Drug Interactions between dyphylline / ephedrine / guaifenesin / phenobarbital and elbasvir / grazoprevir

Consumer information for this interaction is not currently available.

CONTRAINDICATED: Coadministration with potent inducers of CYP450 3A4 may significantly decrease the plasma concentrations of elbasvir and grazoprevir, both of which are substrates of the isoenzyme. In 10 study subjects, administration of elbasvir 50 mg once daily with efavirenz 600 mg once daily decreased elbasvir peak plasma concentration (Cmax), systemic exposure (AUC) and trough plasma concentration (Cmin) by 45%, 54% and 59%, respectively, compared to administration of elbasvir alone. Likewise, when grazoprevir 200 mg once daily and efavirenz 600 mg once daily were given together to 12 study subjects, grazoprevir Cmax, AUC and Cmin decreased by 87%, 83% and 69%, respectively. Efavirenz is generally considered a moderate inducer of CYP450 3A4. More potent inducers such as carbamazepine or phenytoin may interact to an even greater extent.

MANAGEMENT: Given the risk of reduced viral susceptibility and resistance development associated with subtherapeutic antiviral drug levels, concomitant use of elbasvir-grazoprevir with efavirenz or potent CYP450 3A4 inducers is considered contraindicated.

Using grazoprevir together with PHENobarbital is not recommended. Combining these medications may significantly reduce the blood levels of grazoprevir, which may make the medication less effective in treating hepatitis C. Talk to your doctor if you have any questions or concerns. Your doctor may be able to prescribe alternatives that do not interact. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

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