclitaxel, or cisplatin were observed between any of the treatment groups. As expected, based on their known safety profile, the administration of cisplatin and paclitaxel were associated with vomiting, decreased body weight, and transient decreases in white blood cell and absolute neutrophil counts; concomitant bevacizumab administration did not alter the incidence or severity of these toxicological effects. Pharmacokinetic estimates for bevacizumab, paclitaxel and cisplatin indicate that combination of bevacizumab with the two chemotherapeutic agents does not result in a pharmacokinetic interaction. Moreover, the addition of bevacizumab to the chemotherapy regimen did not appear to alter the safety profiles of cisplatin/paclitaxel in cynomolgus monkeys. Results from the present study supported the clinical development of bevacizumab treatment regimens in combination with the chemotherapeutic agents paclitaxel and cisplatin.

Impact of the haplotype CYP3A4*16B harboring the Thr185Ser substitution on paclitaxel metabolism in Japanese patients with cancer

Paclitaxel is one of the most important anticancer drugs for the treatment of various tumors such as non-small cell lung cancer. We investigated the association between CYP3A4 haplotypes and pharmacokinetic parameters of paclitaxel metabolism. This study enrolled 235 Japanese patients with cancer who were receiving paclitaxel. These patients were screened for CYP3A4 gene polymorphisms by either direct sequencing or pyrosequencing. Plasma concentrations of paclitaxel and its 3 metabolites were determined by HPLC in 229 patients. Median values of paclitaxel clearance, normalized for body surface area, were lower in the high-dose group (>or=175 mg/m2, n = 199) than in the low-dose group (<or=100 mg/m2, n = 30), suggesting nonlinearity of pharmacokinetics caused by Cremophor EL. Therefore we mainly used the patients in the high-dose group for further analysis. The median value of the area under the curve (AUC) ratio of 3'-p-hydroxypaclitaxel to paclitaxel was 20% greater (95% confidence interval, 2.4% to 41.7%) in the women than in the men (P = .01). Although no significant difference in paclitaxel clearance was observed among the CYP3A4 haplotypes, 16B-bearing (1/16B) patients (n = 8) showed a 20% lower (95% confidence interval, -58.5 to -11.5%) median AUC ratio of 3'-p-hydroxypaclitaxel to paclitaxel (P = .04) and a 2.4-fold higher median AUC ratio of 6alpha-hydroxypaclitaxel to paclitaxel (P < .001) compaed with those in the wild-type (1/1) patients (n = 180). In contrast, no significant differences were seen between 1/1 and 18B/1 (n = 10) patients for the pharmacokinetic parameters examined. Our results suggest that CYP3A416B is associated with both reduced 3'-p-hydroxylation of paclitaxel and probably increased levels of 6alpha-hydroxypaclitaxel.

Paclitaxel and pegylated liposomal doxorubicin in recurrent head/neck cancer: An unexpected administration interval-dependent pharmacokinetic interaction

2042 Background: Combination of paclitaxel (PTX) with pegylated liposomal doxorubicin (PLD) is an interesting opportunity for recurrent head/neck cancer treatment. Their pharmacokinetic (PK) behavior could be dependent not only on PTX excipient (polyethoxylated castor oil) interference, but also on different iv administration interval between the two drugs. The study endpoint was to evaluate any possible administration interval-dependent PK interaction, when PLD infusion start is delayed from 0 to 24 h after PTX infusion end. Methods: 24 patients affected by recurrent cisplatin pre-treated squamous cellhead/neck cancer were enrolled, receiving PTX 80 mg/m2 q 1w and PLD 12.5 mg/m2 q 2w for 6w/2w rest. Administration interval was 0 h at d1 (PTX-PLD 0) and 24 h at d15 (PTX-PLD 24). Blood sampling was performed at d1–15, PTX and PLD blood levels were analyzed by high performance liquid chromatography techniques, while PK parameters by non-compartmental analysis. Results: PTX PK parameters had large statistically significant differences (median/IQR, PTX-PLD 0 vs. PTX-PLD 24, Mann-Whitney test): Cmax 261/219–531 vs. 407/250–1473 ng/ml p=0.142, AUC 869/688–1331 vs. 3361/969–7853 ng*h/ml p=0.013, Kel 0.39/0.26–0.57 vs. 0.11/0.02–0.26 h⁁−1 p=0.001, Cl 153/89–198 vs. 41/17–138 l/h p=0.013. Similarly, PLD Cmax and AUC were higher in PTX-PLD 24 (Cmax 5.1/3.3–8.1 vs. 6.8/5.3–7.8 mg/l p=0.043, AUC 341/104–1472 vs. 603/106–1006 mg*h/l p=1.000). The overall response rate was 37.5%, including 1 CR (4%); median response duration was 5.5 months (range, 2–16), median overall survival 10 months (range, 2–25+). Conclusions: This exploratory study, having a favourable palliative role in heavily pre-treated patients, showed that PTX PK profile is unexpectedly affected by a different administration interval. In PTX-PLD 0, PTX AUC is fourfold reduced, with a similar increase in Cl, totally due to Kel alteration: therefore, patients could be underexposed to PTX. PLD PK behavior confirmed previous studies results, in which PTX modified PLD disposition, prolonging the duration of its elimination phase and increasing total body exposure to PLD. No significant financial relationships to disclose.

