Background and Importance The use of the antiviral drug nirmatrelvir/ritonavir in nursing home patients with COVID-19 has reduced its main complications, although due to comorbidity and polypharmacy there are often problems with interactions.

Aim and Objectives To evaluate the effectiveness and safety of nirmatrelvir/ritonavir in nursing home patients with COVID-19 infection.

Material and Methods Retrospective observational study including all nursing home patients attended by a Geriatrics Liaison Unit from a hospital in Madrid between May 2022 and July 2023 and treated with nirmatrelvir/ritonavir. We collected the number of referrals to the emergency department, hospitalisations and mortality due to COVID-19 a month after treatment with nirmatrelvir/ritonavir and interactions and adverse events detected associated with the drug.

Sociodemographic, clinical and pharmacological variables were collected from the electronic medical record.

Results A total of 111 patients (76.6% women) with a median age of 89.5 years (68–102) and a Charlson index of 2 (0–5) points were included, from 18 different nursing homes. Overall, 58.6% (65) had dementia, 40.5% (45) Barthel ≤40 and 33.3% (37) impaired renal function receiving reduced doses of nirmatrelvir/ritonavir.

Clinically, 96.4% (107) had mild symptoms (cough, fever, myalgia, diarrhoea) and 0.9% (1) were asymptomatic and 53.2% of them (59) previously received four doses of vaccine. No symptoms were recorded in 2.7% (3) of the patients.

A total of 283 interactions of nirmatrelvir/ritonavir with 62 different chronic drugs were detected: trazodone (8.8%), metamizole (8.1%), quetiapine (7.4%), amlodipine (7.4%), mirtazapine (6%), atorvastatin (4.6%) were the most frequent. We observed at least one interaction in 93.8% of the patients, with a mean number of 2.6 interactions per patient. Eighty-two interactions were severe requiring discontinuation, 180 were moderate of which 81 required monitoring and 99 required drug adjustment including change of dose, frequency, regimen or substitution with another drug.

One month after treatment with nirmatrelvir/ritonavir, 2.7% (3) of patients were referred to the emergency department for Covid-19 of whom 66.7% (2) required hospital admission, while just one patient presented potential adverse reaction to treatment (dysgeusia) and no patient died during this month due to COVID-19.

Conclusion and Relevance Nirmartrelvir/ritonavir is effective and safe for the treatment of Covid-19 in nursing home patients but requires a review of clinical history and drug interactions to adjust chronic treatments during administration.

Conflict of Interest No conflict of interest.