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How many Botulinum toxin molecules or grams are contained in one medical unit of Botox?

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2 Answers 2

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1 unit is approximately 10 pg

Source

One unit of MYOBLOC (botulinum toxin type b) corresponds to the calculated median lethal intraperitoneal dose (LD50) in mice. The method for performing the assay is specific to Solstice Neurosciences' manufacture of MYOBLOC (botulinum toxin type b) . Due to differences in specific details such as the vehicle, dilution scheme and laboratory protocols for various mouse LD50 assays, units of biological activity of MYOBLOC (botulinum toxin type b) cannot be compared to or converted into units of any other botulinum toxin or any toxin assessed with any other specific assay method. Therefore, differences in species sensitivities to different botulinum neurotoxin serotypes preclude extrapolation of animal dose-activity relationships to human dose estimates. The specific activity of MYOBLOC (botulinum toxin type b) ranges between 70 to 130 Units/ng.

UPDATE

10 pg of toxin (150 kDa) is 4 x 109 molecules

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A Botox unit is essentially a measure of a defined amount of biological activity and corresponds to a fixed number of botulinum toxin molecules. The biological potency of these preparations is expressed in mouse units. One mouse unit is defined as the intraperitoneally injected quantity of each pharmaceutical product required to kill 50 per cent (LD50) of an experimental group of female Swiss-Webster mice, each of 20 g body weight. A 100 unit of Botox (Onabotulinum toxin A) contains approximately 5ng (nanograms) of toxin. And hence 1 unit of Onabotulinum toxin A contains approximately 0.05ng of active toxin.

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