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Gemzar (Gemcitabine Hydrochloride) - Description and Clinical Pharmacology

 
 



DESCRIPTION

Gemzar (gemcitabine for injection, USP) is a nucleoside metabolic inhibitor that exhibits antitumor activity. Gemcitabine HCl is 2′-deoxy-2′,2′-difluorocytidine monohydrochloride (β-isomer).

The structural formula is as follows:

The empirical formula for gemcitabine HCl is C9H11F2N3O4 • HCl. It has a molecular weight of 299.66.

Gemcitabine HCl is soluble in water, slightly soluble in methanol, and practically insoluble in ethanol and polar organic solvents.

Gemzar is supplied in a sterile form for intravenous use only. Vials of Gemzar contain either 200 mg or 1 g of gemcitabine HCl (expressed as free base) formulated with mannitol (200 mg or 1 g, respectively) and sodium acetate (12.5 mg or 62.5 mg, respectively) as a sterile lyophilized powder. Hydrochloric acid and/or sodium hydroxide may have been added for pH adjustment.

CLINICAL PHARMACOLOGY

Mechanism of Action

Gemcitabine kills cells undergoing DNA synthesis and blocks the progression of cells through the G1/S-phase boundary. Gemcitabine is metabolized by nucleoside kinases to diphosphate (dFdCDP) and triphosphate (dFdCTP) nucleosides. Gemcitabine diphosphate inhibits ribonucleotide reductase, an enzyme responsible for catalyzing the reactions that generate deoxynucleoside triphosphates for DNA synthesis, resulting in reductions in deoxynucleotide concentrations, including dCTP. Gemcitabine triphosphate competes with dCTP for incorporation into DNA. The reduction in the intracellular concentration of dCTP by the action of the diphosphate enhances the incorporation of gemcitabine triphosphate into DNA (self-potentiation). After the gemcitabine nucleotide is incorporated into DNA, only one additional nucleotide is added to the growing DNA strands, which eventually results in the initiation of apoptotic cell death.

Pharmacokinetics

Absorption and Distribution

The pharmacokinetics of gemcitabine were examined in 353 patients, with various solid tumors. Pharmacokinetic parameters were derived using data from patients treated for varying durations of therapy given weekly with periodic rest weeks and using both short infusions (<70 minutes) and long infusions (70 to 285 minutes). The total Gemzar dose varied from 500 to 3600 mg/m2.

The volume of distribution was increased with infusion length. Volume of distribution of gemcitabine was 50 L/m2 following infusions lasting <70 minutes. For long infusions, the volume of distribution rose to 370 L/m2.

Gemcitabine pharmacokinetics are linear and are described by a 2-compartment model. Population pharmacokinetic analyses of combined single and multiple dose studies showed that the volume of distribution of gemcitabine was significantly influenced by duration of infusion and gender. Gemcitabine plasma protein binding is negligible.

Metabolism

Gemcitabine disposition was studied in 5 patients who received a single 1000 mg/m2/30 minute infusion of radiolabeled drug. Within one (1) week, 92% to 98% of the dose was recovered, almost entirely in the urine. Gemcitabine (<10%) and the inactive uracil metabolite, 2′-deoxy-2′,2′-difluorouridine (dFdU), accounted for 99% of the excreted dose. The metabolite dFdU is also found in plasma.

The active metabolite, gemcitabine triphosphate, can be extracted from peripheral blood mononuclear cells. The half-life of the terminal phase for gemcitabine triphosphate from mononuclear cells ranges from 1.7 to 19.4 hours.

Elimination

Clearance of gemcitabine was affected by age and gender. The lower clearance in women and the elderly results in higher concentrations of gemcitabine for any given dose. Differences in either clearance or volume of distribution based on patient characteristics or the duration of infusion result in changes in half-life and plasma concentrations. Table 10 shows plasma clearance and half-life of gemcitabine following short infusions for typical patients by age and gender.

Table 10: Gemcitabine Clearance and Half-Life for the “Typical” Patient

a Half-life for patients receiving <70 minute infusion.

