Low grade fever with no associated symptoms. Labs are normal but CRP is 6.5. not responding to oral or iv antibiotics. What might be the diagnosis and treatment
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Low-Grade Fever + Elevated CRP (6.5) + No Response to Antibiotics
This clinical picture is the hallmark of Fever of Unknown Origin (FUO) or, more precisely, a non-infectious inflammatory/autoimmune process -- the antibiotic non-response is a critical diagnostic clue pointing away from bacteria.
A CRP of 6.5 mg/L is only mildly elevated (normal <5 mg/L), which actually favors a non-infectious inflammatory or autoinflammatory cause over a typical bacterial infection (bacterial infections tend to push CRP above 40-100 mg/L).
Differential Diagnosis
1. Non-Infectious Inflammatory / Autoimmune (Most Likely Category)
These are the top diagnoses to consider when antibiotics fail:
| Condition | Key Clues |
|---|---|
| Adult-Onset Still's Disease (AOSD) | Quotidian high spikes, salmon-colored evanescent rash, pharyngitis, arthralgias; ferritin dramatically elevated (often >2000 ng/mL) |
| Systemic Lupus Erythematosus (SLE) | Young woman, pancytopenia, low complement, ANA positive |
| Rheumatoid Arthritis (early/seronegative) | Symmetric polyarthritis (wrists, MCPs, PIPs), morning stiffness >1 hour |
| Polymyalgia Rheumatica / Giant Cell Arteritis | Age >50, shoulder/hip girdle pain, elevated ESR, headache/jaw claudication in GCA |
| Sarcoidosis | Bilateral hilar lymphadenopathy, ACE elevated, lymphopenia |
| Inflammatory Bowel Disease | Change in bowel habits, abdominal pain, weight loss |
| Vasculitis (PAN, ANCA-associated) | Multi-system involvement, livedo reticularis, renal/lung involvement |
| Reactive Arthritis | Recent GI or GU infection, sterile arthritis, urethritis, conjunctivitis |
2. Autoinflammatory / Periodic Fever Syndromes
| Condition | Key Clues |
|---|---|
| Familial Mediterranean Fever (FMF) | Mediterranean/Middle Eastern descent, recurrent episodes of fever + serositis (peritonitis, pleuritis, arthritis), responds dramatically to colchicine |
| Schnitzler's Syndrome | Recurrent urticaria, monoclonal IgM/IgG, bone pain |
| Hyper-IgD Syndrome (Mevalonate Kinase Deficiency) | Childhood onset, lymphadenopathy, abdominal pain, elevated IgD |
| TRAPS (TNF Receptor-Associated Periodic Syndrome) | Prolonged fever episodes (>1 week), periorbital edema, myalgia |
3. Occult Infections (Less Likely given CRP 6.5, but must exclude)
| Condition | Key Clues |
|---|---|
| Tuberculosis (extrapulmonary/miliary) | Travel, immunosuppression, normal chest X-ray possible in miliary TB; TST/IGRA testing |
| Culture-negative endocarditis | Heart murmur, risk factors (IVDU, valve disease); HACEK organisms, Coxiella (Q fever), Bartonella can be culture-negative |
| Intra-abdominal abscess | Prior GI surgery, diverticulitis, Crohn's; CT abdomen has high yield |
| Brucellosis / Lyme / EBV / CMV | Exposure history, lymphadenopathy |
4. Malignancy (Must Not Miss)
| Condition | Key Clues |
|---|---|
| Lymphoma (Hodgkin's / NHL) | Night sweats, weight loss, lymphadenopathy, splenomegaly |
| Renal Cell Carcinoma | Hematuria, flank mass |
| Hepatocellular Carcinoma | Chronic liver disease background |
| Leukemia | Cytopenias, fatigue |
Diagnostic Workup
Tier 1 (First-line if not already done):
- ANA, anti-dsDNA, complement (C3/C4) - for SLE
- Serum ferritin - if very high (>2000), strongly suggests AOSD
- ESR (pairs well with CRP)
- Rheumatoid factor + anti-CCP
- LDH, uric acid, protein electrophoresis (SPEP)
- Blood cultures x3 (including prolonged incubation for HACEK)
- TST or IGRA (QuantiFERON) for TB
- HIV serology
- Peripheral blood smear
Tier 2 (Imaging):
- CT chest/abdomen/pelvis - very high yield in FUO (occult abscess, lymphoma, solid tumors)
- Echocardiography (TTE/TEE) if endocarditis possible
- PET-CT - increasingly used in FUO workup; identifies occult malignancy and inflammatory foci
Tier 3 (Targeted):
- Genetic testing for FMF (MEFV gene mutations) if periodic fever pattern
- Bone marrow biopsy if lymphoma/hematologic malignancy suspected
- Tissue biopsy of abnormal lymph nodes or lesions
Treatment
Treatment depends entirely on the diagnosis. Key principles:
Do NOT start empirical glucocorticoids until infectious causes (especially TB) and lymphoma are excluded -- steroids can mask fever while allowing both to progress.
