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Generic name: rimabotulinumtoxinB (Myobloc) [ RYE-ma-BOT-ue-LYE-num-TOX-in-B ]
Brand name: Myobloc
Dosage form: injectable solution (5000 units/mL)
Drug class: Skeletal muscle relaxants

Medically reviewed by on Jul 19, 2023. Written by Cerner Multum.

What is rimabotulinumtoxinB (Myobloc)?

RimabotulinumtoxinB (Myobloc), also called botulinum toxin type B, is made from the bacteria that causes botulism. Botulinum toxin blocks nerve activity in the muscles, causing a temporary reduction in muscle activity.

Myobloc is used to treat cervical dystonia (severe spasms in the neck muscles).

Myobloc is also used to treat chronic drooling (sialorrhea).

Myobloc may also be used for purposes not listed in this medication guide.

Myobloc side effects

Get emergency medical help if you have signs of an allergic reaction: hives; feeling light-headed; difficulty breathing; swelling of your face, lips, tongue, or throat.

The botulinum toxin contained in this medicine can spread to other body areas beyond where it was injected. This has caused serious life-threatening side effects in some people receiving botulinum toxin injections, even for cosmetic purposes.

Call your doctor at once if you have any of these side effects (up to several hours or weeks after an injection):

  • unusual or severe muscle weakness (especially in a body area that was not injected with the medication);

  • trouble breathing, talking, or swallowing;

  • hoarse voice, drooping eyelids;

  • blurred vision, double vision;

  • loss of bladder control;

  • problems with vision; or

  • chest pain.

Common side effects of rimabotulinumtoxinB may include:

  • pain or discomfort where the medicine was injected;

  • headache;

  • dry mouth; or

  • trouble swallowing.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


You should not receive this medicine if you are allergic to botulinum toxin, or if you have an infection in the area where the medicine will be injected.

The botulinum toxin contained in this medication can spread to other body areas beyond where it was injected. This can cause serious life-threatening side effects.

Call your doctor at once if you have a hoarse voice, drooping eyelids, vision problems, severe muscle weakness, loss of bladder control, or trouble breathing, talking, or swallowing. Some of these effects can occur up to several weeks after a botulinum toxin injection.

Before taking this medicine

You should not be treated with Myobloc if you are allergic to botulinum toxin, or if you have an infection in the area where the medicine will be injected.

Tell your doctor if you have ever had a side effect after receiving a botulinum toxin in the past.

Tell your doctor if you have ever had:

Myobloc is made from donated human plasma and may contain viruses or other infectious agents. Donated plasma is tested and treated to reduce the risk of contamination, but there is still a small possibility it could transmit disease. Ask your doctor about any possible risk.

It is not known whether this medicine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

It may not be safe to breastfeed while using this medicine. Ask your doctor about any risk.

How is Myobloc given?

This medicine is injected into a muscle or into a gland. A healthcare provider will give you this injection once every 12 to 16 weeks. Myobloc injections should be spaced at least 3 months apart.

Your injections may be given into more than one area at a time, depending on the condition being treated.

The effects of a Myobloc injection are temporary. Your symptoms may return completely within 3 months after an injection. After repeat injections, it may take less and less time before your symptoms return, especially if your body develops antibodies to the botulinum toxin.

Do not seek botulinum toxin injections from more than one medical professional at a time. If you switch healthcare providers, be sure to tell your new provider how long it has been since your last botulinum toxin injection.

Using this medicine more often than prescribed will not make it more effective and may result in serious side effects.

RimabotulinumtoxinB dosing information

Usual Adult Dose for Cervical Dystonia:

For patients who have demonstrated tolerability to botulinum toxin:
Initial dose: 2500 to 5000 Units IM divided among affected muscles

For patients who have not demonstrated tolerability to botulinum toxin:
-Lower initial doses are recommended

Subsequent dosing should be optimized according to patient's response
-Duration of effect: 12 to 16 weeks (at doses of 5000 to 10,000 Units)

-This drug should be administered by physicians familiar and experienced in the assessment and management of patients with cervical dystonia.

Use: To reduce the severity of abnormal head position and neck pain associated with cervical dystonia.

Usual Adult Dose for Sialorrhea:

Initial dose: 1500 to 3500 Units divided among the parotid and submandibular glands:
--Parotid: 500 to 1500 Units per gland
--Submandibular: 250 Units per gland

Subsequent dosing should be based on patient's response; typical duration of effect for each treatment is up to 3 months, but may vary in individual patients
Frequency of treatment: Generally, no more frequent than every 12 weeks

-Consult package labeling for additional administration guidance including illustration of gland placement.
-In clinical trials, both anatomical landmarks and ultrasound guidance were used for gland location; both methods produced similar reduction in the unstimulated salivary flow rate.

Use: For the treatment of chronic sialorrhea.

What happens if I miss a dose?

Since botulinum toxin has a temporary effect and is given at widely spaced intervals, missing a dose is not likely to be harmful.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may not appear right away, but can include muscle weakness, trouble swallowing, weak or shallow breathing, or loss of movement in any part of your body.

What should I avoid after receiving Myobloc?

Myobloc may impair your vision or depth perception. Be careful if you drive or do anything that requires you to be able to see clearly.

What other drugs will affect Myobloc?

Tell your doctor about all your other medicines, especially:

This list is not complete and many other drugs may affect Myobloc. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Frequently asked questions

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.