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Brand name: Myobloc
Drug class: Other Miscellaneous Therapeutic Agents
VA class: MS900
Chemical name: Botulin B
Molecular formula: C6869H10545N1715O2036S34
CAS number: 93384-44-2

Medically reviewed by on Mar 15, 2022. Written by ASHP.


    Distant Spread of Toxin Effects
  • Effects of any botulinum toxin may spread from local sites of injection, producing symptoms consistent with the mechanism of action of botulinum toxin. (See Distant Spread of Toxin Effects under Cautions.)

  • Symptoms reported hours to weeks following injection.

  • Swallowing and breathing difficulties may be life-threatening; deaths reported.

  • Children treated for limb spasticity probably at highest risk; however, such effects also can occur in adults, particularly those with underlying predisposing conditions. (See Pediatric Use under Cautions.)

  • In both labeled and unlabeled (e.g., spasticity in children) uses, symptoms consistent with the spread of toxin effect reported at doses comparable to or lower than those used in cervical dystonia.


Neurotoxin produced by Clostridium botulinum; disrupts neurotransmission by inhibiting release of acetylcholine from peripheral and ganglionic autonomic cholinergic nerve terminals.

Uses for RimabotulinumtoxinB

Currently, 3 botulinum toxin type A preparations (abobotulinumtoxinA [Dysport], incobotulinumtoxinA [Xeomin], and onabotulinumtoxinA [Botox, Botox Cosmetic]) and one botulinum toxin type B preparation (rimabotulinumtoxinB [Myobloc]) are commercially available in the US. These preparations are not interchangeable; assay methods used to determine potency of botulinum toxins are specific to each individual manufacturer and/or formulation.

Cervical Dystonia

Treatment of cervical dystonia (spasmodic torticollis) to decrease severity of associated abnormal head position and neck pain; designated an orphan drug by FDA for this use.

Botulinum toxins considered first-line therapy for cervical dystonia because of efficacy, relatively low incidence of adverse effects, and temporary dose-related therapeutic effects (compared with surgery).

Also considered effective and safe in patients who are not responsive to type A botulinum toxins.

Appears to be effective in patients who develop tolerance to type A botulinum toxins as well as in those who are responsive to type A botulinum toxins.

Very limited experience in patients not previously treated with botulinum toxin type A (e.g., onabotulinumtoxinA).

Blepharospasm and Associated Facial Nerve Disorders

Has been used in the management of blepharospasm [off-label] or hemifacial spasm [off-label], but efficacy evidence and experience are limited; used principally in patients who have responded previously to onabotulinumtoxinA.

The American Academy of Neurology (AAN) states that onabotulinumtoxinA and incobotulinumtoxinA should be considered as treatment options, and abobotulinumtoxinA may be considered for the treatment, of blepharospasm; AAN does not make a recommendation about rimabotulinumtoxinB for this use due to a lack of data.


Has been used for symptomatic management of severe primary axillary hyperhidrosis [off-label] and focal palmar hyperhidrosis [off-label]; however, efficacy evidence and experience are limited.


Has been used for temporary improvement in appearance of vertical glabellar facial (“frown”) lines [off-label], lateral canthal lines (“crow’s feet”) and horizontal forehead lines in a limited number of individuals; efficacy evidence and experience are limited.

RimabotulinumtoxinB Dosage and Administration


  • Adjust dosage carefully according to response and particular condition treated.

  • Generally, the effective IM dose depends on muscle mass; the larger the muscle, the higher the required dose.

  • Optimal dosages for a number of conditions have not been fully elucidated.

  • If a patient fails to respond, consider possibility of an inadequate drug dose, improperly stored drug solution, and/or misinjection.

Controlling Injection Pain

  • Pretreatment with ice packs or topical or local anesthetics (e.g., lidocaine/prilocaine cream and an occlusive dressing, proparacaine ophthalmic solution) has been recommended.

  • Some clinicians report that topical or local anesthetics are not useful to prevent injection pain since they do not penetrate underlying muscles and/or require additional injections.

  • Dilution with 0.9% sodium chloride injection containing a preservative (benzyl alcohol) has been reported to reduce pain on injection; however, the manufacturer recommends use of 0.9% sodium chloride injection without preservative for dilution.

  • Some clinicians suggest that injection pain (possibly due to acidity of the solution) may be decreased by adding a small amount of sodium bicarbonate to the injection solution. However, the compatibility and stability of such solutions remain to be fully elucidated.