| Diagnosis | Treatment |
|---|---|
| FMF | Colchicine 0.5-1 mg/day (long-term, highly effective) |
| AOSD | NSAIDs first; if refractory - prednisolone, then methotrexate or IL-1 inhibitors (anakinra/canakinumab) |
| SLE | Hydroxychloroquine ± immunosuppressants |
| GCA/PMR | High-dose prednisolone (40-60 mg/day for GCA; 15 mg/day for PMR) |
| RA | NSAIDs, DMARDs (methotrexate); biologic agents if needed |
| Sarcoidosis | Observation or corticosteroids |
| Lymphoma | Chemotherapy (oncology referral) |
| Occult TB | Anti-tuberculous therapy (RHEZ regimen) |
| Autoinflammatory syndromes (general) | Anakinra (IL-1 receptor antagonist) -- highly effective for FMF, CAPS, TRAPS, MKD, Schnitzler's, Still's; consider if FUO persists after full workup with elevated CRP and ferritin |
If FUO remains undiagnosed after full workup:
- NSAIDs or acetaminophen for symptomatic relief
- NSAIDs can have dramatic effect in Still's disease
- Consider anakinra trial if IL-1-driven autoinflammation suspected (serositis + elevated CRP + elevated ferritin pattern)
- Monitor closely; many undiagnosed FUOs resolve spontaneously with a favorable prognosis
Bottom Line
A low-grade fever with mild CRP elevation (6.5 mg/L), normal labs, and no response to antibiotics most strongly points to a non-infectious inflammatory or autoinflammatory condition rather than bacteria. The most important next steps are:
- Detailed history (rash? joint pain? country of origin? travel? family history of periodic fever?)
- Ferritin level (if >2000 - think AOSD)
- Full autoimmune panel (ANA, anti-dsDNA, RF, anti-CCP)
- CT chest/abdomen/pelvis
- TB screening (TST/IGRA)
Sources: Harrison's Principles of Internal Medicine 22E, p. 198-199 | Frameworks for Internal Medicine, p. 282-286 | Goldman-Cecil Medicine, p. 2941
The patient is 2 yrs old.
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2 year old low grade fever elevated CRP not responding to antibiotics differential diagnosis toddler
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Kawasaki disease diagnosis treatment children
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I now have excellent data. Here is the focused pediatric answer:
2-Year-Old: Low-Grade Fever + CRP 6.5 + No Response to Antibiotics
This age shifts the differential dramatically. A toddler aged 1-2 years who fails antibiotics should immediately raise concern for Kawasaki Disease (KD) as the top diagnosis -- it is the #1 cause of acquired heart disease in children and peaks at age 1-2 years. "Incomplete" KD is especially tricky and easy to miss.
Top Diagnoses to Consider
1. Kawasaki Disease (KD) - MOST IMPORTANT TO EXCLUDE
Peak age: 1-2 years. Classic or "complete" KD requires fever ≥5 days plus 4 of 5 features:
| Feature | What to look for |
|---|---|
| Fever ≥5 days | Often the only feature initially |
| Bilateral non-exudative conjunctival injection | Red eyes, no discharge |
| Oropharyngeal changes | "Strawberry tongue," cracked lips, diffuse oral erythema |
| Rash (polymorphous) | Blotchy macular rash on trunk and extremities |
| Peripheral extremity changes | Erythema/edema of palms/soles; later periungual desquamation |
| Cervical lymphadenopathy | ≥1.5 cm |
Incomplete/Atypical KD is common in infants and toddlers -- they may have fever + only 2-3 features and still have KD. CRP elevation supports the diagnosis even if "normal labs" otherwise. Per the 2024 AHA Scientific Statement on KD, 25% of untreated patients develop coronary artery aneurysms -- making early diagnosis urgent.
