Background: Zonisamide(ZNS) is commonly used to treat idiopathic epilepsy in dogs. While acid-base imbalances are well-known side effects of ZNS in humans, little is known about such alterations in dogs.
Objectives: Evaluate and characterize the occurrence of acid-base imbalances in epileptic dogs treated with ZNS and test for correlations with ZNS blood level.
Animals: Fourteen client-owned dogs with confirmed or suspected idiopathic epilepsy receiving ZNS at standard doses. Methods: Prospective longitudinal study. Acid-base parameters, including bicarbonates, PCO2, base excess(BE), chloremia, anion gap, urinary and blood pH, were compared at baseline(T0), 1-2weeks(T1), and 10-14weeks(T2) post-ZNS initiation. ZNS serum level was measured at T1 and/or T2. Metabolic acidosis (MA) criteria were bicarbonates <20mmol/L or BE<-4mmol/L. Data were assessed for normality using a Shapiro-Wilk test and variables were compared using a paired t-test or a Wilcoxon signed-rank test. Spearman rank correlation was used to evaluate correlations between ZNS level and other variables. A p-value <0.05 was considered significant.
Results: All dogs developed MA after treatment initiation. Bicarbonates (mean T0: 22.4mmol/L vs T1: 17.6mmol/L, p<0,0001 and T2: 17.6mmol/L, p<0.0001) and BE (mean T0: -1.5mmol/L vs T1: -6.4mmol/L, p<0.0001 and T2: -6.2mmol/L, p=0.0002) were significantly decreased whereas chloremia (median T0: 116.5mmol/L vs T1: 120mmol/L, p=0.013 and T2: 119mmol/L, p=0.026) increased at T1 and T2 compared to T0. No symptoms of MA other than transiently decreased appetite in 4 dogs were reported. ZNS level was not correlated with any acid-base parameters.
Conclusions and clinical importance: ZNS administration in dogs is associated with the development of MA.