Age Clearance Men
(L/hr/m2)
Clearance Women
(L/hr/m2)
Half-Lifea Men
(min)
Half-Lifea Women
(min)
29 92.2 69.4 42 49
45 75.7 57.0 48 57
65 55.1 41.5 61 73
79 40.7 30.7 79 94

Gemcitabine half-life for short infusions ranged from 42 to 94 minutes, and the value for long infusions varied from 245 to 638 minutes, depending on age and gender, reflecting a greatly increased volume of distribution with longer infusions.

Drug Interactions

When Gemzar (1250 mg/m2 on Days 1 and 8) and cisplatin (75 mg/m2 on Day 1) were administered in NSCLC patients, the clearance of gemcitabine on Day 1 was 128 L/hr/m2 and on Day 8 was 107 L/hr/m2. Analysis of data from metastatic breast cancer patients shows that, on average, Gemzar has little or no effect on the pharmacokinetics (clearance and half-life) of paclitaxel and paclitaxel has little or no effect on the pharmacokinetics of gemcitabine. Data from NSCLC patients demonstrate that Gemzar and carboplatin given in combination does not alter the pharmacokinetics of gemcitabine or carboplatin compared to administration of either single agent. However, due to wide confidence intervals and small sample size, interpatient variability may be observed.

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term animal studies to evaluate the carcinogenic potential of Gemzar have not been conducted. Gemcitabine was mutagenic in an in vitro mouse lymphoma (L5178Y) assay and was clastogenic in an in vivo mouse micronucleus assay. Gemcitabine IP doses of 0.5 mg/kg/day (about 1/700 the human dose on a mg/m2 basis) in male mice had an effect on fertility with moderate to severe hypospermatogenesis, decreased fertility, and decreased implantations. In female mice, fertility was not affected but maternal toxicities were observed at 1.5 mg/kg/day administered intravenously (about 1/200 the human dose on a mg/m2 basis) and fetotoxicity or embryolethality was observed at 0.25 mg/kg/day administered intravenously (about 1/1300 the human dose on a mg/m2 basis).

CLINICAL STUDIES

Ovarian Cancer

The safety and efficacy of Gemzar was studied in a randomized trial of 356 women with advanced ovarian cancer that had relapsed at least 6 months after first-line platinum-based therapy. Patients were randomized to receive either Gemzar 1000 mg/m2 on Days 1 and 8 of a 21-day cycle and carboplatin AUC 4 administered after Gemzar infusion on Day 1 of each cycle (n=178) or to carboplatin AUC 5 administered on Day 1 of each 21-day cycle (n=178). The primary efficacy outcome measure was progression free survival (PFS).

Patient characteristics are shown in Table 11. The addition of Gemzar to carboplatin resulted in statistically significant improvements in PFS and overall response rate as shown in Table 12 and Figure 1. Approximately 75% of patients in each arm received additional chemotherapy for disease progression; 13 of 120 patients in the carboplatin alone arm received Gemzar for treatment of disease progression. There was no significant difference in overall survival between the treatment arms.

Table 11: Randomized Trial of Gemzar plus Carboplatin versus Carboplatin in Ovarian Cancer - Baseline Demographics and Clinical Characteristics

a 5 patients on Gemzar plus carboplatin arm and 4 patients on carboplatin arm with no baseline Eastern Cooperative Oncology Group (ECOG) performance status.

b 2 on Gemzar plus carboplatin arm and 1 on carboplatin arm had platinum-free interval <6 months.

Gemzar/Carboplatin Carboplatin
 Number of randomized patients 178 178
 Median age, years 59 58
     Range 36 to 78 21 to 81
 Baseline ECOG performance status 0-1a 94% 95%
 Disease Status
     Evaluable 8% 3%
     Bidimensionally measurable 92% 96%
 Platinum-free intervalb
     6-12 months 40% 40%
     >12 months 59% 60%
 First-line therapy
     Platinum-taxane combination 70% 71%
     Platinum-non-taxane combination 29% 28%
     Platinum monotherapy 1% 1%
Table 12: Randomized Trial of Gemzar plus Carboplatin versus Carboplatin in Ovarian Cancer - Efficacy Outcomes

a CI=confidence interval.

b Log rank, unadjusted.

c Chi square.

d CR=Complete response.

e PR plus PRNM=Partial response plus partial response, non-measurable disease.

f Independently reviewed cohort - Gemzar/carboplatin (n=121), carboplatin (n=101); independent reviewers unable to measure disease detected by sonography or physical exam.

