Syphilis

Syphilis is a complex, multistage infectious disease caused by the spirochete Treponema pallidum. Its “great imitator” nature makes pharmacotherapy knowledge crucial for supporting diagnosis and treatment.

1. Transmission & Pathophysiology

Route: Primarily sexual (contact with infectious lesions), congenital (vertical transmission), and rarely, via blood transfusion.
Organism: T. pallidum subspecies pallidum. It cannot be cultured routinely; diagnosis relies on serology and darkfield microscopy.
Key Pharmacokinetic Note: The spirochete replicates slowly (30-33 hour doubling time) and penetrates mucosal barriers, explaining the need for long-acting penicillin formulations that maintain bactericidal concentrations over an extended period.

2. Clinical Stages & “Illustrative” Descriptions

Understanding stages is critical for selecting the correct antibiotic regimen and duration.

A. Primary Syphilis

Timing: 3-90 days (avg. 21 days) post-exposure.
Key Lesion: Chancre.
- Description: A single, firm, round, painless ulcer with a clean base and indurated borders. Highly infectious.
- Location: Genital, anal, oropharyngeal.
- Resolution: Heals spontaneously in 3-6 weeks, leading to latency if untreated.
Visual Reference: Search “primary syphilis chancre” on DermNet NZ or CDC’s STD Atlas for classic examples.

B. Secondary Syphilis

Timing: 4-10 weeks after chancre appears.
Manifestations: Systemic and variable. Highly infectious.
- Rash: Non-pruritic, classically involving palms and soles (red-brown macules/papules).
- Mucous Patches: Silvery-gray oral erosions.
- Condylomata Lata: Moist, fleshy, gray-white intertriginous plaques.
- Systemic: Fever, lymphadenopathy, malaise.
Visual Reference: Search “secondary syphilis palmar rash” or “condylomata lata” on the same medical image databases.

C. Latent Syphilis

Definition: Seropositivity without clinical signs. Divided into:
- Early Latent (<1 year): Can still have relapses with infectious lesions.
- Late Latent (>1 year): Not infectious by sexual contact, but risk of progression to tertiary disease and vertical transmission remains.
No visible lesions. Diagnosis is purely serological.

D. Tertiary (Late) Syphilis

Timing: 10-30 years after initial infection.
Manifestations:
- Gummatous: Destructive granulomatous lesions (skin, bone, liver).
- Cardiovascular: Aortitis, aneurysm, aortic regurgitation.
- Neurosyphilis: Can occur at any stage. Includes:
  - Meningovascular: Strokes in young adults.
  - Parenchymatous: General paresis (psychiatric/neurologic decline) and tabes dorsalis (ataxia, lightning pains, Argyll Robertson pupils).

Secondary stage syphilis sores (lesions) on the palms of the hands. Referred to as "palmar lesions." — Secondary stage syphilis sores (lesions) on the palms of the hands. Referred to as “palmar lesions.”

Secondary stage syphilis sores (lesions) on the bottoms of the feet. Referred to as “plantar lesions.” — Secondary stage syphilis sores (lesions) on the palms of the hands. Referred to as “palmar lesions.”

Darkfield micrograph of Treponema pallidum.

Primary stage syphilis sore (chancre) on the surface of a tongue.

Primary stage syphilis sore (chancre) on glans (head) of the penis.

Primary stage syphilis sore (chancre) inside the vaginal opening.

3. Diagnostic Serology: The Pharmacist’s Role in Interpretation

Understanding tests prevents treatment errors.

Non-Treponemal Tests (RPR, VDRL): Measure IgG/IgM antibodies to cardiolipin. Used for screening, quantitative titer monitoring, and assessing treatment response. False positives occur.
Treponemal Tests (TP-PA, EIA/CIA): Detect specific T. pallidum antibodies. Confirm infection, typically remain positive for life.
Reverse Sequence Screening: Common now (treponemal test first). A positive treponemal with negative non-treponemal test may indicate treated, early primary, or late latent syphilis. Clinical correlation is essential.

4. Pharmacotherapy: Core of Clinical Pharmacy Management

Benzathine Penicillin G is the cornerstone.

Stage & Indication	Preferred Regimen	Clinical Pharmacy Considerations & Alternatives for Penicillin Allergy
Primary, Secondary, Early Latent	Benzathine PCN G 2.4 million units IM x 1 dose	True PCN allergy: Doxycycline 100 mg PO BID x 14 days or Tetracycline. Ceftriaxone 1-2g IM/IV daily x 10-14 days is an option (cross-reactivity risk ~1%). Desensitization is required for pregnant patients.
Late Latent, Gummatous, Cardiovascular	Benzathine PCN G 2.4 million units IM weekly x 3 doses	Same alternatives for non-pregnant, but extend doxycycline to 28 days. Cardiovascular syphilis requires close monitoring for Jarisch-Herxheimer reaction.
Neurosyphilis & Ocular Syphilis	Aqueous Crystalline Penicillin G 18-24 million units IV daily (as 3-4 million units q4h) x 10-14 days OR Procaine PCN G 2.4 million units IM daily + Probenecid 500 mg PO QID x 10-14 days	Desensitization is strongly preferred. Ceftriaxone 2g IM/IV daily x 10-14 days can be considered if not anaphylactic allergy. Data on efficacy are limited. Oral regimens are inadequate.
Pregnancy	Penicillin regimen appropriate for stage. No alternatives without desensitization.	Doxycycline/tetracycline are contraindicated. Macrolides (azithromycin) are not recommended due to resistance. IM Penicillin is the only proven therapy to prevent congenital syphilis.

Key Pharmacy Notes:

Jarisch-Herxheimer Reaction: An acute febrile reaction (headache, myalgia) occurring within 24h of treatment, due to cytokine release. Manage with antipyretics. Not an allergic reaction.
Penicillin Shortages: Be prepared with institutional protocols for alternative sourcing or guideline-recommended alternatives.
Follow-up: Serologic titers (RPR/VDRL) should decline 4-fold by 6-12 months post-treatment for early syphilis. Ensure systems are in place for monitoring this.

5. Congenital Syphilis Prevention

Maternal Screening: At first prenatal visit, 28w, and delivery in high-risk areas.
Treatment of Infant: Depends on maternal treatment history, titers, and infant evaluation. Regimens can include Aqueous Crystalline Penicillin G 100,000-150,000 units/kg/day IV (q12h in first week, then q8h) x 10 days or Procaine Penicillin G 50,000 units/kg IM daily x 10 days.

Summary for the Clinical Pharmacist

Stage Dictates Therapy: Confirm the clinical stage before verifying regimen appropriateness.
Penicillin is Paramount: Understand formulations (Benzathine vs. Aqueous). No oral beta-lactams are effective.
Allergy Management: Drive protocols for penicillin allergy assessment and desensitization, especially in pregnancy and neurosyphilis.
Monitor & Educate: Anticipate Jarisch-Herxheimer, ensure serologic follow-up, and counsel on partner notification/treatment to break the transmission cycle.