Reduktion eller øgning af phenytoins plasmakoncen - trationer, phenobarbital og andre krampestillende lægemidler, som er substrater af CYP450 - isoenzymer, er mulig med efavirenz.
There is a potential for reduction or increase in the plasma concentrations of phenytoin, phenobarbital and other anticonvulsants that are substrates of CYP450 isoenzymes with efavirenz.