The pharmacokinetics of 400 microg of oral desmopressin in elderly patients with nocturia, and the correlation between the absorption of desmopressin and clinical effect.

Objective: To investigate the pharmacokinetic profile of oral desmopressin in elderly patients with nocturia, and to analyse any possible correlation between the absorption and clinical effect.
Patients and Methods: In all, 32 patients were screened to determine the baseline number of nocturnal voids and the nocturia index; of these, 24 fulfilled the inclusion criteria and were enrolled for a pharmacokinetic evaluation of oral desmopressin 400 microg. A double-blind, randomized, placebo-controlled, crossover-effect evaluation period was then used to test the association between the absorption of desmopressin and pharmacodynamic effect. Serial plasma samples were collected for 8 h for a pharmacokinetic analysis of desmopressin. The pharmacodynamics after an equivalent oral dose before bedtime were assessed by measuring changes in the number of nocturnal voids, time to first nocturnal void and nocturnal diuresis, from placebo to active treatment.
Results: There was a linear relationship between plasma desmopressin at 2 h after dosing and the area under the plasma concentration curve from 0 to infinity (Pearson's rho 0.923, P < 0.001). Women had a significantly higher plasma desmopressin concentration than men (P = 0.0012) and more adverse events. There was no correlation between plasma desmopressin at 2 h after dosing and the within-patient response in any of the effect variables. Generally, the number of nocturnal voids and nocturnal diuresis were half that with placebo. The time to the first nocturnal void was almost doubled compared with placebo.
Conclusions: There seems to be a relationship between gender, plasma level of desmopressin and the incidence of adverse events. Plasma desmopressin at 2 h after dosing cannot be used to predict the pharmacodynamic response, although desmopressin lowers the nocturnal diuresis and the number of nocturnal voids.