INN monograph
Tamoxifen
Therapeutic agent (verify pharmacological class) · POM
Verified · Updated 01 Aug 2026 · Source: Local active-ingredient clinical extract; FDA drug label via OpenFDA/DailyMed; Professional class pharmacology (Therapeutic agent (verify pharmacological class))
Kenya market
Wholesale / list prices where loaded
Risk first
Contraindications
- 4 CONTRAINDICATIONS SOLTAMOX is contraindicated in patients with known hypersensitivity (e.g., angioedema, serious skin reactions) to tamoxifen or any other SOLTAMOX ingredient [see Adverse Reactions (6.2) ] .
- SOLTAMOX is contraindicated in patients who require concomitant warfarin therapy or have a history of deep vein thrombosis or pulmonary embolus if the indication for treatment is either reduction of breast cancer incidence in high-risk patients or risk reduction of invasive breast cancer after treatment of DCIS [see Warnings and Precautions (5.2) and Drug Interactions (7.2) ].
- Known hypersensitivity to tamoxifen or any other SOLTAMOX ingredient ( 4 ) In patients who require concomitant warfarin therapy or have a history of deep vein thrombosis or pulmonary embolus, if the indication for treatment is either reduction of breast cancer incidence in high-risk patients or risk reduction of invasive breast cancer after treatment of DCIS ( 4 )
Precautions
- 5 WARNINGS AND PRECAUTIONS Uterine malignancies: Promptly evaluate abnormal vaginal bleeding in a woman with current or past tamoxifen use.
- ( 5.1 ) Thromboembolic events: Risk increases with coadministered chemotherapy.
- For treatment of breast cancer, consider risks and benefits in patients with a history of thromboembolic events.
- ( 5.2 ) Embryo-fetal toxicity: Can cause fetal harm.
- Advise females of reproductive potential of the potential risk to a fetus and to use effective contraception.
- ( 5.3 , 8.1 , 8.3 ) Effects on the liver: Liver cancer and liver abnormalities, some fatal, have occurred.
- Perform periodic liver function testing.
- ( 5.4 , 5.9 ) 5.1 Endometrial Cancer, Uterine Sarcoma, and Other Effects on the Uterus Endometrial Cancer and Uterine Sarcoma An increased incidence of uterine malignancies (endometrial adenocarcinoma and uterine sarcoma), including fatal cases, has been reported with tamoxifen treatment.
- The underlying mechanism is unknown, but may be related to the estrogen-like effect of tamoxifen.
- Most uterine malignancies seen with tamoxifen are classified as adenocarcinoma of the endometrium
- however, uterine sarcomas, including malignant mixed mullerian tumors (MMMT), have also been reported.
- Uterine sarcoma was generally associated with a higher FIGO stage (III/IV) at diagnosis, poor prognosis, and short survival.
Point of care
Dosing
Adult
cancer: 20-40 mg per day. For doses greater than 20 mg per day, administer in divided doses (morning and evening). ( 2 ) Adjuvant treatment of breast cancer, DCIS, reduction of breast cancer incidence in women at high risk: 20 mg per day ( 2 ) Metastatic Breast Cancer For patients with breast cancer, the recommended daily dose of SOLTAMOX is 20 to 40 mg. Doses greater than 20 mg per day should be given in divided doses (morning and evening). Adjuvant Treatment of Breast Cancer For use in the adjuvant setting, the recommended dose of SOLTAMOX is 20 mg daily for 5-10 years [see Clinical Studies (14.2) ] . Doses greater than 20 mg daily yield no additional clinical benefit. Ductal Carcinoma in Situ For patients with DCIS, the recommended dose of SOLTAMOX is 20 mg daily for 5 years. Reduction in Breast Cancer Incidence in Women at High Risk In the risk reduction setting, the recommended dose of SOLTAMOX is 20 mg daily for 5 years .
