Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1. Pharmacodynamic properties
Pharmacotherapeutic group: Pyrimidine analogues , ATC code: L01BC06
Capecitabine is a non-cytotoxic fluoropyrimidine carbamate, which functions as an orally administered precursor of the cytotoxic moiety 5-fluorouracil (5-FU). Capecitabine is activated via several enzymatic steps (see section 5.2). The enzyme involved in the final conversion to 5-FU, thymidine phosphorylase (ThyPase), is found in tumour tissues, but also in normal tissues, albeit usually at lower levels. In human cancer xenograft models capecitabine demonstrated a synergistic effect in combination with docetaxel, which may be related to the upregulation of thymidine phosphorylase by docetaxel.
There is evidence that the metabolism of 5-FU in the anabolic pathway blocks the methylation reaction of deoxyuridylic acid to thymidylic acid, thereby interfering with the synthesis of deoxyribonucleic acid (DNA). The incorporation of 5-FU also leads to inhibition of RNA and protein synthesis. Since DNA and RNA are essential for cell division and growth, the effect of 5-FU may be to create a thymidine deficiency that provokes unbalanced growth and death of a cell. The effects of DNA and RNA deprivation are most marked on those cells which proliferate more rapidly and which metabolise 5-FU at a more rapid rate.
Colon and colorectal cancer
Monotherapy with capecitabine in adjuvant colon cancer
Data from one multicentre, randomised, controlled phase III clinical trial in patients with stage III (Dukes’ C) colon cancer supports the use of capecitabine for the adjuvant treatment of patients with colon cancer (XACT Study; M66001). In this trial, 1987 patients were randomised to treatment with capecitabine (1250 mg/m2 twice daily for 2 weeks followed by a 1-week rest period and given as 3-week cycles for 24 weeks) or 5-FU and leucovorin (Mayo Clinic regimen: 20 mg/m2 leucovorin IV followed by 425 mg/m2 intravenous bolus 5-FU, on days 1 to 5, every 28 days for 24 weeks).
Capecitabine was at least equivalent to IV 5-FU/LV in disease-free survival in per protocol population (hazard ratio 0.92; 95% CI 0.80-1.06). In the all-randomised population, tests for difference of capecitabine vs 5-FU/LV in disease-free and overall survival showed hazard ratios of 0.88 (95% CI 0.77 – 1.01; p = 0.068) and 0.86 (95% CI 0.74 – 1.01; p = 0.060), respectively. The median follow up at the time of the analysis was 6.9 years. In a preplanned multivariate Cox analysis, superiority of capecitabine compared with bolus 5-FU/LV was demonstrated. The following factors were pre-specified in the statistical analysis plan for inclusion in the model: age, time from surgery to randomization, gender, CEA levels at baseline, lymph nodes at baseline, and country. In the all-randomised population, capecitabine was shown to be superior to 5-FU/LV for disease-free survival (hazard ratio 0.849; 95% CI 0.739 - 0.976; p = 0.0212), as well as for overall survival (hazard ratio 0.828; 95% CI 0.705 - 0.971; p = 0.0203).
Combination therapy in adjuvant colon cancer
Data from one multicentre, randomised, controlled phase 3 clinical trial in patients with stage III (Dukes’ C) colon cancer supports the use of capecitabine in combination with oxaliplatin (XELOX) for the adjuvant treatment of patients with colon cancer (NO16968 study). In this trial, 944 patients were randomised to 3-week cycles for 24 weeks with capecitabine (1000 mg/m2 twice daily for 2 weeks followed by a 1-week rest period) in combination with oxaliplatin (130 mg/m2 intravenous infusion over 2-hours on day 1 every 3 weeks); 942 patients were randomised to bolus 5-FU and leucovorin. In the primary analysis for DFS in the ITT population, XELOX was shown to be significantly superior to 5-FU/LV (HR=0.80, 95% CI=[0.69; 0.93]; p=0.0045). The 3 year DFS rate was 71% for XELOX versus 67% for 5-FU/LV. The analysis for the secondary endpoint of RFS supports these results with a HR of 0.78 (95% CI=[0.67; 0.92]; p=0.0024) for XELOX vs. 5-FU/LV. XELOX showed a trend towards superior OS with a HR of 0.87 (95% CI=[0.72; 1.05]; p=0.1486) which translates into a 13% reduction in risk of death. The 5 year OS rate was 78% for XELOX versus 74% for 5-FU/LV. The efficacy data is based on a median observation time of 59 months for OS and 57 months for DFS. The rate of withdrawal due to adverse events was higher in the XELOX combination therapy arm (21%) as compared with that of the 5-FU/LV monotherapy arm (9%) in the ITT population.
