Myobloc (RimabotulinumtoxinB) is a neurotoxin that is derived from clostridium botulinum. It is used as an intramuscular injection in patients with localized muscle spasms such as cervical dystonia and blepharospasm

RimabotulinumtoxinB Uses:

• Cervical dystonia:

  • It is used in the treatment of patients with cervical dystonia or spasmodic torticollis.

• Off Label Use of RimabotulinumtoxinB in Adults:

  • It is used as an off-label medicine for the treatment of upper limb spasticity and drooling of saliva.

Myobloc (RimabotulinumtoxinB) Dose in Adults

Myobloc (RimabotulinumtoxinB) Dose in the treatment of Cervical dystonia:

• Initial: 2,500 to 5,000 units administered as intramuscular injections into the affected muscles (divided among the affected muscles in patients previously treated with botulinum toxin);
• Patients who have not received previous treatment should receive lower initial doses. Subsequent doses should be administered as per the patient's response and requirement.

Myobloc (RimabotulinumtoxinB) Dose in the treatment of Sialorrhea (drooling of saliva) (off-label):

• Intraglandular (off-label route):

  • 250 to 1,000 units injected per gland via percutaneous injection (ventral approach) at the submandibular gland, parotid gland, or both. One injection is administered per side with intervals of about 4 to 6 months between treatments.

Use in Children:

Not indicated.

Pregnancy Risk Category: C

• It has not yet been tested in human or animal pregnancies.

Use while breastfeeding

• It is unknown if the drug is excreted from breast milk.
• It is recommended that you use it with caution if you are lactating.

Dose in Kidney Disease:

No dosage adjustment provided in manufacturer’s labeling.

Dose in Liver disease:

No dosage adjustment provided in manufacturer’s labeling.

Common Side Effects of Myobloc (RimabotulinumtoxinB):

• Central Nervous System:

  • Headache
  • Pain

• Gastrointestinal:

  • Dysphagia
  • Xerostomia

• Local:

  • Injection Site Pain

• Neuromuscular & Skeletal:

  • Neck Pain

• Miscellaneous:

  • Infection
  • Antibody Formation

Less Common Side Effects of Myobloc (RimabotulinumtoxinB):

• Cardiovascular:

  • Chest Pain
  • Edema
  • Peripheral Edema
  • Vasolidation

• Central Nervous System:

  • Dizziness
  • Anxiety
  • Chills
  • Confusion
  • Fever
  • Hyperesthesia
  • Malaise
  • Migraine
  • Somnolence
  • Tremor
  • Vertigo

• Dermatologic:

  • Pruritus
  • Bruising

• Endocrine & Metabolic:

  • Hypercholesterolemia

• Gastrointestinal:

  • Nausea
  • Dyspepsia Glossitis
  • Stomatitis
  • Taste Perversion
  • Vomiting

• Genitourinary:

  • Cystitis
  • Urinary Tract Infection
  • Vaginal Moniliasis

• Hematologic:

  • Serum Neutralizing Activity

• Neuromuscular & Skeletal:

  • Torticollis
  • Arthralgia
  • Back Pain
  • Myasthenia
  • Weakness
  • Arthritis
  • Hernia

• Ocular:

  • Amblyopia
  • Vision Abnormal

• Otic:

  • Otitis Media
  • Tinnitus

• Respiratory:

  • Cough
  • Dyspnea
  • Pneumonia

• Miscellaneous:

  • Flu-Like Syndrome
  • Abscess
  • Allergic Reaction
  • Cyst
  • Neoplasm
  • Viral Infection

Contraindications to Myobloc (RimabotulinumtoxinB):

• Allergy reactions to botulinum toxins or any component of this formulation
• Infection at the injection site

Warnings and precautions

• Anaphylaxis or hypersensitivity reactions

  • During treatment, anaphylactic and allergic reactions can occur. At the time of injection, immediate treatment should be provided.

• Formation of antibodies:

  • If the dose is increased or administered frequently, the injection may cause an antibody reaction that could lead to a decrease in the effectiveness of the treatment.

• Cardiovascular events

  • OnabotulinumtoxinA another botulinum poison formulation has been linked to cardiac toxicities, including myocardial injury and cardiac arrhythmias. It should not be used by patients with existing cardiac conditions.

• Dysphagia

  • It can cause dysphagia, which may last up to five months after it has been administered to cervical dystonia.
  • Alternative methods of feeding should be considered if the patient has dysphagia.
  • Dysphagia is more common in patients with smaller neck muscles.

• Systemic toxicities: [US Boxed Warning]

  • Inadvertent injections beyond the site of the injection have been linked to systemic side effects. There have been reports of patients experiencing difficulty breathing, blurred vision, blurred vision, dizziness, dysarthria and dysphonia as a result of inadvertent injections beyond the site of the injection.
  • These symptoms may be experienced by patients within hours or weeks of receiving the injection.
  • Children who receive treatment for unapproved spastic conditions are at greater risk of developing systemic toxicotoxicity.
  • If patients have difficulty breathing, swallowing or speaking, they should immediately seek medical attention.

• Neuromuscular disease

  • It paralyzes the muscle injected and can cause severe weakness in patients suffering from preexisting myopathy or neuromuscular disorders such as Lambert-Eaton Myasthenic Syndrome, myasthenia gravis, and Amytrophic lateral Sclerosis.

• Respiratory disease

  • Patients with chronic respiratory conditions like emphysema or chronic bronchitis should not use it. Patients with chronic respiratory failure depend on their accessory muscles to breathe. This can lead to weakness and difficulty breathing.
  • Acute respiratory failure, dysphagia or aspiration pneumonia may occur in patients who require ventilatory support.

RimabotulinumtoxinB (Myobloc): Drug Interaction

Monitor:

• Monitor for muscle weakness, swallowing difficulty, and difficulty in speaking.
• Monitor the patients for the development of respiratory failure and breathing difficulty especially in those with preexisting pulmonary problems. 

How to administer Myobloc (RimabotulinumtoxinB)?

• When treating cervical dystonia, it is administered intramuscularly. 
• When intramuscularly administering it, a needle of the appropriate size should be used.
• If the muscle cannot be identified through physical examination, it is best to inject it EMG (electromyography).
• Dysphagia incidence is decreased when drug is administered to the upper third of the muscle sternocleidomastoid.
• This means that the injection concentration is increased or reduced per muscle (when injections are done bilaterally or into the muscles of the hyaloid).

Intraglandular (offer-label route).

• Sialorrhea (drooling of saliva) (off-label usage)
  • A needle of the appropriate gauge should be used for percutaneous injections into salivary glands (parotid or submandibular) using the ventral approach.
  • When injecting glands, it is a good idea to use ultrasound guidance.

Mechanism of action of Myobloc (RimabotulinumtoxinB):

• Clostridium botulinum produces RimabotulinumtoxinB, a neurotoxin. 
• It was previously known as botulinum poison type B.
• It inhibits neurotransmitter release and paralyzes muscles by cleaving synaptic VesicleAssociation Membrane Protein (VAMP) which is a component in the protein complex that is responsible for docking the synaptic Vesicle to presynaptic.

Duration:

• It has a duration of action of about 12-16 weeks

Absorption:

• At the usual recommended doses, it is not expected to be present in peripheral blood.

International Brand Names of RimabotulinumtoxinB:

• Myobloc
• Nerbloc
• Neurobloc
• Neuronox

RimabotulinumtoxinB Brand Names in Pakistan:

No Brands Available in Pakistan.