Efficacy of lidocaine spray for pain reduction during rabies immunoglobulin infiltration: a double-blind, randomized, placebo-controlled trial

OBJECTIVES: Rabies immunoglobulin (RIG) infiltration is essential but often intensely painful. This study primarily evaluated the efficacy of 10% lidocaine spray versus a placebo for pain reduction during needle penetration and RIG infiltration, while comparing adverse events and satisfaction levels as secondary objectives. METHODS: This single-center, randomized, double-blind, placebo-controlled, superiority trial utilized a 1:1 allocation ratio among participants (18-65 years) requiring RIG at a university hospital in Bangkok. Patients with major organ disease, lidocaine contraindications, or recent analgesic use were excluded. A 100-mm Visual Analog Scale and 10-point Likert scale were used for pain (up to 30 min after RIG infiltration) and satisfaction assessment, respectively. RESULTS: A total of 76 participants were randomized to the lidocaine or placebo group (n = 38 each). Baseline median pain intensity was similar between groups (lidocaine 18.0 (IQR: 4.0, 28.0) vs placebo 11.5 (IQR: 6.0, 28.0); p = 0.823 after adjusting for wound type and size). Compared with placebo, the lidocaine group reported significantly lower median pain during needle penetration (25.0 (IQR: 17.0, 42.0) vs 56.5 (IQR: 45.0, 75.0); adjusted median difference: -30.8 (95% CI: -43.6, -18.0); p < 0.001) and RIG infiltration (46.5 (IQR: 36.0, 81.0) vs 77.0 (IQR: 66.0, 90.0); adjusted median difference: -33.0 (95% CI, -47.3, -18.7); p < 0.001). No adverse effects were reported during the 30-min observation. Participant satisfaction was significantly higher in the lidocaine group (8.0 (IQR: 7.0, 9.0) vs 6.0 (IQR: 5.0, 6.8); p < 0.001). CONCLUSIONS: Topical 10% lidocaine spray achieved statistically and clinically significant reductions in pain intensity during needle penetration and RIG infiltration compared with placebo. The intervention was well tolerated and associated with higher participant satisfaction. These findings support its use as a simple and efficacious option for procedural pain control in adults aged 18-65 years with the eligible small-to-moderate wound types evaluated in this study. TRIAL REGISTRY: Thai Clinical Trials Registry (TCTR20241127002).