Monotherapy with capecitabine in metastatic colorectal cancer
Data from two identically-designed, multicentre, randomised, controlled phase III clinical trials (SO14695; SO14796) support the use of capecitabine for first line treatment of metastatic colorectal cancer. In these trials, 603 patients were randomised to treatment with capecitabine (1250 mg/m2 twice daily for 2 weeks followed by a 1-week rest period and given as 3-week cycles). 604 patients were randomised to treatment with 5-FU and leucovorin (Mayo regimen: 20 mg/m2 leucovorin intravenous followed by 425 mg/m2 intravenous bolus 5-FU, on days 1 to 5, every 28 days). The overall objective response rates in the all-randomised population (investigator assessment) were 25.7% (capecitabine) vs.
16.7% (Mayo regimen); p <0.0002. The median time to progression was 140 days (capecitabine) vs. 144 days (Mayo regimen). Median survival was 392 days (capecitabine) vs. 391 days (Mayo regimen).
Currently, no comparative data are available on capecitabine monotherapy in colorectal cancer in comparison with first line combination regimens.
Combination therapy in first-line treatment of metastatic colorectal cancer Data from a multicentre, randomised, controlled phase III clinical study (NO16966) support the use of capecitabine in combination with oxaliplatin or in combination with oxaliplatin and bevacizumab for the first-line treatment of metastatic colorectal cancer. The study contained two parts: an initial 2-arm part in which 634 patients were randomised to two different treatment groups, including XELOX or FOLFOX-4, and a subsequent 2x2 factorial part in which 1401 patients were randomised to four different treatment groups, including XELOX plus placebo, FOLFOX-4 plus placebo, XELOX plus bevacizumab, and FOLFOX-4 plus bevacizumab. See table 6 for treatment regimens.
Table 6     Treatment regimens in study NO16966 (mCRC)

Treatment            Starting Dose                         Schedule
2
FOLFOX-4 Oxaliplatin      85 mg/m intravenous 2 hr            Oxaliplatin on Day 1, every 2 weeks or                                                        Leucovorin on Days 1 and 2, every 2 Leucovorin     200 mg/m2 intravenous 2 hr
FOLFOX-4                                                      weeks
+
5-Fluorouracil 400 mg/m2 intravenous bolus,        5-fluorouracil intravenous Bevacizumab followed by 600 mg/m2               bolus/infusion, each on Days 1 and 2, intravenous 22 hr                   every 2 weeks

Placebo or       5 mg/kg intravenous            Day 1, prior to FOLFOX-4, every 2 Bevacizumab      30-90 mins                     weeks
XELOX Oxaliplatin             130 mg/m2 intravenous 2 hr  Oxaliplatin on Day 1, every 3 weeks or
Capecitabine        1000 mg/m2 oral twice daily Capecitabine oral twice daily for 2 XELOX +                                                    weeks (followed by 1 week off- Bevacizumab                                                 treatment) Placebo or       7.5 mg/kg intravenous 30-90 Day 1, prior to XELOX, every 3 Bevacizumab      mins                        weeks
5-Fluorouracil: intravenous bolus injection immediately after leucovorin 
Non-inferiority of the XELOX-containing arms compared with the FOLFOX-4-containing arms in the overall comparison was demonstrated in terms of progression-free survival in the eligible patient population and the intent-to-treat population (see table 7). The results indicate that XELOX is equivalent to FOLFOX-4 in terms of overall survival (see table 7). A comparison of XELOX plus bevacizumab versus FOLFOX-4 plus bevacizumab was a pre-specified exploratory analysis. In this treatment subgroup comparison, XELOX plus bevacizumab was similar compared to FOLFOX-4 plus bevacizumab in terms of progression-free survival (hazard ratio 1.01; 97.5% CI 0.84 - 1.22). The median follow up at the time of the primary analyses in the intent-to-treat population was 1.5 years; data from analyses following an additional 1 year of follow up are also included in table 7. However, the on-treatment PFS analysis did not confirm the results of the general PFS and OS analysis: the hazard ratio of XELOX versus FOLFOX- 4 was 1.24 with 97.5% CI 1.07 - 1.44. Although sensitivity analyses show that differences in regimen schedules and timing of tumor assessments impact the on-treatment PFS analysis, a full explanation for this result has not been found.
