The effects of nirmatrelvir/ritonavir on tacrolimus levels in lung transplant recipients: A single-center study

Background: Lung transplant recipients (LTRs) have a higher risk of hospitalization and mortality due to COVID19 compared with the immunocompetent population. The use of nirmatrelvir/ritonavir (NR), an effective oral treatment for COVID-19, is quite challenging due to its potent drug-drug interactions with immunosuppressants and azole antifungals. As there are few clinical reports of the use of NR in LTRs, we measured tacrolimus levels in patients receiving NR in our hospital to improve safety when prescribing NR.Methods: In total, 48 adult LTRs who received NR between November 19, 2022, and January 19, 2023, at China Japan Friendship Hospital were retrospectively included and followed for 20 days after initiating NR. Tacrolimus was held at least 12 h before initiating NR and re-administered based on the trough levels after completing NR treatment. All concomitant medications, drug concentrations, laboratory results, and genotypes were recorded and analyzed. Results: Most patients showed stable tacrolimus trough levels despite high individual variability. Four patients exhibited supratherapeutic trough levels of tacrolimus (more than 15 ng/mL). Two patients who received 0.5 mg of tacrolimus during NR treatment had trough levels below 3.0 ng/mL. In addition, we found that in 13 patients, the trough levels were 130% of baseline after cessation of tacrolimus, and logistic regression revealed that increased trough level was significantly associated with age more than 60 years. Conclusions: NR can be safely used in LTRs with close monitoring of tacrolimus levels and appropriate dose adjustments. However, more attention should be paid to elderly patients, as NR may more severely affect their drug metabolism. Due to the limited sample size, further studies are needed to guide the optimal use of tacrolimus following treatment with NR and explore the risk factors significantly affecting the interactions between NR and tacrolimus.