Fluoroquinolone exposure in utero did not affect articular cartilage of resulting foals.

BACKGROUND Recent studies have shown that fluoroquinolones, specifically, enrofloxacin and its active metabolite (ciprofloxacin), cross the equine placenta without causing gross or histological lesions in the first and third trimester fetuses or resulting foal. However, it is possible that in utero exposure to fluoroquinolones may cause subtle lesions not detectable by standard means; thus, a more in-depth assessment of potential toxicity is warranted. OBJECTIVES To utilise quantitative magnetic resonance imaging (qMRI), biomechanical testing, and chondrocyte gene expression to evaluate the limbs of foals exposed to enrofloxacin during the third trimester of pregnancy. STUDY DESIGN In vivo and control terminal experiment. METHODS Healthy mares at 280d gestation were assigned into three groups: untreated (n=5), recommended therapeutic (7.5 mg/kg enrofloxacin, PO, SID, n=6), or supratherapeutic (15 mg/kg, PO, SID, n=6) doses for 14d. Mares carried and delivered to term and nursed their foals for ~30d. Two additional healthy foals born from untreated mares were treated postnatally with enrofloxacin (10 mg/kg PO, SID, for five days). By 30d, foal stifles, hocks, elbows, and shoulders were radiographed, foals were euthanised, and foal limbs were analysed by quantitative MRI, structural MRI, biomechanical testing and chondrocyte gene expression. RESULTS Osteochondral lesions were detected with both radiography and structural MRI in foals from both enrofloxacin-treated and untreated mares. Severe cartilage erosions, synovitis, and joint capsular thickening were identified in foals treated with enrofloxacin postnatally. Median cartilage T2 relaxation times differed between joints but did not differ between treatment groups. MAIN LIMITATIONS A small sample size was assessed and there was no long-term follow up. CONCLUSION While further research is needed to address long-term foal outcomes, no differences were seen in advanced imaging, biomechanical testing, or gene expression by 30d of age, suggesting that enrofloxacin may be a safe and useful antibiotic for select bacterial infections in pregnant mares.