Lyme disease
INESSS adult and child guides, March 2021. Serology: INESSS diagnostic aid, May 2025. Tick-bite prophylaxis: INESSS decision aid opens in a new tab
Diagnose
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Workup | Exposure risk, full exam with neurologic exam, other diagnoses INESSS adult guide, p. 2 opens in a new tabINESSS diagnostic aid, p. 2 opens in a new tab |
| Typical erythema migrans | Round or oval redness, at least 5 cm, lasting at least 48 h
Usually 3–30 days after infection, up to 3 months after the bite. INESSS diagnostic aid, p. 2 opens in a new tabINESSS adult guide, p. 1 opens in a new tab |
| Disseminated stages | Multiple EM, neurologic, cardiac or joint involvement |
| Suspected neurologic, cardiac or joint Lyme | Involve a specialist for the assessment and the first-line antibiotic choice Carditis: serial ECGs with oral treatment, cardiac monitoring with IV treatment. |
| EM or cellulitis? | Unsure: treat to cover bothAdults: e.g. Cefuroxime axetil. Children: Amoxicillin-clavulanate.
See Cellulitis INESSS adult guide, p. 3 opens in a new tabINESSS child guide, p. 3 opens in a new tab |
Investigate
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Typical isolated EM | No serology
Make the diagnosis, report it (MADO), treat. INESSS diagnostic aid, p. 2 opens in a new tabINESSS adult guide, p. 3 opens in a new tab |
| Atypical single skin lesion, no other signs | No serologyUnder 5 cm: watch 24–48 h for expansion, mark the border and take a photo. 5 cm or more, or no expansion: discuss with a specialist or experienced colleague. |
| Order serology | Atypical lesion with other early disseminated signs, multiple lesions, cardiac, neurologic or joint involvement |
| Reading two-tier results | Positive IgG with suggestive findings supports the diagnosis Negative with suggestive findings: does not exclude Lyme. Skin, heart or nerve findings: serological test 4–6 weeks later, if indicated. |
| After treatment | No serology to judge response;antibodies persist. Judge response clinically. INESSS diagnostic aid, p. 1, 10 opens in a new tabINESSS adult guide, p. 6 opens in a new tab |
Treat
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Pregnancy | Doxycycline is contraindicated Breastfeeding: may be first line for skin, neurologic or cardiac disease after an informed discussion. |
| Penicillin label | Assess allergy status before choosing another class than a different cephalosporin INESSS adult guide, p. 5, 7 opens in a new tabINESSS child guide, p. 6–7 opens in a new tab |
| Lyme arthritis | Avoid corticosteroids during antibiotics An NSAID may be used for pain. |
| Expected course | Full recovery is the rule, especially when EM is treated earlyReturn if not better, or symptoms recur, at the end of treatment.
Patient watches symptoms with the INESSS follow-up sheet opens in a new tab INESSS adult guide, p. 6 opens in a new tabINESSS child guide, p. 6 opens in a new tab |
| Refer | New neurologic, cardiac or joint signs during treatment, or treatment failure |
| Drug | Dose | Duration |
|---|---|---|
| Isolated EM, no systemic symptoms | ||
| Doxycycline | 100 mg PO BID | 10 days (10–14) |
| Isolated EM with systemic symptoms, or multiple EM | ||
| Doxycycline | 100 mg PO BID | 14 days (14–21) |
| Other options, all skin presentations | ||
| Amoxicillin | 500 mg PO TID | 14 days (14–21) |
| Cefuroxime axetil | 500 mg PO BID | 14 days (14–21) |
| Isolated EM, neither Doxycycline nor a beta-lactam possible | ||
| Azithromycin, not with a heart malformation (QT) | 500 mg PO DIE | 7–10 days |
| Clarithromycin | 500 mg PO BID | 14–21 days |
| Drug | Dose | Duration |
|---|---|---|
| Peripheral nervous system, or 1st-degree AV block with PR < 300 ms | ||
| Doxycycline | 100 mg PO BID | 14 days (14–21) |
| Amoxicillin (other option) | 500 mg PO TID | 14 days (14–21) |
| Cefuroxime axetil (other option) | 500 mg PO BID | 14 days (14–21) |
| Lyme arthritis, first episode or recurrence | ||
| Doxycycline | 100 mg PO BID | 28 days |
| Amoxicillin (other option) | 500 mg PO TID | 28 days |
| Cefuroxime axetil (other option) | 500 mg PO BID | 28 days |
| Specialist-led: CNS or meningitis, PR > 300 ms or high-grade AV block, myocarditis or pericarditis, recurrent arthritis | ||
| Ceftriaxone | 2000 mg IV DIE | CNS: 14 days (10–28) Cardiac: 14 days (14–21) Recurrent arthritis: 14–28 days |
| Cefotaxime (other option) | 2000 mg IV TID | Same as Ceftriaxone |
| Penicillin G (other option) | 18–24 million units IV, divided q4h | Same as Ceftriaxone |
Children
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Doxycycline under 8 | Prescribe only after an informed discussion with the parent or legal guardian No commercial pediatric form; a pharmacy can compound a suspension. |
| Not printed here | See the child guide opens in a new tab for neurologic, cardiac, joint and IV doses (pp. 4–5).Under 8, arthritis starts with Amoxicillin or Cefuroxime axetil. French edition opens in a new tab |
| Drug | Dose | Duration |
|---|---|---|
| All skin presentations | ||
| Doxycycline | 4.4 mg/kg/day PO divided BID (max 100 mg/dose) | Isolated EM, no systemic symptoms: 10 days (10–14) Otherwise: 14 days (14–21) |
| Amoxicillin (other option) | 50 mg/kg/day PO divided TID (max 500 mg/dose) | 14 days (14–21) |
| Cefuroxime axetil (other option) | 30 mg/kg/day PO divided BID (max 500 mg/dose) | 14 days (14–21) |
| Isolated EM, neither Doxycycline nor a beta-lactam possible | ||
| Azithromycin, not with a heart malformation (QT) | 10 mg/kg/day PO (max 500 mg/day) | 7–10 days |
| Clarithromycin | 15 mg/kg/day PO divided BID (max 500 mg/dose) | 14–21 days |
Reviewed 18 October 2026 against the official sources below.
Sources
Blue square: Québec. The code names the body; each section's key gives its full name.