  • IV sedation or general anesthesia may be needed prior to injection in some patients (e.g., those in considerable pain).


Administer by IM injection into affected muscles.

Has been administered intradermally, intracutaneously, sub-Q, or directly into affected glands.

IM Administration

Administer by IM injection into affected muscles.


Commercially available as a sterile solution containing 5000 units of rimabotulinumtoxinB per mL. Do not shake vial.

Myobloc vials are overfilled to ensure delivery of the labeled volume of drug: the vial labeled as containing 2500 units in 0.5 mL actually contains approximately 4100 units in 0.82 mL, the vial labeled as containing 5000 units in 1 mL actually contains approximately 6800 units in 1.36 mL, and the vial labeled as containing 10,000 units in 2 mL actually contains approximately 12,650 units in 2.53 mL. Do not dilute drug solutions in the vial since this may result in a solution with a higher concentration than expected due to overfill.

Allow stopper of the vial to dry thoroughly after cleansing with alcohol before entering vial with a needle to prevent toxin inactivation.

May be diluted with 0.9% sodium chloride injection to obtain desired concentration; however, since the drug solution does not contain a preservative, use diluted solutions within 4 hours of preparation. Diluted solutions reportedly stable for at least 24 hours at 25°C.

Vials are for single use only; discard any unused portions.

Carefully dispose of all used vials, including expired vials and/or equipment used in preparation and administration, as medical waste.

Injection Techniques/Precautions (General)

Targeting the injection to the appropriate muscle(s) may be facilitated by active electromyography (EMG), ultrasonography, palpation of muscle belly, and/or use of anatomic landmarks (e.g., evidence of muscular hypertrophy, stiffness, tenderness, visible abnormal muscular activity).

EMG-guided injections often are recommended to ensure optimal placement of toxin, particularly in patients who have not responded adequately to previous injections, and to minimize adverse effects on nonaffected tissue.

Injection into midbelly of larger muscles where motor end plates are located may enhance benefit.

Injection Techniques/Precautions (Cervical Dystonia)

Clinicians who administer rimabotulinumtoxinB should be familiar with and experienced in the assessment and management of cervical dystonia.

Total dose administered at each treatment session is given as several injections divided among affected muscles.

Identify affected muscles by careful clinical evaluation, including physical examination (e.g., for areas of hypertrophy, pain) and palpation. Palpation of contracting muscles while patient’s head is placed in position most favored by dystonic pulling of neck muscles is reportedly helpful.

EMG guidance may be useful in delineating involved muscles for injection, particularly in obese patients or for muscles difficult to identify by palpation.

Injection Techniques/Precautions (Facial Cosmesis)

Some clinicians suggest that injection procedures be adapted to account for the relatively greater diffusion characteristics of rimabotulinumtoxinB compared with type A.

Appears to have increased diffusion within the muscle (potentially reducing the number of injections and complications) and a somewhat faster onset of action (e.g., within 24–48 hours) than botulinum toxin type A; however, additional experience needed to establish the optimal dose, number of injection sites, and frequency of treatment for facial cosmesis.

Minimize risk of ptosis by avoiding injections near levator palpebrae superioris, especially in individuals with larger brow-depressor complexes.

Do not treat entire forehead and glabellar lines during a single session; high risk of ptosis.

Avoid eyelid ptosis by asking individual to remain upright (e.g., avoid naps in reclining position) for 4 hours following treatment, avoid rubbing or massaging treated area for 4 hours (to prevent excess diffusion and possible weakness of adjacent muscles), and frown and smile repeatedly for at least 1–4 hours following treatment.

When injection sites are marked (e.g., with a ball-point pen) to ensure optimal targeting, avoid injecting directly into marked areas to prevent tattooing of skin.

If concurrent cosmetic alteration of the eyebrow is planned, defer treatment of the lateral eyebrow until after treatment of lateral canthal lines (“crow’s feet”); increased diffusion may accomplish sufficient cosmetic alteration of the eyebrow to eliminate the need for further treatment.


Potency of rimabotulinumtoxinB expressed in units of biologic activity; each unit is equivalent to the median intraperitoneal lethal dose (LD50) in mice.

