INTERACTIONS There are no known drug-drug interactions. Although, fulvestrant is metabolized by CYP 3A4 in vitro , drug interactions studies with ketoconazole or rifampin did not alter fulvestrant pharmacokinetics. Dose adjustment is not needed in patients co-prescribed CYP 3A4 inhibitors or inducers [see Clinical Pharmacology ( 12.3 )] . There are no known drug-drug interactions. ( 7 )
Fulvestrant injection is contraindicated in patients with a known hypersensitivity to the drug or to any of its components. Hypersensitivity reactions, including urticaria and angioedema, have been reported in association with fulvestrant injection [see Adverse Reactions ( 6.2 )]. Hypersensitivity. ( 4 )
AND PRECAUTIONS Risk of Bleeding: Use with caution in patients with bleeding diatheses, thrombocytopenia, or anticoagulant use. ( 5.1 )
Increased
Exposure in Patients with He patic Impairment: Use a 250 mg dose for patients with moderate hepatic impairment. ( 2.2 , 5.2 , 8.6 )
Injection Site
Reaction: Use caution while administering fulvestrant injection at the dorsogluteal injection site due to the proximity of the underlying sciatic nerve. ( 5.3 ) Embryo-Fetal Toxicity: Can cause fetal harm. Advise females of reproductive potential of the potential risk to a fetus and to use effective contraception. ( 5.4 , 8.1 , 8.3 )
Immunoassay
Measurement of Serum Estradiol: Fulvestrant injection can interfere with estradiol measurement by immunoassay, resulting in falsely elevated estradiol levels. ( 5.5 )
5.1 Risk of Bleeding Because fulvestrant injection is administered intramuscularly, it should be used with caution in patients with bleeding diatheses, thrombocytopenia, or anticoagulant use.
5.2 Increased Exposure in Patients with Hepatic Impairment The safety and pharmacokinetics of fulvestrant injection were evaluated in a study in seven subjects with moderate hepatic impairment (Child-Pugh class B) and seven subjects with normal hepatic function. Exposure was increased in patients with moderate hepatic impairment, therefore, a dose of 250 mg is recommended <span class="opacity-50 text-xs">[see Dosage and Administration (2.2) ]</span>. Fulvestrant injection has not been studied in patients with severe hepatic impairment (Child-Pugh class C) <span class="opacity-50 text-xs">[see Use in Specific Populations (8.6) ]</span>.
5.3 Injection Site Reaction Injection site related events including sciatica, neuralgia, neuropathic pain, and peripheral neuropathy have been reported with fulvestrant injection. Caution should be taken while administering fulvestrant injection at the dorsogluteal injection site due to the proximity of the underlying sciatic nerve <span class="opacity-50 text-xs">[see Dosage and Administration (2.3) and Adverse Reactions (6.1) ]</span> .
5.4 Embryo-Fetal Toxicity Based on findings from animal studies and its mechanism of action, Fulvestrant injection can cause fetal harm when administered to a pregnant woman. In animal reproduction studies, administration of fulvestrant to pregnant rats and rabbits during organogenesis resulted in embryo-fetal toxicity at daily doses that are significantly less than the maximum recommended human dose. Advise pregnant women of the potential risk to a fetus. Advise females of reproductive potential to use effective contraception during treatment with fulvestrant injection and for one year after the last dose <span class="opacity-50 text-xs">[see Use in Specific Populations (8.1) , ( 8.3 ) and Clinical Pharmacology (12.1) ]</span>.
5.5 Immunoassay Measurement of Serum Estradiol Due to structural similarity of fulvestrant and estradiol, fulvestrant injection can interfere with estradiol measurement by immunoassay, resulting in falsely elevated estradiol levels.
5.1 Risk of Bleeding Because fulvestrant injection is administered intramuscularly, it should be used with caution in patients with bleeding diatheses, thrombocytopenia, or anticoagulant use.
5.2 Increased Exposure in Patients with Hepatic Impairment The safety and pharmacokinetics of fulvestrant injection were evaluated in a study in seven subjects with moderate hepatic impairment (Child-Pugh class B) and seven subjects with normal hepatic function. Exposure was increased in patients with moderate hepatic impairment, therefore, a dose of 250 mg is recommended <span class="opacity-50 text-xs">[see Dosage and Administration (2.2) ]</span>. Fulvestrant injection has not been studied in patients with severe hepatic impairment (Child-Pugh class C) <span class="opacity-50 text-xs">[see Use in Specific Populations (8.6) ]</span>.
5.3 Injection Site Reaction Injection site related events including sciatica, neuralgia, neuropathic pain, and peripheral neuropathy have been reported with fulvestrant injection. Caution should be taken while administering fulvestrant injection at the dorsogluteal injection site due to the proximity of the underlying sciatic nerve <span class="opacity-50 text-xs">[see Dosage and Administration (2.3) and Adverse Reactions (6.1) ]</span> .
5.4 Embryo-Fetal Toxicity Based on findings from animal studies and its mechanism of action, Fulvestrant injection can cause fetal harm when administered to a pregnant woman. In animal reproduction studies, administration of fulvestrant to pregnant rats and rabbits during organogenesis resulted in embryo-fetal toxicity at daily doses that are significantly less than the maximum recommended human dose. Advise pregnant women of the potential risk to a fetus. Advise females of reproductive potential to use effective contraception during treatment with fulvestrant injection and for one year after the last dose <span class="opacity-50 text-xs">[see Use in Specific Populations (8.1) , ( 8.3 ) and Clinical Pharmacology (12.1) ]</span>.
5.5 Immunoassay Measurement of Serum Estradiol Due to structural similarity of fulvestrant and estradiol, fulvestrant injection can interfere with estradiol measurement by immunoassay, resulting in falsely elevated estradiol levels.