Evidence of partial anti-enuretic response related to poor pharmacodynamic effects of desmopressin nasal spray.

PURPOSE: Desmopressin is an evidence-based medicine level I, category A therapy for monosymptomatic nocturnal enuresis. However, in up to 40% of patients only partial desmopressin response is obtained. While the poor pharmacokinetic characteristics of the different available formulations may have a role in apparent therapy resistance, there are limited data available to support this theory. We sought to identify pharmacodynamic factors involved in partial desmopressin response or desmopressin resistance in children with monosymptomatic nocturnal enuresis, with special emphasis on concentrating performance, and time to reach and duration of maximal urine concentration.

MATERIALS AND METHODS: We evaluated 64 children with monosymptomatic nocturnal enuresis and proved nocturnal polyuria lacking full response to desmopressin treatment. The study involved 2 separate home based test days (A and B), each consisting of 9 timed urine collections starting in the evening 1 hour before desmopressin administration and continuing for 16 hours following desmopressin administration. Test A was done during fluid restriction, and test B was done during an oral fluid load.

RESULTS: Under fluid restriction 16 patients failed to achieve urine concentration greater than 850 mOsmol/l at the midnight collection following desmopressin administration. After an oral fluid load given at the start of the test the majority of patients failed to reach maximal concentration of urine as voided during hydropenia, and 45 patients failed to regain appropriate dilution of urine even when an oral water load of 15 ml/kg (urine osmolality less than 750 mOsmol/l) was given in the morning at the end of the test. This finding is suggestive of a prolonged duration of action of the drug.

CONCLUSIONS: Pharmacodynamic tests reveal a suboptimal effect of desmopressin on urine concentration in a significant percentage of patients, which worsens when fluid is not restricted before desmopressin administration. Also the time to reach maximal antidiuretic effect and the duration of pharmacodynamic action show a wide range, requiring individualization of mode and time of administration. Our data demonstrate that a simple pharmacodynamic test as described may give important information on time of dosing, duration of action and influence of oral fluid intake, allowing individualization of therapy. Data also reveal that desmopressin should be administered at least 1 hour before bedtime, and that in case of therapy resistance a longer interval, up to 2 hours, might further reduce diuresis rate in the early night. Because of the documented prolonged action of desmopressin in some patients, increasing the dose without performing pharmacodynamic testing is no longer acceptable.