Paediatric
8.4 Pediatric Use The safety and effectiveness of SOLTAMOX in pediatric patients have not been established. Tamoxifen Use in McCune-Albright Syndrome The safety and effectiveness of SOLTAMOX for the treatment of girls with McCune-Albright syndrome, including long-term effects, have not been established. A single, uncontrolled multicenter trial of tamoxifen 20 mg once a day was conducted in a heterogeneous group of girls with McCune-Albright syndrome and precocious puberty manifested by physical signs of pubertal development, episodes of vaginal bleeding, and/or advanced bone age (bone age of at least 12 months beyond chronological age). Twenty-eight female pediatric patients, aged 2 to 10 years, were treated for up to 12 months. Effect of treatment on frequency of vaginal bleeding, bone age advancement, and linear growth rate was assessed relative to prestudy baseline. Tamoxifen treatment was associated with a 50% reduction in frequency of vaginal bleeding episodes by patient or family report (mean annualized frequency of 3.56 episodes at baseline and 1.73 episodes on-treatment). Among the patients who reported vaginal bleeding during the prestudy period, 62% (13 out of 21 patients) reported no bleeding for a 6-month period and 33% (7 out of 21 patients) reported no vaginal bleeding for the duration of the trial. Not all patients improved on treatment and a few patients not reporting vaginal bleeding in the 6 months prior to enrollment reported menses on treatment. Tamoxifen therapy was associated with a reduction in mean rate of increase of bone age (defined as the ratio of bone age change and chronological age); individual responses with regard to this endpoint were highly heterogeneous. Linear growth rate (height velocity) was reduced during the course of tamoxifen treatment in a majority of patients (mean change of 1.68 cm/year relative to baseline; change from 7.47 cm/year at baseline to 5.79 cm/year on study). This change was not uniformly seen across all stages of bone maturity; all recorded response failures occurred in patients with bone ages less than 7 years at screening. Mean uterine volume increased after 6 months of treatment and doubled at the end of the one-year study. A causal relationship to tamoxifen 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 uterine effects is recommended. Pharmacokinetics in Pediatric 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 pediatric patients aged 2 to 10 years enrolled in a study of tamoxifen in treating McCune-Albright syndrome. Clearance (CL/F), adjusted for body weight, in female pediatric patients was approximately 2.3-fold higher than in adult female breast cancer patients. In the youngest cohort of female pediatric patients (2 to 6 year olds), CL/F was 2.6-fold higher; in the oldest cohort (7 to 10.9 year olds), CL/F was approximately 1.9-fold higher. Exposure to N-desmethyl tamoxifen was comparable between the pediatric and adult patients. In pediatric patients, an average steady-state peak plasma concentration (Css, max) and AUC were 187 ng/mL and 4,110 ng hr/mL, respectively, and Css, max occurred approximately 8 hours after dosing. Animal Data Direct neonatal exposure of tamoxifen to mice and rats produced: 1) reproductive tract lesions in female rodents (similar to those seen in humans after intrauterine exposure to DES) and 2) functional defects of the reproductive tract in male rodents such as testicular atrophy and arrest of spermatogenesis.
Renal
Review renal impairment dosing; many agents need CrCl/eGFR adjustment.
- CrCl 0–120: Confirm renal dosing in product SmPC / primary label.
Hepatic
Review hepatic impairment dosing; monitor LFTs if agent is hepatically cleared or hepatotoxic.
Safety
Drug interactions
- Professional use: confirm indication, dose, duration, monitoring and patient counselling points against current Kenya STG / EML and the product SmPC.
- Document allergy status and key interactions.
Safety
Adverse effects
- labeling: Uterine malignancies [see Boxed Warning , Warnings and Precautions (5.1) , and Clinical Studies (14.4) ] Thromboembolic events [see Boxed Warning , Warnings and Precautions (5.2) , and Clinical Studies (14.4) ] Embryo-Fetal Toxicity [see Warnings and Precautions (5.3) , and Use in Specific Populations (8.1 , 8.3) ] Liver cancer [see Warnings and Precautions (5.4) ] Most common adverse reactions: hot flashes, mood disturbances, vaginal discharge, vaginal bleeding, nausea, and fluid retention ( 6.1 ).
