Botulinum Toxin Injection for Medically Refractory Neurogenic Bladder in Children: A Systematic Review

The objective was to evaluate the use of botulinum toxin A (BTX-A) injection in children with medically refractory neurogenic bladder. A systematic review of the literature was conducted using three databases (Medline via PubMed, Cochrane, and EMBASE). Articles evaluating BTX-A in children with neurogenic bladder were collected. The clinical and urodynamic parameters were reviewed for the safety and efficacy evaluation. Sixteen studies were selected into this study and a total of 455 children with medical refractory neurogenic bladder were evaluated. All of the patients had received traditional conservative medications such as antimuscarinics and intermittent catheterization as previous treatment. The duration of treatments ranged from 2 months to 5.7 years. Improvements in incontinence and vesicoureteral reflux were the most common clinical outcomes. The detrusor pressure, bladder capacity and bladder compliance improvement were the most common urodynamic parameters which had been reported. However, patient satisfaction with the procedure remained controversial. There was only a minimal risk of minor adverse effects. In all of the studies, BTX-A injection was well tolerated. In conclusion, BTX-A injection appears to be a safe and effective treatment in the management of medically unresponsive neurogenic bladder in children. There is currently no evidence that the use of BTX-A injection could be used as a first-line therapy for neurogenic bladder in children.     

Botulinum toxin A for the Treatment of Overactive Bladder

The standard treatment for overactive bladder starts with patient education and behavior therapies, followed by antimuscarinic agents. For patients with urgency urinary incontinence refractory to antimuscarinic therapy, currently both American Urological Association (AUA) and European Association of Urology (EAU) guidelines suggested that intravesical injection of botulinum toxin A should be offered. The mechanism of botulinum toxin A includes inhibition of vesicular release of neurotransmitters and the axonal expression of capsaicin and purinergic receptors in the suburothelium, as well as attenuation of central sensitization. Multiple randomized, placebo-controlled trials demonstrated that botulinum toxin A to be an effective treatment for patients with refractory idiopathic or neurogenic detrusor overactivity. The urinary incontinence episodes, maximum cystometric capacity, and maximum detrusor pressure were improved greater by botulinum toxin A compared to placebo. The adverse effects of botulinum toxin A, such as urinary retention and urinary tract infection, were primarily localized to the lower urinary tract. Therefore, botulinum toxin A offers an effective treatment option for patients with refractory overactive bladder.     

The overactive bladder: review of current pharmacotherapy in adults. Part 2: treatment options in cases refractory to anticholinergics

In the first part of this review the potential pathophysiological factors involved in the overactive bladder were outlined, and the wide range of first-line anticholinergic pharmacotherapies available for such patients were reviewed. The second part will focus on the intravesical instillation of resiniferatoxin and injections of botulinum toxin into the bladder to treat overactive bladder and detrusor overactivity. Resiniferatoxin has been shown to increase bladder capacity and improve incontinence in patients with neurogenic and non-neurogenic detrusor overactivity. Botulinum toxin has successfully been used to treat neurogenic and idiopathic detrusor overactivity, with improvements observed in bladder capacity, decreases in detrusor pressures on filling and voiding, and increased volumes at first contraction. Further validation is required for both treatments, in the form of large randomised controlled trials, before their use can be considered routine, with particular focus on dosing required.     

Therapeutic Efficacy of Urethral Sphincteric Botulinum Toxin Injections for Female Sphincter Dysfunctions and a Search for Predictive Factors

External urethral sphincter (EUS) dysfunction is a common, bothersome female voiding dysfunction. This study aims to analyze the characteristics of different types of female EUS dysfunction, as well as to determine the outcome predictors of sphincteric botulinum toxin A (BoNT-A) injection. Women receiving sphincteric BoNT-A injections for refractory EUS dysfunction were retrospectively reviewed. A comparison of the baseline clinical, urodynamic parameters and the treatment responses were made for patients with different EUS dysfunctions. A total of 106 females were included. Significantly increased detrusor overactivity, detrusor contracting pressure and the bladder outlet obstruction index with decreased urge sensation were noted in patients diagnosed with dysfunctional voiding or detrusor sphincter dyssynergia comparing to those diagnosed with poor relaxation of the external urethral sphincter. The average subjective improvement rate was 67% for the injection. The therapeutic effect was not affected by the type of EUS dysfunction. The multivariate analysis revealed that bladder neck narrowing and catheterization history were predictive of negative outcomes. There is a distinct urodynamic presentation for each type of female EUS dysfunction. Sphincteric BoNT-A injection provides a good therapeutic outcome for refractory EUS dysfunction. A narrowing bladder neck and a history of catheterization suggest poor therapeutic outcomes.     

