Using lidocaine to reduce pain from benzathine penicillin injections for syphilis treatment

LIMIT Trial - Lidocaine With Intramuscular Injection of Benzathine Penicillin G for Treponema Pallidum Treatment

Phase 3 Interventional Washington University School of Medicine · NCT06391125

This study is testing if adding lidocaine to syphilis treatment injections can help reduce the pain patients feel during and after the shot.

Quick facts

PhasePhase 3
Study typeInterventional
Enrollment48 (estimated)
Ages18 Years and up
SexAll
SponsorWashington University School of Medicine Academic / other
Locations1 site (St Louis, Missouri)
Trial IDNCT06391125 on ClinicalTrials.gov

What this trial studies

This clinical trial aims to evaluate whether the addition of lidocaine to benzathine penicillin G injections can reduce the pain experienced by patients being treated for syphilis infections. Participants will receive either benzathine penicillin G with lidocaine or with normal saline, and their pain levels will be assessed at 10 minutes and 24 hours post-injection. The study is designed as a randomized controlled trial to provide robust evidence on the efficacy of lidocaine in this context. The trial is particularly relevant given the challenges of using lidocaine as a diluent in the US compared to European practices.

Who should consider this trial

Good fit: Ideal candidates for this study are adults aged 18 and older with a confirmed diagnosis of syphilis who are receiving their first injection in a treatment series.

Not a fit: Patients with allergies to penicillin or lidocaine, or those who are pregnant, will not benefit from this study.

Why it matters

Potential benefit: If successful, this approach could significantly improve the comfort of patients receiving treatment for syphilis.

How similar studies have performed: Previous studies have shown that lidocaine can effectively reduce injection pain, suggesting a positive outlook for this trial's approach.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* Adults 18 years of age or above
* Confirmed syphilis diagnosis (reactive RPR with confirmatory treponemal testing)
* Receiving first injection in series if patient requires 3x weekly injections for syphilis treatment

Exclusion Criteria:

* Penicillin allergy (anaphylaxis)
* Lidocaine allergy (anaphylaxis)
* Second or third injection in series if patient requires 3x weekly injections for syphilis treatment
* Pregnancy

Where this trial is running

St Louis, Missouri

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Syphilis InfectionBenzathine Penicillin Adverse ReactionSyphilisSyphilis TreatmentBenzathine Penicillin GLidocaine
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.