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Selective oestrogen receptor modulator (SERM) Pregnancy: Pregnancy Category D (US labelling). Based on its mechanism of action and findings of increased pregnancy loss and fetal malformation in animal studies, toremifene can cause fetal harm when administered to a pregnant woman; there are no adequate and well-controlled studies in pregnant women. Women should be advised not to become pregnant while taking it and women of childbearing potential should use effective non-hormonal contraception during therapy. If used during pregnancy, or if the patient becomes pregnant, she should be apprised of the potential hazard to the fetus.

Toremifene

Brand names: Fareston

Toremifene is an oral selective oestrogen receptor modulator used in the treatment of hormone receptor-positive metastatic breast cancer in postmenopausal women.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 60 mg
Route: Oral (60 mg tablet)
Frequency: Once daily
Treatment is generally continued until disease progression is observed. There is no indication for use in paediatric patients. No UK SPC posology was available in the fetched bundle — this draft is from US labelling (Fareston) and must be verified against the UK SPC. Hypokalaemia or hypomagnesaemia must be corrected before initiating toremifene and these electrolytes monitored periodically during therapy; in patients at increased risk, ECGs should be obtained at baseline and as clinically indicated.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Known hypersensitivity to the drug
  • Congenital or acquired QT prolongation (long QT syndrome)
  • Uncorrected hypokalaemia or uncorrected hypomagnesaemia

Side effects

  • Hot flashes (35%)
  • Sweating (20%)
  • Nausea (14%)
  • Vaginal discharge (13%)
  • Dizziness (9%); also oedema, vomiting and vaginal bleeding. Labelled warnings include QT prolongation (which can result in torsade de pointes), hepatotoxicity, hypercalcaemia and tumour flare, and risk of uterine malignancy

Interactions

  • Drugs that decrease renal calcium excretion, e.g. thiazide diuretics — may increase the risk of hypercalcaemia
  • Agents that prolong the QT interval — should be avoided; if such treatment is required it is recommended that toremifene be interrupted, or the patient closely monitored for QT prolongation if interruption is not possible
  • Strong CYP3A4 inducers — coadministration may result in a relevant decrease in toremifene exposure and should be avoided
  • Strong CYP3A4 inhibitors — coadministration can result in a relevant increase in toremifene exposure and should be avoided
  • CYP2C9 substrates with a narrow therapeutic index such as warfarin or phenytoin — use with caution and with careful monitoring

Clinical monograph

How it works

It competitively binds oestrogen receptors, exerting anti-oestrogenic effects on breast tissue and thereby inhibiting growth of hormone-dependent tumours.

Prescribing in practice

  • It prolongs the QT interval in a dose-related manner, so it should be avoided in those with significant QT prolongation, electrolyte disturbance or concurrent QT-prolonging drugs.
  • It increases the risk of venous thromboembolism and, like other oestrogen modulators, of endometrial changes, so abnormal vaginal bleeding should be investigated.
  • It is metabolised via CYP3A4, so interacting drugs and uncorrected hypokalaemia or hypomagnesaemia should be addressed before and during treatment.

Monitoring

Monitor for cardiac and thromboembolic symptoms, correct electrolyte disturbances, and consider ECG where QT risk factors exist.

Counselling the patient

  • Report palpitations, fainting, leg swelling or breathlessness without delay.
  • Tell your doctor about any unusual vaginal bleeding.
  • Mention all other medicines, as some can affect your heart rhythm when combined with this drug.

Evidence & guidelines

Use is guided by the manufacturer's SPC, with trials showing efficacy comparable to tamoxifen in hormone receptor-positive advanced breast cancer.

Reference: SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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