Background: Nebulized 4% preservative-free lidocaine has been previously shown to reduce airway inflammation in Equine Asthma (Mahalingam-Dhingra 2022). However, 2% multi-use vial, preservative-containing lidocaine is more accessible, less expensive and would increase client compliance. Hypothesis/
Objectives: Methyl paraben, the preservative in multiuse vials, may increase morbidity in children with asthma. Therefore, this study aimed to establish multi-dose safety of 2% preserved lidocaine in horses.Animals: Fourteen clinically healthy, non-asthmatic horses.
Methods: A prospective, randomized, controlled, blinded 2-way crossover study was performed to compare nebulization of 1mg/kg 2% preservative-containing lidocaine via Flexineb twice daily over 4 days, to saline control and no treatment. Clinical parameters, chemokine, cytokine and bronchoalveolar lavage (BAL) cytology, as well as 16S-amplicon sequencing of nasal and tracheal microbiota, before and after each intervention were compared between treatment groups, using paired and related samples analyses, based on data normality (P< 0.05).
Results: Neither saline nor 2% preservative-containing lidocaine nebulization induced evidence of airway inflammation based on BAL cytology, chemokine and cytokine concentrations in epithelial lining fluid, or changes in clinical scoring. A mean 5.9% decrease in BAL fluid neutrophil percentage was noted over time without intervention (control). When comparing intervention effects on BAL cytology, only saline nebulization (compared to control) was associated with a statistically (but not clinically) significant difference in percent neutrophil change (7.7%). Treatment did not impact the operational taxonomic units (OTU) profile of respiratory microbiota.
Conclusions: No differences in outcomes were found in healthy horses nebulized multi-use vial, 2% methyl paraben-containing lidocaine versus saline.
