Botulinum toxin, or botulinum neurotoxin, is a highly potent neurotoxic protein produced by the bacterium Clostridium botulinum and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction, thus causing flaccid paralysis. The toxin causes the disease botulism.

The toxin is also used commercially for medical and cosmetic purposes.

​

The seven main types of botulinum toxin are named types A to G (A, B, C1, C2, D, E, F and G).

New types are occasionally found. Types A and B are capable of causing disease in humans, and are also used commercially and medically.

 

Types C–G are less common; types E and F can cause disease in humans, while the other types cause disease in other animals.

Botulinum toxins are among the most potent toxins known to science. Intoxication can occur naturally as a result of either wound or intestinal infection or by ingesting formed toxin in food.

 

The estimated human lethal dose of type A toxin is 1.3–2.1 ng/kg intravenously or intramuscularly, 10–13 ng/kg when inhaled, or 1000 ng/kg when taken by mouth.

Commercial forms are marketed under the brand names Botox (onabotulinumtoxinA),

Dysport/Azzalure (abobotulinumtoxinA),

Letybo (letibotulinumtoxinA),

Myobloc (rimabotulinumtoxinB) 

Xeomin/Bocouture (incobotulinumtoxinA),

and Jeuveau (prabotulinumtoxinA).

 

Medical uses[edit]

Botulinum toxin is used to treat a number of therapeutic indications, many of which are not part of the approved drug label.[21]

Muscle spasticity[edit]

Botulinum toxin is used to treat a number of disorders characterized by overactive muscle movement, including cerebral palsy,[25][26] post-stroke spasticity,[38] post-spinal cord injury spasticity,[39] spasms of the head and neck,[40] eyelid,[19] vagina,[41] limbs, jaw, and vocal cords.[42] Similarly, botulinum toxin is used to relax the clenching of muscles, including those of the esophagus,[43] jaw,[44] lower urinary tract and bladder,[45] or clenching of the anus which can exacerbate anal fissure.[46] Botulinum toxin appears to be effective for refractory overactive bladder.[47]

Other muscle disorders[edit]

Strabismus, otherwise known as improper eye alignment, is caused by imbalances in the actions of muscles that rotate the eyes. This condition can sometimes be relieved by weakening a muscle that pulls too strongly, or pulls against one that has been weakened by disease or trauma. Muscles weakened by toxin injection recover from paralysis after several months, so injection might seem to need to be repeated, but muscles adapt to the lengths at which they are chronically held,[48] so that if a paralyzed muscle is stretched by its antagonist, it grows longer, while the antagonist shortens, yielding a permanent effect.[49]

In January 2014, botulinum toxin was approved by UK's Medicines and Healthcare products Regulatory Agency for treatment of restricted ankle motion due to lower-limb spasticity associated with stroke in adults.[50][51]

In July 2016, the US Food and Drug Administration (FDA) approved abobotulinumtoxinA (Dysport) for injection for the treatment of lower-limb spasticity in pediatric patients two years of age and older.[52][53] AbobotulinumtoxinA is the first and only FDA-approved botulinum toxin for the treatment of pediatric lower limb spasticity.[54] In the US, the FDA approves the text of the labels of prescription medicines and for which medical conditions the drug manufacturer may sell the drug. However, prescribers may freely prescribe them for any condition they wish, also known as off-label use.[55] Botulinum toxins have been used off-label for several pediatric conditions, including infantile esotropia.[56]

Excessive sweating[edit]

AbobotulinumtoxinA has been approved for the treatment of excessive underarm sweating of unknown cause, which cannot be managed by topical agents.[42][57]

Migraine[edit]

In 2010, the FDA approved intramuscular botulinum toxin injections for prophylactic treatment of chronic migraine headache.[58]

Cosmetic uses[edit]

 

Botulinum toxin being injected in the human face

In cosmetic applications, botulinum toxin is considered relatively safe and effective[59] for reduction of facial wrinkles, especially in the uppermost third of the face.[60] Commercial forms are marketed under the brand names Botox Cosmetic/Vistabel from Allergan, Dysport/Azzalure from Galderma and Ipsen, Xeomin/Bocouture from Merz, Jeuveau/Nuceiva from Evolus, manufactured by Daewoong in South Korea.[37] The effects of botulinum toxin injections for glabellar lines ('11's lines' between the eyes) typically last two to four months and in some cases, product-dependent, with some patients experiencing a longer duration of effect of up to 6 months or longer.[60] Injection of botulinum toxin into the muscles under facial wrinkles causes relaxation of those muscles, resulting in the smoothing of the overlying skin.[60] Smoothing of wrinkles is usually visible three to five days after injection, with maximum effect typically a week following injection.[60] Muscles can be treated repeatedly to maintain the smoothed appearance.[60]

DaxibotulinumtoxinA (Daxxify) is used for the temporary improvement in the appearance of moderate to severe glabellar lines (eyebrows).[16][61] DaxibotulinumtoxinA is an acetylcholine release inhibitor and neuromuscular blocking agent.[16]