Satisfaction with Detrusor OnabotulinumtoxinA Injections and Conversion to Other Bladder Management in Patients with Chronic Spinal Cord Injury

This study investigated the satisfaction with continued detrusor Botox injections for urinary incontinence and conversion to other surgical procedures and bladder management procedures for neurogenic detrusor overactivity (NDO) in patients with chronic spinal cord injury (SCI). A total of 223 patients with chronic SCI underwent detrusor Botox 200U for urodynamically confirmed NDO and urinary incontinence. After initial detrusor Botox injections, patients opted to either continue detrusor Botox injections every six to nine months and on clean intermittent catheterization (CIC), switch to other bladder management procedures, or receive surgical procedures to improve their urinary incontinence, correct emergent complications, or have better voiding conditions without CIC. Urinary incontinence improvement rates and satisfaction with bladder management were assessed and compared between different subgroups, urodynamic parameters, and bladder management procedures. Finally, a total of 154 male and 69 female patients were included, among whom 56 (25.1%), 81 (36.3%), 51 (22.9%), and 35 (15.7%) showed a marked, moderate, mild, and no reduction in urinary incontinence, respectively. However, only 48.4% of the patients continued detrusor Botox injections over the mean follow-up period of seven years. Patients with cervical or thoracic SCI had fair incontinence improvement rates. The presence of high detrusor pressure and higher-grade bladder outlet resistance also predicted a decrease in incontinence. Although more than 50% of the patients switched to other bladder management procedures or received surgical treatment, 69.1% expressed satisfaction with their current status. This large cohort of patients with chronic SCI who received initial detrusor Botox injections revealed that only 48.4% continued with Botox injections. Those who received surgical procedures due to urological complications or demanded change in bladder management could achieve high satisfaction rates.     

Bladder,bowel and sexual dysfunction in multiple sclerosis: management strategies

Although patients with multiple sclerosis (MS) are likely to have problems with bladder, bowel and sexual function, these problems have often been neglected in the past. Bladder dysfunction produces symptoms of urgency, frequency and urge incontinence (due to bladder overactivity and incomplete emptying), and is found in up to 75% of patients with MS. The mainstay of drug treatment for neurogenic bladder overactivity is anticholinergic medication, although intravesical treatments have also been proposed, such as the vanilloids and botulinum toxin, as well as sublingual cannibanoids. There has been much progress with pro-erectile agents in recent years, notably the use of sildenafil citrate, which has been shown to be particularly efficacious in these patients. Other agents include apomorphine hydrochloride and newer phosphodiesterase 5 inhibitors; however, the efficacy of these drugs in patients with MS remains to be proven. Research in female sexual dysfunction is also progressing, although this aspect of patient well being has only recently been addressed; the reported development of a classification system for the condition is likely to help categorise future treatments. Unlike bladder and sexual dysfunction, there have been rather limited advances in the treatment of faecal incontinence and constipation specifically for patients with MS, despite a prevalence of up to 50%. This review highlights the strategies for these types dysfunction commonly seen in patients with MS, with report of recent pharmacological developments.     

Afferent mechanism in the urinary tract

Much of the current research on lower urinary tract dysfunction is focused on afferent mechanisms. The main goals are to define and modulate the signaling pathways by which afferent information is generated and conveyed to the central nervous system. Alterations in bladder afferent mechanisms are a potential source of voiding dysfunction and an emerging source of drug targets. Even some established drug therapies such as muscarinic receptor antagonists, as well as emerging therapies such as botulinum toxin type-A, may act partly through afferent mechanisms. This review presents up-to-date findings on the localization of afferent fiber types within the bladder wall, afferent receptors and transmitters, and how these may communicate with the urothelium, interstitial cells, and detrusor smooth muscle to regulate micturition in normal and pathological bladders. Peripheral and central mechanisms of afferent sensitization and myogenic mechanisms that lead to detrusor overactivity, overactive bladder symptoms, and urgency sensations are also covered as well as new therapeutic approaches and new and established methods of measuring afferent activity.     

