Drug Interaction Report

GENERALLY AVOID: Theoretically, proton pump inhibitors may decrease the gastrointestinal absorption of enteric-coated naproxen, which requires an acidic environment for dissolution. The proposed mechanism is an increase in gastric pH (i.e. decreased gastric acidity) induced by proton pump inhibitors. In patients treated with proton pump inhibitors, the possibility of a reduced or subtherapeutic response to enteric-coated naproxen should be considered.

MANAGEMENT: Concomitant use of these drugs is generally not recommended.

MONITOR: Coadministration with moderate or potent inhibitors of CYP450 2C9, 2C19, 2D6, and/or 2E1 may increase the plasma concentrations of pirfenidone, especially when used in addition to a moderate or potent CYP450 1A2 inhibitor. Pirfenidone is primarily (70% to 80%) metabolized by CYP450 1A2, with minor contribution from CYP450 2C9, 2C19, 2D6, and 2E1. In 25 healthy nonsmokers and 25 smokers who were administered a single dose of pirfenidone with the potent CYP450 1A2 inhibitor fluvoxamine (50 mg at bedtime for 3 days; 50 mg twice a day for 3 days; then 50 mg in the morning and 100 mg at bedtime for 4 days), pirfenidone systemic exposure (AUC) increased approximately 4-fold in nonsmoking subjects and 7-fold in smoking subjects. Fluvoxamine also inhibits CYP450 2C9, 2C19 and 2D6, although the extent to which these effects contribute to the interaction has not been established. The interaction has not been studied with specific inhibitors of other isoenzymes involved in the metabolism of pirfenidone.

MANAGEMENT: Concomitant use of pirfenidone with moderate or potent inhibitors of CYP450 2C9, 2C19, 2D6, and/or 2E1 in addition to a moderate or potent inhibitor of CYP450 1A2 (e.g., certain fluoroquinolones, oral contraceptives, deferasirox, methoxsalen, mexiletine, thiabendazole, ticlopidine, zileuton) should be avoided. No particular precaution is necessary if pirfenidone and CYP450 2C9, 2C19, 2D6, and/or 2E1 inhibitors are coadministered without a moderate or potent CYP450 1A2 inhibitor. However, a prolonged duration of monitoring for adverse effects may be required depending on the elimination half-life of the concomitant drug. For example, it should be noted that rolapitant, a moderate CYP450 2D6 inhibitor, may increase plasma concentrations and the risk of adverse effects of pirfenidone for at least 28 days after administration of rolapitant.

ADJUST DOSING INTERVAL: Food significantly slows the rate but only modestly reduces the extent of absorption of pirfenidone. In healthy, older adult volunteers aged 50 to 66 years, administration of a single 801 mg oral dose of pirfenidone in the fed state resulted in an approximately 50% reduction in peak plasma concentration (Cmax) and a 15% to 20% reduction in systemic exposure (AUC) compared to administration in the fasted state. Median time to reach peak concentration (Tmax) increased from 0.5 hours to 3 hours with food. Less nausea and dizziness were observed in fed subjects compared to fasted subjects.

GENERALLY AVOID: Consumption of grapefruit juice is associated with inhibition of CYP450 1A2 and may increase the plasma concentrations of pirfenidone, which is primarily metabolized by the isoenzyme.

GENERALLY AVOID: Cigarette smoking may reduce pirfenidone exposure due to induction of CYP450 1A2, the isoenzyme primarily responsible for the metabolic clearance of pirfenidone. Following a single 801 mg oral dose of pirfenidone in 25 smokers and 25 healthy nonsmokers, the Cmax and AUC of pirfenidone in smokers were 68% and 46% of those in nonsmokers, respectively.

MANAGEMENT: Pirfenidone should be administered with food to reduce the likelihood of dizziness and gastrointestinal side effects such as nausea, diarrhea, dyspepsia, and vomiting. Patients who experience intolerance to therapy due to these adverse events should be reminded to take pirfenidone with food. If symptoms do not improve, or they worsen in severity, a dosage reduction or discontinuation of therapy may be warranted. Patients should be advised to avoid consumption of grapefruit and grapefruit juice during treatment with pirfenidone. Cigarette smoking should also be avoided during therapy to prevent reduced exposure to pirfenidone.

GENERALLY AVOID: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal (GI) blood loss. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

MANAGEMENT: Patients should be counseled on this potential interaction and advised to refrain from alcohol consumption while taking aspirin or NSAIDs.

MONITOR: Smoking cessation may lead to elevated plasma concentrations and enhanced pharmacologic effects of drugs that are substrates of CYP450 1A2 (and possibly CYP450 1A1) and/or certain drugs with a narrow therapeutic index (e.g., flecainide, pentazocine). One proposed mechanism is related to the loss of CYP450 1A2 and 1A1 induction by polycyclic aromatic hydrocarbons in tobacco smoke; when smoking cessation agents are initiated and smoking stops, the metabolism of certain drugs may decrease leading to increased plasma concentrations. The mechanism by which smoking cessation affects narrow therapeutic index drugs that are not known substrates of CYP450 1A2 or 1A1 is unknown. The clinical significance of this interaction is unknown as clinical data are lacking.

MANAGEMENT: Until more information is available, caution is advisable if smoking cessation agents are used concomitantly with drugs that are substrates of CYP450 1A2 or 1A1 and/or those with a narrow therapeutic range. Patients receiving smoking cessation agents may require periodic dose adjustments and closer clinical and laboratory monitoring of medications that are substrates of CYP450 1A2 or 1A1.