Product Index

Composition

CYTOTAM-10 Tablets

Each film-coated tablet contains: Tamoxifen citrate I.P. equivalent to tamoxifen……………. 10 mg

CYTOTAM-20 Tablets

Each film-coated tablet contains: Tamoxifen citrate I.P. equivalent to tamoxifen …………….. 20 mg

Dosage Form

Oral tablet

Pharmacology

Pharmacodynamics 

Tamoxifen citrate is a non-steroidal agent that has demonstrated potent anti-oestrogenic properties in animal test systems. The anti-oestrogenic effects may be related to its ability to compete with oestrogen for binding sites in target tissues such as breast. Tamoxifen inhibits the induction of rat mammary carcinoma induced by dimethylbenzanthracene (DMBA) and causes the regression of already established DMBA-induced tumours. In this rat model, tamoxifen appears to exert its anti-tumour effects by binding the oestrogen receptors. 

In cytosols derived from human breast adenocarcinomas, tamoxifen competes with oestradiol for oestrogen receptor-protein. 

Pharmacokinetics 

Absorption and Distribution 

Following a single oral dose of 20 mg tamoxifen, an average peak plasma concentration of 40 ng/mL (range: 35 to 45 ng/mL) occurred approximately 5 hours after dosing. The decline in plasma concentrations of tamoxifen is biphasic with a terminal elimination half-life of about 5 to 7 days. The average peak plasma concentration of N-desmethyl tamoxifen is 15 ng/mL (range: 10 to 20 ng/mL). Chronic administration of 10 mg tamoxifen, given twice daily for 3 months to patients, results in average steady-state plasma concentrations of 120 ng/mL (range: 67 to 183 ng/mL) for tamoxifen and 336 ng/mL (range: 148 to 654 ng/mL) for N­-desmethyl tamoxifen. The average steady-state plasma concentrations of tamoxifen and N-desmethyl tamoxifen after administration of 20 mg tamoxifen once daily for 3 months are 122 ng/mL (range: 71 to 183 ng/mL) and 353 ng/mL (range: 152 to 706 ng/mL), respectively. After initiation of therapy, steady-state concentrations for tamoxifen are achieved in about 4 weeks and steady-state concentrations for N-desmethyl tamoxifen are achieved in about 8 weeks, suggesting a half-life of approximately 14 days for this metabolite. In a steady-state, crossover study of 10 mg citrate tamoxifen tablets given twice a day versus a 20 mg tamoxifen citrate tablet given once daily, the 20 mg tamoxifen citrate tablet was bioequivalent to the 10 mg citrate tamoxifen tablets. 

Metabolism

Tamoxifen is extensively metabolized after oral administration. N-desmethyl tamoxifen is the major metabolite found in the plasma of patients The biological activity of N-desmethyl tamoxifen appears to be similar to that of tamoxifen. 4­-Hydroxytamoxifen and a side chain primary alcohol derivative of tamoxifen have been identified as minor metabolites in plasma. Tamoxifen is a substrate of cytochrome (CY) P450 3A, 2C9 and 2D6, and an inhibitor of P-glycoprotein. 

Excretion

Studies in women receiving 20 mg of ¹⁴C-tamoxifen have shown that approximately 65% of the administered dose was excreted from the body over a period of 2 weeks, with faecal excretion as the primary route of elimination. The drug is excreted mainly as polar conjugates, with unchanged drug and unconjugated metabolites accounting for less than 30% of the total faecal radioactivity.

Special Populations

The effects of age, gender and race on the pharmacokinetics of tamoxifen have not been determined. The effects of reduced liver function on the metabolism and pharmacokinetics of tamoxifen have not been determined.

Paediatric Patients

The pharmacokinetics of tamoxifen and N-desmethyl tamoxifen were characterized using a population pharmacokinetic analysis with sparse samples per patient obtained from 27 female paediatric patients aged 2 to 10 years, enrolled in a study designed to evaluate the safety, efficacy and pharmacokinetics of tamoxifen in treating McCune-Albright syndrome Rich data from two tamoxifen citrate pharmacokinetic trials in which 59 postmenopausal women with breast cancer completed the studies were included in the analysis to determine the structural pharmacokinetic model for tamoxifen. A one-compartment model provided the best fit to the data. 

In paediatric patients, an average steady-state peak plasma concentration (Css, max) and the AUC were of 187 ng/mL and 4110 ng hr/mL, respectively, and Css, max occurred approximately 8 hours after dosing. Clearance (CL/F) as body weight adjusted in female paediatric patients was approximately 2.3-fold higher than in female breast cancer patients. In the youngest cohort of female paediatric patients (aged 2 to 6 years), the CL/F was 2.6-fold higher; in the oldest cohort (aged 7 to 10.9 years), the CL/F was approximately 1.9-fold higher. Exposure to N-desmethyl tamoxifen was comparable between the paediatric and adult patients. The safety and efficacy of tamoxifen for girls aged 2 to 10 years with McCune-Albright syndrome and precocious puberty have not been studied beyond 1 year of treatment. The long-term effects of tamoxifen therapy in girls have not been established. In adults treated with tamoxifen, an increase in incidence of uterine malignancies, stroke and pulmonary embolism has been noted

Drug−Drug Interactions

In vitro studies showed that erythromycin, cyclosporin, nifedipine and diltiazem competitively inhibited formation of N-desmethyl tamoxifen with apparent K₁ of 20, 1, 45 and 30 µM, respectively. The clinical significance of these in vitro studies is unknown.