Lab clues that support KD:
- CRP elevated (present here - CRP 6.5)
- Leukocytosis, thrombocytosis (may be absent early)
- Elevated ESR, ALT
- Sterile pyuria on urinalysis
- Hypoalbuminemia, mild anemia
2. Systemic Juvenile Idiopathic Arthritis (sJIA / Still's Disease in children)
This is the pediatric equivalent of AOSD and peaks at 1-5 years of age, with peak around 2 years. Key features:
- Daily spiking fevers (quotidian, once/twice daily), child appears unwell during fever but improves when afebrile
- Evanescent salmon-pink macular rash (80% of patients) - elicited by Koebner phenomenon
- Arthritis may be absent for weeks to months at onset - only arthralgias/myalgias initially
- Lymphadenopathy, hepatosplenomegaly
- Serositis (pericarditis/pleuritis)
- Markedly elevated ferritin, CRP, ESR
This diagnosis is particularly dangerous because it can be complicated by Macrophage Activation Syndrome (MAS) - a life-threatening cytokine storm (occurs in ~10% of sJIA patients).
3. Occult/Deep Infections (Less Likely but Must Exclude)
| Infection | Why to consider |
|---|---|
| Occult UTI | Most common serious bacterial infection in toddlers; may have only fever; get urine by catheter (not bag) |
| Occult bacteremia | Repeat blood cultures; look for hidden source |
| Osteomyelitis | Toddlers may not localise pain well; look for limb pseudoparalysis, point tenderness; MRI most sensitive |
| Septic arthritis | Joint swelling, restricted movement |
| TB | Exposure history; miliary TB can look like FUO |
| Viral (EBV, CMV, HHV-6) | Primary infection in toddlers can cause prolonged fever with mild CRP |
4. Malignancy (Must Not Miss)
| Notes | |
|---|---|
| Leukemia (ALL) | Most common childhood malignancy; low-grade fever + pallor + lymphadenopathy; may have normal CBC early -- repeat smear |
| Lymphoma | Lymphadenopathy, hepatosplenomegaly |
| Neuroblastoma | Adrenal/paraspinal mass; urinary catecholamines |
5. Autoinflammatory Periodic Fever Syndromes
| Syndrome | Key Clue |
|---|---|
| PFAPA (Periodic Fever, Aphthous stomatitis, Pharyngitis, Adenitis) | Most common periodic fever in children; recurrent predictable 3-5 day episodes every 3-8 weeks; complete resolution between attacks |
| FMF | Mediterranean ancestry; recurrent serositis; responds to colchicine |
| Hyper-IgD / MKD | Lymphadenopathy, abdominal pain, elevated IgD |
Workup for a 2-Year-Old in This Scenario
Immediate priority:
- Echocardiography - If KD is being considered (do not delay); look for coronary artery dilation/aneurysm
- Urine (by catheter) - rule out UTI (even without urinary symptoms in toddlers)
- Full blood count + differential - thrombocytosis (KD), leukocytosis; blast cells (leukemia)
- Serum ferritin - if >500-1000 ng/mL, strongly suggests sJIA or MAS
- ESR, LDH, uric acid
- Repeat blood cultures x2 (if not already done with sufficient volume)
- LFTs, albumin - supportive of KD if abnormal
- CXR - hilar adenopathy, cardiomegaly
- ANA, RF - early JIA workup
- Peripheral smear - rule out leukemia
If above unrevealing:
- Bone scan or MRI long bones (osteomyelitis)
- CT chest/abdomen (lymphoma, occult abscess, neuroblastoma)
- Tuberculin skin test / IGRA
- EBV/CMV/HHV-6 serology
