1.1 Adjuvant Treatment of Postmenopausal Women
Exemestane Tablets are indicated for adjuvant treatment of postmenopausal women with estrogen-receptor positive early breast cancer who have received two to three years of tamoxifen and are switched to Exemestane Tablets for completion of a total of five consecutive years of adjuvant hormonal therapy (14.1).
1.2 Advanced Breast Cancer in Postmenopausal Women
Exemestane Tablets are indicated for the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen therapy (14.2).
Exemestane Tablets Dosage and Administration
Recommended Dose
The recommended dose of Exemestane Tablets in early and advanced breast cancer is one 25 mg tablet once daily after a meal.
- adjuvant treatment of postmenopausal women with estrogen-receptor positive early breast cancer who have received two to three years of tamoxifen and are switched to exemestane for completion of a total of five consecutive years of adjuvant hormonal therapy .
- the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen therapy.
Dose Modifications
For patients receiving Exemestane Tablets with a potent CYP 3A4 inducer such as rifampicin or phenytoin, the recommended dose of Exemestane Tablets is 50 mg once daily after a meal.
The safety of chronic dosing in patients with moderate or severe hepatic or renal impairment has not been studied. Based on experience with exemestane at repeated doses up to 200 mg daily that demonstrated a moderate increase in non life-threatening adverse events, dosage adjustment does not appear to be necessary [seeUse In Specific Populations (8.5and8.6)].
Dosage Forms and Strengths
Exemestane Tablets are round, white film coated, biconvex tablets, debossed with product identification "54 571" on one side and plain on the other side. Each tablet contains 25 mg of exemestane.
Contraindications
Hypersensitivity
Exemestane Tablets are contraindicated in patients with a known hypersensitivity to the drug or to any of the excipients.
Pregnancy
Exemestane Tablets can cause fetal harm when administered to a pregnant woman. Based on its mechanism of action exemestane is expected to result in adverse reproductive effects. In non-clinical studies in rats and rabbits, exemestane was embryotoxic, fetotoxic, and abortifacient.
Exemestane Tablets are contraindicated in women who are or may become pregnant. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus.
Exemestane Tablets should not be administered to premenopausal women [see Use in Specific Populations (8.1)].
Warnings and Precautions
Administration with Estrogen-Containing Agents
Exemestane should not be coadministered with estrogen-containing agents as these could interfere with its pharmacologic action.
Laboratory Tests
In patients with early breast cancer, the incidence of hematological abnormalities of Common Toxicity Criteria (CTC) grade ≥1 was lower in the exemestane treatment group, compared with tamoxifen. Incidence of CTC grade 3 or 4 abnormalities was low (approximately 0.1%) in both treatment groups. Approximately 20% of patients receiving exemestane in clinical studies in advanced breast cancer experienced CTC grade 3 or 4 lymphocytopenia. Of these patients, 89% had a pre-existing lower grade lymphopenia. Forty percent of patients either recovered or improved to a lesser severity while on treatment. Patients did not have a significant increase in viral infections, and no opportunistic infections were observed. Elevations of serum levels of AST, ALT, alkaline phosphatase, and gamma glutamyl transferase > 5 times the upper value of the normal range (i.e., ≥ CTC grade 3) have been rarely reported in patients treated for advanced breast cancer but appear mostly attributable to the underlying presence of liver and/or bone metastases. In the comparative study in advanced breast cancer patients, CTC grade 3 or 4 elevation of gamma glutamyl transferase without documented evidence of liver metastasis was reported in 2.7% of patients treated with exemestane and in 1.8% of patients treated with megestrol acetate.
In patients with early breast cancer, elevations in bilirubin, alkaline phosphatase, and creatinine were more common in those receiving exemestane than either tamoxifen or placebo. Treatment-emergent bilirubin elevations (any CTC grade) occurred in 5.3% of exemestane patients and 0.8% of tamoxifen patients on the Intergroup Exemestane Study (IES), and in 6.9% of exemestane treated patients vs. 0% of placebo treated patients in the 027 study. CTC grade 3–4 increases in bilirubin occurred in 0.9% of exemestane treated patients compared to 0.1% of tamoxifen treated patients. Alkaline phosphatase elevations of any CTC grade occurred in 15.0% of exemestane treated patients on the IES compared to 2.6% of tamoxifen treated patients, and in 13.7% of exemestane treated patients compared to 6.9% of placebo treated patients in study 027. Creatinine elevations occurred in 5.8% of exemestane treated patients and 4.3% of tamoxifen treated patients on the IES and in 5.5% of exemestane treated patients and 0% of placebo treated patients in study 027.