Tamoxifen reduced the plasma concentration of letrozole by 37% when these drugs were co-administered. Rifampin, a cytochrome P 450 3A4 inducer, reduced the tamoxifen AUC and Cmax by 86% and 55%, respectively. Aminoglutethimide reduces tamoxifen and N-desmethyl tamoxifen plasma concentrations. Medroxyprogesterone reduces plasma concentrations of N-desmethyl, but not tamoxifen.

In the anastrozole adjuvant trial, co-administration of anastrozole and tamoxifen in breast cancer patients reduced anastrozole plasma concentration by 27%, compared to those achieved with anastrozole alone; however, the co-administration did not affect the pharmacokinetics of tamoxifen or N­-desmethyltamoxifen. Tamoxifen should not be co-administered with anastrozole.

Indications

Metastatic Breast Cancer

CYTOTAM Tablets are effective in the treatment of metastatic breast cancer in women and men. In premenopausal women with metastatic breast cancer, CYTOTAM Tablets are an alternative to oophorectomy or ovarian irradiation. Available evidence indicates that patients whose tumours are oestrogen receptor-positive are more likely to benefit from CYTOTAM Tablets therapy.

Adjuvant Treatment of Breast Cancer

CYTOTAM Tablets are indicated for the treatment of node-positive breast cancer in women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation. In some CYTOTAM Tablets adjuvant studies, most of the benefit to date has been in the subgroup with four or more positive axillary nodes.

CYTOTAM Tablets are indicated for the treatment of axillary node-negative breast cancer in women following total mastectomy or segmental mastectomy, axillary dissection and breast irradiation.

The oestrogen and progesterone receptor values may help to predict whether adjuvant CYTOTAM Tablets therapy is likely to be beneficial.

CYTOTAM Tablets reduce the occurrence of contralateral breast cancer in patients receiving adjuvant CYTOTAM Tablets therapy for breast cancer.

Ductal Carcinoma in Situ (DCIS)

In women with DCIS, following breast surgery and radiation, CYTOTAM Tablets are indicated to reduce the risk of invasive breast cancer. The decision regarding therapy with CYTOTAM Tablets for the reduction in breast cancer incidence should be based upon an individual assessment of the benefits and risks of CYTOTAM Tablets therapy.

Current data from clinical trials support 5 years of adjuvant tamoxifen therapy for patients with breast cancer.

Reduction in Breast Cancer Incidence in High-Risk Women

CYTOTAM Tablets are indicated to reduce the incidence of breast cancer in women at high risk for breast cancer. This effect was shown in a study of 5 years’ planned duration with a median follow-up of 4.2 years. The drug was given to 25% of the participants for 5 years. The long-term effects are not known. In this study, there was no impact of tamoxifen on overall or breast cancer-related mortality.

CYTOTAM Tablets are indicated only for high-risk women. ‘High risk’ is defined as women at least 35 years of age with a 5-year predicted risk of breast cancer

≥1.67%, as calculated by the Gail Model.

There are insufficient data available regarding the effect of tamoxifen on breast cancer incidence in women with inherited mutations (BRCA1, BRCA2) to be able to make specific recommendations on the effectiveness of tamoxifen in these patients.

After an assessment of the risk of developing breast cancer, the decision regarding therapy with tamoxifen for the reduction in breast cancer incidence should be based upon an individual assessment of the benefits and risks of tamoxifen therapy. In the NSABP P-1 trial, tamoxifen treatment lowered the risk of developing breast cancer during the follow-up period of the trial, but did not eliminate breast cancer risk.

Dosage and Administration

For patients with breast cancer, the recommended daily dose of CYTOTAM tablets is 20–40 mg. Dosages greater than 20 mg per day should be given in divided doses (morning and evening).

Current data from clinical trials support 5 years of adjuvant tamoxifen therapy for patients with breast cancer. 

Ductal Carcinoma in Situ (DCIS)

The recommended dose is CYTOTAM tablets 20 mg daily for 5 years. 

Reduction in Breast Cancer Incidence in High-Risk Women

The recommended dose is CYTOTAM tablets 20 mg daily for 5 years. There are no data to support the use of tamoxifen other than for 5 years. 

Contraindications  

CYTOTAM tablets are contraindicated in patients with a known hypersensitivity to the drug or any of its ingredients

Reduction in Breast Cancer Incidence in High-Risk Women and Women with DCIS 

Tamoxifen is contraindicated in women who require concomitant coumarin-type anticoagulant therapy or in women with a history of deep-vein thrombosis or pulmonary embolus.

