CYP2C9 and pulmonary hypertension, primary, 1: Several case reports have described that this agent increases CBZ levels with consequently increased toxicity through CYP3A4 inhibition [54-56], while CYP2C9 and CYP2C19 inhibition may explain the 3-fold increase in serum concentrations of PHT observed after administration of fluvoxamine in a patient [57].