DRUG INTERACTIONS Drug-Drug Interactions
No formal studies to evaluate drug interactions with bexarotene have been conducted. Bexarotene oxidative metabolites appear to be formed by cytochrome P450 3A4.
On the basis of the metabolism of bexarotene by cytochrome P450 3A4, ketoconazole, itraconazole, erythromycin, gemfibrozil, grapefruit juice, and other inhibitors of cytochrome P450 3A4 would be expected to lead to an increase in plasma bexarotene concentrations. Furthermore, rifampin, phenytoin, phenobarbital, and other inducers of cytochrome P450 3A4 may cause a reduction in plasma bexarotene concentrations.
Concomitant administration of Targretin® capsules and gemfibrozil resulted in substantial increases in plasma concentrations of bexarotene, probably at least partially related to cytochrome P450 3A4 inhibition by gemfibrozil. Under similar conditions, bexarotene concentrations were not affected by concomitant atorvastatin administration. Concomitant administration of gemfibrozil with Targretin® capsules is not recommended.
Based on interim data, concomitant administration of Targretin® capsules and tamoxifen resulted in approximately a 35% decrease in plasma concentrations of tamoxifen, possibly through an induction of cytochrome P450 3A4. Based on this known interaction, bexarotene may theoretically increase the rate of metabolism and reduce plasma concentrations of other substrates metabolized by cytochrome P450 3A4, including oral or other systemic hormonal contraceptives (see CLINICAL PHARMACOLOGY: Drug-Drug Interactions and CONTRAINDICATIONS: Pregnancy: Category X). Thus, if treatment with Targretin® capsules is intended in a woman with child-bearing potential, it is strongly recommended that two reliable forms of contraception be used concurrently, one of which should be non-hormonal.
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OVERDOSAGE
Doses up to 1000 mg/m2/day of Targretin® capsules have been administered in short-term studies in patients with advanced cancer without acute toxic effects. Single doses of 1500 mg/kg and 720 mg/kg were tolerated without significant toxicity in rats and dogs, respectively. These doses are approximately 30 and 50 times, respectively, the recommended human dose on a mg/m2 basis.
No clinical experience with an overdose of Targretin® capsules has been reported. Anyoverdose with Targretin® capsules should be treated with supportive care for the signs and symptoms exhibited by the patient.
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CONTRAINDICATIONS
Targretin® capsules are contraindicated in patients with a known hypersensitivity to bexarotene or other components of the product.
Pregnancy: Category X
Targretin® (bexarotene) capsules may cause fetal harm when administered to a pregnant woman. Targretin® capsules must not be given to a pregnant woman or a woman who intends to become pregnant. If a woman becomes pregnant while taking Targretin® capsules, Targretin® capsules must be stopped immediately and the woman given appropriate counseling.
Bexarotene caused malformations when administered orally to pregnant rats during days 7-17 of gestation. Developmental abnormalities included incomplete ossification at 4 mg/kg/day and cleft palate, depressed eye bulge/microphthalmia, and small ears at 16 mg/kg/day. The plasma AUC of bexarotene in rats at 4 mg/kg/day is approximately one third the AUC in humans at the recommended daily dose. At doses greater than 10 mg/kg/day, bexarotene caused developmental mortality. The no effect dose for fetal effects in rats was 1 mg/kg/day (producing an AUC approximately one sixth of the AUC at the recommended human daily dose).
Women of child-bearing potential should be advised to avoid becoming pregnant when Targretin® capsules are used. The possibility that a woman of child-bearing potential is pregnant at the time therapy is instituted should be considered. A negative pregnancy test (e.g., serum beta-human chorionic gonadotropin, beta-HCG) with a sensitivity of at least 50 mlU/L should be obtained within one week prior to Targretin® capsules therapy, and the pregnancy test must be repeated at monthly intervals while the patient remains on Targretin® capsules. Effective contraception must be used for one month prior to the initiation of therapy, during therapy and for at least one month following discontinuation of therapy; it is recommended that two reliable forms of contraception be used simultaneously unless abstinence is the chosen method. Bexarotene can potentially induce metabolic enzymes and thereby theoretically reduce the plasma concentrations of oral or other systemic hormonal contraceptives (see CLINICAL PHARMACOLOGY: Drug-Drug Interactions and PRECAUTIONS: Drug-Drug Interactions). Thus, if treatment with Targretin® capsules is intended in a woman with child-bearing potential, it is strongly recommended that one of the two reliable forms of contraception should be non-hormonal. Male patients with sexual partners who are pregnant, possibly pregnant, or who could become pregnant must use condoms during sexual intercourse while taking Targretin® capsules and for at least one month after the last dose of drug. Targretin® capsules therapy should be initiated on the second or third day of a normal menstrual period. No more than a one month supply of Targretin® capsules should be given to the patient so that the results of pregnancy testing can be assessed and counseling regarding avoidance of pregnancy and birth defects can be reinforced.
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