Warnings and Precautions

General

Decreases in platelet counts, usually to 50,000–1,00,000/mm³, infrequently lower, have been occasionally reported in patients taking tamoxifen for breast cancer. In patients with significant thrombocytopenia, rare haemorrhagic episodes have occurred, but it is uncertain if these episodes are due to tamoxifen therapy Leucopenia has been observed, sometimes in association with anaemia and/or thrombocytopenia. There have been rare reports of neutropenia and pancytopenia in patients receiving tamoxifen; this can sometimes be severe.

Drug Interactions

When tamoxifen is used in combination with coumarin-type anticoagulants, a significant increase in the anticoagulant effect may occur. Where such co-administration exists, careful monitoring of the patient's prothrombin time is recommended.

There is an increased risk of thromboembolic events occurring when cytotoxic agents are used in combination with tamoxifen. 

Tamoxifen reduced letrozole plasma concentrations by 37%. The effect of tamoxifen on metabolism and excretion of other anti-neoplastic drugs, such as cyclophosphamide and other drugs that require mixed function oxidases for activation, is not known. Tamoxifen and N-desmethyl tamoxifen plasma concentrations have been shown to be reduced when co-administered with rifampin or aminoglutethimide. Induction of CYP3A4-mediated metabolism is considered to be the mechanism by which these reductions occur; other CYP3A4-inducing agents have not been studied to confirm this effect. 

A patient receiving tamoxifen with concomitant phenobarbital exhibited a steady-state serum level of tamoxifen lower than that observed for other patients (i.e., 26 ng/mL versus a mean value of 122 ng/mL). However, the clinical significance of this finding is not known. Rifampin induced the metabolism of tamoxifen and significantly reduced the plasma concentrations of tamoxifen in 10 patients. Aminoglutethimide reduces tamoxifen and N-desmethyl tamoxifen plasma concentrations. Medroxyprogesterone reduces plasma concentrations of N-desmethyl, but not tamoxifen

Concomitant bromocriptine therapy has been shown to elevate serum tamoxifen and N-desmethyl tamoxifen. 

Based on clinical and pharmacokinetic results from the anastrozole adjuvant trial, tamoxifen should not be administered with anastrozole. 

Periodic complete blood counts, including platelet counts, and periodic liver function tests should be obtained.

During the Arimidex, Tamoxifen, alone or in Combination (ATAC) trial, more patients receiving anastrozole were reported to have an elevated serum cholesterol compared to patients receiving tamoxifen (9% versus 3.5%, respectively.

Drug/Laboratory Testing Interactions

During postmarketing surveillance, T4 elevations were reported for a few postmenopausal patients, which may be explained by increases in thyroid-binding globulin. These elevations were not accompanied by clinical hyperthyroidism. 

Variations in the karyopyknotic index on vaginal smears and various degrees of oestrogen effect on Pap smears have been infrequently seen in postmenopausal patients given tamoxifen. 

In the postmarketing experience with tamoxifen, infrequent cases of hyperlipidaemias have been reported. Periodic monitoring of plasma triglycerides and cholesterol may be indicated in patients with pre-existing hyperlipidaemias.

Effects in Metastatic Breast Cancer Patients 

As with other additive hormonal therapy (oestrogens and androgens), hypercalcaemia has been reported in some breast cancer patients with bone metastases within a few weeks of starting treatment with tamoxifen. If hypercalcaemia does occur, appropriate measures should be taken and, if severe, tamoxifen should be discontinued.

Effects on the Uterus-Endometrial Cancer and Uterine Sarcoma 

An increased incidence of uterine malignancies has been reported in association with tamoxifen treatment. The underlying mechanism is unknown, but may be related to the oestrogen-like effect of tamoxifen. Most uterine malignancies seen in association with tamoxifen are classified as adenocarcinoma of the endometrium. However, rare uterine sarcomas, including malignant mixed-mullerian tumours (MMMT), have also been reported. Uterine sarcoma is generally associated with a higher International Federation of Gynecology and Obstetrics (FIGO) stage (III/IV) at diagnosis, poorer prognosis, and shorter survival. Uterine sarcoma has been reported to occur more frequently among long-term users (≥2 years) of tamoxifen than non-users. Some of the uterine malignancies (endometrial carcinoma or uterine sarcoma) have been fatal.

Any patient receiving or who has previously received tamoxifen and reporting abnormal vaginal bleeding should be promptly evaluated. Patients receiving or who have previously received tamoxifen should have annual gynaecological examinations and they should promptly inform their physicians if they experience any abnormal gynaecological symptoms, e.g., menstrual irregularities, abnormal vaginal bleeding, changes in vaginal discharge, or pelvic pain or pressure.

There are no data to suggest that routine endometrial sampling in asymptomatic women taking tamoxifen to reduce the incidence of breast cancer would be beneficial.

Non-Malignant Effects on the Uterus

An increased incidence of endometrial changes, including hyperplasia and polyps, have been reported in association with tamoxifen treatment. The incidence and pattern of this increase suggest that the underlying mechanism is related to the oestrogenic properties of tamoxifen. 

