Nirmatrelvir/ritonavir is a protease inhibitor antiviral drug indicated in the treatment of severe acute respiratory syndrome coronavirus-2 infections in high-risk patients for a severe disease. Unfortunately, ritonavir, used to boost nirmatrelvir pharmacokinetics, can also inhibit or induce the metabolism of other co-administered drugs substrates. This may lead to a subsequent risk of adverse drug reaction and lack of efficacy. In this study, we aimed at describing the expert advices provided by the biological pharmacology network of the SFPT (i.e., the therapeutic drug monitoring specialists working in the laboratories of the pharmacology departments in France/Belgium). From February to August 2022, we collected all specialized advices provided by the biological pharmacology network of the SFPT. Seven pharmacology departments actively participated in the study (Brussels Saint-Luc Hospital in Belgium, Caen, Dijon, Nantes, Nancy, Rennes and Toulouse in France). We collected the following data: patient's age, date of nirmatrelvir/ritonavir initiation, clinical department requiring the expert advice, patient's treatments, and advice provided. One hundred and six expert advice on 753 drugs were provided during the seven months of data collection. Two centers provided 83% of all the expert advice (around 8/month). Patients originated form a transplantation department in 65% of the cases. The most common request were for cardiac drugs (28%), immunosuppressive drugs (24%) and endocrine drugs (18%). The advice were distributed as follows: treatment continuation, treatment discontinuation during the antiviral course, dosage adjustment, and treatment switch in 59%, 28%, 11%, and 1.6% of the cases, respectively. Only 2 pieces of advice (0.3%) constituted treatment contra-indications. Drug monitoring was proposed in 10% of prescription lines. Expert advice provided by the biological pharmacology network of the SFPT allows securing the combination of nirmatrelvir/ritonavir with other concomitant drugs. Most of eligible patients to the antiviral drug can benefit from it despite the risk of drug–drug interaction.