Tag Archive for: abobotulinumtoxinA

None the less the study generates some interesting discussion about the formulations, optimal dosing and the dosing equivalence. The study is one of the first to report on the use of AbobotulinumtoxinA at 300 IU as most studies utilised 500 IU. In view of the move to lower doses of OnabotulinumtoxinA to treat refractory OAB of 100–150 IU, this dose seems appropriate. Evidence from a large dose ranging RCT using OnabotulinumtoxinA suggests no further efficacy beyond doses of 150 IU but an increase in voiding dysfunction. Interestingly CISC rates are still high at 300 IU in this study. A recent systematic review tried to assess the 2 formulations in aspects of BTX-A use for various lower urinary tract dysfunction. Due to the heterogenousity of the studies, a lack of standardised or high quality data a direct comparison between the 2 was not formally possible. It was noted that OnabotulinumtoxinA has been studied more extensively compared to AbobotulinumtoxinA and with both formulations CISC rates could be high at the doses used in this study (OnabotulinumtoxinA 43%; AbobotulinumtoxinA 35%). Assessing the compound muscle action potential of the extensor digitorum brevis muscle in healthy volunteers has suggested an AbobotulinumtoxinA to OnabotulinumtoxinA ratio of 1.57:1 (95% confidence interval: 0.77–3.20 units) with the data indicating that a dose-equivalence ratio of 3:1 was just within statistical error limits but ratios over 3:1 were too high. The same author following a review of the literature in treatments outside the urinary tract suggest a ratio of 2–2.5:1 maybe the most appropriate. An animal model of spinal cord injury and neurogenic detrusor overactivity to compare the 2 formulations has recently been published. The minimal effective dose of Abo- and OnabotulinumtoxinA was found to be 10 IU and 7.5 IU, respectively, for significant changes in cystometry.

When should CISC be instigated? Practice seems to vary considerably and thus results difficult to compare. Many clinicians will base CISC decisions on a cut off, typically 100–200 mL or on whether patients are symptomatic with their PVR. Chapple has suggested >40% of the functional capacity as a significant PVR and this to me seems entirely logical. Future studies should consider this as an endpoint regarding CISC.

At present, the decision as to which formulation is used in clinical practice is often based on local pharmacy regulation and financial considerations. Licensing is undoubtedly going to have a significant influence on this practice. OnabotulinumtoxinA is now licensed for use in many parts of the world to treat neurogenic detrsuor overactivity and has recently been approved by the FDA in the USA to treat refractory OAB. At the time of writing this editorial, no formulation is currently approved for refractory OAB in the UK.