What is the optimum dose of type A botulinum toxin for treating neurogenic bladder overactivity?

To assess the effects of two doses of botulinum toxin A (Dysport, Ipsen-Biotech, France; 500 and 1000 Speywood units, SU) injected into the bladder for treating incontinence due to a neurogenic overactive bladder.

In an open-label, prospective study between October 2002 and May 2004, in two centres, we analysed the effects of successive doses of 500 and 1000 SU of Dysport, endoscopically injected into the detrusor muscle. At each step, patients (26 women and 19 men) were re-evaluated at 1 month (clinical evaluation and pressure-flow study). If there was a 'good' clinical response (complete absence of urinary leakage) the patient was observed until incontinence recurred; otherwise a further injection was administered at a higher dose.

The mean (sd, range) follow-up was 22 (0.75, 5-31) months; 11 of the 45 patients (24%) did not respond primarily at 1 month for both doses. The analysis of the two curves of survival with no re-injection of Dysport showed a statistically longer action at 1000 SU (P = 0.016). However, in this group there was one patient with general muscle weakness and asthenia, which could have been related to the injection.

The optimum dose of Dysport for incontinence secondary to a neurogenic overactive bladder is not yet defined; 1000 SU probably has a more prolonged effect than 500 SU but exposes the patient to major complications. Further studies evaluating the clinical effect of 750 SU of Dysport are necessary.