Tamoxifen
In stock
10mg · 20mg
from 29,20 £
In brief
- Tamoxifen tablets in 10mg or 20mg can be ordered through Leader Pharma, choosing anything from a 30-tablet pack to 360, and UK delivery normally takes 9–21 days.
- A selective oestrogen receptor modulator, it is used in the UK for hormone-receptor-positive breast cancer, early or advanced, and to reduce breast cancer risk in women with a strong family history.
- The usual dose is 20 mg once a day; after breast cancer surgery it is commonly taken for five years and occasionally for up to ten, as decided by the oncology team.
- Hot flushes and vaginal discharge are common, while a swollen, painful leg or sudden shortness of breath needs urgent medical attention because of the raised clot risk.
- Tamoxifen must not be taken in pregnancy, and unexpected vaginal bleeding should always be reported because of possible endometrial changes; it is prescription-only in the UK.
Mechanism of action and pharmacokinetics
Functioning as a Selective oestrogen receptor modulator (SERM), tamoxifen specifically blocks oestrogen receptors in breast tissue while acting differently in other areas like bones. Following oral administration, peak concentrations occur within 4-7 hours. The effectiveness significantly depends on CYP2D6 liver enzymes converting tamoxifen into its active metabolite endoxifen. Usual elimination involves biliary excretion with a lengthy 5-7 day half-life. Drugs that inhibit CYP2D6 – such as the antidepressant paroxetine – may reduce tamoxifen's efficacy.
- Primary MoA: Competitive binding at oestrogen receptors (ERα) in breast cancer cells
- Key metabolite: Endoxifen (active compound requiring CYP2D6 pathway)
- Half-life elimination: Approximately 5-7 days necessitates consistent dosing
Licensed indications and treatment protocols
In the UK, tamoxifen is licensed for oestrogen receptor-positive (ER+) breast cancer. Adjuvant therapy - administered after primary treatments like surgery - typically involves daily 20mg doses for 5-10 years to prevent recurrence. For metastatic disease, clinicians might escalate dosage to a divided 40mg daily schedule. Additional indications include ductal carcinoma in situ (DCIS) management and prevention strategies for high-risk patients. Special populations require consideration: patients with hepatic impairment need caution, pregnant women absolutely avoid it due to teratogenic risks, while paediatric oncology specialists rarely prescribe this medication.
Standard treatment phases reflect oncology protocols:
Early stage care: Minimum 5-year adjuvant therapy cycle
Metastatic cases: Continued use during clinical benefit period
Metastatic cases: Continued use during clinical benefit period
Off-label uses and special populations
Tamoxifen sees considerable off-label use beyond its approved breast cancer indications. For managing gynaecomastia—breast tissue enlargement in men—daily doses of 10-20mg are often prescribed short-term. Some fertility treatments incorporate low-dose tamoxifen (male infertility protocols) to boost sperm production, though evidence remains inconclusive.
Specialist guidance is particularly vital for specific populations:
- Paediatric oncology cases (rare tumour types)
- Severe hepatic impairment (dose reduction required)
- Renal dysfunction (enhanced toxicity monitoring essential)
Children receiving tamoxifen require tailored formulations and oncology-team supervision due to unique pharmacodynamics. Providers should scrutinise risk-benefit ratios carefully when prescribing outside oncology.
Dosage and administration guidelines
Tamoxifen protocols vary significantly by clinical indication. Standard breast cancer regimens involve 20mg once daily. Metastatic disease occasionally warrants higher doses (20-40mg/day), typically administered as split morning/evening doses. Unlike many anticancer agents, tamoxifen operates on chronic scheduling—continuing for 5–10 years in adjuvant therapy.
For elderly patients, full dosing usually applies unless comorbidities interfere. Renal impairment warrants vigilant observation but no default dose reduction. Significant hepatic dysfunction requires caution.
Missed dose handling remains straightforward: take the tablet upon realisation without doubling later. Overdoses typically manifest tremors or dizziness and require ECG monitoring and symptomatic support. Swallow tablets whole regardless of food timing; oral solution dosing needs precise measurement.
Side effects profile
Hot flushes are among the most common side effects of tamoxifen, often disrupting sleep and daily comfort. Most adverse reactions prove manageable: nausea, vaginal discharge, arthralgias and transient alopecia rank among frequent complaints.
Clinicians prioritise surveillance for life-threatening complications: endometrial cancer risks escalate significantly beyond 5-year continuous therapy. Any abnormal vaginal bleeding should be reported promptly and investigated. Thromboembolic events (DVTs, pulmonary emboli) represent another critical concern requiring urgent intervention if leg swelling or breathing difficulties emerge.
Vision disturbances like cataracts occasionally develop gradually. Routine liver function testing helps identify hepatotoxicity early. Patients require counselling to differentiate expected effects from reportable symptoms.
Contraindications and precautions
Absolute contraindications include pregnancy (known teratogenic effects), breastfeeding, and confirmed hypersensitivity reactions. A history of venous thromboembolism requires careful assessment and rules out its use for breast cancer risk reduction.
Medication interactions warrant particular caution. Combination with warfarin significantly increases the anticoagulant effect and bleeding risk. Certain antidepressants (notably paroxetine/fluoxetine) hinder tamoxifen's metabolic activation via CYP2D6 inhibition, compromising anticancer efficacy.
Key precautions cover:
- Existing endometrial pathology (accelerates precancerous progression)
- Bone metastases (hypercalcaemia monitoring imperative during initiation)
- Lipid profiles (cholesterol fluctuations possible)
- Blood dyscrasias history (periodic blood counts recommended)
Treatment alternatives comparison
| Medication | Drug class | Optimal patient profile | Primary limitation |
|---|---|---|---|
| Anastrozole | Aromatase inhibitor | Postmenopausal patients | Accelerated bone density loss |
| Fulvestrant | ER antagonist | Metastatic disease progression | Intramuscular administration |
| Raloxifene | SERM | Osteoporosis prevention | Reduced breast carcinoma efficacy |
| Exemestane | Steroidal AI | Aromatase inhibitor intolerance | Androgenic side effects |
In NHS oncology the choice depends mainly on menopausal status: postmenopausal patients are often offered an aromatase inhibitor such as anastrozole, while tamoxifen remains a standard option for premenopausal patients. Switching may be considered for patients with intolerable vasomotor symptoms or thromboembolic risk factors.
Common patient concerns
Alcohol is not contraindicated, but intake should be kept within recommended limits. Tamoxifen is not a contraceptive and can stimulate ovulation in premenopausal women, so effective non-hormonal contraception is needed during treatment.
Missed doses require straightforward management: take when remembered unless nearing next scheduled dose. Driving competency requires monitoring during early adjustment phases as somnolence occasionally occurs during initial weeks.
Implementation guidelines
Take tamoxifen at the same time each day. Tablets should be swallowed whole with water, with or without food. Store below 25°C in the original packaging to protect from moisture.
Pregnancy must be excluded before treatment and avoided during it. Oestrogen-containing products should be avoided regardless of administration route. Visual changes (such as cataracts) should be reported to a doctor.
