Drug treatment of leishmaniasis in dogs is a challenge for veterinary practitioners. Because of its complex pathogenesis, leishmaniasis may manifest with various clinical signs, ranging from mild and non-specific to those reflecting severe involvement of several organs. The immune response plays an important role in the development, outcome and response to treatment of Leishmania infection in dogs. All known anti-Leishmania drugs used in dogs can lead to temporary or permanent remission of clinical signs, but usually none are sufficient to eliminate the infection.

In dogs, the objectives of anti-Leishmania treatment are typically to induce a general reduction of the parasite load, to treat organ damage caused by the parasite, to restore efficient immune responses, to stabilise a drug-induced clinical improvement and to treat clinical relapse.

Therapeutic options and choice of drug regimens for dogs with leishmaniasis should be considered in light of the different clinical forms of the disease. As described in the previous presentation (Leishmaniasis: Diagnostic Criteria), dogs can be classified into four clinical stages of leishmaniasis: A, exposed dogs; B, infected dogs; C, sick dogs (dogs with patent leishmaniasis); and D, severely sick dogs. However, for therapeutic purposes, an additional stage E is suggested, which includes dogs unresponsive to recommended treatment (stage E-a) or dogs that have a relapse of clinical disease soon after completion of recommended treatment (stage E-b).

The most widely used treatment protocol for dogs with leishmaniasis is the combination of meglumine antimoniate and allopurinol. This combination may be administered to all dogs in stage B, C or D, with meglumine antimoniate given at 100 mg/kg, s.c., once a day for 4 weeks and allopurinol at 10 mg/kg, orally, every 12 hours for at least 6 months. The dosage of meglumine antimoniate can be divided in to two equal doses of 50 mg/kg (q12h) or administered for a period ranging from 4 to 8 weeks. In most dogs in stages B and C, this protocol, if correctly applied, should result in a clinical cure that is stable for more than 1 year. Adverse effects have been reported with either drug of the combination. In addition, the protocol should result in a considerable decrease in parasite load for several months, which is necessary for reducing transmission of the parasite to sand flies.

For dogs in stage D with a severe clinical form of the disease, the aforementioned treatment protocol should yield a good chance of improvement but may not result in a clinical cure. In stage D dogs, particularly if renal insufficiency is present, the need for ancillary treatments and the prognosis depend on pre-existing clinical conditions.

Unresponsiveness to a previous course of recommended treatment (stage E-a), occurrence of relapse soon after treatment (stage E-b), development of severe adverse effects, poor owner compliance with drug administration (problems in the application or cost), veterinary clinician preferences and non-governmental approval or availability of drugs in a given country could be reasons for choosing a treatment protocol other than meglumine antimoniate-allopurinol.

Choice of an alternative anti-Leishmania drug or drug combination should be based on the following criteria:

 Anti-Leishmania efficacy as established via clinical trials

 Few potential adverse effects

 Owner compliance with administration

The few alternative regimens that fulfill the aforementioned requirements include miltefosine given for 28 days (2 mg/kg, orally q24h) administered in combination with allopurinol, for at least 6 months (10 mg/kg, orally, q12h); or allopurinol, administered alone for at least 6 months.