There have been a few reports of endometriosis and uterine fibroids in women receiving tamoxifen. The underlying mechanism may be due to the partial oestrogenic effect of tamoxifen. Ovarian cysts have also been observed in a small number of premenopausal patients with advanced breast cancer who have been treated with tamoxifen. 

Tamoxifen has been reported to cause menstrual irregularity or amenorrhoea.

Thromboembolic Effects of Tamoxifen

There is evidence of an increased incidence of thromboembolic events, including deep vein thrombosis and pulmonary embolism, during tamoxifen therapy.

When tamoxifen is co-adminstered with chemotherapy, there may be a further increase in the incidence of thromboembolic effects. For treatment of breast cancer, the risks and benefits of tamoxifen should be carefully considered in women with a history of thromboembolic events. In a small sub-study (N=81) of the NSABP P-1 trial, there appeared to be no benefit to screening women for Factor V Leiden and prothrombin mutations, G20210A, as a means to identify those who may not be appropriate candidates for tamoxifen therapy.

Data from the NSABP P-1 trial show that participants receiving tamoxifen without a history of pulmonary emboli (PE) had a statistically significant increase in pulmonary emboli (18-tamoxifen, 6-placebo, RR=3.01, 95% confidence interval : 1.15–9.27). Three of the pulmonary emboli, all in the tamoxifen arm, were fatal. Of the cases of pulmonary embolism, 87% occurred in women at least 50 years of age at randomization. Among women receiving tamoxifen, the events appeared between 2 and 60 months (average=27 months) from the start of treatment.

In this same population, a non-statistically significant increase in deep-vein thrombosis was seen in the tamoxifen group (30-tamoxifen, 19-placebo; RR=1.59, 95% CI: 0.86–2.98). The same increase in relative risk was seen in women aged ≤49 years and in women ≥50 years, although fewer events occurred in younger women. Women with thromboembolic events were at risk for a second related event (7/ 25 women on placebo, 5/48 women on tamoxifen) and were at risk for complications of the event and its treatment (0/25 on placebo, 4/48 on tamoxifen). Among women receiving tamoxifen, deep-vein thrombosis events occurred between 2 and 57 months (average=19 months) from the start of treatment. 

There was a non-statistically significant increase in stroke among patients randomized to tamoxifen (24-Placebo; 34-tamoxifen; RR=1.42; 95% CI 0.82–2.51). Of the 24 strokes in the placebo group, 6 were considered haemorrhagic in origin, and 10 of the 34 strokes in the tamoxifen group were categorized as haemorrhagic. Of the 34 strokes in the tamoxifen group, 17 were considered occlusive and 7 were considered to be of unknown aetiology. Of the 24 strokes on the placebo arm, 14 were reported to be occlusive and 4 of unknown aetiology. Among these strokes, 3 strokes in the placebo group and 4 strokes in the tamoxifen group were fatal. At the time of randomization, 88% of the strokes occurred in women at least 50 years of age. Among women receiving tamoxifen, the events occurred between 1 and 63 months (average=30 months) from the start of treatment.

Effects on the Liver

Liver Cancer

In the Swedish trial using adjuvant tamoxifen 40 mg/day for 2 to 5 years, three cases of liver cancer have been reported in the tamoxifen-treated group versus 1 case in the observation group. In other clinical trials evaluating tamoxifen, no cases of liver cancer have been reported to date. 

One case of liver cancer was reported in NSABP P-1 in a participant randomized to tamoxifen. 

Non-Malignant Effects

Tamoxifen has been associated with changes in liver enzyme levels and, on rare occasions, with a spectrum of more severe liver abnormalities, including fatty liver, cholestasis, hepatitis and hepatic necrosis. A few of these serious cases included fatalities. In most reported cases, the relationship to tamoxifen is uncertain. However, some positive re-challenges and de-challenges have been reported.

In the NSABP P-1 trial, a few grade 3–4 changes in liver function were observed (10 on placebo and 6 on tamoxifen). Serum lipids were not systematically collected. 

Other Cancers

A number of second primary tumours, occurring at sites other than the endometrium, have been reported following the treatment of breast cancer with tamoxifen in clinical trials. Data from the NSABP B-14 and P-1 studies show no increase in other (non-uterine) cancers among patients receiving tamoxifen. Whether an increased risk for other (non-uterine) cancers is associated with tamoxifen is still uncertain and continues to be evaluated. 

Effects on the Eyes

Ocular disturbances, including corneal changes, decrement in colour vision perception, retinal vein thrombosis, and retinopathy have been reported in patients receiving tamoxifen. An increased incidence of cataracts and the need for cataract surgery have been reported in patients receiving tamoxifen.

