What is the dose of doxycycline (doxy) after a tick bite?

From the Guidelines

The recommended dose of doxycycline for prevention of Lyme disease after a tick bite is a single 200 mg dose for adults and 4.4 mg/kg (up to a maximum dose of 200 mg) for children, taken orally within 72 hours of tick removal. This is based on the 2021 clinical practice guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR) 1. The guidelines recommend this single dose of oral doxycycline for high-risk Ixodes spp. bites in all age groups, over observation, as a strong recommendation with moderate-quality evidence.

• Key considerations for this preventive treatment include:
  • The attached tick must be identified as an Ixodes (deer) tick
  • The tick was likely attached for at least 36 hours
  • The individual is in an area where Lyme disease is common
  • The medication can be started within 72 hours of tick removal
• It is essential to note that doxycycline should be taken with a full glass of water and can be taken with food if it causes stomach upset, as noted in the guidelines 1.
• Potential side effects may include nausea, sun sensitivity, and rarely, allergic reactions, but the benefits of preventing Lyme disease outweigh these risks in high-risk cases, as supported by the guidelines 1.
• However, doxycycline is not recommended for pregnant women or children under 8 years old due to potential effects on bone development and tooth discoloration, highlighting the need for careful consideration of the patient's demographics and medical history before administering the medication.

From the Research

Dose of Doxycycline after Tick Bite

• The recommended dose of doxycycline after a tick bite to prevent Lyme disease is 200mg, as stated in studies 2, 3, 4.
• This dose has been shown to be effective in preventing Lyme disease, with a relative risk reduction of 67% (95% CI 31 - 84%) in one study 2.
• The efficacy of doxycycline in preventing Lyme disease is thought to be due to its ability to prevent the transmission of Borrelia burgdorferi, the causative agent of Lyme disease, from the tick to the human host 5.
• It is recommended that doxycycline be administered within 72 hours of tick removal, as the efficacy of the treatment decreases with time 5.
• Other antibiotics, such as amoxicillin and azithromycin, may also be effective in preventing Lyme disease, but more research is needed to confirm their efficacy 3, 6.

Timing of Doxycycline Administration

• The timing of doxycycline administration is critical, as the efficacy of the treatment decreases with time 5.
• One study found that doxycycline was most effective when administered within 24 hours of tick removal, with a 74% protection rate in mice 5.
• When treatment was delayed until 24 hours after tick removal, the protection rate decreased to 47%, and prophylactic treatment was totally ineffective when delivered ≥2 days after tick removal 5.

Pharmacodynamics of Doxycycline

• The pharmacodynamic parameters of doxycycline for the prevention of Lyme disease are not fully understood, but it is thought that the area under the time-concentration of free antibiotic curve divided by the minimum inhibitory concentration (fAUC/MIC) is an important factor in determining efficacy 6.
• One study found a direct correlation between efficacy rate and fAUC/MIC, but not the maximum concentration of free drug in serum divided by the MIC (fC(max)/MIC) or the time that the free drug concentration remains above the MIC (fT>MIC) 6.