Reductions in Bone Mineral Density (BMD)
Reductions in bone mineral density (BMD) over time are seen with exemestane use. Table 1 describes changes in BMD from baseline to 24 months in patients receiving exemestane compared to patients receiving tamoxifen (IES) or placebo (027). Concomitant use of bisphosphonates, vitamin D supplementation, and calcium was not allowed.
Table 1. Percent Change in BMD from Baseline to 24 months, Exemestane vs. Control
|
IES |
027 |
| BMD |
Exemestane N=29 |
Tamoxifen N=38 |
Exemestane N=59 |
Placebo N=65 |
| Lumbar spine (%) |
-3.14 |
-0.18 |
-3.51 |
-2.35 |
| Femoral neck (%) |
-4.15 |
-0.33 |
-4.57 |
-2.59 |
Adverse Reactions
Exemestane was generally well tolerated and adverse events were usually mild to moderate.
In the adjuvant treatment of early breast cancer, adverse events occurring in ≥10% of patients in any treatment group (exemestane vs tamoxifen) were hot flushes (21.2% vs 19.9%), fatigue (16.1% vs 14.7%), arthralgia (14.6% vs 8.6%), headache (13.1% vs 10.8%), insomnia (12.4% vs 8.9%), and increased sweating (11.8% vs 10.4%). Discontinuation rates due to AEs were similar between exemestane and tamoxifen (6.3% vs 5.1%). Incidence of cardiac ischemic events (myocardial infarction, angina, and myocardial ischemia) were exemestane 1.6%, tamoxifen 0.6%. Incidence of cardiac failure: exemestane 0.4%, tamoxifen 0.3%.
In the treatment of advanced breast cancer, the most common adverse events were mild to moderate and included hot flushes (13% vs 5%), nausea (9% vs 5%), fatigue (8% vs 10%), increased sweating (4% vs 8%), and increased appetite (3% vs 6%) for exemestane and megestrol acetate, respectively.
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
Clinical Trial Experience
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.
Adjuvant Therapy
The data described below reflect exposure to exemestane in 2325 postmenopausal women with early breast cancer. Exemestane tolerability in postmenopausal women with early breast cancer was evaluated in two well-controlled trials: the IES study (14.1) and the 027 study (a randomized, placebo-controlled, double-blind, parallel group study specifically designed to assess the effects of exemestane on bone metabolism, hormones, lipids, and coagulation factors over 2 years of treatment).
The median duration of adjuvant treatment was 27.4 months and 27.3 months for patients receiving exemestane or tamoxifen, respectively, within the IES study and 23.9 months for patients receiving exemestane or placebo within the 027 study. Median duration of observation after randomization for exemestane was 34.5 months and for tamoxifen was 34.6 months. Median duration of observation was 30 months for both groups in the 027 study.
Certain adverse events, which were expected based on the known pharmacological properties and side effect profiles of test drugs, were actively sought through a positive checklist. Signs and symptoms were graded for severity using CTC in both studies. Within the IES study, the presence of some illnesses/conditions was monitored through a positive checklist without assessment of severity. These included myocardial infarction, other cardiovascular disorders, gynecological disorders, osteoporosis, osteoporotic fractures, other primary cancer, and hospitalizations.
Exemestane was generally well tolerated and adverse events were usually mild to moderate. Within the IES study, discontinuations due to adverse events occurred in 6.3% and 5.1% of patients receiving exemestane and tamoxifen, respectively, and in 12.3% and 4.1% of patients receiving exemestane or placebo respectively within study 027.
