Background and Importance The incorporation of nirmatrelvir/ritonavir into the therapeutic arsenal for the treatment of SARS-CoV2 infection has made it necessary for Pharmacy departments to activate circuits and tools that allow us to adequately review the potential multiple interactions that ritonavir can produce.

Aim and Objectives To describe the interactions detected since the beginning of the use of nirmatrelvir/ritonavir in a tertiary hospital.

Material and Methods All patients who received nirmatrelvir/ritonavir from April to the end of August 2022 were included. The patient‘s usual treatment was consulted in the electronic prescription system of the region of Madrid, as well as an interview with the patient, and the medical history was consulted when deemed necessary. For the detection of interactions, the ‘COVID-19 Drug Interactions’ platform of the University of Liverpool was used and Farmaweb, an application of the Madrid Health Service, was used to validate the dispensing of medication. If there are any interacciones the pharmacist notifies the prescribing physician, as well as the necessary adjustments, these treatment modifications are also explained to the patient when the medication is given to them. An Excel table was used to record whether the patient had any interaction and, if there were any, the drugs were recorded.

Results During the study period, these drugs were dispensed to a total of 81 patients, and interactions with the patient‘s usual medication were detected in 61.73% (50 patients). 18 patients had one interaction, 21 patients had 2 interactions, 6 patients had 3, 4 patients had 4 and one patient had 5 potential interactions. The most commonly detected interaction was with atorvastatin (19) followed by metamizole (11), simvastatin (7), amlodipine (6) and tramadol (4).

Conclusion and Relevance The percentage of patients with interactions is very high, and it is very important to review the usual treatment as well as an interview with the patient to identify whether the patient is taking other unregistered medication that could interact.

This has highlighted the importance of interdisciplinary collaboration between the medical team (mainly in the emergency department, where most of these drugs have been prescribed) and the pharmacy team to ensure the correct use of this drug.

Conflict of Interest No conflict of interest