Interaction Checker

Nirmatrelvir/ritonavir (Paxlovid) when used for an extended treatment duration (10 days or longer).

Monday 10 July 2023

A new drug entry has been created for when nirmatrelvir/ritonavir is used off-label for longer than the licenced treatment duration of 5 days. An extended treatment duration of nirmatrelvir/ritonavir may be used in a clinical trial setting or in patients who may be at risk of viral rebound with the standard 5 day treatment (for example, people with underlying medical conditions).

When nirmatrelvir/ritonavir is used for 10 days or more, its interaction profile differs from that of a 5 day treatment duration. For example, induction of CYPs and UGTs by ritonavir may result in clinically significant interactions that are unlikely to occur with a 5 day treatment duration as induction takes several days to reach maximal effect. In addition, the option to manage an interaction by pausing the comedication when nirmatrelvir/ritonavir is administered for 5 days may not be appropriate when nirmatrelvir/ritonavir is used for 10 days or longer.

Interactions with nirmatrelvir/ritonavir for 10 days or longer are available in the website interaction checker and the iChart app. Unless otherwise stated, documents in the Prescribing Resources section of the website refer to a 5 day treatment duration of nirmatrelvir/ritonavir. 

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