BACKGROUND: Coronavirus disease 2019 (COVID-19) infection in lung transplant recipients can be lethal owing to the use of immunosuppressants. Antiviral agents may be administered to these patients. Co-packaged nirmatrelvir-ritonavir is a new agent currently being used in combination.
METHODS: In this report, we present a case of a 64-year-old woman, a lung transplant recipient, who experienced hyponatremia and showed a high serum tacrolimus concentration following the administration of the co-packaged nirmatrelvir-ritonavir combination.
CONCLUSIONS: Although the nirmatrelvir-ritonavir and tacrolimus combination is not contraindicated, other treatment strategies should be considered first, if available, and the dose of tacrolimus should be reduced when using the nirmatrelvir-ritonavir combination. In cases where combination therapy is necessary, serum tacrolimus levels should be closely monitored in lung transplant recipients. Documentation of more such reports is important to identify drug interactions between nirmatrelvir-ritonavir and other agents, with the aim of preventing severe adverse effects.

A 75-year-old woman developed a moderately severe rash about a week and a half after the start of bortezomib (Btb)-based chemotherapy for IgG lambda multiple myeloma; at the time, she was also receiving acyclovir as antiviral prophylaxis in addition to herpes zoster (HZ) vaccination. HZ reactivation rate is high in Btb recipients; therefore, the timing of antiviral prevention is critical in relation to Btb. Attempts were made to identify the offending agent based on the timing of drugs administered and the appearance of skin lesions in relation to other drugs. Both Btb and acyclovir were potential culprits. However, the timing of rash presented on days 9 - 10 revealed the offending agent when the corticosteroid was weaned off while acyclovir continued. A decision was made to administer acyclovir rapid desensitization program (RDP) for our patient.