Coadministration has not been studied but based on metabolism and clearance a pharmacokinetic interaction is unlikely. Efavirenz is primarily metabolized by CYP2B6 and CYP3A4. Due to remdesivir’s rapid clearance, although remdesivir inhibits CYP3A4 it is unlikely to have a significant effect on efavirenz. Remdesivir is a prodrug predominantly metabolised by hydrolase, with some involvement (in vitro) of CYPs 2C8, 2D6 and 3A4. Efavirenz is a moderate inducer but is unlikely to have a clinically significant effect on remdesivir as remdesivir has a moderate-high hepatic extraction ratio and is used for a short duration in the treatment of COVID-19. Remdesivir 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. As the potential risk of a QT interval prolongation relates specifically to homozygous carriers of CYP2B6*6/*6 and given the accumulated years of safety data with efavirenz and such drugs, the contraindication is not reflected in the colour coding of this interaction summary.