Itraconazole inhibits the enzyme ‘CYP3A4’ and the same enzyme metabolites Finasteride.
Does it mean that Itraconazole decrease the effectiveness of Finasteride?
Many drugs and even fruits (grapefruit) can inhibit CYP3A4 but it may not have a significant clinical impact with other medications. Itraconazole from my brief Internet research seems to be a “strong” inhibitor of CYP3A4. Thus in theory it would been you will have less finasteride metabolized by the enzyme and thus have more finasteride circulating in your blood stream. How it relates clinically in treating hair loss is likely not significant since some have taken a larger than recommended dose of finasteride with no significant impact on hair. In the end, I am not a biochemist or deal with theoretical enzyme metabolism.