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Mechanism of Action
ZOLADEX is a synthetic decapeptide analogue of GnRH. ZOLADEX acts as an inhibitor of pituitary gonadotropin secretion when administered in the biodegradable formulation. In animal and in vitro studies, administration of goserelin resulted in the regression or inhibition of growth of the hormonally sensitive dimethylbenzanthracene (DMBA)-induced rat mammary tumor and Dunning R3327 prostate tumor.
Following initial administration in males, ZOLADEX causes an initial increase in serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels with subsequent increases in serum levels of testosterone. Chronic administration of ZOLADEX leads to sustained suppression of pituitary gonadotropins, and serum levels of testosterone consequently fall into the range normally seen in surgically castrated men approximately 2-4 weeks after initiation of therapy. This leads to accessory sex organ regression. In clinical trials with follow-up of more than 2 years, suppression of serum testosterone to castrate levels has been maintained for the duration of therapy.
In females, a similar down-regulation of the pituitary gland by chronic exposure to ZOLADEX leads to suppression of gonadotropin secretion, a decrease in serum estradiol to levels consistent with the postmenopausal state, and would be expected to lead to a reduction of ovarian size and function, reduction in the size of the uterus and mammary gland, as well as a regression of sex hormone-responsive tumors, if present. Serum estradiol is suppressed to levels similar to those observed in postmenopausal women within 3 weeks following initial administration; however, after suppression was attained, isolated elevations of estradiol were seen in 10% of the patients enrolled in clinical trials. Serum LH and FSH are suppressed to follicular phase levels within four weeks after initial administration of drug and are usually maintained at that range with continued use of ZOLADEX. In 5% or less of women treated with ZOLADEX, FSH and LH levels may not be suppressed to follicular phase levels on day 28 post treatment with use of a single 3.6 mg depot injection. In certain individuals, suppression of any of these hormones to such levels may not be achieved with ZOLADEX. Estradiol, LH and FSH levels return to pretreatment values within 12 weeks following the last implant administration in all but rare cases.
The pharmacokinetics of ZOLADEX have been determined in both male and female healthy volunteers and patients. In these studies, ZOLADEX was administered as a single 250 mcg (aqueous solution) dose and as a single or multiple 3.6 mg depot dose by subcutaneous route.
The absorption of radiolabeled drug was rapid, and the peak blood radioactivity levels occurred between 0.5 and 1.0 hour after dosing. The mean (± standard deviation) pharmacokinetic parameter estimates of ZOLADEX after administration of 3.6 mg depot for 2 months in males and females are presented in the following table.
Table 7 : Pharmacokinetic Parameter Estimates
|Peak Plasma Concentration (ng/mL)||2.84 ± 1.81||1.46 ± 0.82|
|Time to Peak Concentration (days)||12-15||8-22|
|Area Under the Curve (0-28 days) (ng.d/mL)||27.8 ± 15.3||18.5 ± 10.3|
|Systemic Clearance (mL/min)||110.5 ± 47.5||163.9 ± 71.0|
Goserelin is released from the depot at a much slower rate initially for the first 8 days, and then there is more rapid and continuous release for the remainder of the 28-day dosing period. Despite the change in the releasing rate of goserelin, administration of ZOLADEX every 28 days resulted in testosterone levels that were suppressed to and maintained in the range normally seen in surgically castrated men.
When ZOLADEX 3.6 mg depot was used for treating male and female patients with normal renal and hepatic function, there was no significant evidence of drug accumulation. However, in clinical trials the minimum serum levels of a few patients were increased. These levels can be attributed to interpatient variation.
The apparent volumes of distribution determined after subcutaneous administration of 250 mcg aqueous solution of goserelin were 44.1 and 20.3 liters for males and females, respectively. The plasma protein binding of goserelin obtained from one sample was found to be 27.3%.
Metabolism of goserelin, by hydrolysis of the C-terminal amino acids, is the major clearance mechanism. The major circulating component in serum appeared to be 1-7 fragment, and the major component presented in urine of one healthy male volunteer was 5-10 fragment. The metabolism of goserelin in humans yields a similar but narrow profile of metabolites to that found in other species. All metabolites found in humans have also been found in toxicology species.
Clearance of goserelin following subcutaneous administration of the solution formulation of goserelin is very rapid and occurs via a combination of hepatic metabolism and urinary excretion. More than 90% of a subcutaneous radiolabeled solution formulation dose of goserelin is excreted in urine. Approximately 20% of the dose in urine is accounted for by unchanged goserelin. The total body clearance of goserelin (administered subcutaneously as a 3.6 mg depot) was significantly (p < 0.05) greater (163.9 versus 110.5 L/min) in females compared to males.
Stage B2-C Prostatic Carcinoma
The effects of hormonal treatment combined with radiation were studied in 466 patients (231 ZOLADEX + flutamide + radiation, 235 radiation alone) with bulky primary tumors confined to the prostate (stage B2) or extending beyond the capsule (stage C), with or without pelvic node involvement.
In this multicentered, controlled trial, administration of ZOLADEX (3.6 mg depot) and flutamide capsules (250 mg t.i.d.) prior to and during radiation was associated with a significantly lower rate of local failure compared to radiation alone (16% vs 33% at 4 years, P < 0.001). The combination therapy also resulted in a trend toward reduction in the incidence of distant metastases (27% vs 36% at 4 years, P =0.058). Median disease-free survival was significantly increased in patients who received complete hormonal therapy combined with radiation as compared to those patients who received radiation alone (4.4 vs 2.6 years, P < 0.001). Inclusion of normal PSA level as a criterion for disease-free survival also resulted in significantly increased median disease-free survival in patients receiving the combination therapy (2.7 vs 1.5 years, P < 0.001).
