PHARMACOKINETICS

Using currently available analytical technology, it is not possible to detect MYOBLOC in the peripheral blood following intramuscular injection at the recommended doses.

CLINICAL STUDIES

Two phase 3, randomized, multi-center, double-blind, placebo controlled studies of the treatment of cervical dystonia were conducted. Both studies enrolled only adult patients who had a history of receiving botulinum toxin type A in an open label manner, with a perceived good response and tolerable adverse effects. Study #301 enrolled patients who were perceived as having an acceptable response to type A toxin, while Study #302 enrolled only patients who had secondarily lost responsiveness to type A toxin. Other eligibility criteria common to both studies were that all subjects had moderate or greater severity of cervical dystonia with at least 2 muscles involved, no neck contractures or other causes of decreased neck range of motion, and no history of any other neuromuscular disorder. Subjects in Study #301 were randomized to receive placebo, 5,000 Units or 10,000 Units of MYOBLOC, and subjects in Study #302 were randomized to receive placebo or 10,000 Units of MYOBLOC. Study agent was administered to subjects in a single treatment session by investigators who selected 2 to 4 muscles per subject from the following: Splenius capitis, Sternocleidomastoid, Levator scapulae, Trapezius, Semispinalis capitis, and Scalene muscles. The total dose was divided between the selected muscles, and from 1 to 5 injections were made per muscle. There were 109 subjects enrolled into Study #301, and 77 into Study #302. Patient evaluations continued for 16 weeks post injection.

The primary efficacy outcome variable for both studies was the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS)-Total Score (scale range of possible scores is 0–87) at Week 4. TWSTRS is comprised of three sub-scales which examine 1) Severity—the severity of the patient's abnormal head position; 2) Pain—the severity and duration of pain due to the dystonia; and 3) Disability— the effects of the abnormal head position and pain on a patient's activities. The secondary endpoints were the Patient Global and Physician Global Assessments of change at Week 4. Both Global Assessments used a 100-point visual-analog scale (VAS). The Patient Global Assessment allows patients to indicate how they feel at the time of their evaluation compared to the pre-injection baseline. Likewise, the Physician Global Assessment indicates the physician's assessment of a patient's change from baseline to Week 4. Scores of 50 indicate no change, 0 much worse, and 100 much better. Results of comparisons of the primary and secondary efficacy variables are summarized in Table 1.

There were no statistically significant differences in results between the 5,000 Units and 10,000 Units doses in Study #301. Exploratory analyses of these two studies suggested that the majority of patients who showed a beneficial response by Week 4 had returned to their baseline status between Weeks 12 to 16 post injection. Although there was a MYOBLOC associated decrease in pain, there remained many patients who experienced an increase in dystonia-related neck pain irrespective of treatment group (see ADVERSE REACTIONS). TWSTRS Total Score at Week 4 and Patient Global Assessment among subgroups by gender or age showed consistent treatment-associated effects across these subgroups (see also PRECAUTIONS: GERIATRICS). There were too few non-Caucasian patients enrolled to draw any conclusions regarding relative efficacy in racial subsets.

MYOBLOC was studied in two phase 2 dose ranging studies, Studies #08 and #09, which preceded the phase 3 studies. Studies #08 and #09 had a study design similar to the phase 3 studies, including eligibility criteria. Study #08 enrolled 85 subjects randomized between doses of placebo, 400 Units, 1,200 Units, or 2,400 Units (21 or 22 subjects per group). Study #09 enrolled 122 subjects and randomized between doses of placebo, 2,500 Units, 5,000 Units, and 10,000 Units (30 or 31 subjects per group). These studies demonstrated efficacy on the TWSTRS-Total, baseline to Week 4, at doses of 2,400 Units, 2,500 Units, 5,000 Units, and 10,000 Units. Study #08 showed mean improvement from baseline on the Week 4 TWSTRS for placebo and 2,400 Units of 2.0 and 8.5 points respectively (from baselines of 42.0 and 42.4 points). Study #09 showed mean improvement from baseline to Week 4 for placebo, 2,500 Units, 5,000 Units, and 10,000 Units of 3.3, 11.6, 12.5, and 16.4 points, respectively (from baselines of 45.5, 45.6, 45.2, and 47.5 points). Study #08 also indicated there is less response for doses below 2,400 Units.