- Urine VMA/HVA (neuroblastoma)
Treatment Based on Most Likely Diagnoses
| Diagnosis | Treatment |
|---|---|
| Kawasaki Disease | Hospital admission + IVIG 2 g/kg IV over 10-12 hours + Aspirin 80-100 mg/kg/day (high dose, divided q6h during acute phase; then low-dose 3-5 mg/kg/day); IVIG within 10 days reduces coronary aneurysm risk 5-fold |
| IVIG-resistant KD | Repeat IVIG or infliximab + corticosteroids (per AHA 2024 guidelines) |
| sJIA | NSAIDs first; then corticosteroids; IL-1 inhibitors (anakinra, canakinumab) or IL-6 inhibitors (tocilizumab) for refractory disease - biologic therapy is now first-line in many centers |
| PFAPA | Single dose of prednisolone (1-2 mg/kg) aborts individual episodes; tonsillectomy may be curative |
| FMF | Colchicine (long-term, highly effective) |
| Occult UTI | Appropriate antibiotic based on urine culture sensitivity |
| Osteomyelitis | IV antibiotics (oxacillin/cefazolin; adjust per culture); surgical drainage if needed |
| Leukemia/Lymphoma | Urgent pediatric oncology referral |
Key Clinical Pearl
In a 2-year-old with fever not responding to antibiotics, always think "Could this be Kawasaki?" first. Incomplete KD is common at this age and CRP elevation is a supportive criterion. The window for IVIG to prevent coronary aneurysms is the first 10 days of fever -- missing this is a serious consequence. Echocardiography is the most important single investigation.
Sources: Rosen's Emergency Medicine, p. 2417 | Firestein & Kelley's Textbook of Rheumatology, p. 2364 | AHA 2024 Scientific Statement on Kawasaki Disease (PMID 39534969)
Methyl prednisolone dosing
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Methylprednisolone Dosing in a 2-Year-Old (Pediatric)
Given the clinical context (KD/sJIA/inflammatory), here are the relevant dosing regimens:
Formulation Note
- IV/IM: Methylprednisolone sodium succinate (Solu-Medrol)
- Oral: Methylprednisolone tablets (Medrol)
- IM depot: Methylprednisolone acetate (Depo-Medrol) - for prolonged effect
- Maximum dose cap: 1000 mg/dose regardless of weight
Dosing by Indication
1. High-Dose "Pulse" IV - sJIA / Systemic Autoimmune / MAS
The most commonly used regimen for severe pediatric inflammatory disease:
| Parameter | Dose |
|---|---|
| Pulse dose | 15-30 mg/kg/dose IV (max 1000 mg/dose) |
| Frequency | Once daily |
| Duration | 3 days (commonly); up to 3-5 days |
| Infusion rate | Over 30-60 minutes (never bolus - risk of arrhythmia) |
| Follow-up | Transition to oral prednisolone 1-2 mg/kg/day, tapered over weeks to months |
- For sJIA: 15-30 mg/kg/dose IV daily x3 days, then oral prednisolone 1-2 mg/kg/day
- For JDM with severe disease (e.g. respiratory muscle involvement): 30 mg/kg/dose IV (max 1g) daily x3 days
- For lupus nephritis: 30 mg/kg/dose IV (max 1g/dose) - 3 pulses in first week, then oral
Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics | Harrison's 22E | Goldman-Cecil Medicine
2. IVIG-Resistant Kawasaki Disease
| Parameter | Dose |
|---|---|
| Pulse dose | 20-30 mg/kg/dose IV (max 1000 mg) |
| Duration | 3 days |
| Given with | Aspirin (low-dose 3-5 mg/kg/day at this stage) |
| Alternative | Infliximab 5 mg/kg IV single dose |
Source: Harriet Lane Handbook 23rd ed.
