FARESTON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FARESTON (FARESTON).
Selective estrogen receptor modulator (SERM) that competitively binds to estrogen receptors, exerting antiestrogenic effects in breast tissue.
| Metabolism | Primarily hepatic via CYP3A4 and CYP1A2; undergoes glucuronidation; active metabolite N-desmethyltoremifene |
| Excretion | FARESTON (toremifene) is extensively metabolized in the liver. Excretion is primarily fecal (approximately 70%) with renal excretion accounting for less than 10% of the dose as unchanged drug and metabolites. |
| Half-life | The terminal elimination half-life of toremifene is approximately 5 days (range 2-10 days). The half-life of its main metabolite, N-desmethyltoremifene, is about 11 days. This long half-life supports once-daily dosing. |
| Protein binding | Toremifene is >99% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | The apparent volume of distribution (Vd) is approximately 580 L (about 8 L/kg for a 70 kg individual), indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability of toremifene is not precisely determined but is estimated to be nearly 100% based on absorption and first-pass metabolism studies. |
| Onset of Action | Clinical response (tumor regression) is typically observed after 4-8 weeks of continuous daily oral dosing. |
| Duration of Action | The therapeutic effect lasts as long as treatment continues. The drug's long half-life results in sustained plasma levels, but clinical duration is not defined as treatment is continuous; effects may persist for weeks after discontinuation due to slow elimination. |
60 mg orally once daily.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for GFR ≥30 mL/min; insufficient data for GFR <30 mL/min. |
| Liver impairment | Contraindicated in Child-Pugh class C; use with caution in class A or B without specific dose reduction guidelines. |
| Pediatric use | Safety and efficacy not established; no recommended dose. |
| Geriatric use | No specific dose adjustment; monitor renal function and electrolyte balance. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for FARESTON (FARESTON).
| Breastfeeding | Not recommended during breastfeeding. Toremifene may be excreted in human milk; M/P ratio not established. Potential for serious adverse reactions in nursing infants, including hormonal disruption. |
| Teratogenic Risk | Pregnancy Category D. First trimester: Risk of fetal harm, including spontaneous abortion and congenital malformations (e.g., craniofacial, cardiac). Second and third trimesters: Potential for fetal hypothalamic-pituitary-gonadal axis disruption, ambiguous genitalia in female fetuses, and other adverse effects based on animal studies. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to toremifene or any excipients","History of thromboembolic disease","Pre-existing endometrial hyperplasia","Patients with long QT syndrome or concurrent use of QT-prolonging drugs"]
| Precautions | ["QT interval prolongation","Hypercalcemia in patients with bone metastases","Endometrial hyperplasia/cancer risk","Thromboembolic events","Ocular toxicity (dose-dependent retinopathy)","Tumor flare"] |
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| Fetal Monitoring |
| Monitor liver function tests (AST, ALT, bilirubin) monthly; serum calcium, complete blood count, and renal function periodically. Fetal monitoring via ultrasound for growth and anatomy; consider fetal echocardiography if exposure in first trimester. |
| Fertility Effects | May impair fertility in both males and females. In females: potential anovulation, menstrual irregularities, and ovarian failure. In males: altered spermatogenesis and reduced sperm count. Effects may be reversible upon discontinuation. |