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Prolongation of the QT Interval
Toremifene has been shown to prolong the QTc interval in a dose- and concentration-related manner [see CLINICAL PHARMACOLOGY]. Prolongation of the QT interval can result in a type of ventricular tachycardia called Torsade de pointes, which may result in syncope, seizure, and/or death.
Toremifene should be avoided in patients with long QT syndrome. Caution should be exercised in patients with congestive heart failure, hepatic impairment and electrolyte abnormalities. Hypokalemia or hypomagnesemia must be corrected prior to initiating toremifene and these electrolytes should be monitored periodically during therapy. Drugs that prolong the QT interval should be avoided. In patients at increased risk, electrocardiograms (ECGs) should be obtained at baseline and as clinically indicated [see DRUG INTERACTIONS and CLINICAL PHARMACOLOGY].
Hypercalcemia and Tumor Flare
As with other antiestrogens, hypercalcemia and tumor flare have been reported in some breast cancer patients with bone metastases during the first weeks of treatment with FARESTON. Tumor flare is a syndrome of diffuse musculoskeletal pain and erythema with increased size of tumor lesions that later regress. It is often accompanied by hypercalcemia. Tumor flare does not imply failure of treatment or represent tumor progression. If hypercalcemia occurs, appropriate measures should be instituted and, if hypercalcemia is severe, FARESTON treatment should be discontinued.
Since most toremifene trials have been conducted in patients with metastatic disease, adequate data on the potential endometrial tumorigenicity of long-term treatment with FARESTON are not available. Endometrial hyperplasia has been reported. Some patients treated with FARESTON have developed endometrial cancer, but circumstances (short duration of treatment or prior antiestrogen treatment or premalignant conditions) make it difficult to establish the role of FARESTON. Endometrial hyperplasia of the uterus was observed in animals treated with toremifene [see Nonclinical Toxicology].
Patients with a history of thromboembolic diseases should generally not be treated with FARESTON. In general, patients with preexisting endometrial hyperplasia should not be given long-term FARESTON treatment. Patients with bone metastases should be monitored closely for hypercalcemia during the first weeks of treatment. Leukopenia and thrombocytopenia have been reported rarely; leukocyte and platelet counts should be monitored when using FARESTON in patients with leukopenia and thrombocytopenia.
Periodic complete blood counts, calcium levels, and liver function tests should be obtained.
Use in Pregnancy
Based on its mechanism of action in humans and findings of increased pregnancy loss and fetal malformation in animal studies, FARESTON can cause fetal harm when administered to a pregnant woman. Toremifene caused embryo-fetal toxicities at maternal doses that were lower than the 60 mg daily recommended human dose on a mg/m² basis. There are no adequate and well-controlled studies in pregnant women using FARESTON. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus [see Use In Specific Populations].
Women of Childbearing Potential
FARESTON is indicated only in postmenopausal women. However, premenopausal women prescribed FARESTON should use effective non-hormonal contraception and should be apprised of the potential hazard to the fetus should pregnancy occur.
Carcinogenesis, Mutagenesis, and Impairment of Fertility
Conventional carcinogenesis studies in rats at doses of 0.12 to 12 mg/kg/day (approximately 1/50 to 2 times the daily maximum recommended human dose of 60 mg, on a mg/m² basis) for up to 2 years did not show evidence of carcinogenicity. Studies in mice at doses of 1.0 to 30.0 mg/kg/day (approximately 1/15 to 2 times the daily maximum recommended human dose of 60 mg, on a mg/m² basis) for up to 2 years revealed increased incidence of ovarian and testicular tumors and increased incidence of osteoma and osteosarcoma. The significance of the mouse findings is uncertain because of the different role of estrogens in mice and the estrogenic effect of toremifene in mice. An increased incidence of ovarian and testicular tumors in mice has also been observed with other human estrogen agonists/antagonists that have primarily estrogenic activity in mice. Endometrial hyperplasia of the uterus was observed in monkeys following 52 weeks of treatment at ≥ 1 mg/kg and in dogs following 16 weeks of treatment at ≥ 3 mg/kg with toremifene (approximately 1/3 and 1.4 times, respectively, the daily maximum recommended human dose of 60 mg, on a mg/m² basis).
Toremifene has not been shown to be mutagenic in in vitro tests (Ames and E. coli bacterial tests). Toremifene is clastogenic in vitro (chromosomal aberrations and micronuclei formation in human lymphoblastoid MCL-5 cells) and in vivo (chromosomal aberrations in rat hepatocytes).