- To report SUSPECTED ADVERSE REACTIONS, contact Mayne Pharma at 1-844-825-8500 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials 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 practice.
- Adverse Reactions in Patients with Metastatic Breast Cancer In patients treated with tamoxifen for metastatic breast cancer, the most frequent adverse reaction was hot flashes.
- Other adverse reactions which were seen less commonly are hypercalcemia, peripheral edema, distaste for food, pruritus vulvae, depression, dizziness, lightheadedness, headache, hair thinning and/or partial hair loss, and vaginal dryness.
- Increased bone, tumor pain and local disease flare have occurred.
- Patients with soft tissue disease may have sudden increases in the size of preexisting lesions, sometimes associated with marked erythema within and surrounding the lesions and/or the development of new lesions.
- When they occurred, the bone pain or disease flares were seen shortly after starting tamoxifen and generally subsided rapidly.
- Premenopausal Women with Metastatic Breast Cancer Table 1 summarizes the incidence of adverse reactions reported at a frequency of 2% or greater from clinical trials that compared tamoxifen therapy to ovarian ablation in premenopausal patients with metastatic breast cancer.
- Table 1: Adverse Reactions (frequency ≥2% in either arm) from Trials Comparing Tamoxifen to Ovarian Ablation in Premenopausal Women with Metastatic Breast Cancer % of Women Tamoxifen N=104 Ovarian Ablation N=100 Adverse Reactions Some women had more than one adverse reaction.
- Flush 33 46 Amenorrhea 16 69 Altered menses 13 5 Oligomenorrhea 9 1 Bone pain 6 6 Menstrual disorder 6 4 Nausea 5 4 Cough/coughing 4 1 Edema 4 1 Fatigue 4 1 Musculoskeletal pain 3 0 Pain 3 4 Ovarian cyst(s) 3 2 Depression 2 2 Abdominal cramps 1 2 Anorexia 1 2 Adverse Reactions in 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 per day or placebo following primary surgery [see Clinical Studies (14.2) ].
- Table 2 presents the most common adverse reactions (mean follow-up of approximately 6.9 years) that were more common on tamoxifen than placebo.
- Table 2: Most Common Adverse Reactions in Women with Axillary Node-Negative Breast Cancer (Study NSABP B-14) % of Women Tamoxifen N=1,422 Placebo N=1,437 Hot flashes 64 48 Fluid retention 32 30 Vaginal discharge 30 15 Nausea 26 24 Irregular menses 25 19 Weight loss (>5%) 23 18 Skin changes 19 15 Increased SGOT 5 3 Increased bilirubin 2 1 Increased creatinine 2 1 Thrombocytopenia Defined as a platelet count of < 100,000/mm 3 2 1 Thrombotic events Two of the tamoxifen-treated patients who had thrombotic events died.
- Deep vein thrombosis 0.8 0.2 Pulmonary embolism 0.5 0.2 Superficial phlebitis 0.4 0 In the Eastern Cooperative Oncology Group (ECOG) adjuvant breast cancer trial [see Clinical Studies (14.2) ] , tamoxifen or placebo was administered for 2 years to women following mastectomy.
- When compared to placebo, tamoxifen showed a higher incidence of hot flashes (19% vs. 8% for placebo).
Use
Indications
- indicated: For treatment of adult patients with estrogen receptor-positive metastatic breast cancer ( 1.1 ) For adjuvant treatment of adult patients with early stage estrogen receptor- positive breast cancer ( 1.2 ) To reduce risk of invasive breast cancer following breast surgery and radiation in adult women with ductal carcinoma in situ (DCIS) ( 1.3 ) To reduce the incidence of breast cancer in adult women at high risk ( 1.4 ) 1.1 Metastatic Breast Cancer SOLTAMOX is indicated for the treatment of adult patients with estrogen receptor-positive metastatic breast cancer.
- 1.2 Adjuvant Treatment of Breast Cancer SOLTAMOX is indicated: for the adjuvant treatment of adult patients with early stage estrogen receptor-positive breast cancer to reduce the occurrence of contralateral breast cancer in adult patients when used as adjuvant therapy for the treatment of breast cancer.