Table 7       Key efficacy results for the non-inferiority analysis of Study NO16966 PRIMARY ANALYSIS
XELOX/XELOX+P/                FOLFOX-4/FOLFOX-4+P/
XELOX+BV                       FOLFOX-4+BV
(EPP*: N=967; ITT**: N=1017)   (EPP*: N = 937; ITT**: N= 1017)
HR
Population                            Median Time to Event (Days)                      (97.5% CI) Parameter: Progression-free Survival
EPP                           241                               259              1.05 (0.94; 1.18) ITT                          244                               259              1.04 (0.93; 1.16) Parameter: Overall Survival
EPP                           577                               549              0.97 (0.84; 1.14) ITT                          581                               553              0.96 (0.83; 1.12) ADDITIONAL 1 YEAR OF FOLLOW UP
HR
Population                            Median Time to Event (Days)                      (97.5% CI) Parameter: Progression-free Survival
EPP                           242                                 259            1.02 (0.92; 1.14) ITT                          244                                 259            1.01 (0.91; 1.12) Parameter: Overall Survival
EPP                           600                                 594            1.00 (0.88; 1.13) ITT                          602                                 596            0.99 (0.88; 1.12) 
*EPP=eligible patient population; **ITT=intent-to-treat population
In a randomised, controlled phase III study (CAIRO), the effect of using capecitabine at a starting dose of 1000 mg/m2 for 2 weeks every 3 weeks in combination with irinotecan for the first-line treatment of patients with metastatic colorectal cancer was studied. 820 Patients were randomised to receive either sequential treatment (n=410) or combination treatment (n=410). Sequential treatment consisted of first- line capecitabine (1250 mg/m2 twice daily for 14 days), second-line irinotecan (350 mg/m2 on day 1), and third-line combination of capecitabine (1000 mg/m2 twice daily for 14 days) with oxaliplatin (130 mg/m2 on day 1). Combination treatment consisted of first-line capecitabine (1000 mg/m2 twice daily for 14 days) combined with irinotecan (250 mg /m2 on day 1) (XELIRI) and second-line capecitabine (1000 mg/m2 twice daily for 14 days) plus oxaliplatin (130 mg/m2 on day 1). All treatment cycles were administered at intervals of 3 weeks. In first-line treatment the median progression-free survival in the intent-to-treat population was 5.8 months (95%CI 5.1 - 6.2 months) for capecitabine monotherapy and 7.8 months (95%CI 7.0 - 8.3 months; p=0.0002) for XELIRI. However this was associated with an increased incidence of gastrointestinal toxicity and neutropenia during first-line treatment with XELIRI (26% and 11% for XELIRI and first line capecitabine respectively).
The XELIRI has been compared with 5-FU + irinotecan (FOLFIRI) in three randomised studies in patients with metastatic colorectal cancer. The XELIRI regimens included capecitabine 1000 mg/m2 twice daily on days 1 to 14 of a three-week cycle combined with irinotecan 250 mg/m2 on day1.
