Clinical benefits of incorporating doxycycline into a canine heartworm treatment protocol

Elizabeth S Myrick,C Thomas Nelson,Thomas A Nelson

doi:10.1186/s13071-017-2446-4

Abstract

BackgroundThe objective of heartworm treatment is to improve the clinical condition of the patient and to eliminate pre-cardiac, juvenile, and adult worm stages with minimal complications. Pulmonary thromboembolisms are an inevitable consequence of worm death and can result in severe pulmonary reactions and even death of the patient. To minimize these reactions, various treatment protocols involving melarsomine, the only adulticidal drug approved by the US Food and Drug Administrations (FDA), in conjunction with macrocyclic lactone heartworm preventives and glucocorticosteroids have been advocated. The discovery of the bacterial endosymbiont Wolbachia in Dirofilaria immitis has led to several experimental studies examining the effects of administering doxycycline to reduce or eliminate Wolbachia organism. These studies have shown a decrease in gross and microscopic pathology of pulmonary parenchyma in experimental heartworm infections pretreated with doxycycline before melarsomine administration.MethodsElectronic medical records from a large veterinary practice in northeast Alabama were searched to identify dogs treated for heartworms with melarsomine from January 2005 through December 2012. The search was refined further to select for dogs that met the following criteria: 1) received two or three doses of ivermectin heartworm preventive prior to melarsomine injections, 2) received one injection of melarsomine followed by two injections 4 to 8 weeks later, and 3) were treated with prednisone following melarsomine injections. The dogs were then divided into those that also were treated with doxycycline 10 mg/kg BID for 4 weeks (Group A, n = 47) and those that did not receive doxycycline (Group B, n = 47). The medical notes of all 94 cases were then reviewed for comments concerning coughing, dyspnea, or hemoptysis in the history, physical exam template, or from telephone conversations with clients the week following each visit. Any dog that died within one year of treatment from either cardiovascular or pulmonary problems was noted.ResultsDogs from Group A receiving doxycycline had fewer respiratory complications (6.52%) and heartworm disease-related deaths (0%) than Group B (19.14% and 4.25%, respectively).ConclusionsAlthough there are not enough cases to indicate statistical significance, the results strongly suggest that including doxycycline into canine heartworm treatment protocols decreases post-treatment complications and mortality in naturally infected clinical cases.

Highlights

The objective of heartworm treatment is to improve the clinical condition of the patient and to eliminate pre-cardiac, juvenile, and adult worm stages with minimal complications
The guidelines discuss that two injections of melarsomine kill 90% of the adult worms, the threeinjection protocol kills 98% of the adult worms [4], and prednisone is the treatment of choice for the inflammation associated with pulmonary thromboembolisms [5, 6]
The discovery of the bacterial endosymbiont Wolbachia in Dirofilaria immitis [7] and evidence that this organism plays a role in the pathogenesis of heartworm disease [8,9,10,11] has led to several experimental studies examining the effects of administering doxycycline to reduce or eliminate the Wolbachia organism from D. immitis. These studies have shown a decrease in gross and microscopic pathology of pulmonary parenchyma in experimental heartworm infections pretreated with doxycycline before melarsomine administration [12, 13]

Summary

Introduction

The objective of heartworm treatment is to improve the clinical condition of the patient and to eliminate pre-cardiac, juvenile, and adult worm stages with minimal complications. The discovery of the bacterial endosymbiont Wolbachia in Dirofilaria immitis has led to several experimental studies examining the effects of administering doxycycline to reduce or eliminate Wolbachia organism These studies have shown a decrease in gross and microscopic pathology of pulmonary parenchyma in experimental heartworm infections pretreated with doxycycline before melarsomine administration. The discovery of the bacterial endosymbiont Wolbachia in Dirofilaria immitis [7] and evidence that this organism plays a role in the pathogenesis of heartworm disease [8,9,10,11] has led to several experimental studies examining the effects of administering doxycycline to reduce or eliminate the Wolbachia organism from D. immitis These studies have shown a decrease in gross and microscopic pathology of pulmonary parenchyma in experimental heartworm infections pretreated with doxycycline before melarsomine administration [12, 13]. Dogs treated with doxycycline and ivermectin prior to receiving melarsomine had less severe arterial lesions and virtual absence of thrombi [13]

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Conclusion