In controlled studies of patients with advanced prostatic cancer comparing ZOLADEX to orchiectomy, the long-term endocrine responses and objective responses were similar between the two treatment arms. Additionally, duration of survival was similar between the two treatment arms in a comparative trial.
In controlled clinical studies using the 3.6 mg formulation every 28 days for 6 months, ZOLADEX was shown to be as effective as danazol therapy in relieving clinical symptoms (dysmenorrhea, dyspareunia and pelvic pain) and signs (pelvic tenderness, pelvic induration) of endometriosis and decreasing the size of endometrial lesions as determined by laparoscopy. In one study comparing ZOLADEX with danazol (800 mg/day), 63% of ZOLADEX-treated patients and 42% of danazol-treated patients had a greater than or equal to 50% reduction in the extent of endometrial lesions. In the second study comparing ZOLADEX with danazol (600 mg/day), 62% of ZOLADEX-treated and 51% of danazol-treated patients had a greater than or equal to 50% reduction in the extent of endometrial lesions. The clinical significance of a decrease in endometriotic lesions is not known at this time; and in addition, laparoscopic staging of endometriosis does not necessarily correlate with severity of symptoms.
In these two studies, ZOLADEX led to amenorrhea in 92% and 80%, respectively, of all treated women within 8 weeks after initial administration. Menses usually resumed within 8 weeks following completion of therapy.
Within 4 weeks following initial administration, clinical symptoms were significantly reduced, and at the end of treatment were, on average, reduced by approximately 84%.
During the first two months of ZOLADEX use, some women experience vaginal bleeding of variable duration and intensity. In all likelihood, this bleeding represents estrogen withdrawal bleeding, and is expected to stop spontaneously.
There is insufficient evidence to determine whether pregnancy rates are enhanced or adversely affected by the use of ZOLADEX.
Trial 0022, was a double-blind, prospective, randomized, parallel-group multicenter trial conducted in 358 premenopausal women with dysfunctional uterine bleeding. Eligible patients were randomized to receive either two depots of ZOLADEX 3.6 mg (n=180) or two placebo injections (n=178) administered four weeks apart. 175 patients in each group underwent endometrial ablation using either diathermy loop alone or in combination with rollerball approximately 2 weeks after the second injection. Endometrial thickness was assessed immediately before surgery using a transvaginal ultrasonic probe. The incidence of amenorrhea was compared between the ZOLADEX and placebo groups at 24 weeks after endometrial ablation.
The median endometrial thickness before surgery was significantly less in the ZOLADEX treatment group (1.50 mm) compared to the placebo group (3.55 mm). Six months after surgery, 40% of patients (70/175) treated with ZOLADEX in Trial 0022 reported amenorrhea as compared with 26% who had received placebo injections (44/171), a difference that was statistically significant.
Trial 0003, was a single center, open-label, randomized trial in premenopausal women with dysfunctional uterine bleeding. The trial allowed for a comparison of 1 depot of ZOLADEX and 2 depots of ZOLADEX administered 4 weeks apart with ablation using Nd: YAG laser occurring 4 weeks after ZOLADEX administration. Forty patients were randomized into each of the ZOLADEX treatment groups.
The median endometrial thickness before surgery was significantly less in the group treated with two depots (0.5 mm) compared to the group treated with one depot (1 mm). No difference in the incidence of amenorrhea was found at 24 weeks (24% in both groups). Of the 74 patients that completed the trial, 53% reported hypomenorrhea and 20% reported normal menses six months after surgery.
The Southwest Oncology Group conducted a prospective, randomized clinical trial (SWOG-8692 [INT- 0075]) in premenopausal women with advanced estrogen receptor positive or progesterone receptor positive breast cancer which compared ZOLADEX with oophorectomy. On the basis of interim data from 124 women, the best objective response (CR+PR) for the ZOLADEX group is 22% versus 12% for the oophorectomy group. The median time to treatment failure is 6.7 months for patients treated with ZOLADEX and 5.5 months for patients treated with oophorectomy. The median survival time for the ZOLADEX arm is 33.2 months and for the oophorectomy arm is 33.6 months.
Subjective responses based on measures of pain control and performance status were observed with both treatments; 48% of the women in the ZOLADEX treatment group and 50% in the oophorectomy group had subjective responses. In the clinical trial (SWOG-8692 [INT-0075]), the mean post treatment estradiol level was reported as 17.8 pg/mL. (The mean estradiol level in post-menopausal women as reported in the literature is 13 pg/mL). During the conduct of the clinical trial, women whose estradiol levels were not reduced to the postmenopausal range, received two ZOLADEX depots, thus, increasing the dose of ZOLADEX from 3.6 mg to 7.2 mg.
Findings were similar in uncontrolled clinical trials involving patients with hormone receptor positive and negative breast cancer. Premenopausal women with estrogen receptor (ER) status of positive, negative, or unknown participated in the uncontrolled (Phase II and Trial 2302) clinical trials. Objective tumor responses were seen regardless of ER status, as shown in the following table.
Table 8 : OBJECTIVE RESPONSE BY ER STATUS
|ER Status||CR + PR/Total No.
Last reviewed on RxList: 7/1/2013
This monograph has been modified to include the generic and brand name in many instances.
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