What is a Botox Unit?

Dear Aglaet

One unit of BOTOX refers to the biological activity of this medication which is a neuromuscular toxin. The toxin is taken up at the terminus of of the nerve that is responsible for stimulating muscle contraction. The effect of the toxin is the prevention of acetylcholine release at the nerve terminus, preventing muscle contraction. The effect of BOTOX is temporary because the nerve eventually replaces the block terminus.

The definition of a unit the amount of BOTOX that when injected into a 18-20 gram Swiss-Webster female mouse is lethal for 50% of the animals. Currently each lot of BOTOX is tested in this fashion to assure the safety of the product. Animal advocates have challenged Allergan, the maker of BOTOX, to use an assay for the product that does not involve animals dying from respiratory arrest. There is a leg paralysis test that could be used. The difficulty is that as you can imagine, the testing of BOTOX is what ensures the safety of BOTOX. The track record of this product is impeccable. The FDA has approved and vetted the safety of BOTOX based on this testing method. Therefore, changing the testing of the drug would require the approval of the FDA and this is improbable.

Now although one unit of Botox is obviously very dangerous if you are an 18 gram mouse, the amount of BOTOX used for a cosmetic service does not appear to associated with systemic side effect. On the other hand, the FDA is now requiring a new warning for the use of Dysport and BOTOX that these treatments in high enough dose can be assoicated with systemic side effects. The systemic side effects appear to only be associated with the very high doses used to treat medical conditions like cervical dystonia and muscle spasm seen in children with cerebral palsy.

Allergan packages BOTOX in the United States market with 100 units of BOTOX. Dysport is now approved for the United States market. It is also a botulinum toxin A. However it is packaged in vials of 300 and 500 units in the United States. These two drugs are not equivalent. While some claim that BOTOX is approximately 3 times stronger than Dysport, this formula is not precise and it takes clinical experience to determine what is the correct dosage for a give person with any of these products.

Botox has 100 units per vial. The effectiveness of the Botox on diminishing muscle movement is dependent on the dose of units given, not the dilution. Doctors must dilute the bottle of Botox powder with saline to make it a liquid. The doctor then knows, based on the amount of liquid added to the bottle, how many units are contained in a given volume of liquid.