What are examples of CYP3A4 inhibitors?

CYP3A4 Inhibitors: Clinical Examples and Classification

CYP3A4 inhibitors include azole antifungals (ketoconazole, itraconazole, voriconazole, posaconazole), macrolide antibiotics (clarithromycin, erythromycin, telithromycin), HIV protease inhibitors (ritonavir, indinavir, nelfinavir, saquinavir, atazanavir), calcium channel blockers (verapamil, diltiazem), the antiarrhythmic amiodarone, and grapefruit juice. 1

Strong CYP3A4 Inhibitors

Azole Antifungals

• Ketoconazole, itraconazole, voriconazole, and posaconazole are potent inhibitors that can more than double plasma concentrations of CYP3A4 substrates. 1
• These agents are contraindicated with rivaroxaban due to significant increases in drug exposure and bleeding risk. 2
• Concomitant use of ketoconazole 400 mg once daily with rivaroxaban resulted in approximately 2.5-fold increase in mean AUC and 1.7-fold increase in mean Cmax. 2
• The NCCN specifically advises avoiding these azole antifungals in patients taking CYP3A4 substrate medications. 1

Macrolide Antibiotics

• Clarithromycin, erythromycin, and telithromycin act as mechanism-based CYP3A4 inhibitors through NADPH-, time-, and concentration-dependent enzyme inactivation. 1, 3
• Clarithromycin 500 mg twice daily leads to a 1.5-fold increase in mean AUC and 1.4-fold increase in Cmax of rivaroxaban. 2
• Erythromycin 500 mg three times daily causes a 1.3-fold increase in both AUC and Cmax of CYP3A4 substrates. 2
• Clarithromycin inhibits CYP3A4 and increases plasma concentrations of imatinib and other tyrosine kinase inhibitors. 2
• Concomitant use of clarithromycin with direct oral anticoagulants is associated with higher rates of hospitalization for major bleeding. 1

HIV Protease Inhibitors

• Ritonavir is the most potent CYP3A4 inhibitor among protease inhibitors, followed by indinavir, nelfinavir, saquinavir, and atazanavir. 1
• Ritonavir 600 mg twice daily resulted in approximately 2.5-fold increase in rivaroxaban exposure. 2
• These agents are contraindicated with rivaroxaban and should be avoided with other CYP3A4 substrates. 2, 1

Moderate CYP3A4 Inhibitors

Calcium Channel Blockers

• Verapamil and diltiazem provide moderate CYP3A4 inhibition and additionally inhibit P-glycoprotein, creating dual drug-interaction potential. 1, 3
• Diltiazem is a substrate of CYP3A4 (major) and a moderate CYP3A4 inhibitor. 2
• Verapamil is a moderate CYP3A4 inhibitor and also inhibits P-glycoprotein. 2
• Concomitant therapy of DOACs with diltiazem or verapamil significantly increases risks of major bleeding (OR = 1.38) and gastrointestinal bleeding (OR = 1.19) compared with DOAC monotherapy. 4
• Doses of simvastatin >10 mg daily and lovastatin >20 mg daily are not recommended when coadministered with diltiazem or verapamil. 2

Antiarrhythmic Agents

• Amiodarone is a weak CYP3A4 inhibitor but also suppresses CYP2C9, CYP2D6, and P-glycoprotein. 1
• Amiodarone causes approximately 75% increase in simvastatin and simvastatin acid AUC and Cmax when coadministered. 2
• The dose of simvastatin should be limited to 20 mg in patients concomitantly taking amiodarone. 2

Other Moderate Inhibitors

• Aprepitant inhibits CYP3A4 and increases imatinib plasma concentrations. 2
• Cyclosporine functions both as a CYP3A4 substrate and inhibitor; imatinib increases cyclosporine plasma concentrations. 2

Dietary CYP3A4 Inhibitors

• Grapefruit juice is a potent CYP3A4 inhibitor and should be avoided when patients are receiving CYP3A4 substrate medications. 1
• Grapefruit juice may increase plasma concentrations of imatinib and should be avoided. 2

Clinical Management Considerations

Drug Interactions Requiring Avoidance

• Co-administration of CYP3A4 inhibitors with terfenadine, astemizole, cisapride, or pimozide is contraindicated due to risk of fatal cardiac arrhythmias (torsades de pointes). 1, 5
• Concomitant use of dabigatran with ciclosporin, itraconazole, ketoconazole, and tacrolimus is contraindicated. 2
• Rivaroxaban should not be used with azole antimycotics or HIV protease inhibitors. 2

Oncology-Specific Considerations

• CYP3A4 inhibition by azoles can lead to toxicity when administered with proteasome inhibitors, tyrosine kinase inhibitors, and vinca alkaloids. 2
• Mold-active azoles should be stopped several days before potentially interacting drugs are given; some institutions consider waiting at least 10 days. 2
• Itraconazole inhibits CYP3A4 and increases imatinib plasma concentrations. 2

Monitoring and Dose Adjustments

• For strong CYP3A4 inhibitors used short-term (≤7 days, such as antifungals and antibiotics), consider interrupting ibrutinib/idelalisib therapy during the duration of inhibitor use. 2
• If a moderate CYP3A4 inhibitor must be used, reduce the ibrutinib/idelalisib dose. 2
• Patients taking concomitant strong or moderate CYP3A4 inhibitors should be monitored more closely for signs of drug toxicity. 2
• Digoxin concentrations should be monitored with verapamil, clarithromycin, erythromycin, itraconazole, cyclosporine, propafenone, and flecainide. 2