General

The recommended dose of capecitabine was determined in an open-label, randomized clinical study, exploring the efficacy and safety of continuous therapy with capecitabine (1331 mg/m2/day in two divided doses, n=39), intermittent therapy with capecitabine (2510 mg/m2/day in two divided doses, n=34), and intermittent therapy with capecitabine in combination with oral leucovorin (LV) (capecitabine 1657 mg/m2/day in two divided doses, n=35; leucovorin 60 mg/day) in patients with advanced and/or metastatic colorectal carcinoma in the first-line metastatic setting. There was no apparent advantage in response rate to adding leucovorin to capecitabine; however, toxicity was increased. Capecitabine, 1250 mg/m2 twice daily for 14 days followed by a 1-week rest, was selected for further clinical development based on the overall safety and efficacy profile of the three schedules studied.

Monotherapy

Data from two open-label, multicenter, randomized, controlled clinical trials involving 1207 patients support the use of capecitabine in the first-line treatment of patients with metastatic colorectal carcinoma. The two clinical studies were identical in design and were conducted in 120 centers in different countries. Study 1 was conducted in the US, Canada, Mexico, and Brazil; Study 2 was conducted in Europe, Israel, Australia, New Zealand, and Taiwan. Altogether, in both trials, 603 patients were randomized to treatment with capecitabine at a dose of 1250 mg/m2 twice daily for 2 weeks followed by a 1-week rest period and given as 3-week cycles; 604 patients were randomized to treatment with 5-FU and leucovorin (20 mg/m2 leucovorin IV followed by 425 mg/m2 IV bolus 5-FU, on days 1 to 5, every 28 days).

In both trials, overall survival, time to progression and response rate (complete plus partial responses) were assessed. Responses were defined by the World Health Organization criteria and submitted to a blinded independent review committee (IRC). Differences in assessments between the investigator and IRC were reconciled by the sponsor, blinded to treatment arm, according to a specified algorithm. Survival was assessed based on a non-inferiority analysis.

The baseline demographics for capecitabine and 5-FU/LV patients are shown in Table 13.

The efficacy endpoints for the two phase 3 trials are shown in Table 14 and Table 15.

Figure 3 Kaplan-Meier Curve for Overall Survival of Pooled Data (Studies 1 and 2)

Capecitabine was superior to 5-FU/LV for objective response rate in Study 1 and Study 2. The similarity of capecitabine and 5-FU/LV in these studies was assessed by examining the potential difference between the two treatments. In order to assure that capecitabine has a clinically meaningful survival effect, statistical analyses were performed to determine the percent of the survival effect of 5-FU/LV that was retained by capecitabine. The estimate of the survival effect of 5-FU/LV was derived from a meta-analysis of ten randomized studies from the published literature comparing 5-FU to regimens of 5-FU/LV that were similar to the control arms used in these Studies 1 and 2. The method for comparing the treatments was to examine the worst case (95% confidence upper bound) for the difference between 5-FU/LV and capecitabine, and to show that loss of more than 50% of the 5-FU/LV survival effect was ruled out. It was demonstrated that the percent of the survival effect of 5-FU/LV maintained was at least 61% for Study 2 and 10% for Study 1. The pooled result is consistent with a retention of at least 50% of the effect of 5-FU/LV. It should be noted that these values for preserved effect are based on the upper bound of the 5-FU/LV vs capecitabine difference. These results do not exclude the possibility of true equivalence of capecitabine to 5-FU/LV (see Table 14, Table 15, and Figure 3).