Gemzar/Carboplatin
(N=178)
Carboplatin
(N=178)
Progression-free Survival
     Median (95% CIa) months 8.6 (8.0, 9.7) 5.8 (5.2, 7.1)
     Hazard Ratio (95% CI) 0.72 (0.57, 0.90)
     p-valueb p=0.0038
Overall Survival
     Median (95% CI) months 18.0 (16.2, 20.3) 17.3 (15.2, 19.3)
     Hazard Ratio (95% CI) 0.98 (0.78, 1.24)
     p-valueb p=0.8977
Investigator Reviewed
Overall Response Rate 47.2% 30.9%
     p-valuec p=0.0016
     CRd 14.6% 6.2%
     PR plus PRNMe 32.6% 24.7%
Independently Reviewed
Overall Response Ratef 46.3% 35.6%
     p-valuec p=0.11
     CRd 9.1% 4.0%
     PR plus PRNMe 37.2% 31.7%

Figure 1: Kaplan-Meier Curve of Progression Free Survival in Gemzar plus Carboplatin versus Carboplatin in Ovarian Cancer (N=356).

Figure 1: Kaplan-Meier Curve of Progression Free Survival in Gemzar plus Carboplatin versus Carboplatin in Ovarian Cancer (N=356).

Breast Cancer

The safety and efficacy of Gemzar were evaluated in a multi-national, randomized, open-label trial conducted in women receiving initial treatment for metastatic breast cancer in women who have received prior adjuvant/neoadjuvant anthracycline chemotherapy unless clinically contraindicated. Patients were randomized to receive Gemzar 1250 mg/m2 on Days 1 and 8 of a 21-day cycle and paclitaxel 175 mg/m2 administered prior to Gemzar on Day 1 of each cycle (n=267) or to receive paclitaxel 175 mg/m2 was administered on Day 1 of each 21-day cycle (n=262). The primary efficacy outcome measure was time to documented disease progression.

A total of 529 patients were enrolled; 267 were randomized to Gemzar and paclitaxel and 262 to paclitaxel alone. Demographic and baseline characteristics were similar between treatment arms (see Table 13). Efficacy results are presented in Table 13 and Figure 2. The addition of Gemzar to paclitaxel resulted in statistically significant improvement in time to documented disease progression and overall response rate compared to paclitaxel alone. There was no significant difference in overall survival.

Table 13: Randomized Trial of Gemzar plus Paclitaxel versus Paclitaxel in Breast Cancer

a Karnofsky Performance Status.

b These represent reconciliation of investigator and Independent Review Committee assessments according to a predefined algorithm.

c Based on the ITT population.

Gemzar/Paclitaxel Paclitaxel
Number of patients 267 262
Demographic/Entry Characteristics
   Median age (years) 53 52
         Range 26 to 83 26 to 75
   Metastatic disease 97% 97%
   Baseline KPSa ≥90 70% 74%
   Number of tumor sites
         1-2 57% 59%
         ≥3 43% 41%
   Visceral disease 73% 73%
   Prior anthracycline 97% 96%
Efficacy Outcomes
   Time to Documented Disease Progressionb
         Median in months
(95% CI)
5.2
(4.2, 5.6)
2.9
(2.6, 3.7)
         Hazard Ratio (95% CI) 0.650 (0.524, 0.805)
   p-value p<0.0001
   Overall Survivalc
         Median Survival in months
(95% CI)
18.6
(16.5, 20.7)
15.8
(14.1, 17.3)
         Hazard Ratio (95% CI) 0.86 (0.71, 1.04)
   p-value Not Significant
   Overall Response Rate 40.8% 22.1%
         (95% CI) (34.9, 46.7) (17.1, 27.2)
   p-value p<0.0001

Figure 2: Kaplan-Meier Curve of Time to Documented Disease Progression in Gemzar plus Paclitaxel versus Paclitaxel Breast Cancer Study (N=529).

