Efficacy of treatment and survival rate of foals with pneumonia: Retrospective comparison of rifampin/azithromycin and rifampin/tulathromycin

Abstract

Rhodococcus equi (R. equi), a Gram-positive facultative intracellular pathogen is one of the most common causes of pneumonia in foals. The retrospective study compares the efficacy of rifampin/azithromycin versus rifampin/tulathromycin for the treatment of R. equi pneumonia in foals. Weekly medical data of foals born in the seasons 2012 to 2016 (i.e. five foaling seasons) that developed pneumonia were collected and analysed. Foals 21 days of age or older with a pulmonary consolidation of more than 1 cm (abscess score ≥ 1 cm) were enrolled for participation in the study. All foals meeting the criteria for inclusion were listed in a spreadsheet and 330 foals affected with pneumonia each year were randomly selected by an online research randomizer. Foals with incorrect or missing data and those that were included in previous treatment studies were excluded from the analysis, resulting in a total enrolment of 1544 foals with pneumonia. The farm established a screening program in 2003 in order to detect foals in the early course of pneumonia, so all foals were examined once weekly starting at the age of two weeks until four and a half months of age. A physical examination of the respiratory tract, body temperature, haematology and an ultrasonographic examination of the lungs were included. Sonography areas with visible consolidation were measured and added to calculate an "abscess score" which represents the extent of pulmonary damage. Weekly medical data were analysed retrospectively. The risk of therapy failure, which means either death or worsening of pneumonia requiring that the foal be switched to another therapy, showed in a univariate comparison of the two treatments, that there was a higher incidence of treatment failure in foals treated with RIF/AZM (32/353, 9.1 %) than in foals that were treated with RIF/TUL (19/406, 4.7 %; Pearson's χ 2 , P = 0.016). In a Kaplan-Meier analysis, there was also a significant difference between the two treatments with respect to their survival functions (Log-rank test, P = 0.045; Figure 1). The incidence of mortality due to R. equi pneumonia was higher in foals that were treated with RIF/AZM (8/353, 2.3 %) than in those that were treated with RIF/TUL (0/406, 0.0 %; Fisher's exact test, P = 0.002). After adjusting for year, age of foals at the beginning of treatment, and abscess score at the beginning of treatment, the risk of treatment failure was not significantly lower for foals that were treated with RIF/TUL compared to those that were treated with RIF/AZM [Hazard Ratio (95 % CI) = 0.75 (0.38, 1.5)]. Age of foals was negatively associated with treatment failure, with the risk of failure decreasing by 30 % for every one-month increase in age at the beginning of treatment [HR (95 % CI) = 0.70 (0.54, 0.91)]. Abscess score was positively associated with treatment failure, with the risk of failure increasing by 4 % for every one cm increase in score [HR (95 % CI) = 1.04 (1.01, 1.07)]. Year was also associated with the risk of treatment failure but it did not meet the proportiona...

Investigation of the relationship between pulmonary lesions based on lung ultrasound and respiratory clinical signs in foals with suspected pulmonary rhodococcosis

“…The occurrence of multiple B-lines and other pleural lesions decreased with the resolution of clinical signs, while lung abscesses persisted beyond the first 4 months of life in approximately one-fourth of all foals examined in the study. Our results are in line with previous studies reporting similar routine monitoring of foals for R. equi infection 5,7,8,27 .…”

Rhodococcus equifoal pneumonia: Update on epidemiology, immunity, treatment and prevention

“…Tulathromycin was not more effective than placebo in a study, 38 but was superior to placebo—albeit less effective than the combination of azithromycin‐rifampin—for treating foals with pneumonia in another study 36 . Tulathromycin in combination with rifampin was associated with fewer treatment failures (defined as death or worsening disease requiring a change to another antimicrobial) than the combination of azithromycin and rifampin 126 . Administration of gamithromycin IM once a week maintains BAL cell concentrations above the MIC against R. equi for 7 days 127 and was noted to be non‐inferior to azithromycin‐rifampin for the treatment of mild to moderate bronchopneumonia in foals 114 .…”

“…36 Tulathromycin in combination with rifampin was associated with fewer treatment failures (defined as death or worsening disease requiring a change to another antimicrobial) than the combination of azithromycin and rifampin. 126 Administration of gamithromycin IM once a week maintains BAL cell concentrations above the MIC against R. equi for 7 days 127 and was noted to be non-inferior to azithromycin-rifampin for the treatment of mild to moderate bronchopneumonia in foals. 114 However, side effects were seen in 58% of the foals; 45% of which showed mild to moderate pain and 35% showed moderate to severe lameness that resolved over a 72-h period.…”