Penicillin Treatment for Syphilis – Simple Facts You Should Know

If you or someone you know has syphilis, the first question is usually “what’s the cure?” The answer is almost always penicillin. This antibiotic has been the go‑to drug for over 70 years and works for every stage of the infection. Below we break down how it’s given, what to expect, and what to do if you’re allergic.

How Penicillin Is Used at Different Stages

Syphilis shows up in stages – early, late latent, and neurosyphilis. For early syphilis (including primary sores, secondary rash, or early latent infection) doctors give a single intramuscular shot of benzathine penicillin G, 2.4 million units. It’s quick, painless, and clears the bug in most people.

Late latent syphilis needs a bit more work. The same dose is repeated once a week for three weeks – three shots total. This extended schedule makes sure the bacteria are fully eliminated, even if they’ve been hiding for years.

Neurosyphilis is the tricky one because the infection has reached the brain or spinal fluid. Here you need intravenous (IV) aqueous penicillin G, usually 18‑24 million units per day, divided into doses every 4 hours for 10‑14 days. This high‑dose IV regimen ensures the drug crosses the blood‑brain barrier.

Allergy? What About Alternatives?

About 10% of people say they’re allergic to penicillin. If you’ve never taken it before, a doctor will do a quick skin test. Mild reactions (like a rash) can be managed with antihistamines, but a severe reaction (anaphylaxis) means you’ll need a different drug.

The most common backup is doxycycline – 100 mg twice daily for 14 days for early syphilis, or 28 days for late disease. It’s not as proven as penicillin, especially for neurosyphilis, but it’s a reasonable choice when penicillin can’t be used.

Another option is ceftriaxone IV, 1‑2 g daily for 10‑14 days. This is used mainly when patients can’t tolerate doxycycline and have a confirmed penicillin allergy.

Side Effects and What to Watch For

Penicillin is generally safe. The most common side effect is a sore at the injection site – a little redness or bruising that clears in a day or two. Some people feel mild fever or headache after the shot; that’s usually harmless.

Serious side effects are rare but include severe allergic reactions, like swelling of the face, throat, or trouble breathing. If any of that happens, call emergency services right away.

After the Shot – Follow‑Up and Testing

Even after you finish treatment, doctors will want to see that the infection is truly gone. They’ll check your blood with a non‑treponemal test (RPR or VDRL) at 6 months, then again at 12 months. A four‑fold drop in the titer means the treatment worked.

If the numbers don’t fall, or if you get re‑exposed, you might need another round of penicillin. Keep any sexual partners informed so they can get tested too – treating one person isn’t enough to stop the spread.

Practical Tips for a Smooth Treatment

Schedule your injection(s) at a clinic that can store penicillin properly; it needs refrigeration. Bring a photo ID and any prescription notes. If you’re nervous about needles, let the nurse know – they can use a smaller gauge needle or a topical numbing spray.

Don’t skip follow‑up appointments, and avoid alcohol or smoking for a couple of days after the shot to give your body the best chance to heal.

Remember, penicillin works, is affordable, and has stood the test of time. If you suspect syphilis, get tested, start treatment, and you’ll be back on track in weeks, not months.