- 1.3 Ductal Carcinoma in Situ In adult women with DCIS, following breast surgery and radiation, SOLTAMOX is indicated to reduce the risk of invasive breast cancer [see Boxed Warning and Clinical Studies (14.3) ] .
- 1.4 Reduction in Breast Cancer Incidence in Women at High Risk SOLTAMOX is indicated to reduce the incidence of breast cancer in adult women at high risk for breast cancer.
- [see Boxed Warning and Clinical Studies (14.4) ] .
Pharmacology
Mode of action
agonist/antagonist.
Full mechanism text
agonist/antagonist. Tamoxifen competes with estrogen for binding to the estrogen receptor, which can result in a decrease in estrogen receptor signaling-dependent growth in breast tissue. Tamoxifen has demonstrated antitumor activity against human breast cancer cell lines xenografted in mice. The drug has been shown to inhibit the induction of rat mammary carcinoma induced by dimethylbenzanthracene (DMBA) and to cause the regression of already established DMBA-induced tumors.
ADME
Pharmacokinetics & PD
| Onset | Product-specific |
|---|---|
| Duration | Product-specific |
| Route | See product SmPC |
| 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 |
| Metabolism | Tamoxifen is extensively metabolized by CYP450 enzymes, including CYP3A, CYP2D6, CYP2C9, CYP2C19, and CYP2B6. N-desmethyltamoxifen, formed predominantly by CYP3A, is the major metabolite found in plasma. The pharmacological activity of N-desmethyltamoxifen is similar to that of t... |
| Elimination | half-life of about 5 to 7 days. The average peak plasma concentration of N- desmethyl tamoxifen, the major metabolite, 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 c... |
| Half-life | of about 5 to 7 days. The average peak plasma concentration of N- desmethyl tamoxifen, the major metabolite, 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 concentrati... |
Full PK/PD text
12 CLINICAL PHARMACOLOGY 12.1 Mechanism of Action Tamoxifen is an estrogen agonist/antagonist. Tamoxifen competes with estrogen for binding to the estrogen receptor, which can result in a decrease in estrogen receptor signaling-dependent growth in breast tissue. Tamoxifen has demonstrated antitumor activity against human breast cancer cell lines xenografted in mice. The drug has been shown to inhibit the induction of rat mammary carcinoma induced by dimethylbenzanthracene (DMBA) and to cause the regression of already established DMBA-induced tumors. 12.3 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, the major metabolite, 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. The steady-state plasma concentrations of endoxifen and 4-hydroxytamoxifen are 29.1 (95% CI 24.6 to 33.6) and 3.7 (95% CI 3.3 to 4.1) 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 tamoxifen tablets given twice a day vs. a 20 mg tamoxifen tablet given once daily, the 20 mg tamoxifen tablet was bioequivalent to the 10 mg tamoxifen tablets. A pharmacokinetic study was performed in healthy perimenopausal and postmenopausal female subjects to evaluate the bioavailability of SOLTAMOX (n=30) in comparison with the commercially available tamoxifen citrate tablets (n=33) under fasting conditions. A third arm evaluated the effect of food on SOLTAMOX (n=16). The rate and extent of absorption of SOLTAMOX was found to be bioequivalent to that of tamoxifen citrate tablets under fasting conditions. There was no difference in bioavailability (C max and AUC) of SOLTAMOX oral solution between fed and fasting states, and therefore SOLTAMOX can be given without regard to meals. Metabolism Tamoxifen is extensively metabolized by CYP450 enzymes, including CYP3A, CYP2D6, CYP2C9, CYP2C19, and CYP2B6. N-desmethyltamoxifen, formed predominantly by CYP3A, is the major metabolite found in plasma. The pharmacological activity of N-desmethyltamoxifen is similar to that of tamoxifen. Endoxifen and 