The cosmetic form of botulinum toxin, often referred to by its product name Botox, is a popular non-surgical injection that temporarily reduces or eliminates frown lines, forehead creases, crows feet near the eyes and thick bands in the neck. The toxin blocks the nerve impulses, temporarily paralyzing the muscles that cause wrinkles while giving the skin a smoother, more refreshed appearance. Studies have also suggested that Botox is effective in relieving migraine headaches, excessive sweating and muscle spasms in the neck and eyes. Botulinum neurotoxin is produced by the gram-negative anaerobic bacterium Clostridium botulinum.



Eight serologically distinct botulinum neurotoxins exist, designated as A, B, C1, C2, D, E, F, and G. Seven are associated with paralysis. Types A, B, E and, rarely, F and G are associated with human botulism.

Dose

The dose of botulinum toxin is expressed in mouse units. One unit is equal to the amount that will kill 50% of a group of 18- to 22-g Swiss Webster mice when injected intraperitoneally. The human lethal dose (LD) for BOTOX (botulinum type A purified neurotoxin complex) is estimated at approximately 3000 units. BOTOX injections of less than 100 units usually are used for cosmetic purposes and of less than 300-600 units for other purposes, thereby allowing a wide safety margin. Recognizing that doses are not interchangeable among different formulations of botulinum toxin (BOTOX, Dysport, Myobloc) is important; to achieve similar clinical effects, different doses are used.

Botulinum toxin formulations

BOTOX is a sterile lyophilized form of botulinum toxin type A. It is produced from a culture of the Hall strain of C botulinum and purified by a series of acid precipitations to a crystalline complex containing the toxin and other proteins. The FDA approved BOTOX in December 1989 as an orphan drug for the treatment of strabismus, hemifacial spasms, and blepharospasm. BOTOX is distributed in 100-unit vials.

The original batch of neurotoxin prepared by Shantz in November 1979 (designated batch 79-11) constituted the original BOTOX formulation and was used until December 1997. It was replaced by a new neurotoxin complex batch designated BCB 2024. The new bulk batch is 5-6 times more potent on a weight basis. In a 100-unit vial, only 4.8 ng of neurotoxin is needed compared to 25 ng of 79-11. The new BOTOX is comparable in clinical efficacy and safety to the old, and a unit dose of new BOTOX provides an equivalent response to the same unit dose of old BOTOX. Hopefully, the reduced protein load of the new BOTOX leads to reduced immunogenicity and a lower incidence of neutralizing antibody formation.

Dysport is another formulation of botulinum toxin type A available in Europe and a few other countries. It is prepared using column-based purification techniques and distributed in 500-unit vials that can be stored at room temperature. BOTOX and Dysport are both botulinum toxin type A preparations but are quite distinct from one another. BOTOX is approximately 4 times more potent on a per unit basis, and Dysport doses often are approximately 4 times the BOTOX doses used to generate a similar clinical effect. Differences in these toxins may relate to differences in the strain of bacterium, preparation, diffusion, and potency testing.

Myobloc is a botulinum toxin type B preparation currently in clinical trials. It is anticipated that it will be distributed as a solution. Little information is available concerning the cosmetic use of Dysport and Myobloc. The remainder of this article therefore focuses on BOTOX, and all unit doses refer to BOTOX unless otherwise specified.

Reconstitution and storage

Store BOTOX in a freezer at or below -5'C. The package insert recommends reconstitution of BOTOX using sterile saline without preservative; 0.9% sodium chloride is the preferred diluent. Some investigators suggest that reconstitution with sterile saline solution with preservative (0.9% benzyl alcohol) reduces microbial contamination and provides a weak local anesthetic effect. However, contamination is rarely a problem, and the anesthetic effect is modest.

BOTOX is denatured easily by bubbling or agitation; gently inject the diluent onto the inside wall of the vial. Discard the vial if a vacuum does not pull the diluent in. The final dilution of BOTOX is mostly a matter of personal preference; 100 units commonly are reconstituted in 1-10 mL of diluent. Theoretically, more concentrated solutions reduce reliability in delivering a specific unit dose, and more dilute solutions lead to greater diffusion of the toxin. The authors prefer to use 2 mL of diluent to prepare a solution of 5 U/0.1 mL (50 U in a 1-mL tuberculin syringe if that much is to be used). Use a 30-gauge 1-inch needle to perform the injections.

Once reconstituted, keep BOTOX refrigerated at 2-8'C. The package insert indicates that reconstituted BOTOX should be used within 4 hours. One study found no loss of activity at 6 hours but a 44% loss after 12 hours and a 70% loss with refreezing at 1-2 weeks. Other authors report no substantial loss of potency in a 10 U/1 mL reconstituted solution kept refrigerated for 1 month. Most practitioners discard unused reconstituted BOTOX after 1-7 days.