Pregnancy

Pregnancy Category D  

Tamoxifen may cause foetal harm when administered to a pregnant woman. Women should be advised not to become pregnant while taking tamoxifen or within 2 months of discontinuing tamoxifen, and should use barrier or non-hormonal contraceptive measures if sexually active. Tamoxifen does not cause infertility, even in the presence of menstrual irregularity. Effects on reproductive functions are expected from the anti-oestrogenic properties of the drug. In reproductive studies in rats at dose levels equal to or below the human dose, non-teratogenic developmental skeletal changes were seen and were found reversible. In addition, in fertility studies in rats and in teratology studies in rabbits using doses at or below those used in humans, a lower incidence of embryo implantation and a higher incidence of foetal death or retarded in utero growth were observed, with slower learning behaviour in some rat pups when compared to historical controls. Several pregnant marmosets were dosed with 10 mg/kg/day (about 2-fold the daily maximum recommended human dose on an mg/m² basis) during organogenesis or in the last half of pregnancy. No deformations were seen and, although the dose was high enough to terminate pregnancy in some animals, those that did maintain pregnancy showed no evidence of teratogenic malformations. 

In rodent models of foetal reproductive tract development, tamoxifen (at doses 0.002- to 2.4-fold the daily maximum recommended human dose on an mg/m² basis) caused changes in both sexes that are similar to those caused by oestradiol, ethynyl oestradiol and diethylstilbestrol. Although the clinical relevance of these changes is unknown, some of these changes, especially vaginal adenosis, are similar to those seen in young women who were exposed to diethylstilbestrol in utero and who have a 1 in 1,000 risk of developing clear-cell adenocarcinoma of the vagina or cervix. To date, in utero exposure to tamoxifen has not been shown to cause vaginal adenosis, or clear-cell adenocarcinoma of the vagina or cervix, in young women. However, only a small number of young women have been exposed to tamoxifen in utero, and a smaller number have been followed long enough (to the age of 15 to 20 years) to determine whether vaginal or cervical neoplasia could occur as a result of this exposure. 

There have been a small number of reports of vaginal bleeding, spontaneous abortions, birth defects and foetal deaths in pregnant women. If this drug is used during pregnancy, or the patient becomes pregnant while taking this drug or within approximately 2 months after discontinuing therapy, the patient should be apprised of the potential risks to the foetus, including the potential long-term risk of a dry eye syndrome (DES)-like syndrome.

Reduction in Breast Cancer Incidence in High-Risk Women — Pregnancy Category D

For sexually active women of childbearing potential, tamoxifen therapy should be initiated during menstruation. In women with menstrual irregularity, a negative beta human chorionic gonadotropin (B-HCG) immediately prior to the initiation of therapy is sufficient.

Lactation

Tamoxifen has been reported to inhibit lactation. Two placebo-controlled studies in over 150 women have shown that tamoxifen significantly inhibits early postpartum milk production. In both studies, tamoxifen was administered within 24 hours of delivery for between 5 and 18 days. The effect of tamoxifen on established milk production is not known.

There are no data that address whether tamoxifen is excreted into human milk. If excreted, there are no data regarding the effects of tamoxifen in breast milk on the breastfed infant or breastfed animals. However, direct neonatal exposure of tamoxifen to mice and rats (not via breast milk) produced 1) reproductive tract lesions in female rodents (similar to those seen in humans after intrauterine exposure to diethylstilbestrol); and, 2) functional defects of the reproductive tract in male rodents, such as testicular atrophy and arrest of spermatogenesis. 

It is not known if tamoxifen is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from tamoxifen, women taking tamoxifen should not breast feed. 

Reduction in Breast Cancer Incidence in High-Risk Women with DCIS

It is not known if tamoxifen is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from tamoxifen, women taking tamoxifen should not breast feed. 

Paediatric Use

The safety and efficacy of tamoxifen for girls aged 2 to 10 years with McCune-Albright syndrome and precocious puberty have not been studied beyond 1 year of treatment. The long-term effects of tamoxifen therapy for girls have not been established. In adults treated with tamoxifen, an increase in the incidence of uterine malignancies, stroke and pulmonary embolism has been noted.

Geriatric Use

In the NSABP P-1 trial, the percentage of women at least 65 years of age was 16%. Women at least 70 years of age accounted for 6% of the participants. A reduction in breast cancer incidence was seen among participants in each of the subsets: a total of 28 and 10 invasive breast cancers were seen among participants aged 65 years and older in the placebo and tamoxifen groups, respectively. Across all other outcomes, the results in this subset reflect the results observed in the subset of women at least 50 years of age. No overall differences in tolerability were observed between older and younger patients. 

In the NSABP B-24 trial, the percentage of women at least 65 years of age was 23%. Women at least 70 years of age accounted for 10% of participants. A total of 14 and 12 invasive breast cancers were seen among participants aged 65 years and older in the placebo and tamoxifen groups, respectively. This subset is too small to reach any conclusions on efficacy. Across all other endpoints, the results in this subset were comparable to those of younger women enrolled in this trial. No overall differences in tolerability were observed between older and younger patients.

Carcinogenesis

A conventional carcinogenesis study in rats at doses of 5, 20 and 35 mg/kg/day (about 1-, 3- and 7-fold the daily maximum recommended human dose on an mg/m² basis) administered by oral gavage for up to 2 years revealed a significant increase in hepatocellular carcinoma at all doses. The incidence of these tumours was significantly greater among rats administered 20 or 35 mg/kg/day (69%), compared to those administered 5 mg/kg/day (14%). In a separate study, rats were administered tamoxifen at 45 mg/kg/day (about 9-fold the daily maximum recommended human dose on an mg/m² basis); hepatocellular neoplasia was exhibited at 3 to 6 months.

