NOLVADEX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NOLVADEX (NOLVADEX).
NOLVADEX (tamoxifen citrate) is a nonsteroidal selective estrogen receptor modulator (SERM) that competitively inhibits estrogen binding to estrogen receptors in breast tissue, thereby blocking estrogen-mediated cell proliferation. It also has partial agonist activity in other tissues such as bone and endometrium.
| Metabolism | Extensively metabolized in the liver via cytochrome P450 enzymes, primarily CYP2D6 (to active metabolite endoxifen) and CYP3A4, with contributions from CYP2B6, CYP2C9, and CYP2C19. Undergoes glucuronidation and sulfation. Endoxifen is further metabolized by CYP3A4. |
| Excretion | Primarily fecal (65%) as conjugates; renal excretion accounts for approximately 25% as metabolites and <0.5% as unchanged drug. Biliary elimination contributes 10%. |
| Half-life | Tamoxifen: 5-7 days (terminal). N-desmethyltamoxifen (active metabolite): 14 days. Steady-state achieved in 3-4 weeks. |
| Protein binding | >99% bound primarily to albumin. |
| Volume of Distribution | 50-60 L/kg, indicating extensive tissue distribution (e.g., breast, liver, uterus). |
| Bioavailability | Oral: Approximately 100% after first pass due to extensive hepatic metabolism; absolute bioavailability is nearly complete but variable. |
| Onset of Action | Oral: Clinical effect (e.g., reduction in tumor size) typically observed within 4 weeks, though full therapeutic response may require 8-12 weeks. |
| Duration of Action | Duration of action extends beyond the dosing interval due to long half-life; once-daily dosing maintains therapeutic levels. Continued effect for weeks after discontinuation. |
| Molecular Weight | 371.5 |
| Action Class | Selective estrogen receptor modulators (SERM)- Breast Cx |
| Brand Substitutes | Valodex 10mg Tablet, Cytotam 10mg Tablet, Entax 10mg Tablet, Mamofen 10 Tablet, Moxifen 10mg Tablet |
20-40 mg orally once daily; for breast cancer, 20 mg/day. For adjuvant therapy, 20 mg/day for 5 years. For ductal carcinoma in situ, 20 mg/day for 5 years. For reduction of breast cancer incidence in high-risk women, 20 mg/day for 5 years.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. For severe renal impairment (CrCl <30 mL/min), use with caution; no specific guidelines, consider reduced dose. |
| Liver impairment | Contraindicated in Child-Pugh class C. For Child-Pugh class B, reduce dose by 50% (e.g., 20 mg every other day). For Child-Pugh class A, no adjustment needed. |
| Pediatric use | Safety and efficacy not established in pediatric patients for FDA-approved indications. Off-label use for gonadotropin-independent precocious puberty: 20 mg orally once daily (monitor for potential risks). |
| Geriatric use | No specific dose adjustment recommended based on age alone; dosing same as adults. Monitor for increased risk of thromboembolic events, endometrial cancer, and cataracts. Start at lower end of dosing range (20 mg/day) if frail or with comorbidities. |
| 1st trimester | Contraindicated: Tamoxifen is an antiestrogen; there is a risk of fetal harm including spontaneous abortion and birth defects. Pregnancy should be excluded before starting therapy. |
| 2nd trimester | Contraindicated: Ongoing risk from antiestrogenic effects. May cause fetal harm based on animal studies. |
| 3rd trimester | Contraindicated: Potential for adverse effects on fetal development. Not recommended during pregnancy. |
Clinical note
Comprehensive clinical and safety monograph for NOLVADEX (NOLVADEX).
| Placental transfer | Tamoxifen and its metabolites have been shown to cross the placenta in animal studies; limited human data suggest transfer occurs. |
| Breastfeeding | Tamoxifen is excreted in human milk and may cause adverse effects in the breastfed infant. Breastfeeding is not recommended during therapy and for at least 3 months after the last dose. |
■ FDA Black Box Warning
WARNING: SERIOUS AND LIFE-THREATENING EVENTS - NOLVADEX has been associated with an increased risk of uterine malignancies (including endometrial cancer and uterine sarcoma), stroke, and pulmonary embolism. These risks increase with duration of therapy and patient age. Use only when benefit outweighs risk. Educate patients about symptoms of these events and seek prompt medical attention.