Altered pharmacokinetics of paclitaxel by the concomitant use of morin in rats

The purpose of this study was to investigate the effect of morin on the pharmacokinetics of orally and intravenously administered paclitaxel in rats. Pharmacokinetic parameters of paclitaxel were determined in rats after an oral (30 mg kg −1) or intravenous (3 mg kg −1) administration of paclitaxel to rats in the presence and absence of morin (3.3 and 10 mg kg −1). Compared to the control given paclitaxel alone, pretreatment with morin 30 min prior to the oral administration of paclitaxel increased C max and AUC of paclitaxel by 70–90% and 30–70%, respectively, while there was no significant change in T max and terminal plasma half-life ( T 1/2) of paclitaxel. Consequently, absolute and relative bioavailability values of paclitaxel in the rats after the pretreatment with morin were significantly higher ( p < 0.05) than those from the control. In contrast, following an intravenous administration of paclitaxel (3.3 mg kg −1), the pharmacokinetic profiles of paclitaxel were not altered significantly in the presence of morin. Those results suggest that the enhanced oral exposure of paclitaxel should be mainly due to the inhibition effect of morin on the gastrointestinal extraction of paclitaxel during the intestinal absorption. Therefore, the concurrent use of morin or morin-containing dietary supplement may provide a therapeutic benefit in the oral delivery of paclitaxel.

Paclitaxel-Carboplatin Combination Chemotherapy in Advanced Breast Cancer: Accumulating Evidence for Synergy, Efficacy, and Safety

Patients with metastatic breast cancer receive multiple lines of cytotoxic chemotherapy, with taxane and anthracycline-based regimens being the most active. Anthracyclines carry the risk of significant cardiotoxicity at high cumulative doses and when combined with trastuzumab, an anti-HER2 antibody. Carboplatin has shown promising single-agent activity in advanced breast cancer, is not a P-glycoprotein substrate, and is conveniently administered on an outpatient basis. Preclinical experiments demonstrated schedule-dependent synergistic cytotoxic effects of the paclitaxel first/carboplatin last (PC) combination. Pharmacokinetic parameters of paclitaxel and carboplatin were studied by Hellenic Cooperative Oncology Group (HECOG) and no significant interaction or correlation with clinical parameters were found. We assessed PC both as salvage as well as first-line treatment of advanced breast cancer patients in phase II studies which disclosed 40-60% response rates and median survival times of 12-20 mo with manageable toxicity. These results were confirmed by other groups and prompted us to the first randomized phase III trial comparing PC to the standard of epirubicin/paclitaxel (EP), a trial that showed equivalent efficacy and tolerable toxicity for PC. Registry retrospective analysis identified factors prognostic for improved outcome: good performance status, low tumor burden, lack of anthracycline exposure and of hormonal maintenance therapy. PC combinations with HER1 or HER2 modulators are being evaluated both by HECOG and by international groups. Paclitaxel coupled with carboplatin provides an alternative therapeutic option for anthracycline-exposed patients and warrants further clinical research in the direction of anthracycline-free management of metastatic breast cancer.

The effect of verapamil on the pharmacokinetics of paclitaxel in rats

The purpose of this study was to investigate the effect of verapamil on the pharmacokinetic parameters of paclitaxel (50 mg/kg) when paclitaxel is co-administered with verapamil (1, 5, and 15 mg/kg) or pretreated with verapamil (5 mg/kg) for 0.5 h, 3 days, and 6 days orally in rats. When paclitaxel was either co-administered or pretreated with verapamil, the peak plasma concentrations (C(max)) of paclitaxel with verapamil were significantly higher (p<0.05 at 5 mg/kg and 0.5 h; p<0.01 at 15 mg/kg, 3 days and 6 days) than that of the control. The areas under the plasma concentration-time curve (AUC) of paclitaxel with verapamil were significantly (p<0.05 at 5 mg/kg and 0.5 h; p<0.01 at 15 mg/kg, 3 days and 6 days) higher than that of the control. The AUCs of paclitaxel were increased with verapamil in the dose dependent manner. The half-life (t(1/2)) of paclitaxel with verapamil was significantly prolonged compared with that of the control, except for 1 mg/kg co-administration. The absolute bioavailability of paclitaxel with verapamil (3.9-5.4%) was significantly (p<0.05 at 5 mg/kg and 0.5 h; p<0.01 at 15 mg/kg, 3 days and 6 days) higher than that of the control (2.2%). The relative bioavailability of paclitaxel pretreated with verapamil was higher than that of co-administration in rats. Based on these results, it might be considered that the pharmacokinetic parameters of paclitaxel was significantly affected by verapamil which is an inhibitor of the metabolizing enzyme (CYP3A4) in the intestinal mucosa and liver, and the p-glycoprotein efflux pump in the intestinal mucosa. If these results are confirmed in humans in a clinical setting, the paclitaxel dose should be adjusted when it is given concomitantly with verapamil.

