Coadministration with efavirenz should be avoided due to the possibility of a reduction in the therapeutic effect of pretomanid. Pretomanid is metabolized in the liver via multiple reductive and oxidative pathways with CYP3A4 mediated metabolism representing 20% of its metabolism. Efavirenz is a moderate inducer of CYP3A4. Coadministration of efavirenz (600 mg twice daily) and pretomanid (200 mg once daily) reduced pretomanid Cmax, AUC and Ctrough by 28%, 35% and 46%, respectively (n=16). Pretomanid has a possible risk of QT prolongation and/or TdP on the CredibleMeds.org website. Efavirenz was shown to prolong the QT interval above the regulatory threshold of concern in homozygous carriers of the CYP2B6*6/*6 allele (i.e. 516T variant in the gene encoding CYP2B6). The European product label for efavirenz contraindicates coadministration with a drug with a known risk of Torsade de Pointes whereas the American product label for efavirenz recommends that alternatives should be considered.