Study #352 was an open label, intrapatient dose-escalation study of 3 treatment sessions where each patient with cervical dystonia sequentially received 10,000 Units, 12,500 Units, and 15,000 Units, at periods of 12 to 16 weeks between treatment sessions irrespective of their response to their previous dose. This study enrolled 145 patients, of whom 125 received all three treatments. Although this was an open label design where investigators and patients knew the dose at each treatment session, there were similar mean improvements on the TWSTRS-Total, from baseline to Week 4, for all three doses.

In the MYOBLOC injected patients (n=112) of the phase 3 studies, 19% had 2 muscles injected, 48% had 3 muscles injected, and 33% had 4 muscles injected. Table 2 indicates the frequency of use for each of the permitted muscles, and the fraction of the total dose of the treatment injected into each muscle, for those patients in whom the muscle was injected.

Lack of Interchangeability between Botulinum Toxin Products

The potency Units of MYOBLOC are specific to the preparation and assay method utilized. They are not interchangeable with other preparations of botulinum toxin products and, therefore, units of biological activity of MYOBLOC cannot be compared to or converted into units of any other botulinum toxin products assessed with any other specific assay method (see DESCRIPTION).

Spread of Toxin Effect

Postmarketing safety data from MYOBLOC and other approved botulinum toxins suggest that botulinum toxin effects may, in some cases, be observed beyond the site of local injection. The symptoms are consistent with the mechanism of action of botulinum toxin and may include asthenia, generalized muscle weakness, diplopia, blurred vision, ptosis, dysphagia, dysphonia, dysarthria, urinary incontinence, and breathing difficulties. These symptoms have been reported hours to weeks after injection. Swallowing and breathing difficulties can be life threatening and there have been reports of death related to spread of toxin effects. The risk of symptoms is probably greatest in children treated for spasticity but symptoms can also occur in adults treated for spasticity and other conditions, and particularly in those patients who have underlying conditions that would predispose them to these symptoms. In unapproved uses, including spasticity in children and adults, and in approved indications, symptoms consistent with spread of toxin effect have been reported at doses comparable to or lower than doses used to treat cervical dystonia.

Dysphagia and Breathing Difficulties in Treatment of Cervical Dystonia

Treatment with MYOBLOC and other botulinum toxin products can result in swallowing or breathing difficulties. Patients with pre-existing swallowing or breathing difficulties may be more susceptible to these complications. In most cases, this is a consequence of weakening of muscles in the area of injection that are involved in breathing or swallowing. When distant effects occur, additional respiratory muscles may be involved.

Deaths as a complication of severe dysphagia have been reported after treatment with botulinum toxin. Dysphagia may persist for several months, and require use of a feeding tube to maintain adequate nutrition and hydration. Aspiration may result from severe dysphagia and is a particular risk when treating patients in whom swallowing or respiratory function is already compromised.

Treatment of cervical dystonia with botulinum toxins may weaken neck muscles that serve as accessory muscles of ventilation. This may result in a critical loss of breathing capacity in patients with respiratory disorders who may have become dependent upon these accessory muscles. There have been postmarketing reports of serious breathing difficulties, including respiratory failure, in cervical dystonia patients. Patients treated with botulinum toxin may require immediate medical attention should they develop problems with swallowing, speech or respiratory disorders. These reactions can occur within hours to weeks after injection with botulinum toxin (see ADVERSE REACTIONS, CLINICAL PHARMACOLOGY).

Pre-Existing Neuromuscular Disorders

Individuals with peripheral motor neuropathic diseases, amyotrophic lateral sclerosis, or neuromuscular junctional disorders (e.g., myasthenia gravis or Lambert-Eaton syndrome) should be monitored particularly closely when given botulinum toxin. Patients with neuromuscular disorders may be at increased risk of clinically significant effects including severe dysphagia and respiratory compromise from typical doses of MYOBLOC (see ADVERSE REACTIONS).