Granulosa cell ovarian tumours and interstitial cell testicular tumours were observed in two separate mouse studies. The mice were administered the trans and racemic forms of tamoxifen for 13 to 15 months at doses of 5, 20 and 50 mg/kg/day (about ½-, 2-, and 5-fold the daily recommended human dose on an mg/m² basis).

Mutagenesis

No genotoxic potential was found in a conventional battery of in vivo and in vitro tests with pro- and eukaryotic test systems with drug-metabolizing systems. However, increased levels of DNA adducts were observed by 32P post-labelling in DNA from rat liver and cultured human lymphocytes. Tamoxifen also has been found to increase levels of micronucleus formation in vitro in the human lymphoblastoid cell line (MCL-5). Based on these findings, tamoxifen is genotoxic in rodent and human MCL-5 cells.

Impairment of Fertility

Tamoxifen produced impairment of fertility and conception in female rats at doses of 0.04 mg/kg/day (about 0.01-fold the daily maximum recommended human dose on an mg/m² basis) when dosed for 2 weeks prior to mating through day 7 of pregnancy. At this dose, fertility and reproductive indices were markedly reduced with total foetal mortality. Foetal mortality was also increased at doses of 0.16 mg/kg/day (about 0.03-fold the daily maximum recommended human dose on an mg/m² basis) when female rats were dosed from days 7 to 17 of pregnancy. Tamoxifen produced abortion, premature delivery and foetal death in rabbits administered doses equal to or greater than 0.125 mg/kg/day (about 0.05-fold the daily maximum recommended human dose on an mg/m² basis). There were no teratogenic changes in either rats or rabbits.

Information for Patients

Reduction in Invasive Breast Cancer and DCIS in Women with DCIS

Women with DCIS treated with lumpectomy and radiation therapy and who are considering tamoxifen to reduce the incidence of a second breast cancer event should assess the risks and benefits of therapy, since treatment with tamoxifen decreased the incidence of invasive breast cancer, but has not been shown to affect survival.

Reduction in Breast Cancer Incidence in High-Risk Women

Women who are at high risk for breast cancer can consider taking tamoxifen therapy to reduce the incidence of breast cancer. Whether the benefits of treatment are considered to outweigh the risks depends on a woman’s personal health history and on how she weighs the benefits and risks. Tamoxifen therapy to reduce the incidence of breast cancer may therefore not be appropriate for all women at high risk for breast cancer. Women who are considering tamoxifen therapy should consult their healthcare professional for an assessment of the potential benefits and risks prior to starting therapy for reduction in breast cancer incidence. Women should understand that tamoxifen reduces the incidence of breast cancer, but may not eliminate the risk. Tamoxifen decreased the incidence of small oestrogen receptor-positive tumours, but did not alter the incidence of oestrogen receptor-negative tumours or larger tumours. In women with breast cancer who were at high risk of developing a second breast cancer, treatment with about 5 years of tamoxifen reduced the annual incidence rate of a second breast cancer by approximately 50%.

Women who are pregnant or who plan to become pregnant should not take tamoxifen to reduce their risk of breast cancer. Effective non-hormonal contraception must be used by all premenopausal women taking tamoxifen and for approximately 2 months after discontinuing therapy if they are sexually active. Tamoxifen does not cause infertility, even in the presence of menstrual irregularity. For sexually active women of childbearing potential, tamoxifen therapy should be initiated during menstruation. In women with menstrual irregularity, a negative B-HCG immediately prior to the initiation of therapy is sufficient.

Two European trials of tamoxifen to reduce the risk of breast cancer were conducted and showed no difference in the number of breast cancer cases between the tamoxifen and placebo arms. These studies had trial designs that differed from that of NSABP P-1, were smaller than NSABP P-1, and enrolled women at a lower risk for breast cancer than those in P-1.

Monitoring during Tamoxifen Therapy

Women taking or having previously taken tamoxifen should be instructed to seek prompt medical attention for new breast lumps, vaginal bleeding, gynaecologic symptoms (menstrual irregularities, changes in vaginal discharge, or pelvic pain or pressure), symptoms of leg swelling or tenderness, unexplained shortness of breath, or changes in vision. Women should inform all care providers, regardless of the reason for evaluation, that they take tamoxifen.

Women taking tamoxifen to reduce the incidence of breast cancer should have a breast examination, a mammogram and a gynaecologic examination prior to the initiation of therapy. These studies should be repeated at regular intervals while on therapy, in keeping with good medical practice. Women taking tamoxifen as adjuvant breast cancer therapy should follow the same monitoring procedures as for women taking tamoxifen for the reduction in the incidence of breast cancer. Women taking tamoxifen as treatment for metastatic breast cancer should review this monitoring plan with their care provider and select the appropriate modalities and schedule of evaluation.

