Drug Interaction Report

ADJUST DOSE: Coadministration with drugs that are both potent multi-pathway CYP450 and P-glycoprotein/breast cancer resistant protein (P-gp/BCRP) inhibitors may significantly increase the plasma concentrations of riociguat, which is primarily metabolized by CYP450 1A1, 3A, 2C8 and 2J2, and is also a substrate of the P-gp/BCRP efflux transporter. Increased levels of riociguat may increase the risk for hypotension. According to the product labeling, administration of riociguat with the potent CYP450 and P-gp/BCRP inhibitor ketoconazole resulted in increases of riociguat peak plasma concentration (Cmax) and systemic exposure (AUC) by approximately 1.5- and 2.5-fold, respectively. The Cmax and AUC of the active metabolite, M1, which has 1/10th to 1/3rd the pharmacologic activity of riociguat, were reduced by approximately 50% and 25%, respectively.

MANAGEMENT: The initiation of drugs that are both potent multi-pathway CYP450 and P-gp/BCRP inhibitors such as itraconazole, ketoconazole, and some HIV protease inhibitors in patients on stable doses of riociguat is not recommended. Some authorities recommend avoiding concomitant use of riociguat during and for 2 weeks after treatment with itraconazole. When riociguat is initiated in patients on stable doses of strong multi pathway CYP450 (especially CYP450 1A1 and CYP450 3A4) and P-gp/BCRP inhibitors, consider a dosage of riociguat of 0.5 mg three times a day and monitor these patients for signs and symptoms of hypotension. Clinical data and dosing adjustment recommendations for riociguat are not currently available for children receiving concomitant systemic treatment with strong CYP450 and P-gp/BCRP inhibitors.

ADJUST DOSING INTERVAL: Food enhances the absorption and oral bioavailability of darunavir administered in combination with low-dose ritonavir. The mechanism is unknown. When administered with food, the peak plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC) of darunavir were approximately 30% higher than when administered in the fasting state. Darunavir exposure was similar for the range of meals studied. The total caloric content of the various meals evaluated ranged from 240 Kcal (12 grams fat) to 928 Kcal (56 grams fat).

MANAGEMENT: To ensure maximal oral absorption, darunavir coadministered with ritonavir should be taken with food. The type of food is not important.

ADJUST DOSE: Smoking may decrease the plasma concentrations of riociguat. The proposed mechanism is induction of the CYP450 1A1-mediated metabolism of riociguat by polycyclic aromatic hydrocarbons present in cigarette smoke. CYP450 1A1 is responsible for the formation of the major active metabolite, M1, which has just 1/3 to 1/10 the pharmacologic activity of riociguat. According to the product labeling, plasma concentrations of riociguat are reduced by 50% to 60% in smokers compared to nonsmokers.

MANAGEMENT: Patients should be advised to stop smoking. Riociguat dosages higher than 2.5 mg three times a day may be considered in cigarette smokers, if tolerated, to match the exposure seen in nonsmoking patients. However, safety and effectiveness of higher dosages have not been established. A dosage reduction should be considered in patients who stop smoking during treatment with riociguat. The tablet form of riociguat can generally be taken with or without food. Some authorities recommend not to switch between fed and fasted riociguat intake because of increased peak plasma levels of riociguat in the fasting compared to the fed state.