Botulinum toxin exerts its effect by cleaving key proteins required for nerve activation. First, the toxin binds specifically to nerves which use the neurotransmitter acetylcholine. Once bound to the nerve terminal, the neuron takes up the toxin into a vesicle. As the vesicle moves farther into the cell, it acidifies, activating a portion of the toxin which triggers it to push across the vesicle membrane and into the cell cytoplasm. Once inside the cytoplasm, the toxin cleaves SNARE proteins preventing the cell from releasing vesicles of neurotransmitter. This stops nerve signaling, leading to paralysis.
The effects of botulinum toxin are different from those of nerve agents involved insofar in that botulism symptoms develop relatively slowly (over several days), while nerve agent effects are generally much more rapid and can be instantaneous. Evidence suggests that nerve exposure (simulated by injection of atropine and pralidoxime) will increase mortality by enhancing botulinum toxin's mechanism of toxicity.
The potency Units of BOTOX (onabotulinumtoxinA) for injection are specific to the preparation and assay method utilized. They are not interchangeable with other preparations of botulinum toxin products and, therefore, units of biological activity of BOTOX cannot be compared to nor converted into units of any other botulinum toxin products assessed with any other specific assay method [see WARNINGS AND PRECAUTIONS and DESCRIPTION] .
No definitive serious adverse event reports of distant spread of toxin effect associated with dermatologic use of BOTOX® Cosmetic at the labeled dose of 20 Units (for glabellar lines), 24 Units (for lateral canthal lines), 40 Units (for forehead lines with glabellar lines), 44 Units (for simultaneous treatment of lateral canthal lines and glabellar lines), and 64 Units (for simultaneous treatment of lateral canthal lines, glabellar lines, and forehead lines) have been reported.
Injection description is very important. It is best to describe the injections as a pinch rather than a bee sting, and to explain that the injections are shallow, with only a half-inch needle. As a result of the superficial technique used with the injections, deep anticoagulation can be continued. The procedure is short, and talking to the patient during the procedure about something other than the injections can help alleviate the patient’s anxiety. It is important to describe onabotulinumtoxinA as a purified protein rather than a toxin or a poison. In addition, stating that it relaxes muscles rather than causing paralysis will be reassuring to the patient. In a very anxious patient, the areas to be injected can be iced first or a local anesthetic cream can be applied. Starting with the trapezius muscle can also help, as these injections are the least painful, and the patient cannot see the needle. Finally, it is important to make sure the injections are performed with a sharp needle, and blunt needles are discarded. Thirty-gauge needles only remain sharp for six to eight needle sticks each.