what is the treatment of choice for canine ehrlichiosis and how long should doxycycline be continued?

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Doxycycline is the treatment of choice for canine monocytic ehrlichiosis (CME), administered at 10 mg/kg PO once daily for 28 days. 67 Minocycline at 10 mg/kg PO twice daily for 28 days is an effective alternative when doxycycline cannot be used. 1012 The 28-day course is the established standard. A 28-day doxycycline regimen clears Ehrlichia canis DNA from blood in most dogs, with PCR negativity achieved by 3 weeks of treatment in the doxycycline group and by day 28 in the minocycline group. 710 Dogs treated during the acute or subclinical phase become PCR negative as clinical parameters improve; dogs treated during the chronic phase may remain intermittently PCR positive despite completing the full course. 1 If coinfection with Rocky Mountain spotted fever is suspected or confirmed, and chronic E. canis infection is also present, treatment duration may need to extend beyond 28 days. 14 Clinical response to doxycycline is rapid when treatment begins during the acute phase. Dogs typically show marked improvement within 24 to 48 hours of initiating therapy. 4 Thrombocytopenia may persist beyond the end of treatment in some dogs — in one comparison of doxycycline and minocycline, 4 of 5 doxycycline-treated dogs and 2 of 5 minocycline-treated dogs remained thrombocytopenic at day 28, with platelet recovery continuing after treatment completion. 10 Clearance is not guaranteed even after a full 28-day course. Rhipicephalus sanguineus ticks fed on doxycycline-treated dogs can still acquire E. canis by PCR, regardless of when treatment was initiated, indicating that tissue-level persistence may occur even when blood PCR clears. 1 In one evaluation of a 20-day course at 10–11.7 mg/kg once daily, 5 of 6 dogs became PCR positive again by day 56–70, and a second 28-day course was required; 4 of those 5 dogs remained PCR negative for the following 3 months. 7 This underscores the importance of completing the full 28-day course and maintaining concurrent tick control. Rifampin h