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Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.
Clinical Trials Experience
Adverse drug reactions are principally due to the antiestrogenic actions of FARESTON and typically occur at the beginning of treatment.
The incidences of the following eight clinical toxicities were prospectively assessed in the North American Study. The incidence reflects the toxicities that were considered by the investigator to be drug related or possibly drug related.
|North American Study|
n = 221
n = 215
Approximately 1% of patients receiving FARESTON (n = 592) in the three controlled studies discontinued treatment as a result of adverse reactions (nausea and vomiting, fatigue, thrombophlebitis, depression, lethargy, anorexia, ischemic attack, arthritis, pulmonary embolism, and myocardial infarction).
Serious adverse reactions occurring in at least 1% of patients receiving FARESTON in the three major trials are listed in the table below.
Three prospective, randomized, controlled clinical studies (North American, Eastern European, and Nordic) were conducted. The patients were randomized to parallel groups receiving FARESTON 60 mg (FAR60) or tamoxifen 20 mg (TAM20) in the North American Study or tamoxifen 40 mg (TAM40) in the Eastern European and Nordic studies. The North American and Eastern European studies also included high-dose toremifene arms of 200 and 240 mg daily, respectively [see Clinical Studies].
|Adverse Reactions||North American||Eastern European||Nordic|
|Cardiac Failure||2||(1)||1||( < 1)||-||1||( < 1)||2||(1)||3||(1.5)|
|Myocardial Infarction||2||(1)||3||(1.5)||1||( < 1)||2||(1)||-||1||( < 1)|
|Arrhythmia||-||-||-||-||3||(1.5)||1||( < 1)|
|Angina Pectoris||-||-||1||( < 1)||-||1||( < 1)||2||(1)|
|Abnormal Visual Fields||8||(4)||10||(5)||-||-||-||1||( < 1)|
|Glaucoma||3||(1.5)||2||(1)||1||( < 1)||-||-||1||( < 1)|
|Pulmonary Embolism||4||(2)||2||(1)||1||( < 1)||-||-||1||( < 1)|
|Thrombophlebitis||-||2||(1)||1||( < 1)||1||( < 1)||4||(2)||3||(1.5)|
|Thrombosis||-||1||( < 1)||1||( < 1)||-||3||(1.5)||4||(2)|
|CVA/TIA||1||( < 1)||-||-||1||( < 1)||4||(2)||4||(2)|
|Elevated Liver Tests**|
|Bilirubin||3||(1.5)||4||(2)||2||(1)||1||( < 1)||2||(1)||3||(1.5)|
|Hypercalcemia||6||(3)||6||(3)||1||( < 1)||-||-||-|
|* Most of the ocular abnormalities were
observed in the North American Study in which on-study and biannual ophthalmic
examinations were performed. No cases of retinopathy were observed in
** Elevated defined as follows: North American Study: AST > 100 IU/L; alkaline phosphatase > 200 IU/L; bilirubin > 2 mg/dL. Eastern European and Nordic studies: AST, alkaline phosphatase, and bilirubin – WHO Grade 1 (1.25 times the upper limit of normal).
Other adverse reactions included leukopenia and thrombocytopenia, skin discoloration or dermatitis, constipation, dyspnea, paresis, tremor, vertigo, pruritus, anorexia, reversible corneal opacity (corneal verticulata), asthenia, alopecia, depression, jaundice, and rigors.
The incidence of AST elevations was greater in the 200 and 240 mg FARESTON dose arms than in the tamoxifen arms. Higher doses of FARESTON were also associated with an increase in nausea.
Approximately 4% of patients were withdrawn for toxicity from the high-dose FARESTON treatment arms. Reasons for withdrawal included hypercalcemia, abnormal liver function tests, and one case each of toxic hepatitis, depression, dizziness, incoordination, ataxia, blurry vision, diffuse dermatitis, and a constellation of symptoms consisting of nausea, sweating, and tremor.
The following adverse reactions were identified during post approval use of FARESTON. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Adverse reactions reported during post approval use of FARESTON have been consistent with clinical trial experience. The most frequently reported adverse reactions related to FARESTON use since market introduction include hot flash, sweating, nausea, and vaginal discharge.
