The family of botulinum neurotoxins includes seven distinct serotypes identified as A, B, C1, D, E, F and G. There are variations in their size and cellular mechanism of action and in their clinical usefulness. Types A, B and F have all shown beneficial effects in humans with A being the longest acting variant to date. Short acting toxins such as E and F may be of value post surgically or after trauma.
Botulinum toxins A and B are currently commercially available worldwide. They are composed of different strains of Clostridium botulinum bacteria and have both distinct and overlapping properties. Both are 150 kD di-chain polypeptides composed of a heavy chain and a light chain linked by a disulphide bond. Both are surrounded by non-toxic proteins during their biosynthesis to form a neurotoxin complex.
Both can be found in a 500 kD form but A can also be found in a 900 kD form, and this has been the size reported for the crystallized type A toxin used clinically. In both A and B neurotoxins the heavy chain is analogous to the key in the lock and is responsible for selective binding of the toxin molecule to presynaptic cholinergic nerve terminals. The light chain acts inside the cell to prevent acetylcholine vesicle release. Within the cell, the light chain of type A cleaves SNAP 25, a 25 kD synaptic cellassociated protein, while the light chain of type B cleaves vesicle-associated membrane protein (VAMP, also called synaptobrevin).
After both type A and type B treatments, collateral sprouting of new nerve terminals occurs after time but eventually the original functional endplate is reestablished so that the sprouts regress as the clinical effects of the drug subside.
From the experience gained from cervical dystonia it appears there are some interesting differences in the clinical use of type B compared to A, in that the doses required with type B are many times greater than those used to treat the same indication with type A. There may also be some difference in immunogenicity and adverse event profile.
Botulinum toxin can elicit an immune response with the production of IgG neutralizing antibodies that will prevent the patient responding to that botulinum toxin in the future. With botulinum toxin A at less than 100 U dosage there are no reports of individuals losing their ability to respond, and it has also been our experience with a combined 30 years of injecting experience that there has been no genuine secondary resistance developed to the toxin.
High doses of protein correlate with increased antigen and in 1997 Allergan produced a new batch of BOTOX with a much lower protein load per dose. Preliminary results and experimental animals in clinical use would seem to confirm that there has been a diminished incidence of antigenic response.
The antigenic potential of botulinum toxin B is not known, but the 50- to 100-fold higher doses required result in a 10–20 times larger protein load per dose. The clinical significance of this is not yet known; however, MYOBLOC contains proportionately less degraded neurotoxin protein, which may reduce its immunogenic potential.
The cosmetic injection of BOTOX is much more like a surgical technique than a traditional simple isolated large muscle injection. Injecting an aliquot of medication into the upper outer quadrant of the thigh does not require the detailed understanding of the underlying musculofacial and skeletal anatomy plus understanding of facial aesthetic principles essential for successful cosmetic injection.
It is my recommendation that the new injecting physician study the appended drawings of facial muscular anatomy, as well as visit a university department of anatomy for an in-depth review of the anatomy and function of the highly complex delicately layered facial musculature.
This should be combined with a study of different facial expressions in repose and in animation in order to understand individual subject variation in patterns of anatomy. Simply taking a ‘recipe’ approach to botulinum toxin injections will not give the refined result the public has come to expect. An individualized approach which combines the study of the individual’s anatomy, their aesthetic needs and the results they would like achieved is the fascinating challenge faced by all injecting physicians.
The dose of botulinum toxin required to achieve a given result will vary with a number of individual variables. Body weight is one such variable, with smaller individuals requiring a smaller dose than larger individuals. Males require a higher dose than females; older individuals also require a higher dose.
Our website is not responsible for the information contained by this article. Articleinput.com is a free articles resource thus practically any visitor can submit an article. However if you notice any copyrighted material, please contact us and we will remove the article(s) in discussion right away.
Note: This article was sent to us by: Chloe L. Robinson at 11162010
1. What you should consider when choosig your cosmetic surgeon
All articles are property of their respective authors. Please read our Privacy Policy!
© 2009 ArticleInput.com.
Partners: Damenmode