onabotulinumtoxinA (Botox)

OnabotulinumtoxinA is an injectable neuro-toxin, that is, a toxic chemical that blocks the ability of nerves to make muscles contract. In other words, it paralyzes muscles. 

OnabotulinumtoxinA is used for the treatment of chronic migraine headaches, axillary hyperhidrosis, upper limb spasticity, cervical dystonia, strabismus, and frown lines.

To cause muscles to contract, nerves release a chemical, acetylcholine, where they meet muscle cells. The acetylcholine attaches to receptors on the muscle cells and causes the muscle cells to contract or shorten. OnabotulinumtoxinA prevents the release of acetylcholine and thereby prevents contraction of the muscle cells. In order to affect the release of acetylcholine, onabotulinumtoxinA must be injected into the muscle.

OnabotulinumtoxinA was approved by the FDA in December 1991.

Side effects of onabotulinumtoxinA include:

• allergic reactions,
• rash,
• itching,
• headache,
• neck pain,
• difficulty swallowing,
• shortness of breath,
• nausea,
• weakness, and dry mouth.

Patients also complain of pain and tenderness at the injection site. Patients treated for blepharospasm may experience

• drooping of the eyelid (ptosis),
• inflammation of the cornea (keratitis),
• eye dryness,
• double vision,
• tearing,
• and sensitivity to light.

Those treated for urinary incontinence may experience:

• difficulty urinating.
• Heart attacks,
• abnormal heart beats, and
• death.

OnabotulinumtoxinA is giving by intramuscular injection. Dosing should be individualized (based on its purpose and the patient in whom it is being used), and the lowest effective dose should be used. OnabotulinumtoxinA is not interchangeable with other preparations of botulinum toxin.

• Chronic Migraine: 155 units divided amongst 31 sites and injected every 12 weeks
• Upper limb spasticity: 75-360 units divided among selected sites. No more than 50 units injected per site; may repeat when effect diminishes but no sooner than every 12 weeks.
• Cervical dystonia: 189-300 units divided among affected muscles. No more than 50 units injected per site.
• Axillary hyperhidrosis: 50 units per arm pit; repeat when effect diminishes.
• Blepharospasm: Initial dose is 1.25-2.5 units. Increase if response is not adequate. There appears to be no benefit in injecting more than 5 units.
• Strabismus: Initial dose is 1.25 to 5 units per muscle; may increase subsequent doses by up to two-fold; maximum dose for each muscle is 25 units.
• Urinary incontinence: 200 units per treatment.

• Administration of onabotulinumtoxinA with other agents (for example, aminoglycosides, curare) that affect neuromuscular function may increase the effect of onabotulinumtoxinA.
• Use of muscle relaxants may increase the occurrence of weakness.
• Use of drugs that block acetylcholine may increase some effects of onabotulinumtoxinA.

There are no adequate studies of onabotulinumtoxinA in pregnant women.

OnabotulinumtoxinA has not been evaluated in nursing mothers

What preparations of botulinum toxin type A are available?

• Powder for Injection: 50, 100, or 200 units

How should I keep botulinum toxin type A stored?

• Unopened vials or reconstituted onabotulinumtoxinA should be refrigerated at 35.6 to 46.4 F (2 to 8 C). Reconstituted toxin should be used within 24 hours.