Deaths due to any cause were reported for 1.3% of the exemestane treated patients and 1.4% of the tamoxifen treated patients within the IES study. There were 6 deaths due to stroke on the exemestane arm compared to 2 on tamoxifen. There were 5 deaths due to cardiac failure on the exemestane arm compared to 2 on tamoxifen.
The incidence of cardiac ischemic events (myocardial infarction, angina, and myocardial ischemia) was 1.6% in exemestane treated patients and 0.6% in tamoxifen treated patients in the IES study. Cardiac failure was observed in 0.4% of exemestane treated patients and 0.3% of tamoxifen treated patients.
Treatment-emergent adverse events and illnesses including all causalities and occurring with an incidence of ≥5% in either treatment group of the IES study during or within one month of the end of treatment are shown in Table 2.
Table 2. Incidence (%) of Adverse Events of all Gradesa and Illnesses Occurring in (≥5%) of Patients in Any Treatment Group in Study IES in Postmenopausal Women with Early Breast Cancer
|
% of patients |
| Body system and Adverse Event by MedDRA dictionary |
Exemestane 25 mg daily (N=2252) |
Tamoxifen 20 mg dailyb (N=2280) |
Eye
|
|
|
-
- Visual disturbancesc
|
5
|
3.8
|
Gastrointestinal
|
|
|
-
- Nauseac
|
8.5 |
8.7 |
General Disorders
|
|
|
-
- Fatiguec
|
16.1 |
14.7 |
Musculoskeletal
|
|
|
-
- Arthralgia
|
14.6 |
8.6 |
-
- Pain in limb
|
9.0 |
6.4 |
-
- Back pain
|
8.6 |
7.2 |
-
- Osteoarthritis
|
5.9 |
4.5 |
Nervous System
|
|
|
-
- Headachec
|
13.1 |
10.8 |
-
- Dizzinessc
|
9.7 |
8.4 |
Psychiatric
|
|
|
-
- Insomniac
|
12.4 |
8.9 |
-
- Depression
|
6.2 |
5.6 |
Skin & Subcutaneous Tissue
|
|
|
-
- Increased sweating3
|
11.8 |
10.4 |
Vascular
|
|
|
-
- Hot flushes3
|
21.2 |
19.9 |
-
- Hypertension
|
9.8 |
8.4 |
In the IES study, as compared to tamoxifen, exemestane was associated with a higher incidence of events in musculoskeletal disorders and in nervous system disorders, including the following events occurring with frequency lower than 5% (osteoporosis [4.6% vs. 2.8%], osteochondrosis and trigger finger [0.3% vs 0 for both events], paresthesia [2.6% vs. 0.9%], carpal tunnel syndrome [2.4% vs. 0.2%], and neuropathy [0.6% vs. 0.1%]. Diarrhea was also more frequent in the exemestane group (4.2% vs. 2.2%). Clinical fractures were reported in 94 patients receiving exemestane (4.2%) and 71 patients receiving tamoxifen (3.1%). After a median duration of therapy of about 30 months and a median follow-up of about 52 months, gastric ulcer was observed at a slightly higher frequency in the exemestane group compared to tamoxifen (0.7% vs. <0.1%). The majority of patients on exemestane with gastric ulcer received concomitant treatment with non-steroidal anti-inflammatory agents and/or had a prior history.
Tamoxifen was associated with a higher incidence of muscle cramps [3.1% vs. 1.5%], thromboembolism [2.0% vs. 0.9%], endometrial hyperplasia [1.7% vs. 0.6%], and uterine polyps [2.4% vs. 0.4%].
Common adverse events occurring in study 027 are described in Table 3.