Undesirable Effects  

Adverse reactions to tamoxifen are relatively mild and rarely severe enough to require discontinuation of treatment in breast cancer patients. 

Continued clinical studies have resulted in further information that better indicates the incidence of adverse reactions with tamoxifen as compared to placebo.

Metastatic Breast Cancer

Increased bone and tumour pain and, also, local disease flare have occurred, which are sometimes associated with a good tumour response. Patients with increased bone pain may require additional analgesics. Patients with soft tissue disease may have sudden increases in the size of pre-existing lesions, sometimes associated with marked erythema within and surrounding the lesions and/or the development of new lesions. When they occur, the bone pain or disease flare is seen shortly after starting tamoxifen and generally subside rapidly. 

In patients treated with tamoxifen for metastatic breast cancer, the most frequent adverse reaction to tamoxifen is hot flashes.

Other adverse reactions which are seen infrequently are hypercalcaemia, peripheral oedema, distaste for food, pruritus vulvae, depression, dizziness, light­headedness, headache, hair thinning and/or partial hair loss, and vaginal dryness.

Premenopausal Women

The following table summarizes the incidence of adverse reactions reported at a frequency of 2% or greater from clinical trials (Ingle, Pritchard, Buchanan), which compared tamoxifen therapy to ovarian ablation in premenopausal patients with metastatic breast cancer. 

Male Breast Cancer

Tamoxifen is well tolerated in males with breast cancer. Reports from the literature and case reports suggest that the safety profile of tamoxifen in males is similar to that seen in women. Loss of libido and impotence have resulted in discontinuation of tamoxifen therapy in male patients. Also, in oligospermic males treated with tamoxifen, luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone and oestrogen levels were elevated. No significant clinical changes were reported.

Adjuvant Breast Cancer

In the NSABP B-14 study, women with axillary node-negative breast cancer were randomized to 5 years of tamoxifen 20 mg/day or placebo, following primary surgery. The reported adverse effects are tabulated below (mean follow-up of approximately 6.8 years) showing adverse events more common on tamoxifen than on placebo. The incidence of hot flashes (64% versus 48%), vaginal discharge (30% versus 15%), and irregular menses (25% versus 19%) were higher with tamoxifen compared with placebo. All other adverse effects occurred with similar frequency in the two treatment groups, with the exception of thrombotic events; a higher incidence was seen in tamoxifen treated patients (through 5 years, 1.7% versus 0.4%). Death was the outcome for 2 patients treated with tamoxifen and who had thrombotic events. 

In the ECOG adjuvant breast cancer trial, tamoxifen or placebo was administered for 2 years to women following mastectomy. When compared to placebo, tamoxifen showed a significantly higher incidence of hot flashes (19% versus 8% for placebo). The incidence of all other adverse reactions was similar in the two treatment groups with the exception of thrombocytopenia, where the incidence for tamoxifen was 10% versus 3% for placebo, an observation of borderline statistical significance. 

In other adjuvant studies, the Toronto study and NATO, women received either tamoxifen or no therapy. In the Toronto study, hot flashes were observed in 29% of patients for tamoxifen versus 1% in the untreated group. In the NATO trial, hot flashes and vaginal bleeding were reported in 2.8% and 2.0% of women, respectively, for tamoxifen versus 0.2% for each in the untreated group.

Anastrozole Adjuvant Trial — Study of Anastrozole Compared to Tamoxifen for Adjuvant Treatment of Early Breast Cancer

At a median follow-up of 33 months, the combination of anastrozole and tamoxifen did not demonstrate any efficacy benefit when compared to tamoxifen therapy given alone in all patients as well as in the hormone receptor-positive subpopulation. This treatment arm was discontinued from the trial. The median duration of adjuvant treatment for safety evaluation was 59.8 months and 59.6 months for patients receiving anastrozole 1 mg and tamoxifen 20 mg, respectively.

Adverse events occurring with an incidence of at least 5% in either treatment group during treatment or within 14 days of the end of treatment* are presented in the following table.

Certain adverse events and combinations of adverse events were prospectively specified for analysis, based on the known pharmacologic properties and side effect profiles of the two drugs (see the following table). 

Patients receiving anastrozole had an increase in joint disorders (including arthritis, arthrosis and arthralgia) compared with patients receiving tamoxifen. Patients receiving anastrozole had an increase in the incidence of all fractures (specifically fractures of the spine, hip and wrist) compared with patients receiving tamoxifen . Patients receiving anastrozole had a decrease in hot flashes, vaginal bleeding, vaginal discharge, endometrial cancer, venous thromboembolic events and ischaemic cerebrovascular events compared with patients receiving tamoxifen. 

Patients receiving tamoxifen had a decrease in hypercholesterolaemia (108 ) compared to patients receiving anastrozole (278 ). Angina pectoris was reported in 71 patients in the anastrozole arm and 51 patients in the tamoxifen arm; myocardial infarction was reported in 37 patients in the anastrozole arm and in 34 patients in the tamoxifen arm.