Pharmacotherapy for overactive bladder: minimally invasive treatment -- botulinum toxins

INTRODUCTION: Considered by many a 'revolution' in the treatment of intractable overactive bladder (OAB) and with an increasing number of centers including it in their practice worldwide, botulinum neurotoxin A (BoNT/A) injected into the bladder wall is a treatment of significant potential. In anticipation of the results of multicenter, placebo-controlled, dose-ranging studies, this is a critical review of the available literature on the use of botulinum toxins in the treatment of either neurogenic or idiopathic OAB. AREAS COVERED: The review is based on the English-language literature published by Medline on the use of botulinum toxins in neurogenic or idiopathic detrusor overactivity/OAB since the seminal publication in 2000. The reader is exposed to the cumulative data as well as to a more critical insight on the clinical efficacy of single and repeat injections of the most widely used formulations, the injection techniques, including different doses, dilutions and injection sites, the mechanism of action, the side effects and the cost-effectiveness of the treatment. EXPERT OPINION: Despite the markedly heterogeneous methodologies, published studies suggest that BoNT/A is effective when a number of outcomes are considered, and is considered safe. As results of large registration studies are awaited, additional research on the optimization of clinical practice parameters such as benefit-risk ratio, injection technique, predictors of response and long-term safety, as well as on the mechanism of action and the cost-effectiveness of the treatment, would be welcome.     

The role of botulinum toxin in neurourology

Botulinum toxin is a presynaptic neuromuscular blocking agent that induces a selective and reversible muscle weakness of up to several months when injected intramuscularly in minute quantities. Different medical disciplines have applied the toxin to treat mainly muscular hypercontraction. For neurourologically impaired patients, the reported successful treatment of neurogenic detrusor overactivity and detrusor sphincter dyssynergia with botulinum-A toxin is a promising alternative option to conservative medication or surgery. This review of the literature presents current indications, techniques for and results of the use of botulinum toxin in neurourologically impaired patients and aims to give an insight into this new therapeutic option.     

Drug treatment of urinary incontinence

Urinary incontinence is usually classified into four types: stress, urge, reflex and overflow incontinence. The first three types of incontinence are due to urine storage dysfunction and the latter is due to urine emptying dysfunction. To improve urine storage dysfunction treatment should be aimed at decreasing detrusor overactivity, increasing bladder capacity and/or increasing outlet resistance, whereas to improve emptying dysfunction, increasing detrusor contractility and/or decreasing outlet resistance are required. This review summarizes the various drugs currently in clinical use and new drugs under investigation.     

BoNT/A1 Secondary Failure for the Treatment of Neurogenic Detrusor Overactivity: An Ex Vivo Functional Study

Management of neurogenic detrusor overactivity (NDO) remains a clinical priority to improve patients’ quality of life and prevent dramatic urological complications. Intradetrusor injection of onabotulinumtoxinA (BoNT/A1, botulinum neurotoxin A1) is approved as second therapeutic line in these patients, demonstrating a good efficacy. However, a loss of its efficacy over time has been described, with no clear understanding of the underlying mechanisms. This paper aims at shedding new light on BoNT/A1 secondary failure in NDO through functional and structural analysis. Three groups of patients (either non-NDO, NDO with no toxin history or toxin secondary failure) were investigated using an ex vivo bladder strip assay. Detrusor strips were tensed in organ baths and submitted to electrical field stimulation to generate contractions. Recombinant BoNT/A1 was then added at various concentrations and contractions recorded for 4 h. Histology exploring BoNT/A1 targets, fibrosis and neuronal markers was also used. Detrusor strips from patients with BoNT/A1 secondary failure displayed a smaller sensitivity to toxin ex vivo at 3 nM compared to the other groups. Histological evaluation demonstrated the presence of cleaved Synaptosomal-Associated Protein, 25 kDa (c-SNAP25) in the detrusor from the toxin-secondary failure population, indicating some remaining in vivo sensitivity to BoNT/A1 despite the therapeutic escape. Moreover, residual c-SNAP25 did not affect parasympathetic-driven contractions observed ex vivo. This study confirms the slightly lower efficacy of BoNT/A1 in the BoNT/A1 secondary failure NDO group, suggesting that the escape from BoNT/A1 efficacy in NDO occurs at least at the parasympathetic level and could imply compensatory mechanisms for detrusor contraction.     