Human Albumin

This product contains albumin, a derivative of human blood. Based on effective donor screening and product manufacturing processes, it carries an extremely remote risk for transmission of viral diseases. A theoretical risk for transmission of Creutzfeldt-Jakob disease (CJD) also is considered extremely remote. No cases of transmission of viral diseases or CJD have ever been identified for albumin.

INFORMATION FOR PATIENTS

The physician should provide a copy of the FDA-Approved Patient Medication Guide and review the contents with the patient. Patients should be advised to inform their doctor or pharmacist if they develop any unusual symptoms (including difficulty with swallowing, speaking or breathing), or if any existing symptom worsens.

Patients should be counseled that if loss of strength, muscle weakness, or impaired vision occur, they should avoid driving a car or engaging in other potentially hazardous activities.

DRUG INTERACTIONS

Co-administration of MYOBLOC and aminoglycosides or other agents interfering with neuromuscular transmission (e.g., curare-like compounds) should only be performed with caution as the effect of the toxin may be potentiated.

The effect of administering different botulinum neurotoxin serotypes at the same time or within less than 4 months of each other is unknown. However, neuromuscular paralysis may be potentiated by co-administration or overlapping administration of different botulinum toxin serotypes.

CARCINOGENESIS, MUTAGENESIS, IMPAIRMENT OF FERTILITY

No long-term carcinogenicity studies in animals have been performed.

PREGNANCY

NURSING MOTHERS

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when MYOBLOC is administered to a nursing woman.

PEDIATRIC USE

Safety and effectiveness in pediatric patients have not been established.

GERIATRIC USE

In the controlled studies summarized in CLINICAL STUDIES, for MYOBLOC treated patients, 152 (74.5%) were under the age of 65, and 52 (25.5%) were aged 65 or greater. For these age groups, the most frequent reported adverse events occurred at similar rates in both age groups. Efficacy results did not suggest any large differences between these age groups.

Very few patients aged 75 or greater were enrolled, therefore no conclusions regarding the safety and efficacy of MYOBLOC within this age group can be determined.

Overview

The most commonly reported adverse events associated with MYOBLOC treatment in all studies were dry mouth, dysphagia, dyspepsia, and injection site pain. Dry mouth and dysphagia were the adverse reactions most frequently resulting in discontinuation of treatment. There was an increased incidence of dysphagia with increased dose in the sternocleidomastoid muscle. The incidence of dry mouth showed some dose-related increase with doses injected into the splenius capitis, trapezius and sternocleidomastoid muscles.

Only nine subjects without a prior history of tolerating injections of type A botulinum toxin have been studied. Adverse event rates have not been adequately evaluated in these patients, and may be higher than those described in Table 3.

Discussion

Adverse reaction rates observed in the clinical trials for a product cannot be directly compared to rates in clinical trials for another product and may not reflect the rates observed in actual clinical practice. However, adverse reaction information from clinical trials does provide a basis for identifying the adverse events that appear to be related to drug use and for approximating rates.

MYOBLOC was studied in both placebo controlled single treatment studies and uncontrolled repeated treatment studies; most treatment sessions and patients were in the uncontrolled studies. The data described below reflect exposure to MYOBLOC at varying doses in 570 subjects, including more than 300 patients with 4 or more treatment sessions. Most treatment sessions were at doses of 12,500 Units or less. There were 57 patients administered a dose of 20,000 or 25,000 Units. All but nine patients had a prior history of receiving type A botulinum toxin and adequately tolerating the treatment to have received repeated doses.

The rates of adverse events and association with MYOBLOC are best assessed in the results from the placebo controlled studies of a single treatment session with active monitoring. The data in Table 3 reflect those adverse events occurring in at least 5% of patients exposed to MYOBLOC treatment in pooled placebo controlled clinical trials. Annual rates of adverse events are higher in the overall data which includes longer duration follow-up of patients with repeated treatment experience. The mean age of the population in these studies was 55-years-old with approximately 66% being female. Most of the patients studied were Caucasian and all had cervical dystonia that was rated as moderate to severe in severity.