Pharmacokinetics of paclitaxel and carboplatin after orthotopic liver transplantation

2095 Background: Paclitaxel is one of the most widely used chemotherapy agents and its metabolism and excretion takes place mainly through hepatic extraction and billiary secretion. Liver transplantation has become a frequent therapy for some hepatic diseases, and some patients become long term survivors after transplant. Those patients require immunosupresive therapy, and are at increased risk to develop tumors. Despite these facts, nothing is known about metabolism and pharmacokinetics of Paclitaxel in recipients of transplanted livers, since no studies have ever been reported. Methods: A 65 year old, male patient that received a transplanted liver in 1995 for ethylic cirrhosis developed metastatic non-small cell lung cancer in 2003. Chemotherapy with Paclitaxel 175 mg/ m2 and Carboplatin AUC =6 was offered, but due to lack of knowledge of Paclitaxel metabolism by transplanted livers, pharmacokinetic studies were done in order to make appropriate dose modifications if required. Blood levels of Paclitaxel and Carboplatin were assessed at different time intervals following drug infusion. Drug concentrations were determined by a validated reverse-phase HPLC method with ultraviolet detection. Pharmacokinetic parameters were estimated by noncompartimental analysis with WinNonlin v.1.5. Results: During the first cycle, pharmacokinetic parameters of Paclitaxel were: AUC 8,63 μ mol x h/ L; Cmax = 2,46 μ mol/ L; CL = 37,1 L/ h.. Similar results were obtained in subsequent cycles. These values are within the expected range in non-transplanted patients with normal liver function (Huizing MT, et al. J Clin Oncol 1993) and therefore can be considered normal. Carboplatin AUC during the first cycle was 7,67mg h/L, reflecting the well-known margin of error for AUC calculated by clinical equations. Conclusions: Recipients of normally functioning transplanted livers can adequately metabolize Paclitaxel and achieve normal plasmatic levels of the drug. Pharmacokinetic monitoring allows treatment with full dose Paclitaxel and Carboplatin to liver transplanted patients if they develop tumors in which these drugs are active. No significant financial relationships to disclose.

Enhanced paclitaxel bioavailability after oral administration of pegylated paclitaxel prodrug for oral delivery in rats

The bioavailability and pharmacokinetic parameters of paclitaxel in a PEGylated paclitaxel prodrug were studied after the oral administration of paclitaxel (25, 50, 100 mg/kg) and prodrug (87.5, 175, 350 mg/kg) in rats. The area under the plasma concentration–time curve (AUC) of paclitaxel by oral paclitaxel were 836, 1602 and 3076 ng/ml h, which increased dose-dependently ( P < 0.006, r = 0.9996). The AUCs of paclitaxel by the oral paclitaxel prodrug were 1646, 3079 and 5998 ng/ml h, also increased dose-dependently ( P < 0.003, r = 0.9999). The AUC of paclitaxel by the intravenous administration of paclitaxel (2 mg/kg) was 3992 ng/ml h. The mean absolute bioavailability (AB%) of paclitaxel was 1.6% by the oral administration of paclitaxel. The mean AB% of paclitaxel by the prodrug was 6.3%, which was 3.94-fold higher than the oral paclitaxel. The peak concentration of paclitaxel ( C max) in the dose of 350 mg/kg (50 mg/kg as paclitaxel) of prodrug was 339 ng/ml, which was significantly higher ( P < 0.01) than the dose of 50 mg/kg of paclitaxel (104 ng/ml). At the same dose of paclitaxel, the AUC of paclitaxel in the prodrug resulted in a remarkable increase, approximately four-fold compared to the oral paclitaxel. It might be considered that the significantly enhanced bioavailability of paclitaxel by the prodrug, which is water-soluble and easy to permeat through the intestinal mucosa, is due to the avoidance of being inhibited by p-glycoprotein efflux pump in the intestinal mucosa and reduction of metabolism by cytochrome-p-450 (CYP3A) in epitherial cells of small intestine. It appears that the development of oral paclitaxel preparations as a prodrug is possible, which will be more convenient than the IV dosage form.

딜티아젬과 파크리탁셀의 약물동태학적 상호작용

The purpose of this study was to investigate the effect of coadministration (2.5, 10, 20 mg/kg) and 3 or 7 days-pretreatment (10 mg/kg) of diltiazem on the pharmacokinetic parameters of paclitaxel (50 mg/kg) given orally in rats. The plasma concentrations of paclitaxel coadministered or pretreated with diltiazem were significantly (p of paclitaxel with diltiazem were significantly (p of paclitaxel with diltiazem were significantly (p and mean residence time (MRT) of paclitaxel with diltiazem was significantly (p and P-glycoprotein, which are respectively engaged in paclitaxel absorption and metabolism in liver and gastrointestinal mucosa.