Pharmacotherapy for overactive bladder: minimally invasive treatment – botulinum toxins

Introduction: Considered by many a ‘revolution’ in the treatment of intractable overactive bladder (OAB) and with an increasing number of centers including it in their practice worldwide, botulinum neurotoxin A (BoNT/A) injected into the bladder wall is a treatment of significant potential. In anticipation of the results of multicenter, placebo-controlled, dose-ranging studies, this is a critical review of the available literature on the use of botulinum toxins in the treatment of either neurogenic or idiopathic OAB.

Areas covered: The review is based on the English-language literature published by Medline on the use of botulinum toxins in neurogenic or idiopathic detrusor overactivity/OAB since the seminal publication in 2000. The reader is exposed to the cumulative data as well as to a more critical insight on the clinical efficacy of single and repeat injections of the most widely used formulations, the injection techniques, including different doses, dilutions and injection sites, the mechanism of action, the side effects and the cost-effectiveness of the treatment.

Expert opinion: Despite the markedly heterogeneous methodologies, published studies suggest that BoNT/A is effective when a number of outcomes are considered, and is considered safe. As results of large registration studies are awaited, additional research on the optimization of clinical practice parameters such as benefit–risk ratio, injection technique, predictors of response and long-term safety, as well as on the mechanism of action and the cost-effectiveness of the treatment, would be welcome.     

Real-World Data Regarding Satisfaction to Botulinum Toxin A Injection into the Urethral Sphincter and Further Bladder Management for Voiding Dysfunction among Patients with Spinal Cord Injury and Voiding Dysfunction

Purpose: This study aimed to investigate improvement in voiding condition after the initial botulinum toxin A (BoNT-A) injection into the urethral sphincter among patients with chronic spinal cord injury (SCI) and voiding dysfunction. Moreover, subsequent surgical procedures and bladder management were evaluated. Materials and Methods: From 2011 to 2020, 118 patients with SCI and dysuria who wanted to void spontaneously received their first BoNT-A injection at a dose of 100 U into the urethral sphincter. Improvement in voiding and bladder conditions after BoNT-A treatment were assessed. Next, patients were encouraged to continually receive BoNT-A injections into the urethral sphincter, convert to other bladder managements, or undergo surgery. After undergoing bladder management and surgical procedures, the patients were requested to report improvement in voiding condition and overall satisfaction to bladder conditions. Then, data were compared. Results: In total, 94 male and 24 female participants were included in this analysis. Among them, 51 presented with cervical, 43 with thoracic, and 24 with lumbosacral SCI. After BoNT-A injections into the urethral sphincter, 71 (60.2%) patients, including 18 (15.3%) with excellent, and 53 (44.9%) with moderate improvement, had significant improvement in voiding condition. Patients with cervical SCI (66.6%), detrusor overactivity and detrusor sphincter dyssynergia (72.0%), partial hand function (80.0%), and incomplete SCI (68.4%) had a better improvement rate than the other subgroups. Only 42 (35.6%) patients continually received treatment with BoNT-A injections into the urethral sphincter. Meanwhile, more than 60% of patients who converted their treatment to augmentation enterocystoplasty (n = 5), bladder outlet surgery (n = 25), BoNT-A injections into the detrusor muscle (n = 20), and medical treatment (n = 55) had moderate and marked improvement in voiding dysfunction and overall satisfaction. Discussion: Although BoNT-A injections into the urethral sphincter could improve voiding condition, only patients with SCI who presented with voiding dysfunction were commonly satisfied. Those whose treatments were converted to other bladder managements, which can promote urinary continence, or to surgical procedures, which can facilitate spontaneous voiding, had favorable treatment outcomes.     

Modulation of urinary bladder innervation: TRPV1 and botulinum toxin A

The persisting interest around neurotoxins such as vanilloids and botulinum toxin (BoNT) derives from their marked effect on detrusor overactivity refractory to conventional antimuscarinic treatments. In addition, both are administered by intravesical route. This offers three potential advantages. First, intravesical therapy is an easy way to provide high concentrations of pharmacological agents in the bladder tissue without causing unsuitable levels in other organs. Second, drugs effective on the bladder, but inappropriate for systemic administration, can be safely used as it is the case of vanilloids and BoNT. Third, the effects of one single treatment might be extremely longlasting, contributing to render these therapies highly attractive to patients despite the fact that the reasons to the prolonged effect are still incompletely understood. Attractive as it may be, intravesical pharmacological therapy should still be considered as a second-line treatment in patients refractory to conventional oral antimuscarinic therapy or who do not tolerate its systemic side effects. However, the increasing off-label use of these neurotoxins justifies a reappraisal of their pharmacological properties.     

