A relative nocturnal polyuria is a characteristic manifestation of primary nocturnal enuresis. The efficiency of treatment with desmopresin in 70% of patients confirms importance of this factor. Aims: The aim of the work was to find out in children, for the sake of rationalization of nocturnal enuresis therapy, if the therapeutic response to desmopresin may be predicted on the basis of determining daily functional capacity of urinary bladder. Patients and methods: The examinations were performed in 48 patients (age 10.2 ± 2.7 years). Patients with daily enuresis, abnormal urinary pathways and/or constipation were excluded from the study. The daily functional capacity of urinary bladder was determined as a maximum value of diuresis after the administration of standard water load, the value being expressed in absolute values (ml) as well as in percentage of age-related capacity of urinary bladder, calculated according to Koff’s formula. After a two-week control period all the patients received treatment with desmopressin (20
g intranasally in the evening) in the course of two weeks. In those subjects who did not respond by at least 50% reduction in the frequency of enuresis episodes as compared with the control period (non-responders) the therapy continued with the administration of oxybutin (OXY) to DDAVP for the period of subsequent two weeks. Results: In 33 patients (65%) there was a desmopressin therapy-related reduction in the frequency of enuresis episodes by more than 50% (so called responders). The weekly frequency of enuresis episodes decreased in the responders from 4.1 ± 0.3 to 0.5 ± 0.1 (P < 0.001), whereas in the decrease in non-responders was less apparent (from 5.6 ± 0.4 to 3.8 ± 0.3, P < 0.05). The responders differed also in the fact that they had more enuresis episodes in the control period (P < 0.02), were older (P < 0.05) and their daily functional capacity of urinary bladder was significantly higher than in the non-responders (P < 0.01). A combined therapy (DDAVP plus OXY) caused a further significant reduction of the „wet nights“ in the non-responders (P < 0.02). Conclusions: The results indicate that the determination of daily functional capacity of urinary bladder may be a useful guide for rational planning in the therapy of nocturnal enuresis in children. The demonstration of the lower daily functional capacity of urinary bladder in non-responders represents a stimulus for further studies with the application of other methods aimed at adjustment of reservoir capacity of urinary bladder (e.g. stretching of bladder, enuresis alarm).

        Key words: primary nocturnal enuresis, desmopressin, oxybutinin, urinary bladder capacity