My vet has always given me Doxycycline for my dogs when they get the Bulls eye rash, but I also found this:
www.cvm.ncsu.edu/vhc/documents/LymeconsstmtACVIM.pdfLook for this on page 5: "13. What Antibiotics can be Used in the
Treatment of Lyme Disease in Dogs?"
an excerpt: " Most authors and ACVIM diplomates in our survey currently recommend administration of doxycycline at 10 mg/kg
PO q24h for a minimum of 1 month (see Fig 3).
Doxycycline was recommended most frequently because of the possibility of other coinfections (RMSF, anaplasmosis, ehrlichiosis, leptospirosis) that could respond to doxycycline and because it is inexpensive and has anti-inflammatory properties. In humans, the recommended treatment for acute Lyme disease is only 10 days of
doxycycline. However, experimentally infected dogs do
not develop clinical disease during the acute phase, and the infection is likely to be more widespread than in humans that have acute Lyme disease with flulike signs or erythema migrans rash."