4-hydroxytamoxifen, identified as minor metabolites, have 100-fold greater affinity for the estrogen receptor and 30 to 100-fold greater potency in suppressing estrogen-dependent cell proliferation than tamoxifen. The polymorphic enzyme CYP2D6 is involved in the formation of endoxifen and 4-hydroxytamoxifen, and it is the key enzyme that catalyzes the formation of endoxifen from N-desmethyltamoxifen. Endoxifen concentrations may differ among patients because of various CYP2D6 genotypes [see Clinical Pharmacology (12.5) ] . Phase 2 enzymes, such as SULT1A1, UGT2B7, and UGT1A4, are associated with tamoxifen clearance from plasma. Excretion Studies in women receiving 20 mg of 14 C tamoxifen showed that approximately 65% of the administered dose was excreted from the body over a period of 2 weeks, with fecal 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 fecal radioactivity. Specific Populations The effects of age, gender, and race on the pharmacokinetics of tamoxifen in adults have not been determined. Some data are available on tamoxifen pharmacokinetics in children [see Use in Specific Populations (8.4) ] . The effects of reduced liver function on the metabolism and pharmacokinetics of tamoxifen have not been determined. Drug-Drug Interactions Aromatase Inhibitors Anastrozole In the ATAC trial, coadministration of anastrozole and tamoxifen in breast cancer patients reduced the anastrozole plasma concentration by 27% compared to that achieved with anastrozole alone; however, the coadministration did not affect the pharmacokinetics of tamoxifen or N-desmethyltamoxifen [see Clinical Studies (14.2) ] . Letrozole Tamoxifen reduced the plasma concentration of letrozole by 38% when these drugs were coadministered. CYP P450 3A4 Inducers Rifampin, a cytochrome P450 3A4 inducer, reduced tamoxifen AUC and C max by 86% and 55%, respectively. CYP2D6 Inhibitors Although concomitant administration of CYP2D6 inhibitors reduces the plasma concentration of endoxifen, a potent metabolite, the clinical significance is not well established [see Drug Interactions (7.4) ] . The mean steady-state endoxifen plasma concentration in patients taking CYP2D6 inhibitors was significantly reduced compared to those not taking concomitant CYP2D6 inhibitors (14.8 ± 10.6 versus 26.7 ± 15.4 ng/mL). The mean steady-state plasma concentration of endoxifen in CYP2D6 normal metabolizers who were not receiving CYP2D6 inhibitors was 31.4 ± 14.7 ng/mL compared to 8.8 ± 3.5 ng/mL in CYP2D6 normal metabolizers receiving potent CYP2D6 inhibitors (e.g., paroxetine, fluoxetine) with tamoxifen. The plasma levels of endoxifen in CYP2D6 normal metabolizers taking potent CYP2D6 inhibitors were similar to the levels observed in CYP2D6 poor metabolizers taking no CYP2D6 inhibitors (8.8 versus 7.2 ng/mL) . Effects of Other Drugs on Tamoxifen Aminoglutethimide Aminoglutethimide reduces tamoxifen and N-desmethyl tamoxifen plasma concentrations. Medroxyprogesterone Medroxyprogesterone reduces the plasma concentration of N-desmethyl tamoxifen, but not that of tamoxifen. 12.5 Pharmacogenomics The impact of CYP2D6 polymorphisms on the efficacy of tamoxifen is not well established. CYP2D6 poor metabolizers carrying two non-functional alleles exhibit significantly lower endoxifen plasma concentrations compared to patients carrying one or more fully functional alleles of CYP2D6. In patients with estrogen receptor-positive breast cancer who were participating in the WHEL (Women's Health Eating and Living) Study (NCT00003787), the mean (SD) serum concentration of endoxifen was 22.8 (11.3), 15.9 (9.2), 8.1 (4.9) and 5.6 (3.8) ng/mL in 27 ultrarapid, 1,097 normal, 164 intermediate and 82 poor metabolizers (p<0.001), respectively. This finding is consistent with other published studies that report lower endoxifen concentrations in poor metabolizers compared to normal metabolizers.
