Clinical course and radiographic resolution of pneumonia in dogs treated with a shorter versus longer course of antimicrobials: a randomized, double-masked, placebo-controlled study.

Objective: To describe clinical and radiographic outcomes in dogs with uncomplicated pneumonia receiving a shorter (2-week) versus longer (4-week) duration of antimicrobial therapy.

Animals: 30 client-owned dogs with radiographic evidence of pneumonia.

Methods: Dogs were randomly assigned to either a 2-week course of antimicrobials followed by a 2-week course of placebo medication (2-week group) or a 4-week course of antimicrobials (4-week group). All study investigators and owners were masked to the treatment group. Dogs were reevaluated at 12 ± 2 days and again at 28 ± 2 days for a physical examination and thoracic radiography. Standard documentation at visits included owner-reported clinical signs, nurse-acquired history, the clinician's physical examination, the number of affected lung lobe segments, and the global radiographic severity scores assigned. Outcomes investigated included the persistence of clinical and radiographic signs of pneumonia.

Results: 28 dogs (93.3%) experienced complete resolution of clinical signs by the first visit, and no dogs in either group experienced relapse of clinical signs during the study period. Eighteen of 30 dogs (60%) and 25 of 30 dogs (83%) experienced complete resolution of radiographic lesions at the first and second study visits, respectively. The remaining 5 dogs (17%) had either stable (4 dogs) or continued (1 dog) improvement in radiographic lesions.

Clinical relevance: Resolution of clinical and radiographic signs followed similar courses in dogs with uncomplicated pneumonia receiving a 2-week course of antimicrobials compared to a 4-week course. Clinical signs may be more useful for guiding discontinuation of antimicrobial therapy for pneumonia than radiographic signs.