The proportion of infections in patients with vascular anomalies treated with sirolimus: a retrospective study

Sirolimus, an mTOR inhibitor, is an effective treatment for vascular anomalies (VA), particularly lymphatic malformations. However, its immunosuppressive properties raise concerns regarding infection risk, while the role of antibiotic prophylaxis remains unclear. This study aims to evaluate the proportion of infections and associated factors among pediatric VA patients treated with sirolimus. We conducted a retrospective single-center study that included pediatric patients who received sirolimus between January 2019 and June 2025 at King Faisal Specialist Hospital & Research Center. Infections occurring within 12 months of therapy initiation were collected. Among 95 patients, the median age was 12 years. Lymphatic (46.3%) and veno-lymphatic (34.7%) malformations were the most common subtypes. During therapy, 63.2% developed at least one infection, with a median of three infections per affected patient. Respiratory infections predominated (80%), skin/soft tissue (11.7%), and bloodstream infections (5%). Infections resulted in emergency visits (70.0%), hospitalization (23.3%), and intensive care admission (28.6% of hospitalized cases), with one infection-related death. Sirolimus dose adjustment and temporary discontinuation occurred in 58.3% and 40.0% of cases, respectively. Patients with infections received a lower initial sirolimus dose than those without infections (median [IQR]: 1.20 [0.76–1.60] vs. 1.60 [1.20–1.80] mg/m²; p = 0.023). Antibiotic prophylaxis rates did not differ significantly between groups (28.3% vs. 25.7%; p = 0.817). Infections were common and clinically significant among pediatric VA patients receiving sirolimus and frequently affected treatment continuity. Antibiotic prophylaxis was not associated with lower infection rates. Close monitoring and risk-adapted infection prevention strategies may help optimize sirolimus therapy.