Table 3. Incidence of Selected Treatment-Emergent Adverse Events of all CTC Grades* Occurring in ≥ 5% of Patients in Either Arm in Study 027
| Adverse Event |
Exemestane N=73 (% incidence) |
Placebo N=73 (% incidence) |
| Hot flushes |
32.9 |
24.7 |
| Arthralgia |
28.8 |
28.8 |
| Increased sweating |
17.8 |
20.6 |
| Alopecia |
15.1 |
4.1 |
| Hypertension |
15.1 |
6.9 |
| Insomnia |
13.7 |
15.1 |
| Nausea |
12.3 |
16.4 |
| Fatigue |
11.0 |
19.2 |
| Abdominal pain |
11.0 |
13.7 |
| Depression |
9.6 |
6.9 |
| Diarrhea |
9.6 |
1.4 |
| Dizziness |
9.6 |
9.6 |
| Dermatitis |
8.2 |
1.4 |
| Headache |
6.9 |
4.1 |
| Myalgia |
5.5 |
4.1 |
| Edema |
5.5 |
6.9 |
| Anxiety |
4.1 |
5.5 |
* Most events were CTC grade 1–2
Treatment of Advanced Breast Cancer
A total of 1058 patients were treated with exemestane 25 mg once daily in the clinical trials program. Only one death was considered possibly related to treatment with exemestane; an 80-year-old woman with known coronary artery disease had a myocardial infarction with multiple organ failure after 9 weeks on study treatment. In the clinical trials program, only 3% of the patients discontinued treatment with exemestane because of adverse events, mainly within the first 10 weeks of treatment; late discontinuations because of adverse events were uncommon (0.3%).
In the comparative study, adverse reactions were assessed for 358 patients treated with exemestane and 400 patients treated with megestrol acetate. Fewer patients receiving exemestane discontinued treatment because of adverse events than those treated with megestrol acetate (2% vs. 5%). Adverse events that were considered drug related or of indeterminate cause included hot flashes (13% vs. 5%), nausea (9% vs. 5%), fatigue (8% vs. 10%), increased sweating (4% vs. 8%), and increased appetite (3% vs. 6%) for exemestane and megestrol acetate, respectively. The proportion of patients experiencing an excessive weight gain (>10% of their baseline weight) was significantly higher with megestrol acetate than with exemestane (17% vs. 8%). Table 4 shows the adverse events of all CTC grades, regardless of causality, reported in 5% or greater of patients in the study treated either with exemestane or megestrol acetate.
Table 4. Incidence (%) of Adverse Events of all Grades* and Causes Occurring in ≥5% of Advanced Breast Cancer Patients In Each Treatment Arm in the Comparative Study
|
Body system and Adverse Event by WHO ART dictionary
|
Exemestane
25 mg once daily (N=358)
|
Megestrol Acetate
40 mg QID (N=400)
|
Autonomic Nervous
|
|
|
| Increased sweating |
6 |
9 |
| Body as a Whole |
|
|
| Fatigue |
22 |
29 |
| Hot Flashes |
13 |
6 |
| Pain |
13 |
13 |
| Influenza-like symptoms |
6 |
5 |
| Edema (includes edema, peripheral edema, leg edema) |
7 |
6 |
| Cardiovascular |
|
|
| Hypertension |
5 |
6 |
| Nervous |
|
|
| Depression |
13 |
9 |
| Insomnia |
11 |
9 |
| Anxiety |
10 |
11 |
| Dizziness |
8 |
6 |
| Headache |
8 |
7 |
| Gastrointestinal |
|
|
| Nausea |
18 |
12 |
| Vomiting |
7 |
4 |
| Abdominal pain |
6 |
11 |
| Anorexia |
6 |
5 |
| Constipation |
5 |
8 |
| Diarrhea |
4 |
5 |
| Increased appetite |
3 |
6 |
| Respiratory |
|
|
| Dyspnea |
10 |
15 |
| Coughing |
6 |
7 |
Less frequent adverse events of any cause (from 2% to 5%) reported in the comparative study for patients receiving Exemestane Tablets 25 mg once daily were fever, generalized weakness, paresthesia, pathological fracture, bronchitis, sinusitis, rash, itching, urinary tract infection, and lymphedema.
Additional adverse events of any cause observed in the overall clinical trials program (N = 1058) in 5% or greater of patients treated with exemestane 25 mg once daily but not in the comparative study included pain at tumor sites (8%), asthenia (6%), and fever (5%). Adverse events of any cause reported in 2% to 5% of all patients treated with exemestane 25 mg in the overall clinical trials program but not in the comparative study included chest pain, hypoesthesia, confusion, dyspepsia, arthralgia, back pain, skeletal pain, infection, upper respiratory tract infection, pharyngitis, rhinitis, and alopecia.