In the largest study (BICC-C), patients were randomised to receive either open label FOLFIRI (n=144), bolus 5-FU (mIFL) (n=145) or XELIRI (n=141) and were additionally randomised to receive either double-blind treatment with celecoxib or placebo. Median PFS was 7.6 months for FOLFIRI, 5.9 months for mIFL (p=0.004) for the comparison with FOLFIRI), and 5.8 months for XELIRI (p=0.015). Median OS was 23.1 months for FOLFIRI, 17.6 months for mIFL (p=0.09), and 18.9 months for XELIRI (p=0.27). Patients treated with XELIRI experienced excessive gastrointestinal toxicity compared with FOLFIRI (diarrhoea 48% and 14% for XELIRI and FOLFIRI respectively).
In the EORTC study patients were randomised to receive either open label FOLFIRI (n=41) or XELIRI (n=44) with additional randomisation to either double-blind treatment with celecoxib or placebo. Median PFS and overall survival (OS) times were shorter for XELIRI versus FOLFIRI (PFS 5.9 versus 9.6 months and OS 14.8 versus 19.9 months), in addition to which excessive rates of diarrhoea were reported in patients receiving the XELIRI regimen (41% XELIRI, 5.1% FOLFIRI).
In the study published by Skof et al, patients were randomised to receive either FOLFIRI or XELIRI .
Overall response rate was 49% in the XELIRI and 48% in the FOLFIRI arm (p=0.76). At the end of treatment, 37% of patients in the XELIRI and 26% of patients in the FOLFIRI arm were without evidence of the disease (p=0.56). Toxicity was similar between treatments with the exception of neutropenia reported more commonly in patients treated with FOLFIRI.
Montagnani et al used the results from the above three studies to provide an overall analysis of randomised studies comparing FOLFIRI and XELIRI treatment regimens in the treatment of mCRC.
A significant reduction in the risk of progression was associated with FOLFIRI (HR, 0.76; 95%CI, 0.62- 0.95; P <0.01), a result partly due to poor tolerance to the XELIRI regimens used.
Data from a randomised clinical study (Souglakos et al, 2012) comparing FOLFIRI + bevacizumab with XELIRI + bevacizumab showed no significant differences in PFS or OS between treatments. Patients were randomised to receive either FOLFIRI plus bevacizumab (Arm-A, n=167) or XELIRI plus bevacizumab (Arm-B, n-166). For Arm B, the XELIRI regimen used capecitabine 1000 mg/m2 twice daily for 14 days + irinotecan 250 mg/m2 on day 1. Median progression-free survival (PFS) was 10.0 and 8.9 months; p=0.64, overall survival 25.7 and 27.5 months; p=0.55 and response rates 45.5 and 39.8%; p=0.32 for FOLFIRI-Bev and XELIRI-Bev, respectively. Patients treated with XELIRI + bevacizumab reported a significantly higher incidence of diarrhoea, febrile neutropenia and hand-foot skin reactions than patients treated with FOLFIRI + bevacizumab with significantly increased treatment delays, dose reductions and treatment discontinuations.
