Section I: Neurotoxin

Botulinum Toxin, Immunologic Considerations with Long-Term Repeated Use, with Emphasis on Cosmetic Applications

The botulinum neurotoxins as both antigens and pharmaceutical agents

The previous generation of botulinum toxin scientists was able to study the biochemical, medical, and physiologic properties of neurotoxin from various Clostridium botulinum strains by recognizing immunologically defined subtypes. Their motivation initially was fueled by the necessity for vaccine manufacturing for industrial and military use. Later, the various immunotypes became characterized by different amino acid homologies, cell membrane receptors, and cytoplasmic acceptor proteins.

Neutralizing versus nonneutralizing antibodies in patients receiving repeated injections

Despite the clinical history of secondary immunity after repeated botulinum toxin use, tests designed for detecting antibody have been problematic [2], [3], [4], [5]. The mouse neutralizing antibody (MNA) test has been considered the gold standard; however, this test has been designed for adequacy for toxoid immunization. This in vivo test for botulinum neutralization uses a mouse death as an endpoint. Other names for this assay include the mouse protection assay (MPA) or the mouse blocking

The immunologic problem and cosmetic application

Although immunity to repeated botulinum injections for lower dose facial indications has been reported [3], [8], [11], this complication has not been studied systemically in the cosmetic indications for Botox [9] or any other facial application. In the early experience of blepharospasm management, a few patients initially showing excellent results became nonresponders after several years of repeated injections [3]. Although sporadic cases demonstrated immunity, large-scale systematic testing

Tachyphylaxis (reduced response after repeated injections)

A phenomenon of decreased responsiveness has been noted after many years of therapy without characteristic immunoresistance. Tachyphylaxis is decreased, but not obliterated, drug responsiveness after repeated injections. The longest duration of facial applications has been noted with essential blepharospasm and Meige disease. In a group of patients treated for over 5 years with repeated eyelid injections, 15% of a group of 75 noted substantially decreased responsiveness. Many patients within

Use of facial lines and creases to determine resistance

Given the problem with in vivo and in vitro antibody tests, efforts have been made to evaluate resistance using clinical tests. The simplest clinical method is to test a muscle for contractility changes 2 to 3 weeks after injection using some endpoint to measure tone and muscular force [5], [14], [15], [16]. For patients who have blepharospasm, the inability to sustain a forceful squeezed lid closure against the examiner's attempts to open palpebral fissures is an indication of appropriate

The changes in composition of Botox and the antigenicity issue

Before 1998, the immunity issue was rapidly becoming apparent for large dose indications such as cervical dystonia [17]. Repeated injections over a period of 4 to 5 years appeared to be causing a neutralizing antibody rate of close to 20% over this time period. Although never systematically studied for the neutralizing antibody rate, the general impression was that the rate of immunity and secondary resistance was considerably lower for low dose injection therapy, such as for blepharospasm,

Antigenicity and the amount of toxin in the vials

Aside from terms such as the specific activity and protein load, which may be confusing, the major consideration relative to antigenicity is the amount of toxin in the vials. A lesser amount of toxin is better based on retrospective experience with multiple indications requiring a spectrum of doses. Animal studies examining repetitive injections of pure neurotoxin (less toxin protein) compared with commercially available Botox indicated a substantial difference in the incidence of secondary

Future products for therapeutic and cosmetic use

Efforts have been put forth by industry to produce pure preparations of botulinum toxin type A to decrease antigenic exposure to patients receiving the injections over many years. Preparations with increased purity do not seem to alter the dose requirement or complication rates in published studies in high and low dose indications. Such products may provide the best chance for avoiding immunologic related resistance after many years of therapy.

Botulinum toxin is a unique pharmaceutical agent in