Many medications used to treat infectious diseases are metabolized by liver enzymes including CYP2C19. Trough voriconazole concentrations found to be lower in patients with CYP2C19 ultra-rapid metabolizers compared to poor metabolizers resulting in delay in achieving therapeutic level. This may be critical in life-threatening infections such as invasive aspergillosis. CPIC guideline recommends that patients with CYP2C19 ultra-rapid or rapid metabolizer status to receive an alternative agent other than voriconazole as therapeutic level may not be achievable. Patients with CYP2C19 poor metabolizer status should use an alternative agent due to high risk for developing adverse effects.
It is well described that HLA-B*5701 screening reduces the risk of hypersensitivity reaction to abacavir.

Frequency of Cytochrome P450 (CYP2C19) Metabolizer Types in the population