Because of differences in assay methods, units of biologic activity of rimabotulinumtoxinB cannot be compared with or converted to units of any other botulinum toxin (e.g., abobotulinumtoxinA, incobotulinumtoxinA, onabotulinumtoxinA).


Cervical Dystonia

Titrate initial and subsequent dosage considering previous response, adverse reactions, and severity of dystonia based on head and neck position, localization of pain, mass of target muscles and their proximity to critical toxin-sensitive anatomic structures (e.g., larynx, pharynx), and muscular hypertrophy.

Patients with a history of tolerating botulinum toxin treatment: Initially, total recommended dose per treatment session is 2500–5000 units divided among affected muscles. Total initial doses as high as 10,000 units per treatment session have been used.

Toxin treatment-naive patients: Use a lower initial dose. (See Botulinum Toxin-naive Patients under Cautions.)

Duration of response to 5000–10,000 units is generally 12–16 weeks.

Primary Axillary Hyperhidrosis†

2000 units per axilla, distributed among 25 sites about 2 cm apart, suggested.

Anhidrosis following rimabotulinumtoxinB injection may occur within 3–5 days, with peak effect in 1–2 weeks and duration 9–16 weeks; duration of response with 2000 or 4000 units per axilla does not appear dose related.

Palmar Hyperhidrosis†

7500–9000 units in each palm, distributed among 30–35 sites, suggested.

Duration of muscle weakness (e.g., 2–3 weeks) following treatment with rimabotulinumtoxinB appears similar to that with onabotulinumtoxinA.

Glabellar Facial (“Frown”) Lines†

Total dose of 2400–3000 units divided among 6 injection sites used; total dose of 2000–3000 units divided among 3 injection sites also suggested.

Injection procedure for rimabotulinumtoxinB may differ from that for onabotulinumtoxinA based on relatively greater diffusion of rimabotulinumtoxinB.

Lateral Canthal Lines (“Crow’s Feet”)†

1500 units divided among 3 injection sites per side (total dosage 3000 units) has been used; wrinkle severity was reduced by day 30 and generally had returned to baseline between days 90 and 120.

750 units divided among 3 injection sites per side also has been used (total dosage 1500 units if both sides treated); resolution of wrinkles occurred at 7 days.

Horizontal Forehead Lines†

1000–2500 units on each side of forehead suggested. Some clinicians suggest that injections be placed slightly higher than the equator of the brow (no lower than 2.5–4 cm above the brow) to account for increased diffusion of rimabotulinumtoxinB.

If planning to treat both glabellar and horizontal forehead lines, may treat glabellar facial lines first and reevaluate again in 2 weeks to determine if further treatment needed.

Prescribing Limits


Cervical Dystonia

Do not exceed recommended dosage or frequency of administration; safety and efficacy of higher dosages not established.

Special Populations

Geriatric Patients

Select dosage with caution because of age-related decreases in hepatic, renal, and/or cardiac function and potential for concomitant disease and drug therapy.

Cautions for RimabotulinumtoxinB


  • Hypersensitivity to rimabotulinumtoxinB or any ingredient in the formulation.

    Infection at proposed injection site(s).



Distant Spread of Toxin Effects

Potential for systemic spread of toxin effects beyond local sites of injection; manifested as unintended muscular weakness in noncontiguous anatomic structures and other potentially life-threatening adverse effects. (See Boxed Warning.)

Monitor patients for possible systemic effects (e.g., dysphagia, dysphonia, respiratory compromise, generalized weakness) following administration.

Weakness of adjacent muscles commonly reported with botulinum toxin administration.

Adverse effects consistent with mechanism of botulinum toxin action (e.g., asthenia/unexpected loss of strength or generalized muscle weakness, blurred vision, breathing difficulties/respiratory impairment, diplopia, dysarthria, dysphagia, dysphonia, hoarseness, ptosis, urinary incontinence) reported in both children and adults receiving botulinum toxin for a variety of conditions in a wide range of dosages.

Risk of toxin spread probably highest in children treated for spasticity (currently not an FDA-labeled use for rimabotulinumtoxinB). (See Pediatric Use under Cautions.)

In some cases, swallowing and breathing difficulties required hospitalization, mechanical ventilation, or feeding tubes and/or resulted in death. (See Dysphagia and Breathing Difficulties under Cautions.)

