Today's Veterinary Practice

JUL-AUG 2012

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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AMERICAN HEARTWORM SOCIETY'S HEARTWORM HOTLINE | UÊ nh>nViminÌÊ ovÊ ÛiÀ- micidal efficacy of ivermectin, if using slow-kill method. AHS Recommen- dation: The American Heartworm Society rec- ommends that, if the slow-kill method is used (only out of necessity), doxycycline should be repeated in 60 days, so the dog receives iver- mectin monthly and doxycycline 1 month on, 2 months off, 1 month on, 2 months off, etc, until the antigen test is negative.8 While there Figure 3. My preferred approach to adulticidal therapy in virtually all (severely affected or not) dogs infected with heartworms includes 3 doses of melarsomine, unless oth- erwise dictated by owner finances. Macrolide prophylaxis is begun at the time of diag- nosis, if not already in use. Note: If microfilaremic, care should be taken to prevent or observe and treat adverse reactions, based on microfilarial numbers and macrolide used. It is imperative to eliminate microfilariae from patients receiving macrolides to reduce the chance of resistance to macrocyclic lactones developing. To view a similar algorithm depicting the American Heartworm Society's therapy recommendations, see the 2012 Guidelines of the American Heartworm Society, Table 3, at heartwormsociety.org. 2% of L3 reaching adulthood. UÊ vÊÌhiÊl>ÀÛ>iÊÀi>VhÊÈxÊ`>ÞÃÊLivoÀiÊ`oÝÞVÞVliniÊiÃÊ initiated, only 52% reach adulthood.7 Therefore, in addition to reducing adverse effects from heartworm death, doxycycline begun on the day of diagnosis will help close the poten- tial seasonal window of continuous infection, which means that, during certain times of year when exposure is continuous (warmest months), the host may have developing larvae of all stages. Doxycycline Dosing Currently the best data we have argues that the dos- age, if tolerated, is 10 mg/kg PO Q 12 H for 30 days, administered prior to adulticidal therapy (Figure 3). vÊÌhiÃÊ`oÃiÊiÃÊnoÌÊÌoliÀ>Ìi`]ÊiÌÊV>nÊLiÊÀi`ÕVi`ÊÌoÊxÊm}É kg PO Q 12 H.7 Author Recommendation: Ê >`ÛoV>ÌiÊ >Ê ÃiVon`Ê month's delay in adulticidal therapy to allow the par- asite to deteriorate maximally and, thereby, further reduce the pulmonary reaction to worm death. Benefits include: UÊ*ÀiÛinÌionÊ ovÊ m>ÌÕÀ>ÌionÊ ovÊ ÀiVinÌlÞÊ >VµÕiÀi`Ê infection (tissue phases) UÊ,i`ÕVi`Ê«Õlmon>ÀÞÊÀi>VÌionÊÌoÊ`Þin}ÊÜoÀmà UÊ oÀiÊ À>«i`Ê >n`Ê Vom«liÌiÊ iÀ>`iV>ÌionÊ ovÊmiVÀo- filariae (potentially reducing risk of heartworm resistance to macrocyclic lactones) are no data that dem- onstrate the efficacy of this approach, there are data that indicate recru- descence of Wolbachia by 300 days postdoxycy- cline.5 nÊÃÕmm>ÀÞ]ÊiÌÊ>««i>ÀÃÊ that doxycycline not only has a role in the management of heart- worm infection, but that this role will continue to grow and be further refined. ■ Figure Credits Figure 2. Courtesy Dr. Laura Kramer Figure 3. Modified from Atkins CE, Miller MW. Is there a bet- ter way to administer heartworm adulticidal therapy? Vet Med 2003; 98:310-317. (References continued on page 20) Clarke Atkins, DVM, Dip- lomate ACVIM (Internal Medicine & Cardiology), is the Jane Lewis Seaks Distinguished Professor of Companion Animal Medicine at North Carolina State University. He is also a member of the Today's Veterinary Practice Edito- rial Peer Review Board and American Heart- worm Society's Executive Board. Dr. Atkins received the 2004 Norden Award for excellence in teaching. His research involves canine and feline heartworm disease and pharmaco- logic therapies for cardiac disease. Dr. Atkins received his DVM from University of California– Davis and completed his internship at Angell Memorial Animal Hospital in Boston, MA. July/August 2012 Today's Veterinary Practice 43 Doxycycline in the Management of Heartworm Disease

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