Local anaesthetic to reduce injection pain in patients who are prescribed intramuscular benzathine penicillin G: a systematic review and meta-analysis.

Background: Three to 4-weekly intramuscular injections of benzathine penicillin G (BPG) for a prolonged period (e.g., 10 years, until age 40 years, or lifelong) are recommended for preventing group A streptococcal infections that cause recurrent acute rheumatic fever (ARF) and potential progression to rheumatic heart disease (RHD). The duration of treatment, frequency and local pain associated with BPG injections may lead to reduced compliance. Shorter courses of BPG are recommended for the treatment of syphilis and Streptococcal infections. We aimed to assess the effects of local anaesthesia in reducing injection pain in patients who are being treated with BPG. Methods: In this systematic review and meta-analysis, we searched the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, Conference Proceedings Citation Index-Science and LILACS from database inception up to May 4, 2024, and performed additional searches for grey literature. Randomised controlled trials comparing BPG vs. BPG administered alongside local anaesthetics were included. Randomized controlled trials using BPG, irrespectively of indication, and testing any local anaesthetic agent for pain alleviation were considered eligible. We applied GRADE to assess the quality of evidence. Summary data were extracted from included trials. The primary outcome was injection pain, assessed through mean differences. A random-effects model was utilized to account for study heterogeneity. This study is registered with PROSPERO, CRD42022342437. Findings: Database searches identified a total of 3958 records, and 3 additional records were retrieved from grey literature searches. After removal of duplicates, screening of abstracts and full-text review, eight trials were included, combining a total of 489 patients (151 patients with RHD). Immediate pain level, as reported by patients, was of high intensity in most studies. Low intensity pain was still reported at 24 h. Administration of lidocaine mixed with BPG was associated with a significant reduction in immediate post-injection pain (mean difference -3.84, 95% confidence interval -6.19 to -1.48, P = 0.0001; 4 studies; I Interpretation: In patients receiving intramuscular BPG injections, moderate quality quantitative evidence suggests that BPG injections diluted with lidocaine or mepivacaine may improve post-injection pain scores compared to BPG injections diluted with sterile water. Procaine may also have a benefit, but quality of evidence was lower. Most studies included small patient samples and assessed pain levels at different timepoints. Due to insufficient data we were not able to assess the impact of injection volume, and local anaesthetics' dose on pain intensity and duration of pain relief. Funding: WHO.