Effect of antiepileptic drug monotherapy on urinary pH in children and young adults

Sulthiame impairs mitochondrial function in vitro and may trigger onset of visual loss in Leber hereditary optic neuropathy

Background

Leber hereditary optic neuropathy (LHON) is the most common mitochondrial disorder and characterized by acute or subacute painless visual loss. Environmental factors reported to trigger visual loss in LHON mutation carriers include smoking, heavy intake of alcohol, raised intraocular pressure, and some drugs, including several carbonic anhydrase inhibitors. The antiepileptic drug sulthiame (STM) is effective especially in focal seizures, particularly in benign epilepsy of childhood with centrotemporal spikes, and widely used in pediatric epileptology. STM is a sulfonamide derivate and an inhibitor of mammalian carbonic anhydrase isoforms I–XIV.

Results

We describe two unrelated patients, an 8-year-old girl and an 11-year-old boy, with cryptogenic focal epilepsy, who suffered binocular (subject #1) or monocular (subject #2) visual loss in close temporal connection with starting antiepileptic pharmacotherapy with STM. In both subjects, visual loss was due to LHON. We used real-time respirometry in fibroblasts derived from LHON patients carrying the same mitochondrial mutations as our two subjects to investigate the effect of STM on oxidative phosphorylation. Oxygen consumption rate in fibroblasts from a healthy control was not impaired by STM compared with a vehicle control. In contrast, fibroblasts carrying the m.14484T>C or the m.3460G>A LHON mutation displayed a drastic reduction of the respiration rate when treated with STM compared to vehicle control.

Conclusions

Our observations point to a causal relationship between STM treatment and onset or worsening of visual failure in two subjects with LHON rather than pure coincidence. We conclude that antiepileptic medication with STM may pose a risk for visual loss in LHON mutation carriers and should be avoided in these patients.

Stability-Indicating High-Performance Liquid Chromatography Assay for the Determination of Sulthiame in Pharmaceutical Dosage Forms

A stability-indicating assay by reversed-phase high performance liquid chromatography method was developed and validated for the determination of sulthiame (STM). The chromatographic separation was achieved on a reversed-phase NovaPack C18 column and an isocratic mobile phase consisting of deionized water:methanol (70:30, v/v). The flow rate was 1.0 mL/min (ultraviolet detection at 210 nm). The STM was separated within 2.83 min. The linearity of the method was demonstrated in the range of 20.0–200.0 μg/mL and a coefficient of determination of r² = 0.9999. The limits of detection and quantification were 4.2 and 9.5 μg/mL, respectively. The intraday and interday precisions were less than 1%. Accuracy of the method ranged from 98.3% to 101.7%, with a relative standard deviation of <1%. STM was degraded by accelerated breakdown in alkaline, acidic, or oxidative stress conditions. This method allows accurate and reliable determination of STM for drug stability assay in pharmaceutical studies.

Zonisamide Induces Crystalluria without Urinary pH Changes in Children and Young Adults

Purpose. Adjunctive zonisamide therapy was demonstrated to be beneficial for multiple-disabled patients with refractory childhood-onset epilepsy. Zonisamide is well tolerated, but urolithiasis and calcium sludge in the bladder were sometimes described in patients treated with antiepileptic drug polytherapy including zonisamide. In previous studies, alkaline urine and crystalluria were shown to be risk factors for urolithiasis. Therefore, the effects of zonisamide addition and withdrawal on the urinary pH and crystalluria were investigated in patients treated with antiepileptic drug polytherapy to clarify the cause of urolithiasis induced by zonisamide. Methods. The urinary pH and the degree of crystalluria were retrospectively studied in epilepsy patients one month after the addition or withdrawal of zonisamide as part of their antiepileptic drug treatment regimen over the previous three years. Results. A total of 27 zonisamide-on patients and 16 zonisamide-off patients were enrolled in the study. The urinary pH did not change after the addition or withdrawal of zonisamide. However, the degree of crystalluria significantly increased after the addition (P < 0.001) of zonisamide and decreased after its withdrawal (P < 0.01). Conclusions. Zonisamide induces crystalluria without alkalinization of the urine. Crystalluria should be carefully monitored in patients treated with zonisamide to prevent urolithiasis.

Effect of antiepileptic drug polytherapy on urinary pH in children and young adults

OBJECTS

The relationship between antiepileptic drugs (AEDs) polytherapy and urinary pH was studied to demonstrate the effect and difference of AED polytherapy compared to monotherapy.

MATERIALS AND METHODS

A total of 271 urine samples from patients receiving AED polytherapy aged from 7 months to 35 years were enrolled. Two AEDs were co-administered to 215 patients, three AEDs to 45 patients, four AEDs to ten patients, and five AEDs to one patient.

RESULTS

The distribution of urinary pH shifted to the alkaline range with increasing numbers of co-administered AEDs (p < 0.0001). The distribution of urinary pH shifted to the alkaline side with AED polytherapy that included valproate (p < 0.05) or acetazolamide (p < 0.03). The distribution of urinary pH did not change with or without zonisamide, carbamazepine, phenobarbital, phenytoin, or clonazepam.

CONCLUSIONS

Urinary pH should be monitored in patients receiving AED polytherapy, particularly those receiving valproate, acetazolamide, or various AEDs in combination.