Effect of carbamazepine on urinary volume and osmolality, water clearance, and serum osmolality in patients with primary enuresis.

OBJECTIVE

In this study we investigate the effects of carbamazepine (CBZ) on urinary volume, frequency of micturition, serum and urine osmolality, osmotic and creatinine clearance, and free water clearance in patients with primary nocturnal enuresis. This information might help in our understanding of the mechanism of action of CBZ in management of patients with enuresis.

PATIENTS AND METHODS

The study comprised eight patients with primary enuresis (age range, 8-14 yr) who wet at night on a daily basis. Enuretics were given, CBZ 200 mg each night; urine volume, urinary osmolality and electrolytes, serum osmolality and electrolytes, osmotic clearance, fractional excretion of sodium, and free water clearance were assayed before CBZ treatment and after 15 d of treatment. Frequencies of bed-wetting and dry nights were observed during treatment.

RESULTS

Mean number (+/-SD) of dry nights was increased from zero dry nights (daily bed-wetting) to 9.7 (2.8) per 15 d of treatment (65%). CBZ decreased the 24-h urinary volume by 41%, the night volume by 45%, the day volume by 38%, and frequency of micturition by 28%. CBZ increased the 24-h urinary osmolality by 43%. Serum osmolality changed significantly from 283.7 mOsm/l to 277.2 mOsm/l. CBZ decreased osmotic clearance by 37% and free water clearance by 34%. Creatinine clearance was decreased by 19% after CBZ treatment (p < 0.05).

CONCLUSION

CBZ reduced urine volume, increased urine osmolality, and decreased the free water clearance, the osmotic clearance, and the frequency of micturition in enuretics; this might help in understanding its mechanism of action.