Sub-Antimicrobial Dosage Scheme of Doxycycline for the Chronic Treatment of Bronchiectasis in a Dog

Abstract

A 9-month-old German shepherd dog was examined because of a chronic cough, exercise intolerance and labored breathing, as well as recurrent episodes of lethargy with anorexia. Multifocal severe bronchiectasis and neutrophilic bronchitis was found with thoracic computed tomography and cytology of bronchoalveolar lavage fluid, respectively. While oral azithromycin was administered, clinical signs were absent. However, stopping azithromycin lead repeatedly to presumed bacterial pneumonia within 1-2 months. With sub-antimicrobial dosed oral doxycycline (initially 1.5 mg/kg once daily for 3 months, then 0.7-0.5 mg/kg once daily for 6 months), the dog remained free from clinical signs. Bronchiectasis is characterized by marked irreversible bronchial dilation. Accumulation of intraluminal mucopurulent material and neutrophilic inflammation cause chronic cough and recurrent bacterial pneumonia. For therapy, life-long oral antibiotics are recommended. Chronic antibiotic administration, however, can select resistant bacterial strains. Though both azithromycin and doxycycline possess anti-inflammatory effects, doxycycline has these off-target properties at a sub-antimicrobial dose. In this report, a chronic sub-antimicrobial dose of doxycycline resulted in the resolution of chronic cough, exercise intolerance and labored breathing, and prevented recurrence of suspected bacterial pneumonia in the long-term in a dog with severe bronchiectasis. Beneficial effect of doxycycline is probably related to its anti-inflammatory effects rather than its antimicrobial properties.

Keywords: antibiotics; bacterial pneumonia; matrix metalloproteinase; prevention.

Figure 1

Computed tomographic scan of a 9-month-old German shepherd dog with multifocal bronchiectasis of unknown origin. Left of the animal is on the left side of the image. (A) Severe dilation of the lobal bronchus in the center of the left caudal lung lobe can be appreciated. The right caudal lung lobe has a larger volume compared to that of the left one and has normal tapering bronchi to the periphery. (B) Severe saccular dilation and lack of tapering to the periphery of the lobal bronchus of the right cranial lung lobe can be appreciated.

Figure 1

Computed tomographic scan of a 9-month-old German shepherd dog with multifocal bronchiectasis of unknown origin. Left of the animal is on the left side of the image. (A) Severe dilation of the lobal bronchus in the center of the left caudal lung lobe can be appreciated. The right caudal lung lobe has a larger volume compared to that of the left one and has normal tapering bronchi to the periphery. (B) Severe saccular dilation and lack of tapering to the periphery of the lobal bronchus of the right cranial lung lobe can be appreciated.