Botox (OnabotulinumtoxinA)

Approved uses

Blepharospasm associated with dystonia, age 12 and over

1.25 to 2.5 Units injected into each of 3 sites per affected eye

Watch for exposure keratopathy afterwards: reduced blinking is the mechanism, not a coincidence

Strabismus, age 12 and over

Dose selected from the prism dioptre correction required, or from the previous response to treatment

Contraindications

BOTOX is contraindicated: In patients who are hypersensitive to any botulinum toxin product or to any of the components in the formulation. In the presence of infection at the proposed injection site(s).

Available Forms

Injection, vials of 50, 100 and 200 Units of onabotulinumtoxinA for reconstitution.

Mechanism of Action

BOTOX blocks neuromuscular transmission by binding to acceptor sites on motor or autonomic nerve terminals, entering the nerve terminals, and inhibiting the release of acetylcholine. This inhibition occurs as the neurotoxin cleaves SNAP-25, a protein integral to the successful docking and release of acetylcholine from vesicles situated within nerve endings. When injected intramuscularly at therapeutic doses, BOTOX produces partial chemical denervation of the muscle resulting in a localized reduction in muscle activity. In addition, the muscle may atrophy, axonal sprouting may occur, and extrajunctional acetylcholine receptors may develop.