| Serious Effects |
PregnancyHistory of deep vein thrombosis or pulmonary embolismKnown hypersensitivity to tamoxifen or any component of the formulationConcurrent warfarin therapy (increased risk of bleeding)
| Precautions | Increased risk of endometrial cancer, uterine sarcoma, and other uterine malignancies; perform baseline gynecologic exam and monitor for abnormal bleeding, Increased risk of thromboembolic events (DVT, PE, stroke); avoid in patients with history of thromboembolism, Hepatotoxicity: elevated liver enzymes, hepatitis, and hepatic steatosis; monitor periodic liver function tests, Ocular effects: cataracts, retinopathy; perform periodic eye exams, Hypercalcemia: may occur in patients with bone metastases; monitor serum calcium, Bone density loss: may cause decreased bone mineral density in premenopausal women; consider calcium and vitamin D supplementation, QT prolongation: use caution with other QT-prolonging drugs or electrolyte imbalances, Fetal harm: can cause fetal harm if used during pregnancy; advise women of childbearing age to use effective contraception |
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| Lactation Rating | L5 (Avoid) |
| Teratogenic Risk | Nolvadex (tamoxifen) is classified as FDA Pregnancy Category D. There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience. First trimester exposure is associated with spontaneous abortions, birth defects (including craniofacial, genital, and skeletal anomalies), and fetal death. Second and third trimester exposure may cause fetal harm including pulmonary hypoplasia and growth retardation. Use is contraindicated during pregnancy. |
| Fetal Monitoring | Women of reproductive potential should undergo pregnancy testing prior to initiation and monthly during therapy. During pregnancy, if exposure occurs, monitor fetal growth and development with ultrasound and consider amniocentesis for genetic analysis if anomalies suspected. Postnatal monitoring of the infant for endocrine and developmental effects is recommended. Maternal monitoring includes liver function tests, serum calcium, and ophthalmologic exams for retinal changes. |
| Fertility Effects | Tamoxifen may induce ovulation and increase fertility in premenopausal women. It can cause ovarian cyst formation and menstrual irregularities. Long-term use may lead to premature ovarian failure and reduced fertility. Contraception counseling is recommended for women of childbearing potential. |
| Food/Dietary | Avoid grapefruit and grapefruit juice as they inhibit CYP3A4, potentially altering tamoxifen metabolism. Avoid St. John's wort. No other specific dietary restrictions, but maintain a balanced diet. Alcohol should be limited due to increased risk of liver enzyme elevation. |
| Clinical Pearls | NOLVADEX (tamoxifen) is a selective estrogen receptor modulator (SERM) indicated for the treatment and prevention of breast cancer. Monitor for endometrial hyperplasia and thromboembolic events. Use with caution in patients with history of DVT/PE. CYP2D6 inhibitors (e.g., paroxetine) reduce conversion to active metabolite endoxifen; avoid coadministration. Tamoxifen can cause tumor flare in bone metastases. Discontinue 2-3 months before attempting pregnancy due to long half-life. Regular gynecologic exams and ophthalmologic monitoring recommended. |
| Patient Advice | Take exactly as prescribed; do not skip doses. · Report any unusual vaginal bleeding, pelvic pain, or changes in vision immediately. · Avoid grapefruit juice as it may affect drug levels. · Use effective non-hormonal contraception during therapy and for 2 months after stopping. · Do not take St. John's wort or other herbal supplements without consulting your doctor. · Report leg swelling, chest pain, or shortness of breath promptly. · May cause hot flashes, nausea, or fatigue; these are not reasons to stop without consulting your doctor. · Attend all scheduled gynecologic and eye exams. |