Results from the adjuvant trial bone sub-study at 12 and 24 months demonstrated that patients receiving anastrozole had a mean decrease in both lumbar spine and total hip bone mineral density (BMD), compared to baseline. Patients receiving tamoxifen had a mean increase in both lumbar spine and total hip BMD compared to baseline.

Ductal Carcinoma in Situ (DCIS)

The type and frequency of adverse events in the NSABP B-24 trial were consistent with those observed in the other adjuvant trials conducted with tamoxifen.

Reduction in Breast Cancer Incidence in High-Risk Women

In the NSABP P-1 Trial, there was an increase in five serious adverse effects in the tamoxifen group: endometrial cancer (33 cases in the tamoxifen group versus 14 in the placebo group); pulmonary embolism (18 cases in the tamoxifen group versus 6 in the placebo group); deep vein thrombosis (30 cases in the tamoxifen group versus 19 in the placebo group); stroke (34 cases in the tamoxifen group versus 24 in the placebo group); cataract formation (540 cases in the tamoxifen group versus 483 in the placebo group) and cataract surgery (101 cases in the tamoxifen group versus 63 in the placebo group).

The following table presents the adverse events observed in NSABP P-1 by treatment arm. Only adverse events more common on tamoxifen than placebo are shown.

In the NSABP P-1 trial, 15.0% and 9.7% of participants receiving tamoxifen and placebo therapy, respectively, withdrew from the trial for medical reasons. The following are the medical reasons for withdrawing from tamoxifen and placebo therapy, respectively: hot flashes (3.1% versus 1.5%) and vaginal discharge (0.5% versus 0.1%). 

In the NSABP P-1 trial, 8.7% and 9.6% of participants receiving tamoxifen and placebo therapy, respectively, withdrew for non-medical reasons. 

On the NSABP P-1 trial, hot flashes of any severity occurred in 68% of women on placebo and in 80% of women on tamoxifen. Severe hot flashes occurred in 28% of women on placebo and 45% of women on tamoxifen. Vaginal discharge occurred in 35% and 55% of women on placebo and tamoxifen, respectively; and was severe in 4.5% and 12.3%, respectively. There was no difference in the incidence of vaginal bleeding between the treatment arms.

Paediatric Patients — McCune-Albright Syndrome

Mean uterine volume increased after 6 months of treatment and doubled at the end of the 1-year study. A causal relationship has not been established; however, as an increase in the incidence of endometrial adenocarcinoma and uterine sarcoma has been noted in adults treated with tamoxifen, continued monitoring of McCune-Albright patients treated with tamoxifen for long-term effects is recommended. The safety and efficacy of tamoxifen for girls aged two to 10 years with McCune-Albright syndrome and precocious puberty have not been studied beyond 1 year of treatment. The long-term effects of tamoxifen therapy in girls have not been established.

Postmarketing Experience

Less frequently reported adverse reactions are vaginal bleeding, vaginal discharge, menstrual irregularities, skin rash and headaches. Usually these have not been of sufficient severity to require dosage reduction or discontinuation of treatment. Very rare reports of erythema multiforme, Stevens-Johnson syndrome, bullous pemphigoid, and interstitial pneumonitis, and rare reports of hypersensitivity reactions, including angio-oedema, have been reported with tamoxifen therapy. In some of these cases, the time to onset was more than 1 year. Rarely, elevation of serum triglyceride levels, in some cases with pancreatitis, may be associated with the use of tamoxifen.

If you experience any side effects, talk to your doctor or pharmacist or write to drugsafety@cipla.com. You can also report side effects directly via the national pharmacovigilance program of India by calling on 1800 180 3024.  

By reporting side effects, you can help provide more information on the safety of this product.

Overdosage

Signs observed at the highest doses following studies to determine lethal dose (LD₅₀) in animals were respiratory difficulties and convulsions.

Acute overdosage in humans has not been reported. In a study of advanced metastatic cancer patients, which specifically determined the maximum tolerated dose of tamoxifen in evaluating the use of very high doses to reverse multidrug resistance, acute neurotoxicity manifested by tremor, hyper-reflexia, unsteady gait and dizziness were noted. These symptoms occurred within 3 to 5 days of beginning tamoxifen and cleared within 2 to 5 days after stopping therapy. No permanent neurologic toxicity was noted. A seizure was experienced by 1 patient several days after tamoxifen was discontinued and neurotoxic symptoms had resolved. The causal relationship of the seizure to tamoxifen therapy is unknown. Doses given in these patients were all greater than the 400 mg/m² loading dose, followed by maintenance doses of 150 mg/m² of tamoxifen given twice a day. 

In the same study, prolongation of the QT interval on the electrocardiogram was noted when patients were given doses higher than the 250 mg/m² loading dose, followed by maintenance doses of 80 mg/m² of tamoxifen given twice a day. For a woman with a body surface area of 1.5 m², the minimal loading dose and maintenance doses given at which neurological symptoms and QT changes occurred were at least 6-fold higher in respect to the maximum recommended dose.

No specific treatment for overdosage is known; treatment must be symptomatic. 

Shelf-Life

3 years

Storage and Handling Instructions