Kaletra contains lopinavir and ritonavir, both of which are inhibitors of the P450 isoform CYP3A. Kaletra should not be co-administered with medicinal products that are highly dependent on CYP3A for clearance and for which elevated plasma concentrations are associated with serious and/or life threatening events. These medicinal products include terfenadine. Coadministration is likely to result in increased plasma concentrations of terfenadine. Concomitant administration of Kaletra and terfenadine is contraindicated as it may increase the risk of serious arrhythmias from this agent.
Kaletra Summary of Product Characteristics, AbbVie Ltd, January 2021.