CYP 3A4 probably only marginally engaged in the metabolism of fulvestrant, no evidence of CYP3A4/CYP2C9 inhibition or induction in vivo. Side effects such as nausea, anorexia and vomiting may be potentially porphyrinogenic through reduction in caloric intake.

Fulvestrant, a 7α-alkylsulfinyl analog of estradiol, is an estrogen antagonist.

Fulvestrant is used for the treatment of oestrogen-receptor positive, locally advanced or metastatic breast cancer in postmenopausal women. In is administered as an intramuscular injection. Common adverse reactions of fulvestrant that can be confused with an acute porphyric attack are back pain, nausea, vomiting and diarrhoea. Side effects such as nausea, anorexia and vomiting may be potentially porphyrinogenic through reduction in caloric intake.

The metabolism of fulvestrant has not been fully evaluated. Studies using human liver preparations and recombinant human enzymes indicate that CYP3A4 is the only P450 isoenzyme involved in the oxidation of fulvestrant; however non-P450 routes appear to be more predominant in vivo. A clinical interaction study with midazolam (substrate of CYP3A4) demonstrated that fulvestrant does not inhibit CYP3A4. Clinical interaction studies with rifampicin (inducer of CYP3A4) and ketoconazole (inhibitor of CYP3A4) showed no clinically relevant change in fulvestrant clearance.