The effects of body weight and combination drug therapy on the serum concentrations of zonisamide in 94 epileptic dogs: An epidemiological analysis

To clarify the effects of background factors such as body weight, combination drug therapy with phenobarbital (PB) and potassium bromide (KBr), age, gender, neuter status, and blood collection time on the serum concentrations of zonisamide (ZNS) in 94 epileptic dogs, serum ZNS concentrations of 141 samples from 94 epileptic dogs were measured by high-performance liquid chromatography with UV detection. Serum ZNS concentrations were divided by the dosage of ZNS, to obtain normalized ZNS concentrations. Multiple linear regression analysis revealed that body weight and combination therapies with KBr, PB, and KBr + PB affected the normalized ZNS concentrations, and normalized ZNS concentrations were positively correlated with body weight. The normalized ZNS concentrations in dogs with PB combination therapy were lower when compared with those concentrations in dogs receiving ZNS alone, but were higher in dogs receiving KBr combination therapy. These results suggest that serum ZNS concentrations are influenced by body weight and combination drug therapies using KBr, PB, and KBr + PB. This information of ZNS characteristics may be useful in determining the initial and modified doses of ZNS in the therapy of epileptic dogs. and half-life of ZNS. However, such factors have not been evaluated so far in epileptic dogs. The present study quantitatively examined whether body weight and PB and/ or KBr combination drug therapies altered ZNS concentrations by using an epidemiological method.