Data from a multicentre, randomised, controlled phase II study (AIO KRK 0604) supports the use of capecitabine at a starting dose of 800 mg/m2 for 2 weeks every 3 weeks in combination with irinotecan and bevacizumab for the first-line treatment of patients with metastatic colorectal cancer. 120 Patients were randomised to a modified XELIRI regimen with capecitabine (800 mg/m2 twice daily for two weeks followed by a 7-day rest period), irinotecan (200 mg/m2 as a 30 minute infusion on day 1 every 3 weeks), and bevacizumab (7.5 mg/kg as a 30 to 90 minute infusion on day 1 every 3 weeks); 127 patients were randomised to treatment with capecitabine (1000 mg/m2 twice daily for two weeks followed by a 7-day rest period), oxaliplatin (130 mg/m2 as a 2 hour infusion on day 1 every 3 weeks), and bevacizumab (7.5 mg/kg as a 30 to 90 minute infusion on day 1 every 3 weeks). Following a mean duration of follow-up for the study population of 26.2 months, treatment responses were as shown below: 
Table 8     Key efficacy results for AIO KRK study

XELOX + bevacizumab           Modified XELIRI+            Hazard ratio bevacizumab                  95% CI
(ITT: N=127)               (ITT: N= 120)                P value
Progression-free Survival after 6 months
-
ITT                                76%                       84%
95% CI                           69 - 84%                  77 - 90%
Median progression free survival
ITT                           10.4 months                 12.1 months                  0.93 95% CI                         9.0 -12.0                   10.8 -13.2               0.82 - 1.07 P=0.30


      Median overall survival
ITT                              24.4 months                        25.5 months                   0.90 95% CI                            19.3 - 30.7                        21.0 - 31.0              0.68 - 1.19 
P=0.45

Combination therapy in second-line treatment of metastatic colorectal cancer Data from a multicentre, randomised, controlled phase III clinical study (NO16967) support the use of capecitabine in combination with oxaliplatin for the second-line treatment of metastastic colorectal cancer. In this trial, 627 patients with metastatic colorectal carcinoma who have received prior treatment with irinotecan in combination with a fluoropyrimidine regimen as first line therapy were randomised to treatment with XELOX or FOLFOX-4. For the dosing schedule of XELOX and FOLFOX-4 (without addition of placebo or bevacizumab), refer to table 6. XELOX was demonstrated to be non-inferior to FOLFOX-4 in terms of progression-free survival in the per-protocol population and intent-to-treat population (see table 9). The results indicate that XELOX is equivalent to FOLFOX-4 in terms of overall survival (see table 9). The median follow up at the time of the primary analyses in the intent-to-treat population was 2.1 years; data from analyses following an additional 6 months of follow up are also included in table 9.
Table 9      Key efficacy results for the non-inferiority analysis of Study NO16967 PRIMARY ANALYSIS
XELOX                                   FOLFOX-4
(PPP*: N=251; ITT**: N=313)            (PPP*: N = 252; ITT**: N= 314) HR
Population                            Median Time to Event (Days)                            (95% CI) Parameter: Progression-free Survival
PPP                          154                                     168                1.03 (0.87; 1.24) ITT                          144                                     146                0.97 (0.83; 1.14) Parameter: Overall Survival
PPP                          388                                     401                1.07 (0.88; 1.31) ITT                          363                                     382                1.03 (0.87; 1.23) ADDITIONAL 6 MONTHS OF FOLLOW UP
HR
Population                            Median Time to Event (Days)                            (95% CI) Parameter: Progression-free Survival
PPP                          154                                     166                1.04 (0.87; 1.24) ITT                          143                                     146                0.97 (0.83; 1.14) Parameter: Overall Survival
PPP                          393                                     402                1.05 (0.88; 1.27) ITT                          363                                     382                1.02 (0.86; 1.21) *PPP=per-protocol population; **ITT=intent-to-treat population

Advanced gastric cancer
Data from a multicentre, randomised, controlled phase III clinical trial in patients with advanced gastric cancer supports the use of capecitabine for the first-line treatment of advanced gastric cancer (ML17032).
In this trial, 160 patients were randomised to treatment with capecitabine (1000 mg/m2 twice daily for 2 weeks followed by a 7-day rest period) and cisplatin (80 mg/m2 as a 2-hour infusion every 3 weeks). A total of 156 patients were randomised to treatment with 5-FU (800 mg/m2 per day, continuous infusion on days 1 to 5 every 3 weeks) and cisplatin (80 mg/m2 as a 2-hour infusion on day 1, every 3 weeks).
Capecitabine in combination with cisplatin was non-inferior to 5-FU in combination with cisplatin in terms of progression-free survival in the per protocol analysis (hazard ratio 0.81; 95% CI 0.63 - 1.04).