Muscarinic stimulation of the rat isolated whole bladder: pathophysiological models of detrusor overactivity

1 Hypotheses as to the pathophysiological basis of bladder detrusor muscle overactivity (DO) have identified both central nervous and peripheral mechanisms as likely contributory factors. In this paper, we describe peripheral autonomous bladder activity in two animal models of DO and discuss how the differences observed between the two models support the likelihood that clinical DO has a multifactorial basis. 2 A total of 12 adult female Sprague-Dawley rats underwent obstruction or sham operation for 1 or 4 weeks. Six adult female spontaneously hypertensive rats (SHR) were compared with normal Wistar controls. Bladders were microsurgically removed and mounted in whole organ tissue baths. Recordings of intravesical pressure in response to the muscarinic receptor agonist arecaidine were performed under standardized conditions. 3 In the partially obstructed rat bladder, the amplitude of pressure fluctuations elicited by the muscarinic agonist arecaidine was significantly increased compared with sham-operated animals. The tonic component of the response was no different for the two groups. No difference from controls was apparent in the SHR. 4 We conclude that alterations in autonomous bladder activity in the obstructed rat model suggest that peripheral functional changes contribute to the pathophysiological abnormality. In contrast, the fundamental abnormality in the SHR appears to be at a more central level. The observations support the supposition that lesions at widely separate sites can give rise to apparently similar abnormalities of lower urinary tract function.     

A型肉毒毒素治疗偏侧面肌痉挛临床分析

目的观察国产及进口A型肉毒毒素(BTX-A)治疗偏侧面肌痉挛(HFS)的临床效果。方法总结2013年5月至2015年11月就诊于我院门诊的215例HFS患者及39例接受BTX-A治疗HFS患者的临床特点,包括性别、面部受累部位、病情程度、发病年龄及病程等特点;比较注射保妥适32例次和衡力20例次的肉毒素用量、治疗效果、疗效持续时间及不良反应,总结重复注射及药物互换时的疗效,总结注射部位与常规注射部位的变化。结果 215例HFS中,女性154例,占71.63%;面部受累左侧略占优势;平均发病年龄45岁,平均病程24个月;病情程度中及重度169例。在接受BTX-A治疗的39例中,女性、受累左侧面部和病情程度重居多,重复治疗7例,共注射52例次。保妥适组和衡力组间肉毒素用量比较差异无统计学意义(P=0.087),治疗效果亦无显著差异(P=1.000),治疗平均有效时间组间差异无统计学意义(P=0.309),不良反应无明显差异(P=0.849)。重复注射及药物互换时无疗效减退。根据痉挛肌肉受累部位不同,注射部位在常规部位上增加了耳后镫骨肌和颈部颈阔肌。结论局部注射国产和进口BTX-A治疗HFS同样疗效显著,毒副作用少、安全性高,可重复使用。并且重复注射时,进口和国产BTX-A可以互换,注射部位增加了镫骨肌和颈阔肌,能更好改善痉挛肌肉群症状。     

Role of 5-HT receptors in treatment of overactive bladder

Normal bladder function requires coordinated detrusor relaxation and urethral sphincter contraction during the filling phase and the reverse during micturition. This is achieved by the integration of excitatory, inhibitory, and sensory nerve activity in control centers in the spinal cord, pons, and forebrain. It is possible that much of bladder pathology is related to disturbances in the vesical ganglia, sensory reflex loops, and central control of micturition. Experimental studies in animals have revealed that spinal reflex circuits involved in voiding function exhibit a dense serotonergic innervation, multiple 5-HT receptors, and sensitivity to 5-HT receptor agonists and antagonists, and 5-HT reuptake inhibitors. Activity in the serotonergic pathway generally enhances urine storage by facilitating the vesical sympathetic reflex pathway and inhibiting the parasympathetic voiding pathway. Thus, 5-HT receptor antagonists and reuptake inhibitors represent important targets for the development of new treatments of detrusor overactivity and urinary incontinence. Among the drugs modulating the bladder function through 5HT receptor, duloxetine, a potent and selective inhibitor of 5-HT and NE reuptake, is presently undergoing clinical trials for stress urinary incontinence after being shown to be effective in animal models of this condition.     

