Clinical situation
A 27-year-old man presents with a 1-week painless genital ulcer and 3-day purulent urethral discharge. Both nontreponemal (RPR) and treponemal tests are reactive, and Neisseria gonorrhoeae is identified on urethral swab. The painless chancre of short duration indicates primary syphilis, which is classified as early syphilis.
Why a single dose of benzathine penicillin G 2.4 million units is correct
Primary, secondary, and early latent syphilis are collectively termed early syphilis. The standard treatment for early syphilis in a nonpregnant adult without penicillin allergy is benzathine penicillin G 2.4 million units administered intramuscularly as a one-time dose [1][4]. This regimen achieves treponemicidal serum concentrations for 2–4 weeks, which is sufficient to eradicate Treponema pallidum during the early stage when the organism burden is lower and dissemination is still limited. The 1-week duration of the chancre places the infection firmly in the primary stage, so a single injection is appropriate.
Why the other options are incorrect
Doxycycline 100 mg orally twice daily for 14 days is an alternative for early syphilis only when the client has a documented penicillin allergy. This client has no drug allergies, so penicillin remains the first-line agent [4].
Benzathine penicillin G 2.4 million units weekly for 3 weeks is reserved for late latent syphilis or syphilis of unknown duration, where longer exposure is needed because treponemes may be dividing more slowly in sequestered sites. A 1-week chancre does not meet that criterion.
Benzathine penicillin G 1.2 million units as a single dose is an insufficient dose for early syphilis in adults. The 2.4 million-unit dose is required to achieve adequate tissue penetration and sustained treponemicidal levels [1].
Clinical reasoning and nursing implications
The presence of a painless chancre with reactive serology confirms primary syphilis, while the purulent urethral discharge indicates concurrent gonococcal urethritis. These are two distinct infections requiring separate treatment. The nurse should anticipate administering benzathine penicillin G 2.4 million units deep intramuscularly as a single dose for the syphilis, and a separate regimen—typically ceftriaxone monotherapy—for the gonorrhea .
Benzathine penicillin G is a repository form that must be given deep intramuscularly, usually in the dorsogluteal or ventrogluteal site, to avoid subcutaneous irritation and ensure slow absorption. The nurse should observe the client for 30 minutes after injection because anaphylaxis, though rare, can occur.
Watch out! The Jarisch-Herxheimer reaction—fever, chills, myalgia, and worsening of the chancre within 24 hours of treatment—is common in early syphilis and should be anticipated, not mistaken for drug allergy.
Key point! Staging determines the penicillin schedule. Early syphilis (primary, secondary, early latent) = one dose of 2.4 million units. Late latent or unknown duration = three weekly doses of 2.4 million units. The 1-week chancre makes this early syphilis [1][4].
Comparison of syphilis treatment by stage| Stage | Regimen | Rationale |
|---|
| Primary syphilis (chancre, 1 week) | Benzathine penicillin G 2.4 million units IM once | Early infection; single dose achieves cure [1][4] |
| Secondary syphilis | Benzathine penicillin G 2.4 million units IM once | Early disseminated stage; same single-dose principle [1] |
| Early latent syphilis (less than 1 year) | Benzathine penicillin G 2.4 million units IM once | Classified as early syphilis [1] |
| Late latent or unknown duration | Benzathine penicillin G 2.4 million units IM weekly for 3 weeks | Slower treponemal division requires prolonged exposure |
| Penicillin allergy (early syphilis) | Doxycycline 100 mg orally twice daily for 14 days | Alternative only when penicillin is contraindicated [4] |
Supporting evidence
A multicenter randomized noninferiority trial directly compared one dose versus three weekly doses of benzathine penicillin G 2.4 million units in persons with early syphilis, with or without HIV, and found the single-dose regimen to be noninferior [1]. This supports the clinical practice of treating primary syphilis with a one-time injection. The 2021 CDC STI guidelines and the 2024 AEDV consensus also maintain benzathine penicillin G as first-line therapy for early syphilis, with doxycycline reserved for penicillin-allergic individuals [4]. Serologic discordance can occur in very early primary syphilis, but this client already has reactive RPR and treponemal tests, so the diagnosis is serologically confirmed and treatment should proceed without delay .
References (research sources)
- [1]
One Dose versus Three Doses of Benzathine Penicillin G in Early Syphilis.Research articleHook EW, Dionne JA, Workowski K, McNeil CJ, Taylor SN, Batteiger TA (2025) · DOI: 10.1056/NEJMoa2401802
- [4]
[Translated article] AEDV Expert Consensus for the Management of Syphilis.GuidelineFuertes de Vega L, de la Torre García JM, Suarez Farfante JM, Ceballos Rodríguez MC (2024) · DOI: 10.1016/j.ad.2024.08.006