Toremifene produced impairment of fertility and conception in male and female rats at doses ≥ 25.0 and 0.14 mg/kg/day, respectively (approximately 4 times and 1/50 the daily maximum recommended human dose of 60 mg, on a mg/m² basis). At these doses, sperm counts, fertility index, and conception rate were reduced in males with atrophy of seminal vesicles and prostate. In females, fertility and reproductive indices were markedly reduced with increased pre-and post-implantation loss. In addition, offspring of treated rats exhibited depressed reproductive indices. Toremifene produced ovarian atrophy in dogs administered doses ≥ 3 mg/kg/day (approximately 1.5 times the daily maximum recommended human dose of 60 mg, on a mg/m² basis) for 16 weeks. Cystic ovaries and reduction in endometrial stromal cellularity were observed in monkeys at doses ≥ 1 mg/kg/day (about 1/3 the daily maximum recommended human dose of 60 mg, on a mg/m² basis) for 52 weeks.
Use In Specific Populations
Pregnancy Category D [see WARNINGS AND PRECAUTIONS.]
Based on its mechanism of action in humans and findings of increased pregnancy loss and fetal malformation in animal studies, FARESTON can cause fetal harm when administered to a pregnant woman. Toremifene caused embryo-fetal toxicities at maternal doses that were lower than the 60 mg daily recommended human dose on a mg/m² basis. There are no adequate and well-controlled studies in pregnant women using FARESTON. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus.
In animal studies, toremifene crossed the placenta and accumulated in the rodent fetus. Administration of toremifene to pregnant rats during organogenesis at doses of approximately 6% the daily maximum recommended human dose of 60 mg (on a mg/m² basis) resulted in signs of maternal toxicity and increased preimplantation loss, increased resorptions, reduced fetal weight, and fetal anomalies. Fetal anomalies include malformation of limbs, incomplete ossification, misshapen bones, ribs/spine anomalies, hydroureter, hydronephrosis, testicular displacement, and subcutaneous edema. Maternal toxicity may have contributed to these adverse embryo-fetal effects. Similar embryo-fetal toxicities occurred in rabbits that received toremifene at doses approximately 40% the daily recommended human dose of 60 mg (on a mg/m² basis). Findings in rabbits included increased preimplantation loss, increased resorptions, and fetal anomalies, including incomplete ossification and anencephaly.
Animal doses resulting in embryo-fetal toxicities were ≥ 1.0 mg/kg/day in rats and ≥ 1.25 mg/kg/day in rabbits.
In rodent models of fetal reproductive tract development, toremifene produced inhibition of uterine development in female pups similar to effects seen with diethylstilbestrol (DES) and tamoxifen. The clinical relevance of these changes is not known. Neonatal rodent studies have not been conducted to assess the potential for toremifene to cause other DES-like effects in offspring (i.e., vaginal adenosis). Vaginal adenosis in animals occurred following treatment with other drugs of this class and has been observed in women exposed to diethylstilbestrol in utero.
It is not known if toremifene is excreted in human milk. Toremifene is excreted in the milk of lactating rats. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from FARESTON, a decision should be made to either discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
There is no indication for use of FARESTON in pediatric patients.
The pharmacokinetics of toremifene were studied in 10 healthy young males and 10 elderly females following a single 120 mg dose under fasting conditions. Increases in the elimination half-life (4.2 versus 7.2 days) and the volume of distribution (457 versus 627 L) of toremifene were seen in the elderly females without any change in clearance or AUC.
The median ages in the three controlled studies ranged from 60 to 66 years. No significant age-related differences in FARESTON effectiveness or safety were noted.
The pharmacokinetics of toremifene and N-demethyltoremifene were similar in normals and in patients with impaired kidney function.
The mean elimination half-life of toremifene was increased by less than twofold in 10 patients with hepatic impairment (cirrhosis or fibrosis) compared to subjects with normal hepatic function. The pharmacokinetics of Ndemethyltoremifene were unchanged in these patients. Ten patients on anticonvulsants (phenobarbital, clonazepam, phenytoin, and carbamazepine) showed a twofold increase in clearance and a decrease in the elimination half-life of toremifene.
The pharmacokinetics of toremifene in patients of different races has not been studied.
Fourteen percent of patients in the North American Study were non-Caucasian. No significant race-related differences in FARESTON effectiveness or safety were noted.
Last reviewed on RxList: 6/3/2011
This monograph has been modified to include the generic and brand name in many instances.
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