tamoxifen citrate: clinical use

Prescribing considerations

• Confirm the licensed indication and assess individual benefits against venous thromboembolism, uterine and ocular risks.
• For primary prevention, treatment should follow specialist risk assessment, shared decision-making and appropriate breast surveillance.
• Obtain personal and family venous-thromboembolism history; consider thrombophilia assessment when the history suggests inherited risk.
• Review perioperative and immobility-associated thrombosis risk rather than asking patients to interrupt breast-cancer treatment independently.
• Review CYP2D6 inhibitors, anticoagulants, hormonal products and QT-prolonging medicines before prescribing.
• Exclude pregnancy where relevant and counsel about non-hormonal contraception.

Contraindications and cautions

• Hypersensitivity to tamoxifen or product excipients.
• Pregnancy; the selected oral solution also lists breastfeeding as contraindicated.
• Concurrent anastrozole therapy.
• For primary prevention: previous deep-vein thrombosis or pulmonary embolism, or required coumarin anticoagulation.
• For infertility treatment: personal or family history of confirmed idiopathic venous thromboembolism or a known thrombophilic genetic defect.
• Hereditary fructose intolerance for the selected sorbitol-containing oral solution.

Monitoring

• Investigate non-menstrual or postmenopausal bleeding, menstrual changes, persistent discharge, pelvic pain or pressure promptly.
• Use ECG and electrolyte monitoring before and during treatment when QT-prolongation risk factors, cardiac disease or interacting medicines are present.
• Assess new visual symptoms promptly; the oral-solution SmPC advises ophthalmological assessment when treatment begins.
• Monitor coagulation closely if coumarin anticoagulation is used for an indication where the combination is not contraindicated.
• Consider blood counts, liver function and calcium according to clinical context, symptoms and concomitant treatment.
• Continue indication-appropriate breast surveillance.

Clinical pharmacology

Tamoxifen is a tissue-selective oestrogen receptor modulator. It is highly protein-bound and extensively metabolised, mainly through CYP3A4 and CYP2D6, to active metabolites including endoxifen. Tamoxifen and its principal metabolites have prolonged elimination.

Formulation and product differences

• The selected tablet is licensed for breast cancer treatment, primary prevention and stimulation of ovulation in anovulatory infertility.
• The selected oral solution is licensed for breast cancer treatment and primary prevention, but not infertility.
• The oral solution contains ethanol, sorbitol, glycerol and propylene glycol and is unsuitable in hereditary fructose intolerance.
• The oral solution should be protected from light, not refrigerated or frozen, and discarded three months after first opening.

Oral solution

Route: Oral

Strengths: 10 mg/5 mL

Tablet

Route: Oral

Strengths: 10 mg, 20 mg