I assume this effect is dependent on the duration the drug is used but--suggest you print this report and give to your doc. When faced with any med side effect profile, the issue is always balancing benefits/negatives.
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Profound Hypocitraturia Follows Topiramate Therapy

NEW YORK  Aug 22 - Topiramate therapy can induce profound declines in urinary citrate levels, which may lead to urinary stones, according to a report in the July issue of Urology.

Several case reports in the last decade have highlighted topiramate-associated urolithiasis, the authors explain, but prospective investigation of the phenomenon has been limited.

Dr. Brad W. Warner and colleagues from the University of Kentucky, Lexington, assessed changes in urinary citrate levels in four patients scheduled to begin topiramate therapy.

Mean urinary citrate levels declined by 65% after a 50-mg dose and by 52.9% after a 75-mg dose of topiramate, the authors report. In the two patients taking 100 mg of topiramate, urinary citrate levels declined by 74% and 62% from baseline.

"The average final citrate level was 215.5 mg/day, well below the 320 mg/day generally accepted as defining hypocitraturia," the investigators point out.

Urine volume and urine creatinine levels did not change significantly with rising doses of topiramate, the report indicates, and there were no significant changes in urinary calcium or urinary pH.

After a mean follow-up of 11.4 months, two of the four patients had developed symptomatic urolithiasis, the researchers note.

"These findings provide a basis for possible increased stone risk in patients taking topiramate," the authors conclude. "Citrate replacement therapy may be considered in these patients, but the efficacy of this therapy in the topiramate population is unknown."

"Prescribing physicians need to be made aware of the potential risk of stone formation in patients treated with topiramate," writes Dr. Margaret S. Pearle from University of Texas Southwestern Medical Center, Dallas, in a related editorial.

More studies with longer follow-up and serial imaging will be needed to establish the incidence of stone formation in topiramate-treated patients.

Urology 2008;72:29-33. [Medscape, 9/1/08]