Epirubicin is an anthracycline cytotoxic agent. Although it is known that anthracyclines can interfere with a number of biochemical and biological functions within eukaryotic cells, the precise mechanisms of epirubicin’s cytotoxic and/or antiproliferative properties have not been completely elucidated.
Epirubicin forms a complex with DNA by intercalation of its planar rings between nucleotide base pairs, with consequent inhibition of nucleic acid (DNA and RNA) and protein synthesis. Such intercalation triggers DNA cleavage by topoisomerase II, resulting in cytocidal activity. Epirubicin also inhibits DNA helicase activity, preventing the enzymatic separation of double-stranded DNA and interfering with replication and transcription. Epirubicin is also involved in oxidation/reduction reactions by generating cytotoxic free radicals. The antiproliferative and cytotoxic activity of epirubicin is thought to result from these or other possible mechanisms.
Epirubicin is cytotoxic in vitro to a variety of established murine and human cell lines and primary cultures of human tumors. It is also active in vivo against a variety of murine tumors and human xenografts in athymic mice, including breast tumors.
Epirubicin pharmacokinetics are linear over the dose range of 60 to 150 mg/m2 and plasma clearance is not affected by the duration of infusion or administration schedule. Pharmacokinetic parameters for epirubicin following 6- to 10-minute, single-dose intravenous infusions of epirubicin at doses of 60 to 150 mg/m2 in patients with solid tumors are shown in Table 1. The plasma concentration declined in a triphasic manner with mean half-lives for the alpha, beta, and gamma phases of about 3 minutes, 2.5 hours, and 33 hours, respectively.
Table 1. Summary of Mean (±SD) Pharmacokinetic Parameters in Patients1 with Solid Tumors Receiving Intravenous Epirubicin 60 to 150 mg/m2
| Dose 2 (mg/m 2 ) || C max 3 (mcg/mL) || (mcg•h/mL) AUC 4 || t 1/2 5 (hours) || CL 6 (L/hour) || Vss 7 (L/kg) |
|1 Advanced solid tumor cancers, primarily of the lung|
|2 N=6 patients per dose level|
|3 Plasma concentration at the end of 6 to 10 minute infusion|
|4 Area under the plasma concentration curve|
|5 Half-life of terminal phase|
|6 Plasma clearance|
|7 Steady state volume of distribution|
|60||5.7 ± 1.6||1.6 ± 0.2||35.3 ± 9||65 ± 8||21 ± 2|
|75||5.3 ± 1.5||1.7 ± 0.3||32.1 ± 5||83 ± 14||27 ± 11|
|120||9.0 ± 3.5||3.4 ± 0.7||33.7 ± 4||65 ± 13||23 ± 7|
|150||9.3 ± 2.9||4.2 ± 0.8||31.1 ± 6||69 ± 13||21 ± 7|
Following intravenous administration, epirubicin is rapidly and widely distributed into the tissues. Binding of epirubicin to plasma proteins, predominantly albumin, is about 77% and is not affected by drug concentration. Epirubicin also appears to concentrate in red blood cells; whole blood concentrations are approximately twice those of plasma.
Epirubicin is extensively and rapidly metabolized by the liver and is also metabolized by other organs and cells, including red blood cells. Four main metabolic routes have been identified:
(1) reduction of the C-13 keto-group with the formation of the 13(S)-dihydro derivative, epirubicinol; (2) conjugation of both the unchanged drug and epirubicinol with glucuronic acid; (3) loss of the amino sugar moiety through a hydrolytic process with the formation of the doxorubicin and doxorubicinol aglycones; and (4) loss of the amino sugar moiety through a redox process with the formation of the 7-deoxy-doxorubicin aglycone and 7-deoxy-doxorubicinol aglycone. Epirubicinol has in vitro cytotoxic activity one-tenth that of epirubicin. As plasma levels of epirubicinol are lower than those of the unchanged drug, they are unlikely to reach in vivo concentrations sufficient for cytotoxicity. No significant activity or toxicity has been reported for the other metabolites.
Epirubicin and its major metabolites are eliminated through biliary excretion and, to a lesser extent, by urinary excretion. Mass-balance data from 1 patient found about 60% of the total radioactive dose in feces (34%) and urine (27%). These data are consistent with those from 3 patients with extrahepatic obstruction and percutaneous drainage, in whom approximately 35% and 20% of the administered dose were recovered as epirubicin or its major metabolites in bile and urine, respectively, in the 4 days after treatment.
Pharmacokinetics in Special Populations
A population analysis of plasma data from 36 cancer patients (13 males and 23 females, 20 to 73 years) showed that age affects plasma clearance of epirubicin in female patients. The predicted plasma clearance for a female patient of 70 years of age was about 35% lower than that for a female patient of 25 years of age. An insufficient number of males > 50 years of age were included in the study to draw conclusions about age-related alterations in clearance in males. Although a lower epirubicin starting dose does not appear necessary in elderly female patients, and was not used in clinical trials, particular care should be taken in monitoring toxicity when epirubicin is administered to female patients > 70 years of age. (See PRECAUTIONS.)