Figure 2: Kaplan-Meier Curve of Time to Documented Disease Progression in Gemzar plus Paclitaxel versus Paclitaxel Breast Cancer Study (N=529).

Non-Small Cell Lung Cancer (NSCLC)

The safety and efficacy of Gemzar was evaluated in two randomized, multicenter trials.

28-Day Schedule

A multinational, randomized trial compared Gemzar plus cisplatin to cisplatin alone in the treatment of patients with inoperable Stage IIIA, IIIB, or IV NSCLC who had not received prior chemotherapy. Patients were randomized to receive Gemzar 1000 mg/m2 on Days 1, 8, and 15 of a 28-day cycle with cisplatin 100 mg/m2 administered on Day 1 of each cycle or to receive cisplatin 100 mg/m2 on Day 1 of each 28-day cycle. The primary efficacy outcome measure was overall survival. A total of 522 patients were enrolled at clinical centers in Europe, the US, and Canada. Patient demographics and baseline characteristics (shown in Table 14) were similar between arms with the exception of histologic subtype of NSCLC, with 48% of patients on the cisplatin arm and 37% of patients on the Gemzar plus cisplatin arm having adenocarcinoma. Efficacy results are presented in Table 14 and Figure 3 for overall survival.

21-Day Schedule

A randomized (1:1), multicenter trial was conducted in 135 patients with Stage IIIB or IV NSCLC. Patients were randomized to receive Gemzar 1250 mg/m2 on Days 1 and 8, and cisplatin 100 mg/m2 on Day 1 of a 21-day cycle or to receive etoposide 100 mg/m2 intravenously on Days 1, 2, and 3 and cisplatin 100 mg/m2 on Day 1 of a 21 -day cycle.

There was no significant difference in survival between the two treatment arms (Log rank p=0.18, two-sided, see Table 14). The median survival was 8.7 months for the Gemzar plus cisplatin arm versus 7.0 months for the etoposide plus cisplatin arm. Median time to disease progression for the Gemzar plus cisplatin arm was 5.0 months compared to 4.1 months on the etoposide plus cisplatin arm (Log rank p=0.015, two-sided). The objective response rate for the Gemzar plus cisplatin arm was 33% compared to 14% on the etoposide plus cisplatin arm (Fisher's Exact p=0.01, two-sided).

Figure 3: Kaplan-Meier Survival Curve in Gemzar plus Cisplatin versus Cisplatin in Patients with NSCLC Study (N=522).

Figure 3: Kaplan-Meier Survival Curve in Gemzar plus Cisplatin versus Cisplatin in Patients with NSCLC Study (N=522).

Table 14: Randomized Trials of Gemzar plus Cisplatin in Patients with NSCLC

a 28-day schedule — Gemzar plus cisplatin: Gemzar 1000 mg/m2 on Days 1, 8, and 15 and cisplatin 100 mg/m2 on Day 1 every 28 days; Single-agent cisplatin: cisplatin 100 mg/m2 on Day 1 every 28 days.

b 21-day schedule — Gemzar plus cisplatin: Gemzar 1250 mg/m2 on Days 1 and 8 and cisplatin 100 mg/m2 on Day 1 every 21 days; Etoposide plus Cisplatin: cisplatin 100 mg/m2 on Day 1 and intravenous etoposide 100 mg/m2 on Days 1, 2, and 3 every 21 days.

c N/A Not applicable.

d Karnofsky Performance Status.

e CI=confidence intervals.

f p-value two-sided Fisher's Exact test for difference in binomial proportions; log rank test for time-to-event analyses.

