Efficacy of an injectable, sustained-release formulation of moxidectin against patent heartworm (Dirofilaria immitis) infection in dogs. Efficacia della moxidectina in formulazione iniettabile nella profilassi della filariosi cardiopolmonare (Dirofilaria immitis) del cane.

A field study was carried out to evaluate the ability of a single injection of a sustained-release formulation of moxidectin (moxidectin SR) to protect dogs naturally exposed to heartworm (D i r o f i l a r i a i m m i t i s) infection. Ninety seven client dogs of different ages (6-month- 1-year-old), sex and breed were included in the study. Seventy three dogs were subcutaneously injected at 0.17 mg/kg bw (0.05 ml/kg of the microsphere riconstituted suspension) on May 99 to evaluate the tolerability and the efficacy of the treatment during a transmission season. A second injection was done in November 99 to evaluate the ability of the drug to protect dogs after 12 months from the treatment. Parasitological examinations (Knott test for circulating microfilariae and an antigen test) were carried out on Day 0, before the first injection, and after 90 days to confirm that dogs were heartworm free. Further examinations were done on day 180, before the second injection, and on 7 (Day 210), 11 (Day 330) and 20 months (Day 600: 360 days of activity of moxidectin SR plus parasite prepatency) after the second injection. Twenty four dogs, treated once a month for 5 consecutive months during the trial with moxidectin tablet formulation were included in the study as positive controls. To assess the actual infection risk throughout the study, 3 groups of dogs (18, 26 and 27 respectively) referred by their owners as not prophylactically treated against heartworm in the previous transmission season, were examined for the infection in May 99, June 00 and June 01 (negative control group). No side effects were observed in the moxidectin-treated dog. From both moxidectin-treated groups, no dog was positive at parasitological examinations throughout the study period. Negative control dogs showed a percentage of positivity of 44-63%, demonstrating that dogs included in the study were exposed to an actual risk of infection. On the basis of these results, it is possible to conclude that a single subcutaneous injection of moxidectin SR is safe and able to protect dogs against heartworm infection as long as 11-12 months.