Given that a number of adverse side effects have been associated with the use of Zonisamide (ZNS), we aimed to investigate risk factors associated with the incidence of renal lithiasis in patients with epilepsy taking ZNS. Sixty patients diagnosed with epilepsy taking ZNS for at least 1 year were included. Risk factors for renal lithiasis were noted, including 1) age; 2) presence of an intellectual or motor disability; 3) treatment duration and dose and plasma levels of ZNS; and 4) use of polytherapy. Of 60 patients taking ZNS, eight patients (13.3%) were diagnosed with renal lithiasis, as determined by abdominal ultrasonography and computed tomography.
A Mann-Whitney U test revealed that patients diagnosed with renal lithiasis had a significantly longer duration of ZNS treatment relatively to patients who did not develop renal lithiasis (p=0.019).
Subjects were divided into two subgroups by dosing period. One group comprised subjects with a dosing period less than X years and the other group comprised subjects with a dosing period more than X years. Statistical analysis by Fisher's exact test showed a high incidence of renal lithiasis in those with a dosing period more X years than in those with a dosing period less than X years in the X=6 years (p=0.019), 10, and 11 years (p=0.024, p=0.018) groups. Additionally odds ratio was highest in the X=10 and 11 years groups.
Renal lithiasis-positive group showed a lower blood concentration of ZNS (10.6 μg/ml) than the renal lithiasis-negative group (17.4 μg/ml). However, the reason for this finding could not be ascertained. In addition, other risk factors of renal lithiasis were not significant.
Based on these findings, the author recommends that the dosing period for treatment with ZNS should be restricted to less than 10 years, and for patients who have received over 10 years of with ZNS, treatment with other anti-epileptic drugs should be considered.
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