Syphilis Treatment: How It Is Cured, and How You Know It Worked

อัปเดตล่าสุด: 22 สิงหาคม 2026

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Men arrive at my clinic with a syphilis result and one of two stories. Either they have just been diagnosed and are frightened, or they were treated somewhere else, their blood test is still positive months later, and they have been told — or have concluded — that the treatment failed. The second group is much larger than it should be, and most of them were never actually treatment failures at all. This article is mainly about why.

A note on what this article is. It explains how syphilis is treated and followed up so that you understand what is being done and what to expect. It does not print drug doses or schedules: the course depends on the stage of the infection, on whether it has reached the nervous system, on pregnancy and on allergy, and getting that wrong is how inadequate treatment happens. This page was originally written from the CDC’s 2015 recommendations, which have since been superseded by the CDC 2021 sexually transmitted infections treatment guidelines; the essentials described here have not changed.

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The Treatment Itself Is the Simple Part

Syphilis remains fully sensitive to penicillin. It has never developed resistance to it, which is remarkable for an organism we have been treating since the 1940s. First-line treatment is an intramuscular injection of long-acting benzathine penicillin, and how many injections you need depends entirely on the stage: early infection needs less, late or long-standing infection needs a longer course. This is exactly why staging — how long you have had it, which is often unknown — is part of the assessment rather than a formality.

Three situations change the answer completely, and they are the reason self-treatment or a borrowed prescription is dangerous here:

• Penicillin allergy. An oral antibiotic can be substituted in some circumstances — but not in all of them, and the decision is not interchangeable with the injection.
• Pregnancy. Penicillin is the only treatment that reliably protects the baby. A pregnant woman with penicillin allergy is desensitised to penicillin and then treated with it, rather than given an alternative. Untreated syphilis in pregnancy causes stillbirth and congenital syphilis, so this is not a corner to cut.
• Involvement of the nervous system, eye or ear. This needs intravenous penicillin in hospital — the intramuscular injection does not reach those tissues adequately. And it does not only happen late: it can occur at any stage, including early infection.

Get Help Urgently for These

Whether you are being treated or awaiting treatment, these need same-day assessment rather than a routine appointment — attend an emergency department or call 1669 in Thailand:

• Any change in vision — blurring, floaters, a red painful eye, or loss of vision. Ocular syphilis can destroy sight and is treated as an emergency
• New hearing loss, ringing in the ears or vertigo
• Severe headache, neck stiffness, confusion, or weakness or numbness in a limb
• In pregnancy: fever, contractions or reduced fetal movement after a treatment injection

The Reaction That Frightens People on the First Night

Within a day of the first injection, many people develop fever, chills, headache, aching muscles and sometimes a flare of the rash. This is the Jarisch–Herxheimer reaction. It is not a penicillin allergy and it is not the infection getting worse — it is the body’s inflammatory response to large numbers of bacteria dying at once, and it usually settles within about a day with rest, fluids and simple fever medication.

Knowing this in advance matters, because a man who is not warned assumes he is allergic, stops, and leaves himself untreated. Two qualifications belong with it, though: in pregnancy the reaction can provoke contractions and fetal distress and needs monitoring, and any reaction that is severe, that includes breathing difficulty, facial or throat swelling, or that does not settle as expected, should be assessed rather than assumed to be Herxheimer.

What You Have To Do Afterwards

• No sexual contact, including oral sex, until treatment is complete, any sores have fully healed, and at least seven days have passed. Syphilis sores are highly infectious, and condoms do not cover every site where a sore can sit.
• Partners must be told and assessed. Recent partners are usually treated presumptively — that is, treated on the basis of the exposure rather than waiting for their own test to turn positive, because a test taken too early can be negative in someone who is nonetheless infected.
• Get tested for the other infections. Gonorrhoea and chlamydia travel with syphilis; a urine PCR panel covers several at once. HIV testing, and pre- or post-exposure prophylaxis, are handled by the Infectious Diseases department at Bangkok Hospital Headquarters rather than in the urology clinic — and PEP is time-critical, needed within 72 hours of a high-risk exposure.
• Keep the follow-up blood tests. They are the only way anyone can tell whether the treatment worked.

A Correction: Your Blood Test May Never Turn Negative

An earlier version of this article stated that the VDRL typically becomes negative six to twelve months after successful treatment. That is not reliably true, and it has caused a great deal of unnecessary alarm — so it is corrected here.

There are two different kinds of syphilis blood test, and confusing them is the root of the problem. I have written about the distinction in detail in why there are two kinds of syphilis test, but in short:

• The treponemal test (TPHA, TPPA and similar) usually stays positive for the rest of your life, cured or not. It is not a measure of cure and repeating it tells you nothing about whether treatment worked.
• The nontreponemal test (VDRL or RPR) is reported as a titre, and it is the one that is followed. Cure is judged by a fourfold fall in that titre over an expected period — for example from 1:32 to 1:8 — not by the test turning negative.