In patients ≤50 years of age, mean clearance values in adult male and female patients were similar. The clearance of epirubicin is decreased in elderly women (see Pharmacokinetics in Special Populations - Age).
The pharmacokinetics of epirubicin in pediatric patients have not been evaluated.
The influence of race on the pharmacokinetics of epirubicin has not been evaluated.
Epirubicin is eliminated by both hepatic metabolism and biliary excretion and clearance is reduced in patients with hepatic dysfunction. In a study of the effect of hepatic dysfunction, patients with solid tumors were classified into 3 groups. Patients in Group 1 (n=22) had serum AST (SGOT) levels above the upper limit of normal (median: 93 IU/L) and normal serum bilirubin levels (median: 0.5 mg/dL) and were given epirubicin doses of 12.5 to 90 mg/m2. Patients in Group 2 had alterations in both serum AST (median: 175 IU/L) and bilirubin levels (median: 2.7 mg/dL) and were treated with an epirubicin dose of 25 mg/m2 (n=8). Their pharmacokinetics were compared to those of patients with normal serum AST and bilirubin values, who received epirubicin doses of 12.5 to 120 mg/m2. The median plasma clearance of epirubicin was decreased compared to patients with normal hepatic function by about 30% in patients in Group 1 and by 50% in patients in Group 2. Patients with more severe hepatic impairment have not been evaluated. (See WARNINGS and DOSAGE AND ADMINISTRATION.)
No significant alterations in the pharmacokinetics of epirubicin or its major metabolite, epirubicinol, have been observed in patients with serum creatinine < 5 mg/dL. A 50% reduction in plasma clearance was reported in four patients with serum creatinine ≥ 5 mg/dL (see WARNINGS and DOSAGE AND ADMINISTRATION). Patients on dialysis have not been studied.
Coadministration of paclitaxel or docetaxel did not affect the pharmacokinetics of epirubicin when given immediately following the taxane.
Coadministration of cimetidine (400 mg twice daily for 7 days starting 5 days before chemotherapy) increased the mean AUC of epirubicin (100 mg/m2) by 50% and decreased its plasma clearance by 30% (see PRECAUTIONS).
Drugs metabolized by cytochrome P-450 enzymes
No systematic in vitro or in vivo evaluation has been performed to examine the potential for inhibition or induction by epirubicin of oxidative cytochrome P-450 isoenzymes.
Two randomized, open-label, multicenter studies evaluated the use of Epirubicin Hydrochloride Injection 100 to 120 mg/m2 in combination with cyclophosphamide and fluorouracil for the adjuvant treatment of patients with axillary-node positive breast cancer and no evidence of distant metastatic disease (Stage II or III). Study MA-5 evaluated 120 mg/m2 of epirubicin per course in combination with cyclophosphamide and fluorouracil (CEF120 regimen). This study randomized premenopausal and perimenopausal women with one or more positive lymph nodes to an epirubicin- containing CEF-120 regimen or to a CMF regimen. Study GFEA-05 evaluated the use of 100 mg/m2 of epirubicin per course in combination with fluorouracil and cyclophosphamide (FEC-100). This study randomized pre- and postmenopausal women to the FEC-100 regimen or to a lower-dose FEC-50 regimen. In the GFEA-05 study, eligible patients were either required to have ≥ 4 nodes involved with tumor or, if only 1 to 3 nodes were positive, to have negative estrogen- and progesterone-receptors and a histologic tumor grade of 2 or 3. A total of 1281 women participated in these studies. Patients with T4 tumors were not eligible for either study. Table 2 shows the treatment regimens that the patients received. The primary endpoint of the trials was relapse-free survival, ie, time to occurrence of a local, regional, or distant recurrence, or disease-related death. Patients with contralateral breast cancer, second primary malignancy or death from causes other than breast cancer were censored at the time of the last visit prior to these events.
