However, in spite of the fact bicalutamide is metabolized by CYP3A4, there is no evidence of clinically significant drug interactions when bicalutamide at a dosage of 150 mg/day or less is co-administered with drugs that inhibit or induce cytochrome P450 enzyme activity.In-vitro studies suggest that bicalutamide may be able to inhibit CYP3A4 and, to a lesser extent, CYP2C9, CYP2C19, and CYP2D6. Conversely, animal studies suggest that bicalutamide may induce cytochrome P450 enzymes. In a clinical study, bicalutamide co-administered with the CYP3A4 substrate midazolam caused only a small and statistically non-significant increase in midazolam levels (+27%) presumably due to CYP3A4 inhibition. However, this was well below the increases with potent CYP3A4 inhibitors like ketoconazole (+1500%), itraconazole (+1000%), and erythromycin (+350%), and is considered to not be clinically important. There is no indication of clinically significant enzyme inhibition or induction with bicalutamide at doses of 150 mg/day or below.Because bicalutamide circulates at relatively high concentrations and is highly protein-bound, it has the potential to displace other highly protein-bound drugs like warfarin, phenytoin, theophylline, and aspirin from plasma binding proteins. This could, in turn, result in increased free concentrations of such drugs and increased effects and/or side effects, potentially necessitating dosage adjustments. Bicalutamide has specifically been found to displace coumarin anticoagulants like warfarin from their plasma binding proteins (namely albumin) in vitro, potentially resulting in an increased anticoagulant effect, and for this reason, close monitoring of prothrombin time and dosage adjustment as necessary is recommended when bicalutamide is used in combination with these drugs.
Relative to GnRH analogues and the steroidal antiandrogen (SAA) cyproterone acetate (CPA), bicalutamide monotherapy has a much lower incidence and severity of hot flashes and sexual dysfunction. In addition, unlike GnRH analogues and CPA, bicalutamide monotherapy is not associated with decreased bone mineral density or osteoporosis. Conversely, bicalutamide monotherapy is associated with much higher rates of breast tenderness, gynecomastia, and feminization in men than GnRH analogues and CPA. However, gynecomastia with bicalutamide is rarely severe and discontinuation rates due to this side effect are fairly low. These differences in side effects between bicalutamide monotherapy, GnRH analogues, and CPA are attributed to the fact that whereas GnRH analogues and CPA suppress estrogen production, bicalutamide monotherapy does not lower estrogen levels and in fact actually increases them.Bicalutamide does not share the risk of neuropsychiatric side effects like depression and fatigue as well as cardiovascular side effects like coagulation changes, blood clots, fluid retention, ischemic cardiomyopathy, and adverse serum lipid changes that CPA has been associated with. It has a much lower risk of hepatotoxicity than flutamide and CPA and of interstitial pneumonitis than nilutamide. The drug also does not share the unique risks of diarrhea with flutamide and nausea, vomiting, visual disturbances, and alcohol intolerance with nilutamide. Unlike enzalutamide, bicalutamide is not associated with seizures or related central side effects like anxiety and insomnia. However, although the risk of adverse liver changes with bicalutamide is low, enzalutamide differs from bicalutamide in having no known risk of elevated liver enzymes or hepatotoxicity.