Kenya
Brands & prices
| Brand | Company | Pack | KES |
|---|---|---|---|
| Nolvadex | AstraZeneca | Standard Commercial Pack | — |
| Tamoxifen, by Metro | Distributed by Metro Pharmaceuticals Limited | Standard Commercial Pack | — |
| Tamoxifen, Novartis Access Program | Novartis Pharma | Standard Commercial Pack | — |
Special populations
Pregnancy & lactation
Pregnancy
8.1 Pregnancy Risk Summary SOLTAMOX can cause fetal harm when administered to a pregnant woman . There are no adequate and well- controlled studies of tamoxifen in pregnant women. There are limited postmarketing reports of vaginal bleeding, spontaneous abortions, birth defects, and fetal deaths in pregnant women taking tamoxifen. In a primate model administration of tamoxifen at doses 2 times higher than the maximum recommended human dose resulted in spontaneous abortion. In rat and rabbit studies, doses of tamoxifen less than or equal to human doses resulted in increased embryotoxicity, abortions, and altered learning behaviors. Additionally, rodent models showed reproductive tract changes often associated with DES in offspring of both sexes [ see Data ]. Advise pregnant women of the potential risk to a fetus, including the potential long-term risk of a DES-like syndrome. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. Data Animal Data In embryofetal development studies in rats using doses significantly below those used in humans (0.01 to 0.03 times the recommended human dose on a mg/m 2 basis), a lower incidence of embryo implantation and a higher incidence of fetal death or delayed in utero growth occurred, along with slower learning behavior in some rat pups when compared to historical controls. When pregnant rabbits received tamoxifen during organogenesis, abortion and premature delivery occurred at doses of greater than 0.125 mg/kg/day (about 0.05 times the daily maximum recommended human dose on a mg/m 2 basis). Although reversible nonteratogenic skeletal variations occurred in rat reproductive studies at doses less than or equal to the human dose, there were no teratogenic changes in either rats or rabbits. In pregnant marmosets, administration of 10 mg/kg/day tamoxifen (about 2 times the daily maximum recommended human dose on a mg/m 2 basis) during organogenesis or in the last half of pregnancy terminated pregnancy in some animals. In pregnancies that continued, there were no malformations or deformations in offspring. In rodent models of fetal reproductive tract development, tamoxifen (at doses 0.002 to 2.4 times the daily maximum recommended human dose on a mg/m 2 basis) caused changes in both sexes that are similar to those caused by estradiol, ethynylestradiol 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 age 15 to 20) to determine whether vaginal or cervical neoplasia could occur as a result of this exposure.
Lactation
Lactation: Advise not to breastfeed. ( 8.2 ) Females and males of reproductive potential: Verify pregnancy status of females prior to initiation of tamoxifen. Advise females to use effective contraception. ( 8.3 ) 8.1 Pregnancy Risk Summary SOLTAMOX can cause fetal harm when administered to a pregnant woman . There are no adequate and well- controlled studies of tamoxifen in pregnant women. There are limited postmarketing reports of vaginal bleeding, spontaneous abortions, birth defects, and fetal deaths in pregnant women taking tamoxifen. In a primate model administration of tamoxifen at doses 2 times higher than the maximum recommended human dose resulted in spontaneous abortion. In rat and rabbit studies, doses of tamoxifen less than or equal to human doses resulted in increased embryotoxicity, abortions, and altered learning behaviors. Additionally, rodent models showed reproductive tract changes often associated with DES in offspring of both sexes [ see Data ]. Advise pregnant women of the potential risk to a fetus, including the potential long-term risk of a DES-like syndrome. