Co-administration of Kaletra with sildenafil or tadalafil is expected to substantially increase their concentrations and may result in associated adverse events such as hypotension, syncope, visual changes and prolonged erection. Coadministration increased tadalafil AUC by 2-fold due to CYP3A inhibition by Kaletra. Particular caution must be used when prescribing tadalafil  for erectile dysfunction in patients receiving Kaletra with increased monitoring for adverse events including hypotension, syncope, visual changes and prolonged erection. When coadministered with Kaletra for erectile dysfunction, tadalafil doses must not exceed 10 mg every 72 hours.
Kaletra Summary of Product Characteristics, AbbVie Ltd, January 2021.

Particular caution should be used when prescribing PDE5 inhibitors (sildenafil, tadalafil or vardenafil) in patients receiving Kaletra. Coadministration of Kaletra with these drugs is expected to increase their concentrations and may result in an increase in associated adverse reactions including hypotension, syncope, visual changes and prolonged erection. When using tadalafil for erectile dysfunction, it is recommended not to exceed a tadalafil dose of 10 mg every 72 h and to use with increased monitoring for adverse events.
Kaletra Prescribing Information, AbbVie Ltd, October 2020.