Cancer patients suffer from immunosuppression and are at risk of developing a severe COVID-19 infection. These patients may be treated for 5 or 10 days with nirmatrelvir /ritonavir (NMV/r), a new drug for treating severe COVID-19 infection. Ritonavir is a potent inhibitor of CYP3A4 and substrate of CYP3A4 and P-gp, which may cause clinically relevant drug-drug interactions (DDIs) despite the short treatment. DDIs may lead to increased concentrations and toxicity of antineoplastic agents or loss of efficacy of NMV/r.

Guzmán Cordero et al. have studied the severity and pharmacist detection of clinically relevant DDIs between NMV/r and antineoplastic agents. This prospective study allowed pharmacists to make interventions before starting the treatment with NMV/r and avoid the adverse events the DDIs could have caused.

The pharmacists used databases to check potential DDIs between NMV/r and antineoplastic agents. They found high variability in the severity classification of DDIs, which highlights the importance of considering multiple sources of information when making clinical decisions about drug interactions.

The study shows that more than 75% of cancer patients may suffer DDIs if they start treatment with NMV/r without an intervention, of which almost 20% of their comedication could increase the risk of adverse effects (toxicity).

The safety of the treatment was not studied due to the lack of evaluation of the adverse effects of DDIs during the therapy of NMV/r. Therefore, the efficacy of the pharmaceutical intervention cannot be determined.

Due to the high prevalence of DDIs involved with the treatment of NMV/r in oncohaematology patients, pharmacists play a crucial role in verifying prescribed treatments, detecting interactions, mitigating medication-related problems, and optimizing drug therapy for these patients.

Prospective studies with DDIs have not yet been conducted and can help gain insight into DDIs in treatments and optimize patient care. You can find more information about the study and an overview of DDIs with NMV/r via this link.