The median progression-free survival was 5.6 months (capecitabine + cisplatin) versus 5.0 months (5-FU + cisplatin). The hazard ratio for duration of survival (overall survival) was similar to the hazard ratio for progression-free survival (hazard ratio 0.85; 95% CI 0.64 - 1.13). The median duration of survival was 10.5 months (capecitabine + cisplatin) versus 9.3 months (5-FU + cisplatin).


Data from a randomised multicentre, phase III study comparing capecitabine to 5-FU and oxaliplatin to cisplatin in patients with advanced gastric cancer supports the use of capecitabine for the first-line treatment of advanced gastric cancer (REAL-2). In this trial, 1002 patients were randomised in a 2x2 factorial design to one of the following 4 arms:
- ECF: epirubicin (50 mg/m2 as a bolus on day 1 every 3 weeks), cisplatin (60 mg/m2 as a two hour infusion on day 1 every 3 weeks) and 5-FU (200 mg/m2 daily given by continuous infusion via a central line).
- ECX: epirubicin (50 mg/m2 as a bolus on day 1 every 3 weeks), cisplatin (60 mg/m2 as a two hour infusion on day 1 every 3 weeks), and capecitabine (625 mg/m2 twice daily continuously).
- EOF: epirubicin (50 mg/m2 as a bolus on day 1 every 3 weeks), oxaliplatin (130 mg/m2 given as a 2 hour infusion on day 1 every three weeks), and 5-FU (200 mg/m2 daily given by continuous infusion via a central line).
- EOX: epirubicin (50 mg/m2 as a bolus on day 1 every 3 weeks), oxaliplatin (130 mg/m2 given as a 2 hour infusion on day 1 every three weeks), and capecitabine (625 mg/m2 twice daily continuously).
The primary efficacy analyses in the per protocol population demonstrated non-inferiority in overall survival for capecitabine- vs 5-FU-based regimens (hazard ratio 0.86; 95% CI 0.8 - 0.99) and for oxaliplatin- vs cisplatin-based regimens (hazard ratio 0.92; 95% CI 0.80 - 1.1). The median overall survival was 10.9 months in capecitabine-based regimens and 9.6 months in 5- FU based regimens. The median overall survival was 10.0 months in cisplatin-based regimens and 10.4 months in oxaliplatin- based regimens.
Capecitabine has also been used in combination with oxaliplatin for the treatment of advanced gastric cancer. Studies with capecitabine monotherapy indicate that capecitabine has activity in advanced gastric cancer.
Colon, colorectal and advanced gastric cancer: meta-analysis
A meta-analysis of six clinical trials (studies SO14695, SO14796, M66001, NO16966, NO16967, M17032) supports capecitabine replacing 5-FU in mono- and combination treatment in gastrointestinal cancer. The pooled analysis includes 3097 patients treated with capecitabine-containing regimens and 3074 patients treated with 5-FU-containing regimens. Median overall survival time was 703 days (95% CI: 671; 745) in patients treated with capecitabine-containing regimens and 683 days (95% CI: 646; 715) in patients treated with 5-FU-containing regimens. The hazard ratio for overall survival was 0.94 (95% CI: 0.89; 1.00, p=0.0489) indicating that capecitabine-containing regimens are non-inferior to 5-FU- containing regimens.
Breast cancer
Combination therapy with capecitabine and docetaxel in locally advanced or metastatic breast cancer Data from one multicentre, randomised, controlled phase III clinical trial support the use of capecitabine in combination with docetaxel for treatment of patients with locally advanced or metastatic breast cancer after failure of cytotoxic chemotherapy, including an anthracycline. In this trial, 255 patients were randomised to treatment with capecitabine (1250 mg/m2 twice daily for 2 weeks followed by 1-week rest period and docetaxel 75 mg/m2 as a 1 hour intravenous infusion every 3 weeks). 256 patients were randomised to treatment with docetaxel alone (100 mg/m2 as a 1 hour intravenous infusion every 3 weeks). Survival was superior in the capecitabine + docetaxel combination arm (p=0.0126). Median survival was 442 days (capecitabine + docetaxel) vs. 352 days (docetaxel alone). The overall objective response rates in the all-randomised population (investigator assessment) were 41.6% (capecitabine + docetaxel) vs. 29.7% (docetaxel alone); p = 0.0058. Time to progressive disease was superior in the capecitabine + docetaxel combination arm (p<0.0001). The median time to progression was 186 days (capecitabine + docetaxel) vs. 128 days (docetaxel alone).