Other Warnings/Precautions

Lack of Interchangeability Among Botulinum Toxin Preparations

The method used to determine potency of each botulinum toxin is specific to the individual manufacturer and/or preparation; therefore, units of biologic activity for rimabotulinumtoxinB cannot be compared with or converted to units of any other botulinum toxin.

Dysphagia and Breathing Difficulties

Dysphagia is most common serious adverse effect reported in patients with cervical dystonia. Results from diffusion of the toxin to tissues (e.g., posterior pharyngeal muscles) outside the injected muscles. Rarely, dysphagia may require placement of gastric feeding tube.

Rarely, fatal aspiration pneumonia or other serious debilities may develop subsequent to dysphagia.

Risk increased in patients with cervical dystonia and smaller neck muscle mass (e.g., female) receiving bilateral injections and/or relatively high doses into the sternocleidomastoid muscle.

Use lowest effective dose in such high-risk muscles.

Immediate medical attention may be required if patients develop problems with swallowing, speech, or respiratory disorders.

Preexisting Neuromuscular Disorders

Increased risk of serious adverse systemic effects (e.g., severe dysphagia, muscle weakness, respiratory compromise) with recommended doses in patients with neuromuscular disorders (e.g., peripheral motor neuropathic diseases [e.g., amyotrophic lateral sclerosis, motor neuropathy] or neuromuscular junction disorders [e.g., myasthenia gravis, Lambert-Eaton syndrome]); exercise caution in such patients. May be related to use of higher dosages in such patients.

Rarely, extreme sensitivity to systemic effects of usual doses reported in patients with known or unrecognized neuromuscular disorders; some patients experienced several months of severe dysphagia and required a gastrostomy or nasogastric tube.

Serious systemic effects related to distant spread of botulinum toxin reported more often and with greater severity in children with cerebral palsy. (See Pediatric Use under Cautions.)

Risk of Viral Disease Transmission

Formulation contains albumin derived from human blood. Remote risk of transmission of Creutzfeldt-Jakob disease (CJD) via albumin component; however, no cases identified to date.

Botulinum Toxin-naive Patients

Clinical experience in patients who have not previously tolerated treatment with botulinum toxin type A is limited.

Initiate treatment with lower doses than those recommended for patients with a history of tolerating such treatment.

Injection-related Effects

Ecchymosis reported.

Administer with caution to patients with thrombocytopenia or a bleeding disorder (e.g., hemophilia) or those receiving anticoagulant therapy.


Antibodies to the drug may develop in patients receiving repeated treatment; may have neutralizing activity. Such patients may still respond to the drug.

Clinical importance not determined. Not known if patients with neutralizing antibodies to botulinum toxin type A are at increased risk of developing tolerance to botulinum toxin type B.

Neutralizing antibodies generally not detected until after 6 months of treatment.

Patients who develop tolerance to botulinum toxin type A may respond to botulinum toxin type B or other botulinum toxin serotypes (e.g., botulinum toxin type F); however, long-term response to other serotypes in such patients not fully elucidated.

Reporting Adverse Effects or Overdosage

If the patient receives an overdose of rimabotulinumtoxinB or the drug is injected into the wrong muscle (i.e., misinjection), contact the local or state health department to process a request for botulism antitoxin through the CDC Drug Service. If a response is not received within 30 minutes, contact the CDC Emergency Operations Center directly at 770-488-7100. Information about the antitoxin is available at [Web].

Botulism antitoxin will not reverse any botulinum toxin-induced muscle weakness evident at the time of antitoxin administration but may stabilize the deficits.

Specific Populations


Category C.


Not known whether distributed into human milk. Use with caution.

Pediatric Use

Safety and efficacy not established in children <18 years of age with cervical dystonia.

Serious systemic toxicity resembling botulism (e.g., dysphagia, respiratory failure) reported during postmarketing experience in children <16 years of age. Such effects observed with rimabotulinumtoxinB doses of 388–625 units/kg. Severe cases involving death or hospitalization or requiring use of gastric feeding tubes and/or mechanical ventilation have occurred, principally in children with cerebral palsy-associated limb spasticity. No deaths or serious complications requiring intubation or ventilatory support reported among such cases of botulism in adults.

Geriatric Use

Safety and/or efficacy in those ≥65 years of age similar to that in younger adults.

Safety and efficacy data in patients ≥75 years of age insufficient for any comparison to that in younger adults.

Common Adverse Effects

Treatment of cervical dystonia: Dry mouth, dysphagia, dyspepsia, injection-site pain.