Read the Fareston (toremifene) Side Effects Center for a complete guide to possible side effects
Drugs that Decrease Renal Calcium Excretion
Drugs that decrease renal calcium excretion, e.g., thiazide diuretics, may increase the risk of hypercalcemia in patients receiving FARESTON.
Agents that Prolong QT
The administration of FARESTON with agents that have demonstrated QT prolongation as one of their pharmacodynamic effects should be avoided. Should treatment with any of these agents be required, it is recommended that therapy with FARESTON be interrupted. If interruption of treatment with FARESTON is not possible, patients who require treatment with a drug that prolongs QT should be closely monitored for prolongation of the QT interval. Agents generally accepted to prolong QT interval include Class 1A (e.g., quinidine, procainamide, disopyramide) and Class III (e.g., amiodarone, sotalol, ibutilide, dofetilide) antiarrhythmics; certain antipsychotics (e.g., thioridazine, haloperidol); certain antidepressants (e.g., venlafaxine, amitriptyline); certain antibiotics (e.g., erythromycin, clarithromycin, levofloxacin, ofloxacin); and certain anti-emetics (e.g., ondansetron, granisetron). In patients at increased risk, electrocardiograms (ECGs) should be obtained and patients monitored as clinically indicated [see BOXED WARNING and WARNINGS AND PRECAUTIONS].
Effect of Strong CYP3A4 Inducers on Toremifene
Strong CYP3A4 enzyme inducers, such as dexamethasone, phenytoin, carbamazepine, rifampin, rifabutin, phenobarbital, St. John's Wort, lower the steady-state concentration of toremifene in serum.
Effect of Strong CYP3A4 Inhibitors on Toremifene
In a study of 18 healthy subjects, 80 mg toremifene once daily coadministered with 200 mg of ketoconazole twice daily increased the toremifene Cmax and AUC by 1.4- and 2.9-fold, respectively. N-demethyltoremifene Cmax and AUC were reduced by 56% and 20%, respectively.
The administration of FARESTON with agents that are strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, clarithromycin, atazanavir, indinavir, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin, and voriconazole) increase the steady-state concentration in serum and should be avoided. Grapefruit juice may also increase plasma concentrations of toremifene and should be avoided. Should treatment with any of these agents be required, it is recommended that therapy with FARESTON be interrupted. If interruption of treatment with FARESTON is not possible, patients who require treatment with a drug that strongly inhibits CYP3A4 should be closely monitored for prolongation of the QT interval [see BOXED WARNING and WARNINGS AND PRECAUTIONS].
Effect of Toremifene on CYP3A4 Substrates
In a study of 20 healthy subjects, 2 mg midazolam once daily (days 6 and 18) coadministered with toremifene as a 480 mg loading dose followed by 80 mg once daily for 16 days. Following coadministration on days 6 and 18 relevant increases in midazolam and α-hydroxymidazolam Cmax and AUC were not observed. Following coadministration on day 18 midazolam and α-hydroxymidazolam Cmax and AUC were reduced by less than 20%.
Clinically relevant exposure changes in sensitive substrates due to inhibition or induction of CYP3A4 by toremifene appear unlikely.
Effect of Toremifene on CYP2C9 Substrates
In a study of 20 healthy subjects, 500 mg tolbutamide once daily (days 7 and 19) coadministered with toremifene as a 480 mg loading dose followed by 80 mg once daily for 16 days. Following coadministration on days 7 and 19 plasma tolbutamide Cmax and AUC were increased by less than 30%. A reduction of similar magnitude was observed for hydroxytolbutamide and carboxytolbutamide Cmax and AUC.
Toremifene is a weak inhibitor of CYP2C9. Concomitant use of CYP2C9 substrates with a narrow therapeutic index such as warfarin or phenytoin with FARESTON should be done with caution and requires careful monitoring (e.g., substrate concentrations (if possible), appropriate laboratory markers, and signs and symptoms of increased exposure).
Read the Fareston Drug Interactions Center for a complete guide to possible interactions
Last reviewed on RxList: 3/20/2017
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