Monotherapy with capecitabine after failure of taxanes, anthracycline containing chemotherapy, and for whom anthracycline therapy is not indicated
Data from two multicentre phase II clinical trials support the use of capecitabine monotherapy for treatment of patients after failure of taxanes and an anthracycline-containing chemotherapy regimen or for whom further anthracycline therapy is not indicated. In these trials, a total of 236 patients were treated with capecitabine (1250 mg/m2 twice daily for 2 weeks followed by 1-week rest period). The overall objective response rates (investigator assessment) were 20% (first trial) and 25% (second trial). The median time to progression was 93 and 98 days. Median survival was 384 and 373 days.
All indications
A meta-analysis of 14 clinical trials with data from over 4700 patients treated with capecitabine monotherapy or capecitabine in combination with different chemotherapy regimens in multiple indications (colon, colorectal, gastric and breast cancer), showed that patients on capecitabine who developed hand-foot syndrome (HFS) had a longer overall survival compared to patients who did not develop HFS: median overall survival 1100 days (95% CI 1007; 1200) vs 691 days (95% CI 638; 754) with a hazard ratio of 0.61 (95% CI 0.56; 0.66).

Pharmacokinetic Properties

5.2. Pharmacokinetic properties
The pharmacokinetics of capecitabine have been evaluated over a dose range of 502- 3514 mg/m2/day.
The parameters of capecitabine, 5'-deoxy-5-fluorocytidine (5'-DFCR) and 5'- deoxy-5-fluorouridine (5'- DFUR) measured on days 1 and 14 were similar. The AUC of 5-FU was 30%-35% higher on day 14.
Capecitabine dose reduction decreases systemic exposure to 5-FU more than dose-proportionally, due to non-linear pharmacokinetics for the active metabolite.
Absorption
After oral administration, capecitabine is rapidly and extensively absorbed, followed by extensive conversion to the metabolites, 5'-DFCR and 5'-DFUR. Administration with food decreases the rate of capecitabine absorption, but only results in a minor effect on the AUC of 5'-DFUR, and on the AUC of the subsequent metabolite 5-FU. At the dose of 1250 mg/m2 on day 14 with administration after food intake, the peak plasma concentrations (Cmax in μg/ml) for capecitabine, 5'-DFCR, 5'-DFUR, 5-FU and FBAL were 4.67, 3.05, 12.1, 0.95 and 5.46 respectively. The time to peak plasma concentrations (Tmax in hours) were 1.50, 2.00, 2.00, 2.00 and 3.34. The AUC0-∞ values in μg•h/ml were 7.75, 7.24, 24.6, 2.03 and 36.3.
Distribution
In vitro human plasma studies have determined that capecitabine, 5'-DFCR, 5'-DFUR and 5-FU are 54%, 10%, 62% and 10% protein bound, mainly to albumin.
Biotransformation
Capecitabine is first metabolised by hepatic carboxylesterase to 5'-DFCR, which is then converted to 5'- DFUR by cytidine deaminase, principally located in the liver and tumour tissues. Further catalytic activation of 5'-DFUR then occurs by thymidine phosphorylase (ThyPase). The enzymes involved in the catalytic activation are found in tumour tissues but also in normal tissues, albeit usually at lower levels.
The sequential enzymatic biotransformation of capecitabine to 5-FU leads to higher concentrations within tumour tissues. In the case of colorectal tumours, 5-FU generation appears to be in large part localised in tumour stromal cells. Following oral administration of capecitabine to patients with colorectal cancer, the ratio of 5-FU concentration in colorectal tumours to adjacent tissues was 3.2 (ranged from 0.9 to 8.0). The ratio of 5-FU concentration in tumour to plasma was 21.4 (ranged from 3.9 to 59.9, n=8) whereas the ratio in healthy tissues to plasma was 8.9 (ranged from 3.0 to 25.8, n=8).