Interactions for RimabotulinumtoxinB

Specific Drugs





Potential for prolonged paralytic effect of toxin

Use concomitantly with caution

Anti-infective agents interfering with neuromuscular transmission (aminoglycosides, lincosamides, polymyxins)

Potential for prolonged paralytic effect of toxin

Use concomitantly with caution

Botulinum toxin treatment, concurrent or sequential

Possible increased paralytic effect with concurrent or sequential use within several months of administration of rimabotulinumtoxinB

Data on concurrent or sequential use of botulinum toxins lacking

Magnesium salts (magnesium sulfate)

Potential for prolonged paralytic effect of toxin

Use concomitantly with caution

Neuromuscular blocking agents (e.g., atracurium, succinylcholine)

Potential for prolonged paralytic effect of toxin

Use concomitantly with caution


Potential for prolonged paralytic effect of toxin

Use concomitantly with caution

RimabotulinumtoxinB Pharmacokinetics



No formal pharmacokinetic studies; manufacturer states that drug is not expected to be present in peripheral circulation in measurable concentrations following IM or intradermal injection of recommended doses.


Duration of response to 5000–10,000 units in cervical dystonia is generally 12–16 weeks.





Stable for up to 48 months at 2–8°C when stored in unopened vials; do not freeze or shake. Do not use after the expiration date marked on the vial.

Reportedly stable for up to 9 months when stored in unopened vials at 15–30ºC.

Use solutions diluted with 0.9% sodium chloride injection without preservatives within 4 hours of preparation.


For information on systemic interactions resulting from concomitant use, see Interactions.


Drug Compatibility

Buffering agents (e.g., sodium bicarbonate) reportedly may destabilize the toxin and/or alter its diffusion characteristics.


  • Induces chemical denervation and flaccid paralysis by disruption of neurotransmission; inhibits release of acetylcholine at presynaptic cholinergic nerve terminals of the peripheral nervous system and at ganglionic nerve terminals of the autonomic nervous system.

  • Inhibits sweat production by blocking release of acetylcholine, which mediates sympathetic neurotransmission in eccrine glands.

  • Induces neuromuscular blockade via a zinc-dependent endopeptidase, which blocks vesicles containing acetylcholine from fusing with the terminal membrane of the motor neuron.

  • Without acetylcholine release, the muscle is unable to contract and flaccid paralysis ensues.

  • At therapeutic doses, muscular paralysis limited to injected muscle; however, weakness or paralysis of adjacent muscles may occur as a result of local diffusion.

  • Selective chemodenervation is reversible; although muscular atrophy occurs, regeneration of extrajunctional receptors and terminals limits the duration of activity to a few months.

  • Recovery of neuromuscular activity occurs through neurogenesis of axonal sprouts and motor end plates.

  • Functional recovery develops in 3–6 months, but sprouting and remodeling may continue for as long as 3 years.

  • Response in autonomic disorders involving excessive glandular secretion (e.g., hyperhidrosis) may be longer than in conditions involving overactivity of striated or smooth muscle; additional study needed to elucidate mechanism in glandular and non-muscle tissue.

Advice to Patients

  • Inform patients with cervical dystonia of possibility of dysphagia (typically mild to moderate); rarely, severe dysphagia occurs, sometimes associated with aspiration, dyspnea, pneumonia, and need to reestablish an airway.

  • Inform patients of possible systemic effects (e.g., weakness, shortness of breath, respiratory complications, swallowing difficulties) following local injection.

  • Advise patients and/or caregivers to seek immediate medical attention if unexpected muscle weakness or swallowing, speech, or respiratory disorders occur. Advise patients to avoid driving a car or engaging in other potentially hazardous activities if they have such symptoms.

  • Advise previously sedentary patients to resume activity gradually following treatment.

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as any concomitant illnesses (e.g., neuromuscular disorders).

  • Importance of women informing their clinician if they are or plan to become pregnant or plan to breast-feed.

  • Importance of informing patients of other important precautionary information. (See Cautions.)


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.



Dosage Forms


Brand Names




5000 units/mL


Solstice Neurosciences

AHFS DI Essentials™. © Copyright 2023, Selected Revisions March 25, 2019. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

† Off-label: Use is not currently included in the labeling approved by the US Food and Drug Administration.

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Frequently asked questions