Medically Reviewed on 9/8/2023

Brand Name: Myobloc

Generic Name: botulinum toxin

Drug Class: Neuromuscular Blockers, Botulinum Toxins

What is Myobloc, and what is it used for?

Myobloc (botulinum toxin) is a prescription medicine used in adults that is injected into:

  • muscles and used to treat the abnormal head position and neck pain that happens with cervical dystonia (CD).
  • glands that make saliva and is used to treat long-lasting (chronic) drooling (sialorrhea).

It is not known whether Myobloc is safe or effective in children.


The effects of Myobloc (botulinum toxin type b) and all botulinum toxin products may spread from the area of injection to produce symptoms consistent with botulinum toxin effects. These may include

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. 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, 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, cases of spread of effect have occurred at doses comparable to those used to treat cervical dystonia and at lower doses.

What are the side effects of Myobloc?

Myobloc can cause serious side effects including:

  • allergic reactions. Symptoms of an allergic reaction to Myobloc may include:
  • Tell your doctor or get medical help right away if you get wheezing, or trouble breathing, or if you get dizzy or faint.

The most common side effects of Myobloc in people with cervical dystonia include:

The most common side effects of Myobloc in people with sialorrhea include dry mouth and trouble swallowing (dysphagia).

These are not all the possible side effects of Myobloc. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. You may also report side effects to Solstice Neurosciences at 1-888-461-2255.

What is the dosage for Myobloc?

Instructions for Safe Use

  • 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 cannot be compared to or converted into units of any other botulinum toxin products.
  • Each single-dose vial should only be used during one session and only for one patient. Discard any remaining solution in the vial.
  • Myobloc is ready to use; no reconstitution required.
  • Myobloc may be diluted with 0.9% Sodium Chloride Injection. Once diluted, the product must be used within 4 hours as the formulation does not contain a preservative.

Dosing for Cervical Dystonia

  • The recommended initial dosage of Myobloc for cervical dystonia patients with a prior history of tolerating botulinum toxin injections is 2,500 Units to 5,000 Units divided among affected muscles.
  • Patients without a prior history of tolerating botulinum toxin injections should receive a lower initial dosage. Subsequent dosing should be determined by the patient’s individual response.
  • Myobloc should be administered by physicians familiar with and experienced in the assessment and management of patients with cervical dystonia.
  • The duration of effect in patients responding to Myobloc treatment for cervical dystonia has been observed in studies to be between 12 and 16 weeks at doses of 5,000 Units or 10,000 Units.

Dosing for Chronic Sialorrhea

Dosing Information
  • The recommended dosage of Myobloc for chronic sialorrhea is 1,500 Units to 3,500 Units, divided among the parotid and submandibular glands (Table 1). Patient response to treatment should be considered when determining subsequent Myobloc dosage.
  • The typical duration of effect of each treatment is up to 3 months; however, the effect may vary in individual patients.
  • The frequency of Myobloc repeat treatments should be determined by clinical response but should generally be no more frequent than every 12 weeks.

Table 1: Dosing by Gland for Chronic Sialorrhea in Adults

Gland Recommended Dosage
Parotid 500 Units to 1,500 Units per gland
Submandibular 250 Units per gland


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What drugs interact with Myobloc?

Aminoglycosides and Other Agents Interfering with Neuromuscular Transmission

  • 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.

Anticholinergic Drugs

  • Use of anticholinergic drugs after administration of Myobloc may potentiate systemic anticholinergic effects.

Other Botulinum Neurotoxin Products

  • The effect of administering different botulinum toxin products at the same time or within several months of each other is unknown. Excessive neuromuscular weakness may be exacerbated by administration of another botulinum toxin prior to the resolution of the effects of a previously administered botulinum toxin.

Muscle Relaxants

  • Excessive weakness may also be exaggerated by administration of a muscle relaxant before or after administration of Myobloc.

Pregnancy and breastfeeding

  • There are no adequate data on the developmental risks associated with the use of Myobloc in pregnant women.
  • No developmental toxicity was observed in pregnant rats administered Myobloc by intramuscular injection during gestation and lactation, at doses producing maternal toxicity.
  • There are no data on the presence of Myobloc in human milk, the effects on the breastfed infant, or the effects on milk production.
  • The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for Myobloc and any potential adverse effects on the breastfed infant from Myobloc or from the underlying maternal condition.


Myobloc is a prescription medicine used in adults that is injected into muscles and used to treat the abnormal head position and neck pain that happens with cervical dystonia (CD), and into glands that make saliva and is used to treat long-lasting (chronic) drooling (sialorrhea). Serious side effects of Myobloc include allergic reactions with symptoms such as itching, rash, redness, swelling, wheezing, trouble breathing, or dizziness or feeling faint.

Treatment & Diagnosis

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Report Problems to the Food and Drug Administration

You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

Medically Reviewed on 9/8/2023
All sections courtesy of the U.S. Food and Drug Administration