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 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.

GENERALLY AVOID: Excessive use of alcohol or products containing alcohol together with ketoconazole or levoketoconazole may potentiate the risk of liver injury. Serious hepatotoxicity has been reported with levoketoconazole. Hepatotoxicity requiring liver transplantation has been reported with the use of oral ketoconazole, of which levoketoconazole is an enantiomer. Some patients had no obvious risk factors for liver disease. In addition, use of alcohol or products containing alcohol during ketoconazole or levoketoconazole therapy may result in a disulfiram-like reaction in some patients. Symptoms of disulfiram-like reaction include flushing, rash, peripheral edema, nausea, and headache.

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of ketoconazole or levoketoconazole. The mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. Inhibition of hepatic CYP450 3A4 may also contribute. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition. Pharmacokinetic interactions involving grapefruit juice are also subject to a high degree of interpatient variability, thus the extent to which a given patient may be affected is difficult to predict.

When administered to healthy volunteers with a high-fat meal (875 calories; 62% fat), levoketoconazole systemic exposure (AUC) increased by 30% while peak plasma concentration (Cmax) did not change and the time to reach Cmax (Tmax) was delayed from 2 to 4 hours, compared to fasted conditions.

MANAGEMENT: Levoketoconazole may be administered with or without food. Excessive consumption of alcohol should generally be avoided during ketoconazole or levoketoconazole therapy. Patients should preferably avoid or limit consumption of grapefruit, grapefruit juice, or any supplement containing grapefruit extract during ketoconazole or levoketoconazole therapy. Patients receiving ketoconazole or levoketoconazole should be instructed to contact their doctor immediately if they experience swelling, skin rash, itching, loss of appetite, fatigue, nausea, vomiting, abdominal pain, dark colored urine, light colored stools, and/or yellowing of the skin or eyes, as these may be signs and symptoms of liver damage.