Botulinum Toxin Type-A (Botulax®) Treatment in Patients with Intractable Chronic Occipital Neuralgia: A Pilot Study

Intractable chronic occipital neuralgia (ON) is an uncommon type of headache often experienced by patients in outpatient neurological clinics. Among patients unresponsive to oral neuralgia medications, needling or injections with several drugs were suggested alternatives for treating chronic ON. This study aimed to determine the effectiveness and safety of botulinum toxin type-A (BTX-A) injection treatments, where eight patients with unilateral chronic ON received BTX-A injections at the pain sites. The pain relief effect was observed 2 weeks after receiving the injections, gradually showing improvements up to 12 weeks after injection. There were no adverse events or changes from baseline in serologic studies and vital signs in any of the participants. The treatment’s pain-relieving effects were confirmed through regular, 12-week follow-ups, confirming the safety and effectiveness of BTX-A on chronic ON and suggesting that this method is an effective, novel alternative option for chronic ON treatment.     

Does Reduction of Number of Intradetrusor Injection Sites of aboBoNTA (Dysport?) Impact Efficacy and Safety in a Rat Model of Neurogenic Detrusor Overactivity?

Intradetrusor injections of Botulinum toxin A—currently onabotulinumtoxinA—is registered as a second-line treatment to treat neurogenic detrusor overactivity (NDO). The common clinical practice is 30 × 1 mL injections in the detrusor; however, protocols remain variable and standardization is warranted. The effect of reducing the number of injection sites of Dysport^® abobotulinumtoxinA (aboBoNTA) was assessed in the spinal cord-injured rat (SCI). Nineteen days post-spinalization, female rats received intradetrusor injections of saline or aboBoNTA 22.5 U distributed among four or eight sites. Two days after injection, continuous cystometry was performed in conscious rats. Efficacy of aboBoNTA 22.5 U was assessed versus aggregated saline groups on clinically-relevant parameters: maximal pressure, bladder capacity, compliance, voiding efficiency, as well as amplitude, frequency, and volume threshold for nonvoiding contractions (NVC). AboBoNTA 22.5 U significantly decreased maximal pressure, without affecting voiding efficiency. Injected in four sites, aboBoNTA significantly increased bladder capacity and compliance while only the latter when in eight sites. AboBoNTA significantly reduced NVC frequency and amplitude. This preclinical investigation showed similar inhibiting effects of aboBoNTA despite the number of sites reduction. Further studies are warranted to optimize dosing schemes to improve the risk-benefit ratio of BoNTA-based treatment modalities for NDO and further idiopathic overactive bladder.     

Botulinum neurotoxin serotypes A and B preparations have different safety margins in preclinical models of muscle weakening efficacy and systemic safety.

This preclinical study compared the muscle weakening efficacy, duration, and safety margin of the recently approved botulinum toxin type B (BTX-B; Myobloc/Neurobloc) to botulinum toxin type A (BTX-A; BOTOX((R))). Mice received a single hind limb intramuscular injection of BTX-B (1-150U/kg) or BTX-A (1-120U/kg). An observer who was masked to treatment assessed the magnitude and duration of muscle weakening efficacy on a 0-4 scale using the digit abduction scoring assay. Safety margins were determined as the ratio of the IM median lethal dose to the IM dose that produced half-maximal muscle weakness in the DAS. BTX-A produced muscle weakness at lower doses than BTX-B (IM ED(50): 6.2+/-0.6 vs. 20.8+/-1.4U/kg, respectively) (p<0.0001). BTX-A at 29U/kg and BTX-B at 67U/kg produced comparable peak DAS scores of approximately 4 indicating maximal muscle weakness. At these doses, the duration of BTX-A was longer, with a return to baseline by day 36 compared to a return to baseline by day 14 with BTX-B. The mean dose that was lethal in 50% of mice was lower for BTX-A than BTX-B (81.4+/-3.5 vs. 104.6+/-1.9U/kg, respectively) (p<0.001) and the safety margin was higher (13.9+/-1.7 vs. 5.4+/-0.3, respectively (p<0.001). These results indicate that the BTX-A:BTX-B dose ratio for muscle weakening efficacy is different from the ratio for systemic effects following IM injections and suggest that no single dose ratio is adequate to compare these preparations. The in vivo differences found are consistent with the different clinical profiles reported for these two products.