Post-Marketing Experience
The following adverse reactions have been identified during post approval use of exemestane. Because reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Cases of hepatitis including cholestatic hepatitis have been observed in clinical trials and reported through post-marketing surveillance.
Drug Interactions
Drugs That Induce CYP 3A4
In a pharmacokinetic interaction study of 10 healthy postmenopausal volunteers pretreated with potent CYP 3A4 inducer rifampicin 600 mg daily for 14 days followed by a single dose of exemestane 25 mg, the mean plasma Cmax and AUC 0–∞ of exemestane were decreased by 41% and 54%, respectively.
Significant pharmacokinetic interactions mediated by inhibition of CYP isoenzymes therefore appear unlikely. Comedications that induce CYP 3A4 (e.g., rifampicin, phenytoin, carbamazepine, phenobarbital, or St. John’s wort) may significantly decrease exposure to exemestane. Dose modification is recommended for patients who are also receiving a potent CYP 3A4 inducer [see Dosage and Administration (2.2)].
Drugs That Inhibit CYP 3A4
In a clinical pharmacokinetic study, coadministration of ketoconazole, a potent inhibitor of CYP 3A4, has no significant effect on exemestane pharmacokinetics. Although no other formal drug-drug interaction studies have been conducted, significant effects on exemestane clearance by CYP isoenzyme inhibitors appear unlikely.
USE IN SPECIFIC POPULATIONS
Pregnancy
Pregnancy Category X. See “Contraindications” section.
Exemestane can cause fetal harm when administered to a pregnant woman and the clinical benefit to premenopausal women with breast cancer has not been demonstrated. Exemestane Tablets are contraindicated in women who are or may become pregnant. There are no adequate and well-controlled studies of exemestane in pregnant women.
In non-clinical studies in rats and rabbits, exemestane was embryotoxic, fetotoxic, and abortifacient. Radioactivity related to 14C-exemestane crossed the placenta of rats following oral administration of 1 mg/kg exemestane. The concentration of exemestane and its metabolites was approximately equivalent in maternal and fetal blood. When rats were administered exemestane from 14 days prior to mating until either days 15 or 20 of gestation, and resuming for the 21 days of lactation, an increase in placental weight was seen at 4 mg/kg/day (approximately 1.5 times the recommended human daily dose on a mg/m2 basis). Prolonged gestation and abnormal or difficult labor was observed at doses equal to or greater than 20 mg/kg/day. Increased resorption, reduced number of live fetuses, decreased fetal weight, and retarded ossification were also observed at these doses. No malformations were noted when exemestane was administered to pregnant rats during the organogenesis period at doses up to 810 mg/kg/day (approximately 320 times the recommended human dose on a mg/m2 basis). Daily doses of exemestane, given to rabbits during organogenesis, caused a decrease in placental weight at 90 mg/kg/day (approximately 70 times the recommended human daily dose on a mg/m2 basis). Abortions, an increase in resorptions, and a reduction in fetal body weight were seen at 270 mg/kg/day. There was no increase in the incidence of malformations in rabbits at doses up to 270 mg/kg/day (approximately 210 times the recommended human dose on a mg/m2 basis).
If this drug is used during pregnancy, or if the patient becomes pregnant while receiving this drug, the patient should be apprised of the potential hazard to the fetus and the potential risk for pregnancy loss.
Nursing Mothers
Exemestane Tablets are only indicated in postmenopausal women. However, radioactivity related to exemestane appeared in rat milk within 15 minutes of oral administration of radiolabeled exemestane. Concentrations of exemestane and its metabolites were approximately equivalent in the milk and plasma of rats for 24 hours after a single oral dose of 1 mg/kg 14C-exemestane. It is not known whether exemestane is excreted in human milk. Because many drugs are excreted in human milk, and because of the potential for serious adverse reaction in nursing infants from exemestane, a decision should be made whether to discontinue the drug, taking into account the importance of the drug to the mother.
Pediatric Use
Safety and effectiveness in pediatric patients have not been established.
Geriatric Use
The use of exemestane in geriatric patients does not require special precautions.