3. Standard Anti-inflammatory (Non-pulse)
| Route | Dose |
|---|---|
| IV/IM (general anti-inflammatory) | 0.5-1.7 mg/kg/day divided q6-12h |
| Oral (general) | 0.5-1 mg/kg/day once daily or divided |
| Asthma (acute) | 1-2 mg/kg/day IV or oral (max 60 mg/day), for 3-10 days |
| Asthma (maintenance) | 0.2-1.6 mg/kg/day orally once daily or on alternate days |
4. Croup (for reference in this age group)
- 1-2 mg/kg IV single dose (AAP recommendation)
Summary Table - Quick Reference
| Indication | Dose | Route | Duration |
|---|---|---|---|
| Pulse (sJIA, lupus, MAS) | 15-30 mg/kg/dose (max 1g) | IV over 30-60 min | Daily x 3 days |
| IVIG-resistant KD | 20-30 mg/kg/dose (max 1g) | IV | Daily x 3 days |
| General anti-inflammatory | 0.5-1.7 mg/kg/day | IV/IM | Divided q6-12h |
| Oral maintenance | 0.5-1 mg/kg/day | PO | Taper as tolerated |
| Acute asthma | 1-2 mg/kg/day | IV or PO | 3-10 days |
Important Safety Points in a Toddler
- Never give IV bolus - always infuse over at least 30 minutes (cardiac arrhythmia risk)
- Monitor glucose - corticosteroids cause hyperglycemia, especially with pulse dosing
- Blood pressure monitoring during infusion
- Do NOT use pulse steroids empirically if infection (especially TB) or lymphoma not yet excluded
- Gastric protection (omeprazole/ranitidine) should be co-prescribed
- For a 2-year-old (~12-13 kg): a pulse dose of 30 mg/kg = ~360-390 mg/dose IV; well within the 1g cap
Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics | Harrison's Principles of Internal Medicine 22E, p. 1631 | Goldman-Cecil Medicine | Harriet Lane Handbook 23rd Edition, p. 251 | Drugs.com Methylprednisolone Dosage Guide
Inj dexa dose per kg
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I now have comprehensive data from the authoritative pediatric reference. Here is the complete answer:
Injection Dexamethasone - Dose Per kg (Pediatric)
Available injection: 4 mg/mL and 10 mg/mL (sodium phosphate) - can be given IV, IM, or PO
Dosing by Indication
| Indication | Dose | Frequency | Max Dose | Notes |
|---|---|---|---|---|
| Anti-inflammatory (general) | 0.08-0.3 mg/kg/24 hr | ÷ Q6-12h | - | IV/IM/PO |
| Croup | 0.6 mg/kg/dose | Single dose (×1) | 16 mg | PO preferred; IV/IM if vomiting |
| Acute Asthma | 0.6 mg/kg/dose | Q24h × 1-2 doses | 16 mg | >2 days increases metabolic adverse effects |
| Cerebral Edema - Loading | 1-2 mg/kg/dose | Single loading dose (×1) | 16 mg/24h | IV/IM |
| Cerebral Edema - Maintenance | 1-2 mg/kg/24 hr | ÷ Q4-6h | 16 mg/24h | Limited data in children |
| Airway Edema / Pre-extubation | 0.5 mg/kg/dose | Q6h × 6 doses | 10 mg/dose | Start 6-12 hr before extubation |
| Bacterial Meningitis (H. influenzae) | 0.15 mg/kg/dose | Q6h × 2-4 days | - | Give 10-20 min before first antibiotic dose |
| Antiemetic (chemo-induced) - Initial | 10 mg/m²/dose | - | 20 mg | IV |
| Antiemetic - Subsequent | 5 mg/m²/dose | Q6h | - | IV |
| Acute Mountain Sickness | 0.15 mg/kg/dose | Q6h | - | PO/IV/IM |
| ITP | 0.6 mg/kg/day | Daily × 4 days | - | Repeat Q4 weeks × 6 cycles |
Quick Reference for a 2-Year-Old (~12 kg)
| Indication | Dose | = Amount at 12 kg |
|---|---|---|
| Anti-inflammatory | 0.08-0.3 mg/kg | ~1-3.6 mg per day |
| Croup / Asthma | 0.6 mg/kg | ~7.2 mg single dose |
| Cerebral edema load | 1-2 mg/kg | ~12-24 mg |
| Meningitis adjunct | 0.15 mg/kg Q6h | ~1.8 mg per dose |
| Pre-extubation | 0.5 mg/kg Q6h × 6 | ~6 mg per dose |
Key Points
- Dexamethasone is ~6-7x more potent than prednisolone (no mineralocorticoid effect)
- Meningitis: Give the first dose 10-20 minutes before the first antibiotic - timing is critical
- Croup: Oral dexamethasone is equally effective as IV/IM - prefer oral to avoid trauma in toddlers; 0.15-0.3 mg/kg may suffice for mild-moderate croup, 0.6 mg/kg for moderate-severe
- Avoid in active untreated infections, fungal/viral/mycobacterial infections
- Monitor blood glucose - dexamethasone causes hyperglycemia
- Benzyl alcohol in some preparations - avoid in neonates
Source: Harriet Lane Handbook 23rd Edition, p. 1102-1103 | Textbook of Family Medicine 9e
Dose of benzyl penicillin for congenital syphilis
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Benzyl Penicillin G - Dose for Congenital Syphilis
The choice of penicillin formulation and dose depends on the clinical scenario and CSF status.