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. Data Animal Data In embryofetal development studies in rats using doses significantly below those used in humans (0.01 to 0.03 times the recommended human dose on a mg/m 2 basis), a lower incidence of embryo implantation and a higher incidence of fetal death or delayed in utero growth occurred, along with slower learning behavior in some rat pups when compared to historical controls. When pregnant rabbits received tamoxifen during organogenesis, abortion and premature delivery occurred at doses of greater than 0.125 mg/kg/day (about 0.05 times the daily maximum recommended human dose on a mg/m 2 basis). Although reversible nonteratogenic skeletal variations occurred in rat reproductive studies at doses less than or equal to the human dose, there were no teratogenic changes in either rats or rabbits. In pregnant marmosets, administration of 10 mg/kg/day tamoxifen (about 2 times the daily maximum recommended human dose on a mg/m 2 basis) during organogenesis or in the last half of pregnancy terminated pregnancy in some animals. In pregnancies that continued, there were no malformations or deformations in offspring. In rodent models of fetal reproductive tract development, tamoxifen (at doses 0.002 to 2.4 times the daily maximum recommended human dose on a mg/m 2 basis) caused changes in both sexes that are similar to those caused by estradiol, ethynylestradiol 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 age 15 to 20) to determine whether vaginal or cervical neoplasia could occur as a result of this exposure. 8.2 Lactation Risk Summary There is no information regarding the presence of tamoxifen or its metabolites in human milk or its effects on the breastfed infant. Additional information from juvenile animal studies suggests a potential for serious long- term adverse effects for breastfed infants exposed to tamoxifen through breast milk [see Use in Specific Populations (8.4) ] . Because of the potential for serious adverse reactions in breastfed infants from tamoxifen, advise a woman not to breastfeed during treatment with SOLTAMOX and for 3 months following the last dose. 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 unknown. 8.3 Females and Males of Reproductive Potential Pregnancy Testing A negative pregnancy test should be confirmed in females of reproductive potential before initiation of SOLTAMOX therapy. Contraception Females SOLTAMOX can cause fetal harm. Advise females of reproductive potential to use effective nonhormonal contraception during treatment with SOLTAMOX and for 2 months following the last dose [see Use in Specific Populations (8.1) ] . Infertility Females Based on animal studies, SOLTAMOX may impair embryo implantation in females of reproductive potential, however, may not reliably cause infertility. Advise women that SOLTAMOX does not always cause infertility, even in the presence of menstrual irregularity [see Nonclinical Toxicology (13.1) ] . 8.4 Pediatric Use The safety and effectiveness of SOLTAMOX in pediatric patients have not been established. Tamoxifen Use in McCune-Albright Syndrome The safety and effectiveness of SOLTAMOX for the treatment of girls with McCune-Albright syndrome, including long-term effects, have not been established. A single, uncontrolled multicenter trial of tamoxifen 20 mg once a day was conducted in a heterogeneous group of girls with McCune-Albright syndrome and precocious puberty manifested by physical signs of pubertal development, episodes of vaginal bleeding, and/or advanced bone age (bone age of at least 12 months beyond chronological age). Twenty-eight female pediatric patients, aged 2 to 10 years, were treated for up to 12 months. Effect of treatment on frequency of vaginal bleeding, bone age advancement, and linear growth rate was assessed relative to prestudy baseline. Tamoxifen treatment was associated with a 50% reduction in frequency of vaginal bleeding episodes by patient or family report (mean annualized frequency of 3.56 episodes at baseline and 1.73 episodes on-treatment). Among the patients who reported vaginal bleeding during the prestudy period, 62% (13 out of 21 patients) reported no bleeding for a 6-month period and 33% (7 out of 21 patients) reported no vaginal bleeding for the duration of the trial. Not all patients improved on treatment and a few patients not reporting vaginal bleeding in the 6 months prior to enrollment reported menses on treatment. Tamoxifen therapy was associated with a reduction in mean rate of increase of bone age (defined as the ratio of bone age change and chronological age); individual responses with regard to this endpoint were highly heterogeneous. Linear growth rate (height velocity) was reduced during the course of tamoxifen treatment in a majority of patients (mean change of 1.68 cm/year relative to baseline; change from 7.47 cm/year at baseline to 5.79 cm/year on study). This change was not uniformly seen across all stages of bone maturity; all recorded response failures occurred in patients with bone ages less than 7 years at screening. Mean uterine