Hepatic Insufficiency
The pharmacokinetics of exemestane have been investigated in subjects with moderate or severe hepatic insufficiency (Childs-Pugh B or C). Following a single 25-mg oral dose, the AUC of exemestane was approximately 3 times higher than that observed in healthy volunteers.
The safety of chronic dosing in patients with moderate or severe hepatic impairment has not been studied. Based on experience with exemestane at repeated doses up to 200 mg daily that demonstrated a moderate increase in non life-threatening adverse events, dosage adjustment does not appear to be necessary.
Renal Insufficiency
The AUC of exemestane after a single 25-mg dose was approximately 3 times higher in subjects with moderate or severe renal insufficiency (creatinine clearance <35 mL/min/1.73 m2) compared with the AUC in healthy volunteers. The safety of chronic dosing in patients with moderate or severe renal impairment has not been studied. Based on experience with exemestane at repeated doses up to 200 mg daily that demonstrated a moderate increase in non life- threatening adverse events, dosage adjustment does not appear to be necessary.
Overdosage
Clinical trials have been conducted with exemestane given as a single dose to healthy female volunteers at doses as high as 800 mg and daily for 12 weeks to postmenopausal women with advanced breast cancer at doses as high as 600 mg. These dosages were well tolerated. There is no specific antidote to overdosage and treatment must be symptomatic. General supportive care, including frequent monitoring of vital signs and close observation of the patient, is indicated.
A male child (age unknown) accidentally ingested a 25-mg tablet of exemestane. The initial physical examination was normal, but blood tests performed 1 hour after ingestion indicated leucocytosis (WBC 25000/mm3 with 90% neutrophils). Blood tests were repeated 4 days after the incident and were normal. No treatment was given.
In mice, mortality was observed after a single oral dose of exemestane of 3200 mg/kg, the lowest dose tested (about 640 times the recommended human dose on a mg/m2 basis). In rats and dogs, mortality was observed after single oral doses of exemestane of 5000 mg/kg (about 2000 times the recommended human dose on a mg/m2 basis) and of 3000 mg/kg (about 4000 times the recommended human dose on a mg/m2 basis), respectively.
Convulsions were observed after single doses of exemestane of 400 mg/kg and 3000 mg/kg in mice and dogs (approximately 80 and 4000 times the recommended human dose on a mg/m2 basis), respectively.
Exemestane Tablets Description
Exemestane Tablets for oral administration contain 25 mg of exemestane, an irreversible, steroidal aromatase inactivator. Exemestane is chemically described as 6-methylenandrosta-1,4-diene-3,17-dione. Its molecular formula is C20H24O2 and its structural formula is as follows:
The active ingredient is a white to slightly yellow crystalline powder with a molecular weight of 296.41. Exemestane is freely soluble in N, N-dimethylformamide, soluble in methanol, and practically insoluble in water.
Each Exemestane Tablet contains the following inactive ingredients: magnesium stearate, mannitol, microcrystalline cellulose, Opadry II (white), polysorbate 80, povidone, and sodium starch glycolate. Opadry II (white) contains hypromellose, polyethylene glycol, polydextrose, titanium dioxide, and triacetin.
Exemestane Tablets - Clinical Pharmacology
Mechanism of Action
Breast cancer cell growth may be estrogen-dependent. Aromatase is the principal enzyme that converts androgens to estrogens both in pre- and postmenopausal women. While the main source of estrogen (primarily estradiol) is the ovary in premenopausal women, the principal source of circulating estrogens in postmenopausal women is from conversion of adrenal and ovarian androgens (androstenedione and testosterone) to estrogens (estrone and estradiol) by the aromatase enzyme in peripheral tissues. Estrogen deprivation through aromatase inhibition is an effective and selective treatment for some postmenopausal patients with hormone-dependent breast cancer.
Exemestane is an irreversible, steroidal aromatase inactivator, structurally related to the natural substrate androstenedione. It acts as a false substrate for the aromatase enzyme, and is processed to an intermediate that binds irreversibly to the active site of the enzyme, causing its inactivation, an effect also known as “suicide inhibition.” Exemestane significantly lowers circulating estrogen concentrations in postmenopausal women, but has no detectable effect on adrenal biosynthesis of corticosteroids or aldosterone. Exemestane has no effect on other enzymes involved in the steroidogenic pathway up to a concentration at least 600 times higher than that inhibiting the aromatase enzyme.
