Imidafenacin with high affinity to muscarinic type 3 receptor is prescribed for alleviating OAB symptoms. Yamazaki T [1] reported data of imidafenacin with facilitative effects on antidiuretic hormone (ADH) related pathway. We hypothesized that imidafenacin-induced decrease of urine volume at night might be derived from concentration of urine osmolality (Uosm) as a result of enhancing the ADH related pathway. The hypothesis is described in the Figure below. This is the first study to evaluate the effectiveness of imidafenacin on Uosm in clinical practice.

A total of 52 OAB patients who had never been administered anti-cholinergic agents entered our study. Male and female patients numbered 33 and 19, respectively. We examined casual Uosm, urinary sodium (Na) and Creatinine (Cre) levels at first void in the morning, nocturnal polyuria index (Npi) based on frequency volume charts, International Prostate Symptom Score (IPSS), overactive bladder symptom score (OABSS), maximum urinary flow (Qmax) and residual urine (RU) every four weeks until the eight week visit after administration of imidafenacin. We applied Tanaka’s method [2] to estimate each patient’s 24-hour urinary Na excretion (24HUNa), which is calculated from age, height, body weight, and casual urine samples of Na and Cre. We also classified the patients into two groups according to baseline Uosm: under and over 500 (Groups A and B, respectively).

Following the administration of imidafenacin, IPSS and OABSS improved significantly in all 52 patients. Npi decreased significantly, and Uosm, 24HUNa, Qmax and RU did not change at the eight week visit. The number of patients in Groups A and B was 24 each. Npi decreased, and Uosm increased significantly in Group A at eight weeks. The incidence of nocturia also improved in Group A at eight weeks [Table]. 24HUNa did not change significantly in either Group.

Our results have shown that Npi has decreased significantly in all patients after administration of imidafenacin. The amount of urinary Na excretion was reported to affect night time urine volume [3]. No significant difference of 24HUNa was observed, so this kind of effectiveness could be excluded. The patients with low baseline Uosm significantly decreased their Npi and increased their Uosm. We have demonstrated that the patients who have responded well to imidafenacin treatment have low baseline levels of Uosm.

The beneficial effects of nocturnal antidiuresis of imidafenacin depend on patient’s low baseline levels of Uosm.

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Int J Urol. 2017 May; 24(5):384-389.