Botulinum Toxin

Botulinum toxin, also called “miracle poison,” is one of the most poisonous biological substances known.
Botulinum toxin (BoNT) is produced by the bacterium Clostridium botulinum, an anaerobic, gram-positive, spore-forming rod commonly found on plants, in soil, water and intestinal tracts of animals. And related species. BoNT is often shortened to Botox, it is a neurotoxin protein.
Because BoNT is a neurotoxin it prevent the release of neurotransmitter acetylcholine from axon ending at the neuromuscular junction, thus causing flaccid paralysis (Flaccid paralysis is a neurological condition characterized by weakness or paralysis and reduced muscle tone without other obvious cause (e.g., trauma). This abnormal condition may be caused by disease or by trauma affecting the nerves associated with the involved muscles).

Biochemical Aspects

Disease caused by BoNT is commonly known as botulism. This toxin is also used commercially for medical and cosmetic purposes.
The seven main type of botulinum toxin are names as A to G (A, B, C1, C2, D, E, F and G). new types are occasionally found. Type A, B, E and F are commonly known to cause disease in humans. While other types can cause disease in other animals. Botulinum toxin A and B are used in medicine to treat various muscle spasms.
Botulinum toxins are the most protein toxins known.
The estimated human lethal does of type A toxin is 1.3 – 2.1 no/kg intravenously or intramuscularly. 10 – 13 ng/kg when inhaled, or 1000 ng/kg when taken by mouth.
Commercial forms are marked under the brand names Botox (onabotulinumtoxin A), Dysport / Azzalure (abobotulinumtoxin A), Xeomin / Bocouture (incobotulinumtoxin A) and Juneau (prabotulinumtoxin A).
How botulinum toxin works:
All the serotypes interfere with neural transmission by blocking the release of acetylcholine, which is the principal neurotransmitter at the neuromuscular junction. inter muscular administration of botulinum toxin acts at the neuromuscular junction to cause muscle paralysis by inhabiting the release of acetylcholine from presynaptic motor neurone.
Botulinum toxins act at four different sites in the body: The neuromuscular junction, autonomic ganglia, postganglionic parasympathetic nerve endings and postganglionic sympathetic nerve endings that release acetylcholine.
Botulinum toxin require 24-72 hours to take effect, it is the time required to disrupt the synaptosomal process. In some individual it may reach up to 5 days. Peaking at about 10 days, the effect of botulinum toxin lasts nearly 8-12 weeks.

Medical Use:

Botulinum toxin was approved for the treatment of numerous disorders of spasticity and a host of other conditions. Currently it is used in almost every sub-specialty of medicine. In 2002, the FDA approved the use o Botox (Botulinum toxin-A) for the cosmetic purpose of temporarily reducing labeller forehead frown lines.
Botulinum toxin is used to treat a number of therapeutic indications, many of which are not part of the approved drug label.
Botulinum toxin can be used to rest muscle spasticity, muscle disorders, excessive sweating, migraine, cosmetic dermatology etc.

Side effects:

While botulinum toxin has been tested for treatment, serious side effects from its use can occur. Most commonly, botulinum toxin can be injected into the wrong muscle group or with time spread from the injection site, causing temporary paralysis of unintended muscles.
side effects from cosmetic use generally result from unintended paralysis of facial muscles. Theses include partial facial paralysis, muscle weakness, and trouble swallowing. Side effects are not limited to direct paralysis, however, and can also include headaches, flu-like symptoms, and allergic reactions.
Just as cosmetic treatments those only last a number of months, paralysis side effects can have the same duration, but in some cases these side effects have been reported to last longer.

Reference:
PubMed Central