volume increased after 6 months of treatment and doubled at the end of the one-year study. A causal relationship to tamoxifen 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 uterine effects is recommended. Pharmacokinetics in Pediatric 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 pediatric patients aged 2 to 10 years enrolled in a study of tamoxifen in treating McCune-Albright syndrome. Clearance (CL/F), adjusted for body weight, in female pediatric patients was approximately 2.3-fold higher than in adult female breast cancer patients. In the youngest cohort of female pediatric patients (2 to 6 year olds), CL/F was 2.6-fold higher; in the oldest cohort (7 to 10.9 year olds), CL/F was approximately 1.9-fold higher. Exposure to N-desmethyl tamoxifen was comparable between the pediatric and adult patients. In pediatric patients, an average steady-state peak plasma concentration (Css, max) and AUC were 187 ng/mL and 4,110 ng hr/mL, respectively, and Css, max occurred approximately 8 hours after dosing. Animal Data Direct neonatal exposure of tamoxifen to mice and rats produced: 1) reproductive tract lesions in female rodents (similar to those seen in humans after intrauterine exposure to DES) and 2) functional defects of the reproductive tract in male rodents such as testicular atrophy and arrest of spermatogenesis. 8.5 Geriatric Use Ductal Carcinoma in Situ 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 65 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. Reduction in Breast Cancer Incidence in Women at High Risk 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 65 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.
Diet
Food & alcohol
- Drug & food interactions (label) 7 DRUG INTERACTIONS Anastrozole and letrozole: Should not be used in combination with tamoxifen. ( 7.1 ) Warfarin: Do not use in patients taking tamoxifen for DCIS and for reduction in breast cancer incidence in women at high risk. ( 4 ) Closely monitor coagulation indices for increased anticoagulant effect when used with tamoxifen for metastatic breast cancer or as adjuvant therapy. ( 7.2 ) 7.1 Aromatase Inhibitors Anastrozole The combination of anastrozole and tamoxifen did not demonstrate any benefit when compared to tamoxifen alone and should be avoided in all patients [see Clinical Studies (14.2) ] . In the ATAC trial, coadministration of anastrozole and tamoxifen in breast cancer patients reduced the anastrozole plasma concentration by 27% compared to that achieved with anastrozole alone. The tamoxifen concentration was not altered [see Clinical Pharmacology (12.3) ]. Letrozole The concomitant use of letrozole with tamoxifen is not recommended because the efficacy of the combination in the adjuvant treatment of breast cancer has not been established. Tamoxifen reduced the plasma concentration of letrozole by 38% when these drugs were co-administered [see Clinical Pharmacology (12.3) ]. 7.2. Warfarin A marked increase in anticoagulant effect may occur when tamoxifen is used in combination with warfarin. Closely monitor coagulation indices in patients who are taking tamoxifen for either the treatment of metastatic breast cancer or as adjuvant therapy who require concomitant use of warfarin [see Contraindications (4) ] . 7.3 Inducers of CYP3A4 Strong CYP3A4 inducers should not be used with tamoxifen. Strong CYP3A4 inducers (e.g., rifampin) reduce tamoxifen AUC and C max [see Clinical Pharmacology (12.3) ] . 7.4 Strong Inhibitors of CYP2D6 The impact on the efficacy of tamoxifen with co-administration of strong CYP2D6 inhibitors (e.g., paroxetine) is not well established. Some studies have shown that the efficacy of tamoxifen may be reduced when the drugs are co-administered as a result of reduced levels of potent active metabolites of tamoxifen . However, other studies have failed to demonstrate such an effect [see Clinical Pharmacology (12.3) ] . 7.5 Drug-Laboratory Test Interactions There are postmarketing reports of T 4 elevations in postmenopausal patients taking tamoxifen that 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 estrogen effect on Pap smears have been seen in postmenopausal patients taking tamoxifen.
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Source: Local active-ingredient clinical extract; FDA drug label via OpenFDA/DailyMed; Professional class pharmacology (Therapeutic agent (verify pharmacological class))
Last reviewed: 01 Aug 2026
Decision support only — not a substitute for clinical judgment, product SmPC, or Kenya STG/EML.