MYOBLOC SIDE EFFECTS

SIDE EFFECTS

The following clinically significant adverse reactions to MYOBLOC are discussed in greater detail in other sections of the labeling:

• Spread of Toxin Effect
• Lack of Interchangeability Between Botulinum Toxin Products
• Hypersensitivity Reactions
• Dysphagia and Breathing Difficulties
• Human Albumin and Transmission of Viral Diseases

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in clinical trials of another drug and may not reflect the rates observed in practice.

Cervical Dystonia

In the treatment of cervical dystonia, MYOBLOC was studied in both placebo-controlled single treatment studies and open-label repeated treatment studies; most treatment sessions and patients were in the uncontrolled studies. The data described below reflect exposure to MYOBLOC at varying dosages in 570 subjects, including more than 300 patients with 4 or more treatment sessions. Most treatment sessions were at dosages of 12,500 Units or less.

Adverse reactions occurring in at least 5% of patients exposed to MYOBLOC treatment in pooled placebo-controlled clinical trials are shown in Table 2. The mean age of the population in these studies was 55 years, and approximately 66% were female. Most of the patients studied were Caucasian, and all had moderate to severe symptoms of cervical dystonia.

The most common adverse reactions (greater than 5% of MYOBLOC-treated patients at any dosage and at least 5% more common than placebo) in studies of cervical dystonia (Studies 1, 2, and 4) were dry mouth, dysphagia, injection site pain, and headache. 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.

In the cervical dystonia program, only nine patients without a prior history of tolerating injections of type A botulinum toxin have been studied. Adverse reaction rates have not been adequately evaluated in these patients and may be higher than those described in Table 1.

Table 1: Adverse Reactions in at Least 5% of MYOBLOC-Treated Patients and Greater than Placebo, Following Single Treatment Session in Controlled Cervical Dystonia Studies (Studies 1, 2, and 4)

In the overall clinical trial experience with MYOBLOC in cervical dystonia (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 reactions reported as a reason for discontinuation from repeated treatment studies. These adverse reactions 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 in cervical dystonia (by body system):

Body as a Whole: chest pain, chills, hernia, malaise, abscess, cyst, viral infection; Respiratory: dyspnea, pneumonia; Nervous System: migraine; anxiety, hyperesthesia, vertigo, vasodilation; Digestive System: gastrointestinal disorder; Skin and Appendages: pruritis; Urogenital System: urinary tract infection, cystitis; Special Senses: amblyopia, abnormal vision; Metabolic and Nutritional Disorders: edema; Hemic and Lymphatic System: ecchymosis.

Chronic Sialorrhea

In the double-blind placebo-controlled studies (Study 1 and Study 2), 166 patients were treated with a single treatment of MYOBLOC (1,500 Units; 2,500 Units; or 3,500 Units) and 75 patients received placebo. The mean age of patients treated with MYOBLOC in these studies was 65 years; 83% of the patients were male; and 95% were White. Four MYOBLOC-treated patients and three patients on placebo discontinued because of an adverse event. One patient discontinued because of dry mouth (3,500 Unit dose). The adverse reactions that occurred in at least 5% of MYOBLOC-treated patients and were more frequent than placebo are shown in Table 2.

Table 2: Adverse Reactions in At Least 5% of MYOBLOC-Treated Patients and Greater than Placebo in Pooled Chronic Sialorrhea Studies (Studies 1 and 2)

Immunogenicity

As with all therapeutic proteins, there is potential for immunogenicity. The detection of antibody formation is highly dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of antibody (including neutralizing antibody) positivity in an assay may be influenced by several factors, including assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies in the studies described below with the incidence of antibodies in other studies or to other rimabotulinumtoxinB products may be misleading.

Cervical Dystonia

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.

Chronic Sialorrhea

Immunogenicity potential was not further evaluated for MYOBLOC in the treatment of chronic sialorrhea.

Postmarketing Experience

The following adverse reactions have been reported during postmarketing use of MYOBLOC: angioedema, urticaria, rash, constipation, dry eye, and accommodation disorder. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.