Three Penicillin Options
| Formulation | Route | Use When |
|---|---|---|
| Aqueous crystalline benzyl penicillin G | IV | CSF abnormal, symptomatic, confirmed/probable congenital syphilis |
| Procaine penicillin G | IM | Alternative to IV; no IV access |
| Benzathine penicillin G | IM | CSF normal, asymptomatic, low-risk scenarios |
Scenario-Based Dosing (CDC / WHO Guidelines)
Scenario 1: Confirmed / Probable Congenital Syphilis
(Symptomatic infant, or abnormal CSF, or abnormal evaluation)
Aqueous crystalline benzyl penicillin G (IV) - PREFERRED:
| Age | Dose | Frequency | Duration |
|---|---|---|---|
| First 7 days of life | 50,000 units/kg/dose IV | Every 12 hours (Q12h) | 10 days total |
| After 7 days of life | 50,000 units/kg/dose IV | Every 8 hours (Q8h) | 10 days total |
| Total daily dose | 100,000-150,000 units/kg/day |
OR Procaine penicillin G (IM) - if no IV access:
- 50,000 units/kg/dose IM once daily x 10 days
Scenario 2: Possible Congenital Syphilis
(Normal exam but abnormal labs, or incomplete maternal treatment)
Same as Scenario 1:
- Aqueous benzyl penicillin G: 50,000 units/kg/dose IV Q12h (first 7 days) then Q8h x 10 days
- OR Procaine penicillin G 50,000 units/kg IM once daily x 10 days
- OR Benzathine penicillin G 50,000 units/kg IM single dose (only if full evaluation is normal and follow-up is certain)
Scenario 3: Congenital Syphilis Less Likely
(Normal exam, neonatal titre ≤4x maternal titre, mother adequately treated ≥30 days before delivery)
- Benzathine penicillin G: 50,000 units/kg IM single dose
Scenario 4: Congenital Syphilis Unlikely
(Normal exam, maternal treatment complete, no reinfection)
- No treatment required, but close serologic follow-up
- May consider benzathine penicillin G 50,000 units/kg IM single dose if follow-up uncertain
Older Infants and Children (>1 month)
If diagnosed late (not evaluated at birth):
- Aqueous benzyl penicillin G: 50,000 units/kg/dose IV Q4-6h x 10 days
- Max: up to adult dose
- CSF must be examined first; if abnormal, full 10-day IV course is mandatory
- After completing 10-day IV course, some guidelines recommend benzathine penicillin G 50,000 units/kg IM (max 2.4 million units) as a follow-on single dose
Quick Reference Summary
| Formulation | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Aqueous benzyl penicillin G | 50,000 units/kg/dose | IV | Q12h (<7 days old) / Q8h (>7 days old) | 10 days |
| Procaine penicillin G | 50,000 units/kg/dose | IM | Once daily | 10 days |
| Benzathine penicillin G | 50,000 units/kg/dose | IM | Single dose | Once |
Important Points
- Aqueous IV penicillin G is preferred over IM procaine when IV access is available (WHO/CDC)
- If any part of the evaluation is abnormal or not done, or CSF is bloody/uninterpretable - give the full 10-day IV course; do NOT use single-dose benzathine
- No alternative to penicillin is recommended for congenital syphilis - if allergic, the infant must be desensitized
- Watch for Jarisch-Herxheimer reaction within first 6-8 hours of treatment (fever, rash flare, myalgia) - treat symptomatically with antipyretics
- Follow-up serology at 1, 2, 3, 6, and 12 months after treatment
Sources: Goldman-Cecil Medicine, p. 3226 | CDC STI Treatment Guidelines - Congenital Syphilis | WHO Guidelines for Treatment of Treponema pallidum
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