Situation: A public health nurse runs adolescent-friendly health services on weekend afternoons at a Rural Health Unit (RHU). Adolescents from the municipality come for counseling, immunization, and reproductive health services. A 17-year-old boy comes with his father, who consents to his treatment. He has had a painless genital ulcer for 2 weeks, and his syphilis infection has been confirmed per protocol. He has no penicillin allergy. The physician orders benzathine penicillin G 2.4 million units by deep intramuscular (IM) injection. Which plan for giving the drug and counseling him is CORRECT?

Two rules apply. A painless ulcer present for 2 weeks is a primary chancre, which is early syphilis, so benzathine penicillin G 2.4 million units is given deep intramuscularly (IM) once; the weekly dose for 3 weeks is for late latent syphilis or syphilis of unknown duration. Fever and aches within 24 hours are the Jarisch–Herxheimer reaction, which is expected and is not an allergy; the client is still observed for 15 to 30 minutes after injection with adrenaline (epinephrine) available.

Clinical context and staging
A painless genital ulcer that has been present for 2 weeks is the classic presentation of a primary syphilitic chancre. Because the lesion is still in the primary stage, this is classified as early syphilis. The correct treatment for early syphilis in an adolescent without penicillin allergy is benzathine penicillin G 2.4 million units given as a single deep intramuscular injection. The three-weekly-dose regimen is reserved for late latent syphilis or syphilis of unknown duration, not for a primary chancre of only two weeks’ duration ^[1][2].

The staging of syphilis determines both the dose and the number of injections, so recognizing the painless chancre as primary syphilis is the key to selecting the one-time regimen. A randomized trial comparing one dose with three weekly doses in early syphilis supports the use of a single injection in this population ^[2].

Stage	Presentation	Benzathine penicillin G regimen
Primary syphilis	Painless chancre, usually within 2–6 weeks after exposure	2.4 million units IM once
Secondary syphilis	Rash, mucocutaneous lesions, lymphadenopathy	2.4 million units IM once
Early latent syphilis	Asymptomatic, infection acquired within the previous year	2.4 million units IM once
Late latent or unknown duration	Asymptomatic, duration greater than one year or unknown	2.4 million units IM weekly for 3 weeks

Jarisch–Herxheimer reaction versus penicillin allergy
Within the first 24 hours after the injection, the adolescent may develop fever, chills, myalgia, headache, or malaise. This constellation is the Jarisch–Herxheimer reaction, an expected immunologic response to the rapid killing of treponemes and release of inflammatory cytokines. It is not an allergic reaction and does not require discontinuation of penicillin ^[3].

Fever and body aches within 24 hours of benzathine penicillin G for early syphilis should be interpreted as the Jarisch–Herxheimer reaction, which is self-limited and expected, not as evidence of penicillin allergy. A secondary analysis of a randomized trial documented this reaction prospectively and confirmed that it occurs commonly after treatment of early syphilis with benzathine penicillin G ^[3].

Key point! A true penicillin allergy presents with urticaria, angioedema, bronchospasm, or anaphylaxis, typically within minutes to a few hours. The Jarisch–Herxheimer reaction is a febrile, flu-like syndrome that peaks around 6–12 hours and resolves spontaneously.

Nursing and safety considerations
Even though the Jarisch–Herxheimer reaction is expected, the adolescent should still be observed for 15 to 30 minutes after the intramuscular injection. Emergency equipment, including epinephrine, must be immediately available because anaphylaxis, although rare, can occur with any penicillin preparation ^[1]. The injection must be given deep into a large muscle mass, such as the dorsogluteal or ventrogluteal site, to reduce local pain and ensure proper absorption.

Watch out! Do not confuse observation for anaphylaxis with treatment of the Jarisch–Herxheimer reaction. Observation with epinephrine available is a universal safety measure for any injectable penicillin; the fever and aches themselves are managed supportively with fluids, rest, and antipyretics if needed.

Counseling points for the adolescent and father
The adolescent and his father should be informed that the single injection treats the infection, but serologic follow-up is required to confirm cure. The Jarisch–Herxheimer reaction may occur and is not a reason to stop treatment or to label the adolescent as penicillin-allergic. Partners within the appropriate look-back period must also be evaluated and treated to prevent reinfection ^[1]. In this RHU setting, the weekend adolescent-friendly service supports confidential, developmentally appropriate counseling while still involving the father as the consenting guardian.

The correct plan is a single deep IM injection of benzathine penicillin G 2.4 million units, with anticipatory guidance that fever and aches within 24 hours represent the expected Jarisch–Herxheimer reaction, not an allergy.