Thymidine phosphorylase activity was measured and found to be 4 times greater in primary colorectal tumour than in adjacent normal tissue. According to immunohistochemical studies, thymidine phosphorylase appears to be in large part localised in tumour stromal cells.
5-FU is further catabolised by the enzyme dihydropyrimidine dehydrogenase (DPD) to the much less toxic dihydro-5-fluorouracil (FUH2). Dihydropyrimidinase cleaves the pyrimidine ring to yield 5-fluoro- ureidopropionic acid (FUPA). Finally, β-ureido-propionase cleaves FUPA to -fluoro-β-alanine (FBAL) which is cleared in the urine. Dihydropyrimidine dehydrogenase (DPD) activity is the rate limiting step.
Deficiency of DPD may lead to increased toxicity of capecitabine (see section 4.3 and 4.4).
Elimination
The elimination half-life (t1/2 in hours) of capecitabine, 5'-DFCR, 5'-DFUR, 5-FU and FBAL were 0.85, 1.11, 0.66, 0.76 and 3.23 respectively. Capecitabine and its metabolites are predominantly excreted in urine; 95.5% of administered capecitabine dose is recovered in urine. Faecal excretion is minimal (2.6%).
The major metabolite excreted in urine is FBAL, which represents 57% of the administered dose. About 3% of the administered dose is excreted in urine unchanged.
Combination therapy
Phase I studies evaluating the effect of capecitabine on the pharmacokinetics of either docetaxel or paclitaxel and vice versa showed no effect by capecitabine on the pharmacokinetics of docetaxel or paclitaxel (Cmax and AUC) and no effect by docetaxel or paclitaxel on the pharmacokinetics of 5’-DFUR.
Pharmacokinetics in special populations
A population pharmacokinetic analysis was carried out after capecitabine treatment of 505 patients with colorectal cancer dosed at 1250 mg/m2 twice daily. Gender, presence or absence of liver metastasis at baseline, Karnofsky Performance Status, total bilirubin, serum albumin, ASAT and ALAT had no statistically significant effect on the pharmacokinetics of 5'-DFUR, 5-FU and FBAL.
Patients with hepatic impairment due to liver metastases
According to a pharmacokinetic study in cancer patients with mild to moderate liver impairment due to liver metastases, the bioavailability of capecitabine and exposure to 5-FU may increase compared to patients with no liver impairment. There are no pharmacokinetic data on patients with severe hepatic impairment.
Patients with renal impairment
Based on a pharmacokinetic study in cancer patients with mild to severe renal impairment, there is no evidence for an effect of creatinine clearance on the pharmacokinetics of intact drug and 5-FU.
Creatinine clearance was found to influence the systemic exposure to 5’-DFUR (35% increase in AUC when creatinine clearance decreases by 50%) and to FBAL (114% increase in AUC when creatinine clearance decreases by 50%). FBAL is a metabolite without antiproliferative activity.
Elderly
Based on the population pharmacokinetic analysis, which included patients with a wide range of ages (27 to 86 years) and included 234 (46%) patients greater or equal to 65, age has no influence on the pharmacokinetics of 5'-DFUR and 5-FU. The AUC of FBAL increased with age (20% increase in age results in a 15% increase in the AUC of FBAL). This increase is likely due to a change in renal function.
Ethnic factors
Following oral administration of 825 mg/m2 capecitabine twice daily for 14 days, Japanese patients (n=18) had about 36% lower Cmax and 24% lower AUC for capecitabine than Caucasian patients (n=22).
Japanese patients had also about 25% lower Cmax and 34% lower AUC for FBAL than Caucasian patients. The clinical relevance of these differences is unknown. No significant differences occurred in the exposure to other metabolites (5'-DFCR, 5'-DFUR, and 5-FU).