Trial 28-day Schedule a 21-day Schedule b
Treatment Arm Gemzar plus Cisplatin Cisplatin Gemzar plus Cisplatin Etoposide plus Cisplatin
Number of patients 260 262 69 66
Demographic/Entry Characteristics
     Male 70% 71% 93% 92%
Median age, years 62 63 58 60
     Range 36 to 88 35 to 79 33 to 76 35 to 75
Stage IIIA 7% 7% N/Ac N/Ac
Stage IIIB 26% 23% 48% 52%
Stage IV 67% 70% 52% 49%
Baseline KPSd 70 to 80 41% 44% 45% 52%
Baseline KPSd 90 to 100 57% 55% 55% 49%
Efficacy Outcomes
Survival
     Median in months 9.0 7.6 8.7 7.0
     (95% CIe) months 8.2, 11.0 6.6, 8.8 7.8, 10.1 6.0, 9.7
p-valuef p=0.008 p=0.18
Time to Disease Progression
     Median in months 5.2 3.7 5.0 4.1
     (95% CIe) months 4.2, 5.7 3.0, 4.3 4.2, 6.4 2.4, 4.5
     p-valuef p=0.009 p=0.015
Tumor Response 26% 10% 33% 14%
     p-valuef p<0.0001 p=0.01

Pancreatic Cancer

The safety and efficacy of Gemzar was evaluated in two trials, a randomized, single-blind, two-arm, active-controlled trial conducted in patients with locally advanced or metastatic pancreatic cancer who had received no prior chemotherapy and in a single-arm, open-label, multicenter trial conducted in patients with locally advanced or metastatic pancreatic cancer previously treated with 5-FU or a 5-FU-containing regimen. The first trial randomized patients to receive Gemzar 1000 mg/m2 intravenously over 30 minutes once weekly for 7 weeks followed by a one-week rest, then once weekly dosing for 3 consecutive weeks every 28-days in subsequent cycles (n=63) or to 5-fluorouracil (5-FU) 600 mg/m2 intravenously over 30 minutes once weekly (n=63). In the second trial, all patients received Gemzar 1000 mg/m2 intravenously over 30 minutes once weekly for 7 weeks followed by a one-week rest, then once weekly dosing for 3 consecutive weeks every 28-days in subsequent cycles.

The primary efficacy outcome measure in both trials was "clinical benefit response". A patient was considered to have had a clinical benefit response if either of the following occurred:

  • The patient achieved a ≥50% reduction in pain intensity (Memorial Pain Assessment Card) or analgesic consumption, or a 20-point or greater improvement in performance status (Karnofsky Performance Status) for a period of at least 4 consecutive weeks, without showing any sustained worsening in any of the other parameters. Sustained worsening was defined as 4 consecutive weeks with either any increase in pain intensity or analgesic consumption or a 20-point decrease in performance status occurring during the first 12 weeks of therapy.

OR

  • The patient was stable on all of the aforementioned parameters, and showed a marked, sustained weight gain (≥7% increase maintained for ≥4 weeks) not due to fluid accumulation.

The randomized trial enrolled 126 patients across 17 sites in the US and Canada. The demographic and entry characteristics were similar between the arms (Table 15). The efficacy outcome results are shown in Table 15 and for overall survival in Figure 4. Patients treated with Gemzar had statistically significant increases in clinical benefit response, survival, and time to disease progression compared to those randomized to receive 5-FU. No confirmed objective tumor responses were observed in either treatment arm.

Table 15: Randomized Trial of Gemzar versus 5-Fluorouracil in Pancreatic Cancer

a Karnofsky Performance Status.

b p-value for clinical benefit response calculated using the two-sided test for difference in binomial proportions. All other p-values are calculated using log rank test.

Gemzar 5-FU
Number of patients 63 63
Demographic/Entry Characteristics
      Male
54% 54%
Median age 62 years 61 years
      Range 37 to 79 36 to 77
Stage IV disease 71% 76%
Baseline KPSa ≤70 70% 68%
Efficacy Outcomes
Clinical benefit response 22.2% 4.8%
p-valueb p=0.004
Survival
      Median 5.7 months 4.2 months
      (95% CI) (4.7, 6.9) (3.1, 5.1)
      p-valueb p=0.0009
Time to Disease Progression
      Median 2.1 months 0.9 months
      (95% CI) (1.9, 3.4) (0.9, 1.1)
      p-valueb p=0.0013

Figure 4: Kaplan-Meier Survival Curve.

Figure 4: Kaplan-Meier Survival Curve.

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