Antibodies and Botulinum Toxin Type A Therapy

Antibodies are proteins produced by the immune system to help fight infections or dispose of other foreign agents that enter the body. In some individuals treated with BTX-A, antibodies may develop, bind to the drug, and inactivate it. This renders BTX ineffective in weakening muscle contractions associated with dystonia. It is estimated that approximately five percent of individuals with cervical dystonia who have been treated regularly with relatively higher doses of BTX-A develop antibodies. Once a patient forms antibodies to a particular serotype of BTX (immunoresistance), further injections of that particular serotype of BTX are typically ineffective. Physicians should, therefore, use the smallest amount of BTX-A necessary to achieve therapeutic benefit; extend the time interval between treatment sessions as long as possible (with at least three months between treatments); and, if possible, avoid the use of "booster" injections. A new, lower protein form of BOTOX®-A is available. It is theorized that lower protein may lead to lower rates of antibody formation (reduced immunogenicity).

See E-MOVE Article: BTX-A current bulk toxin vs. original (AAN report)

On occasion, a patient may not respond to therapy with BTX-A. So-called "primary non-responders" are patients who do not respond to their first injection of BTX. Secondary non-response may occur as the result of a technical problem, such as an inappropriate site of injection into the wrong muscle, a dose that is inadequate to provide a clinical effect, or disease progression. The toxin may weaken the muscle; however, the degree of relaxation may not provide symptomatic relief for the patient. In addition, some patients on combination therapies for segmental or generalized dystonias may fail to take their oral medications, leading to a general increase in symptoms (masking the local effects of BTX-A). If failure to respond continues, it is possible that the patient has antibody-mediated resistance (immunoresistance).

It is important that patients work with their physicians to set appropriate treatment goals and tailor the course of treatment to meet these goals. There is no formal "recipe" that works for every patient. Each individual is unique and responds differently to BTX-A therapy.

	Botulinum Toxins and Cervical Dystonia Bibliography