In the overall clinical trial experience with MYOBLOC (570 patients, including the uncontrolled studies), most cases of dry mouth or dysphagia were reported as mild or moderate in severity. Severe dysphagia was reported by 3% of patients. Severe dry mouth was reported by 6% of patients. Dysphagia and dry mouth were the most frequent adverse events reported as a reason for discontinuation from repeated treatment studies. These adverse events led to discontinuation from further treatments with MYOBLOC in some patients even when not reported as severe.

The following additional adverse events were reported in 2% or greater of patients participating in any of the clinical studies (COSTART terms, by body system):

Body as a Whole: allergic reaction, fever, headache related to injection, chest pain, chills, hernia, malaise, abscess, cyst, neoplasm, viral infection; Musculoskeletal: arthritis, joint disorder; Cardiovascular System: migraine; Respiratory: dyspnea, lung disorder, pneumonia; Nervous System: anxiety, tremor, hyperesthesia, somnolence, confusion, pain related to CD/torticollis, vertigo, vasodilation; Digestive System: gastrointestinal disorder, vomiting, glossitis, stomatitis, tooth disorder; Skin and Appendages: pruritis; Urogenital System: urinary tract infection, cystitis, vaginal moniliasis; Special Senses: amblyopia, otitis media, abnormal vision, taste perversion, tinnitus; Metabolic and Nutritional Disorders: peripheral edema, edema, hypercholesterolemia; Hemic and Lymphatic System: ecchymosis.

Postmarketing

The following adverse events have been reported during postmarketing use for approved and unapproved indications: angioedema, urticaria, rash and constipation.

Immunogenicity

A two-stage assay was used to test for immunogenicity and neutralizing activity induced by treatment with MYOBLOC. In order to account for varying lengths of follow-up, life-table analysis methods were used to estimate the rates of development of immune responses and neutralizing activity. During the repeated treatment studies, 446 subjects were followed with periodic ELISA based evaluations for development of antibody responses against MYOBLOC. Only patients who showed a positive ELISA assay were subsequently tested for the presence of neutralizing activity against MYOBLOC in the mouse neutralization assay (MNA). 12% of patients had positive ELISA assays at baseline. Patients began to develop new ELISA responses after a single treatment session with MYOBLOC. By six months after initiating treatment, estimates for ELISA positive rate were 20%, which continued to rise to 36% at one year and 50% positive ELISA status at 18 months. Serum neutralizing activity was primarily not seen in patients until after 6 months. Estimated rates of development were 10% at one year and 18% at 18 months in the overall group of patients, based on analysis of samples from ELISA positive individuals. The effect of conversion to ELISA or MNA positive status on efficacy was not evaluated in these studies, and the clinical significance of development of antibodies has not been determined.

The data reflect the percentage of patients whose test results were considered positive for antibodies to MYOBLOC in both an in vitro and in vivo assay. The results of these antibody tests are highly dependent on the sensitivity and specificity of the assays. Additionally, the observed incidence of antibody positivity in an assay may be influenced by several factors including sample handling, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies to MYOBLOC with the incidence of antibodies to other products may be misleading.

Store under refrigeration at 2°- 8°C (36°- 46°F).

DO NOT FREEZE. DO NOT SHAKE.

Protect from light. No U.S. Standard of Potency.

Ready to use; no reconstitution required. The recommended storage condition for MYOBLOC is refrigeration at 2°-8°C.

MYOBLOC may be diluted with normal saline. Once diluted, the product must be used within 4 hours as the formulation does not contain a preservative.

All vials of expired MYOBLOC and equipment used in the administration of MYOBLOC should be carefully discarded according to standard medical waste practices.

Do not use after the expiration date stamped on the vial.

Discard unused portion.

Single-use vial.

Rx ONLY