Ritonavir may decrease plasma levels of phenobarbital due to CYP2C9 and CYP2C19 induction. Due to phenobarbital inducing effect, a reduction in Reyataz exposure cannot be ruled out. Phenobarbital should be used with caution in combination with Reyataz/ritonavir. When Reyataz/ritonavir is coadministered with phenobarbital, a dose adjustment of phenobarbital may be required. Close monitoring of patient's virologic response should be exercised. Coadministration of Reyataz without ritonavir is not recommended with phenobarbital.

Ritonavir is expected to decrease plasma levels of phenobarbital. When Reyataz with ritonavir is coadministered with phenobarbital, a dose adjustment of phenobarbital may be required. Plasma concentrations of atazanavir may be decreased when phenobarbital is administered with Reyataz without ritonavir. Coadministration of phenobarbital and Reyataz without ritonavir is not recommended.