Formulary
Tamoxifen: Indications, Dosing, Side Effects and Interactions
An anti-oestrogen which induces gonadotrophin release by occupying oestrogen receptors in the hypothalamus, thereby interfering with feedback mechanisms;...
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Tamoxifen: Indications, Dosing, Side Effects and Interactions
An anti-oestrogen which induces gonadotrophin release by occupying oestrogen receptors in the hypothalamus, thereby interfering with feedback mechanisms;...
Drug action
An anti-oestrogen which induces gonadotrophin release by occupying oestrogen receptors in the hypothalamus, thereby interfering with feedback mechanisms; chorionic gonadotrophin is sometimes used as an adjunct in the treatment of female infertility.
Indications and dose
**Pre- and perimenopausal women with oestrogen-receptor-positive breast cancer not previously treated with tamoxifen**
- **Adult** (By Mouth): 20 mg daily.
**Anovulatory infertility**
- **Adult** (By Mouth): Initially 20 mg daily on days 2, 3, 4 and 5 of cycle, if necessary the daily dose may be increased to 40 mg then 80 mg for subsequent courses; if cycles irregular, start initial course on any day, with subsequent course starting 45 days later or on day 2 of cycle if menstruation occurs.
**Gynaecomastia [prevention in men undergoing long-term bicalutamide treatment, if radiotherapy unsuccessful]**
- **Adult** (By Mouth): 20 mg once weekly.
**Breast cancer [chemoprevention in women at moderate-to-high risk]**
- **Adult** (By Mouth): 20 mg daily for 5 years.
Cautions
Acute porphyrias
Contraindications
Treatment of infertility contra-indicated if personal or family history of idiopathic venous thromboembolism or genetic predisposition to thromboembolism
Side effects
Common or very common Alopecia; anaemia; cataract; cerebral ischaemia; constipation; depression; diarrhoea; dizziness; embolism and thrombosis; fatigue; fluid retention; haemorrhage; headache; hepatic disorders; hot flush; hypersensitivity; hypertriglyceridaemia; muscle complaints; nausea; neoplasms; retinopathy; sensation abnormal; skin reactions; taste altered; uterine disorders; vomiting; vulvovaginal disorders Uncommon Hypercalcaemia; interstitial pneumonitis; leucopenia; pancreatitis; thrombocytopenia; vision disorders Rare or very rare Agranulocytosis; angioedema; corneal changes; cutaneous lupus erythematosus; cutaneous vasculitis; nerve disorders; neutropenia; ovarian and fallopian tube disorders; QT interval prolongation; radiation recall reaction; severe cutaneous adverse reactions (SCARs); tumour flare Side-effects, further information Endometrial changes Increased endometrial changes, including hyperplasia, polyps, cancer, and uterine sarcoma reported; prompt investigation required if abnormal vaginal bleeding including menstrual irregularities, vaginal discharge, and pelvic pain or pressure in those receiving (or who have received) tamoxifen. Risk of thromboembolism Tamoxifen can increase the risk of thromboembolism particularly during and immediately after major surgery or periods of immobility (consider interrupting treatment and initiating anticoagulant measures).
Interactions
**Severe interactions:**
- When tamoxifen is used in combination with coumarin-type anticoagulants, a significant increase in anticoagulant effect may occur.
**Other interactions (8):**
- When tamoxifen is used in combination with cytotoxic agents for the treatment of breast cancer, there is increased risk of thromboembolic events occurring (see also sections 4.4 and 4.8).
- The use of tamoxifen in combination with anastrozole as adjuvant therapy has not shown improved efficacy compared with tamoxifen alone.
- As tamoxifen is metabolised by cytochrome P450 3A4, care is required when co- administering with drugs, such as rifampicin, known to induce this enzyme as tamoxifen levels may be reduced.
- Pharmacokinetic interaction with CYP2D6 inhibitors, showing a reduction in plasma level of an active tamoxifen metabolite, 4-hydroxy-Ndesmethyl-tamoxifen (endoxifen), has been reported in the...
- Reduced efficacy of tamoxifen has been reported with concomitant usage of some SSRI antidepressants (e.g.
- As a reduced effect of tamoxifen cannot be excluded, co-administration with potent CYP2D6 inhibitors (e.g.
Pregnancy
Avoid-possible effects on fetal development.
Breast feeding
Suppresses lactation. Avoid unless potential benefit outweighs risk.
Medicinal forms
Solution,Tablet,Solution
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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