A proportion of properly treated people never become negative at all: the titre falls, then settles at a low level and stays there indefinitely. This is called the serofast state. It is well recognised, it does not mean the infection persists, and it does not mean more penicillin is needed. It is, in my experience, the single commonest reason a man is told at another clinic that his treatment failed — and then retreated unnecessarily, sometimes more than once.

What genuinely does warrant re-evaluation is the opposite pattern: a titre that fails to fall as expected, or that rises fourfold. That means either true treatment failure or, far more often, reinfection from an untreated partner — and the answer to the second is not simply another injection for you.

คำถามที่พบบ่อย

How is syphilis treated?

With an intramuscular injection of long-acting benzathine penicillin. The number of injections depends on the stage of infection, which is why staging is part of the assessment. Syphilis has never become resistant to penicillin. An oral alternative can be used in some penicillin-allergic patients, but not in pregnancy — where the woman is desensitised and treated with penicillin instead — and not where the nervous system, eye or ear is involved, which requires intravenous penicillin in hospital.

My syphilis blood test is still positive after treatment. Did it fail?

Usually not. The treponemal test (TPHA, TPPA) stays positive for life in most people and is not a measure of cure. The nontreponemal test (VDRL, RPR) is the one followed, and cure is judged by a fourfold fall in the titre, not by it becoming negative. Some fully treated people settle at a low positive titre permanently — the serofast state — which does not mean persisting infection and does not need more penicillin. Retreatment on that basis is a common and avoidable mistake.

When does syphilis treatment genuinely need repeating?

When the nontreponemal titre fails to fall as expected, or rises fourfold. That indicates either true treatment failure or, more commonly, reinfection from an untreated partner. Both need re-evaluation rather than an automatic repeat injection, and reinfection is not solved by treating you again while the source goes untreated.

I felt feverish and unwell the night after my injection. Am I allergic?

Most likely not. Fever, chills, headache, muscle aches and a flare of rash within a day of the first injection is the Jarisch–Herxheimer reaction — an inflammatory response to large numbers of bacteria dying at once. It is not an allergy and usually settles within about a day with rest, fluids and simple fever medication. But breathing difficulty, facial or throat swelling, or a reaction that is severe or does not settle should be assessed rather than assumed. In pregnancy the reaction can provoke contractions and fetal distress and needs monitoring.

When is syphilis an emergency?

Any change in vision, a red painful eye, new hearing loss, ringing in the ears or vertigo, or severe headache with neck stiffness, confusion or limb weakness. Syphilis can involve the eye, ear and nervous system at any stage, including early infection, and those require intravenous treatment in hospital rather than the usual injection. Attend an emergency department or call 1669 in Thailand.

Do my partners need treatment?

Yes. Recent partners are usually treated presumptively, on the basis of the exposure rather than waiting for their own test to turn positive, because a test taken soon after exposure can be negative in someone who is infected. Avoid sexual contact, including oral sex, until treatment is complete, any sores have healed, and at least seven days have passed.

นัดหมายแพทย์

Dr. Soarawee Weerasopone provides confidential testing and treatment for sexually transmitted infections at โรงพยาบาลกรุงเทพ สำนักงานใหญ่ และที่โรง สมิติเวช ศรีราชา พยาบาลชลบุรี – ฝ ศัลยศาสตร์ยูโรวิทยา ่ายบริการ 088-022-1445. HIV testing and PrEP or PEP are handled by the Infectious Diseases department rather than the urology clinic. Questions about cost are answered by the hospital rather than by Dr. Soarawee — for Bangkok Hospital, by email to bhquro@bdms.co.th.

โรงพยาบาลกรุงเทพฯ มีบริการแพทย์ทางไกลสำหรับผู้ป่วยที่ไม่สามารถมาพบแพทย์ด้วยตนเอง รวมถึงผู้ป่วยต่างชาติ กรุณาแจ้งล่วงหน้าทางอีเมลไปยังแผนกศัลยกรรมทางเดินปัสสาวะที่ bhquro@bdms.co.th. Blood testing and treatment injections require an in-person visit. Samitivej Sriracha is in-person only.

ข้อจำกัดความรับผิดชอบ This article is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters. It is educational only, is not medical advice, and does not create a doctor–patient relationship. It gives no drug doses or schedules: the correct course depends on the stage of infection, on pregnancy, on allergy and on whether the nervous system, eye or ear is involved, and syphilis must not be self-treated. Local guidance may differ from the international guidance described here. No diagnosis, prescription or individual medical advice is given through personal messaging channels or social media, and Dr. Soarawee operates no public social media account — any account offering private consultation in his name is fraudulent. For any change in vision, new hearing loss, or severe headache with neck stiffness or confusion, go to an emergency department or call 1669 in Thailand.