[Therapeutic effects of intrarectal administration of oxybutynin]

Oxybutynin is a drug of choice in the treatment of the detrusor instability. However the therapeutic doses given orally produce very often side effects due to oxybutynin anticholinergic properties (atropine-like action). The responsible compound is mainly the active oxybutynin metabolite-N-desethyl-oxybutynin, which is the result of the oxybutynin metabolism in liver (so-called first pass metabolism). Therefore it seems, that an attempt of the drug administration via the intrarectal route is an interesting alternative, which maintains the high oxybutynin concentration with the simultaneous reduction of the N-desethyl-oxybutynin.

We qualified 20 patients for our study (12 men and 8 women, mean age 45.6) with the urodynamically proven detrusor instability. Patients with a neurogenic origin of detrusor instability were excluded from the study. Patients treated with oral oxybutynin in a dose of 5 mg b.i.d. and with strongly pronounced atropine-like side effects, making impossible the continuation of the therapy were offered an intrarectal form of oxybutynin in a dose of 5 mg b.i.d. Treatment efficiency was evaluated on the base of the patients symptoms (side effects, urgency, incontinence, frequency).

15 patients (75%) had pronounced side effects, leading to the oral treatment discontinuation. The average time of the oral oxybutynin treatment was 1.5 weeks (3 days to 4 weeks). During the oral therapy these patients complained of the side effects of different magnitude: dry mouth (15 patients--100%), gastro-intestinal disorders (3 patients--20%), drowsiness (1 patient--6.7%). These side effects forced them to stop the oxybutynin oral therapy. After the change of the drug form from oral to the intrarectal one, none of the patients resigned from the treatment. 13.3% of the patients complained of the mild intensity dry mouth. After the one-month therapy period a complete disappearing of the unstable detrusor symptoms was reported by 5 patients (25%), while all others reported their significant reduction.

The intrarectal oxybutynin administration shows the therapeutic efficacy comparable with the intravesical administration with reference to unstable detrusor symptoms reduction. Intrarectal administration reduces the oxybutynin side effects in comparison with the oral one.