When to start antibiotics after a tick bite? - briefly
In Lyme‑endemic areas, give a single prophylactic dose of doxycycline within 72 hours after removing a tick that was attached for ≥36 hours. Begin a full antibiotic course promptly if erythema migrans or other Lyme‑associated symptoms appear.
When to start antibiotics after a tick bite? - in detail
A bite from a hard‑bodied tick may transmit Borrelia burgdorferi, the agent of Lyme disease. The decision to begin antimicrobial therapy depends on several measurable factors.
If the tick is identified as an adult or nymph of the Ixodes species, has been attached for at least 36 hours, and the bite occurred in a region where Lyme disease is endemic, a single dose of doxycycline (200 mg for adults, 4 mg/kg for children ≥ 8 years) should be administered within 72 hours of removal. This regimen is endorsed by the CDC as prophylaxis and reduces the risk of infection by approximately 87 %.
When doxycycline is contraindicated (allergy, age < 8 years, pregnancy, or lactation), alternative regimens require a full 5‑day course:
- Amoxicillin 500 mg three times daily (adults) or 50 mg/kg/day divided TID (children).
- Cefuroxime axetil 500 mg twice daily (adults) or 30 mg/kg/day divided BID (children).
These alternatives must be started promptly after tick removal, ideally within 72 hours, but may still be effective if initiated later, provided the bite meets the attachment‑time and endemic‑area criteria.
If the above criteria are not satisfied—short attachment, non‑Ixodes tick, or exposure in a low‑risk area—routine prophylaxis is not recommended. Instead, monitor for early manifestations (erythema migrans, fever, headache, myalgia) for up to 30 days. Should any symptom develop, initiate a full therapeutic course of doxycycline (100 mg BID for 10–21 days) or the appropriate alternative based on patient age and pregnancy status.
Key points for clinicians:
- Confirm tick species and attachment duration.
- Verify geographic risk of Lyme disease.
- Give single‑dose doxycycline within 72 hours when criteria are met.
- Use 5‑day amoxicillin or cefuroxime if doxycycline cannot be used.
- Absent prophylactic indications, observe for signs of infection and treat promptly if they appear.