Pharmacodynamics
Effect on Estrogens: Multiple doses of exemestane ranging from 0.5 to 600 mg/day were administered to postmenopausal women with advanced breast cancer. Plasma estrogen (estradiol, estrone, and estrone sulfate) suppression was seen starting at a 5 mg daily dose of exemestane, with a maximum suppression of at least 85% to 95% achieved at a 25 mg dose. Exemestane 25 mg daily reduced whole body aromatization (as measured by injecting radiolabeled androstenedione) by 98% in postmenopausal women with breast cancer. After a single dose of exemestane 25 mg, the maximal suppression of circulating estrogens occurred 2 to 3 days after dosing and persisted for 4 to 5 days.
Effect on Corticosteroids: In multiple-dose trials of doses up to 200 mg daily, exemestane selectivity was assessed by examining its effect on adrenal steroids. Exemestane did not affect cortisol or aldosterone secretion at baseline or in response to ACTH at any dose. Thus, no glucocorticoid or mineralocorticoid replacement therapy is necessary with exemestane treatment.
Other Endocrine Effects: Exemestane does not bind significantly to steroidal receptors, except for a slight affinity for the androgen receptor (0.28% relative to dihydrotestosterone). The binding affinity of its 17-dihydrometabolite for the androgen receptor, however, is 100 times that of the parent compound. Daily doses of exemestane up to 25 mg had no significant effect on circulating levels of androstenedione, dehydroepiandrosterone sulfate, or 17-hydroxyprogesterone, and were associated with small decreases in circulating levels of testosterone. Increases in testosterone and androstenedione levels have been observed at daily doses of 200 mg or more. A dose-dependent decrease in sex hormone binding globulin (SHBG) has been observed with daily exemestane doses of 2.5 mg or higher. Slight, nondose-dependent increases in serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels have been observed even at low doses as a consequence of feedback at the pituitary level. Exemestane 25 mg daily had no significant effect on thyroid function [free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH)].
Coagulation and Lipid Effects: In study 027 of postmenopausal women with early breast cancer treated with exemestane (N=73) or placebo (N=73), there was no change in the coagulation parameters activated partial thromboplastin time [APTT], prothrombin time [PT], and fibrinogen. Plasma HDL cholesterol was decreased 6 to 9% in exemestane treated patients; total cholesterol, LDL cholesterol, triglycerides, apolipoprotein-A1, apolipoprotein-B, and lipoprotein-a were unchanged. An 18% increase in homocysteine levels was also observed in exemestane treated patients compared with a 12% increase seen with placebo.
Pharmacokinetics
Following oral administration to healthy postmenopausal women, exemestane is rapidly absorbed. After maximum plasma concentration is reached, levels decline polyexponentially with a mean terminal half-life of about 24 hours. Exemestane is extensively distributed and is cleared from the systemic circulation primarily by metabolism. The pharmacokinetics of exemestane are dose proportional after single (10 to 200 mg) or repeated oral doses (0.5 to 50 mg). Following repeated daily doses of exemestane 25 mg, plasma concentrations of unchanged drug are similar to levels measured after a single dose.
Pharmacokinetic parameters in postmenopausal women with advanced breast cancer following single or repeated doses have been compared with those in healthy, postmenopausal women. Exemestane appeared to be more rapidly absorbed in the women with breast cancer than in the healthy women, with a mean -tmax of 1.2 hours in the women with breast cancer and 2.9 hours in the healthy women. After repeated dosing, the average oral clearance in women with advanced breast cancer was 45% lower than the oral clearance in healthy postmenopausal women, with corresponding higher systemic exposure. Mean AUC values following repeated doses in women with breast cancer (75.4 ng·h/mL) were about twice those in healthy women (41.4 ng·h/mL).
Absorption: Following oral administration of radiolabeled exemestane, at least 42% of radioactivity was absorbed from the gastrointestinal tract. Exemestane plasma levels increased by approximately 40% after a high-fat breakfast.
Distribution: Exemestane is distribu