Table 2. Treatment Regimens Used in Phase 3 Studies of Patients with Early Breast Cancer
|1In women who underwent lumpectomy, breast irradiation was to be administered after completion of study chemotherapy.|
|2Patients also received prophylactic antibiotic therapy with trimethoprim-sulfamethoxazole or fluoroquinolone for the duration of their chemotherapy.|
|3All women were to receive breast irradiation after the completion of chemotherapy.|
|MA-51 N=716|| CEF-120 (total, 6 cycles)2 N=356||Cyclophosphamide ||75 mg/m2 PO, d 1 to 14, q 28 days|
|Epirubicin Hydrochloride Injection ||60 mg/m2 IV, d 1 & 8, q 28 days |
|Fluorouracil||500 mg/m2 IV, d 1 & 8, q 28 days |
| CMF (total, 6 cycles) N=360||Cyclophosphamide||100 mg/m2 PO, d 1 to 14, q 28 days|
|Methotrexate||40 mg/m2 IV, d 1 & 8, q 28 days|
|Fluorouracil||600 mg/m2 IV, d 1 & 8, q 28 days|
|GFEA-053 N=565|| FEC-100 (total, 6 cycles) N=276||Fluorouracil||500 mg/m2 IV, d 1, q 21 days|
|Epirubicin Hydrochloride Injection||100 mg/m2 IV, d 1, q 21 days|
|Cyclophosphamide||500 mg/m2 IV, d 1, q 21 days |
| FEC-50 (total, 6 cycles) N=289 ||Fluorouracil||500 mg/m2 IV, d 1, q 21 days|
|Tamoxifen 30 mg daily x 3 years,||Epirubicin Hydrochloride Injection||50 mg/m2 IV, d 1, q 21 days|
|postmenopausal women, any receptor status||Cyclophosphamide||500 mg/m2 IV, d 1, q 21 days|
In the MA-5 trial, the median age of the study population was 45 years. Approximately 60% of patients had 1 to 3 involved nodes and approximately 40% had ≥ 4 nodes involved with tumor. In the GFEA-05 study, the median age was 51 years and approximately half of the patients were postmenopausal. About 17% of the study population had 1 to 3 positive nodes and 80% of patients had ≥ 4 involved lymph nodes. Demographic and tumor characteristics were well-balanced between treatment arms in each study.
The efficacy endpoints of relapse-free survival (RFS) and overall survival (OS) were analyzed using Kaplan-Meier methods in the intent-to-treat (ITT) patient populations in each study. Results for endpoints were initially analyzed after up to 5 years of follow-up and these results are presented in the text below and in Table 3. Results after up to 10 years of follow-up are presented in Table 3. In Study MA-5, epirubicin-containing combination therapy (CEF-120) showed significantly longer RFS than CMF (5-year estimates were 62% versus 53%, stratified logrank for the overall RFS p=0.013). The estimated reduction in the risk of relapse was 24% at 5 years. The OS was also greater for the epirubicin-containing CEF-120 regimen than for the CMF regimen (5-year estimate 77% versus 70%; stratified logrank for overall survival p=0.043; non-stratified logrank p=0.13). The estimated reduction in the risk of death was 29% at 5 years.
In Study GFEA-05, patients treated with the higher-dose epirubicin regimen (FEC-100) had a significantly longer 5- year RFS (estimated 65% versus 52%, logrank for the overall RFS p=0.007) and OS (estimated 76% versus 65%, logrank for the overall survival p=0.007) than patients given the lower dose regimen (FEC-50). The estimated reduction in risk of relapse was 32% at 5 years. The estimated reduction in the risk of death was 31% at 5 years. Results of follow-up up to 10 years (median follow-up = 8.8 years and 8.3 years, respectively for Study MA-5 and Study GFEA-05) are presented in Table 3.
Although the trials were not powered for subgroup analyses, in the MA-5 study improvements in favor of CEF-120 vs. CMF were observed, in RFS and OS both in patients with 1-3 node positive and in those with ≥4 node positive tumor involvement. In the GFEA-05 study improvements in RFS and OS were observed in both pre- and postmenopausal women treated with FEC-100 compared to FEC-50.
Table 3. Efficacy Results from Phase 3 Studies of Patients with Early Breast Cancer*
|MA-5 Study||GFEA-05 Study|
|*Based on Kaplan-Meier estimates|
|**Patients in MA-5 were stratified by nodal status (1 to 3, 4 to 10, and > 10 positive nodes), type of initial surgery (lumpectomy versus mastectomy), and by hormone receptor status (ER or PR positive (≥10 fmol), both negative (<10 fmol), or unknown staus). Patients in GFEA-05 were stratified by nodal status (1 to 3, 4 to 10, and > 10 positive nodes).|
|†Hazard ratio: CMF:CEF-120 in MA-5, FEC-50:FEC-100 in GFEA-05|
| RFS at 5 yrs (%) ||62||53||65||52|
|2-sided 95% CI||(0.60, 0.96)||(0.52,0.89)|
|Log-rank Test stratified**||(p = 0.013)||(p = 0.007)|
| OS at 5 yrs (%) ||77||70||76||65|
|2-sided 95% CI||(0.52, 0.98)||(0.51,0.92)|
|Log-rank Test stratified**||(p = 0.043) ||(p = 0.007)|
|(unstratified p = 0.13)|
| RFS at 10 yrs (%) ||51||44||49||43|
|2-sided 95% CI||(0.63, 0.95)||(0.62,0.99)|
|Log-rank Test stratified**||(p = 0.017)||(p = 0.040)|
|(unstratified p = 0.023)||(unstratified p = 0.09)|
| OS at 10 yrs (%) ||61||57||56||50|
|2-sided 95% CI||(0.65, 1.04)||(0.58,0.96)|
|Log-rank Test stratified**||(p = 0.100) ||(p = 0.023)|
|(unstratified p = 0.18)||(unstratified p = 0.039)|
The Kaplan-Meier curves for RFS and OS from Study MA-5 are shown in Figures 1 and 2 and those for Study GFEA-05 are shown in Figures 3 and 4.
See Table 3 for statistics on 5 and 10 year analyses.