Botulinum Toxin

Two forms of BTX, type A (BTX-A, BOTOX® or Dysport®) and type B (BTX-B, Myobloc™ or NeuroBloc®) are commercially available. BTX temporarily weakens spastic muscles, allowing more normal limb positioning and function. To administer BTX, the physician places a small needle into the spastic muscle. Once the physician has confirmed the placement of the needle, the BTX is then injected.

The major side effects of treatment with BTX are dry mouth, blurred vision, excess weakness, or mild flu-like symptoms. BTX should be used with extreme caution in people with neuromuscular diseases such as myasthenia gravis or amyotrophic lateral sclerosis (also known as Lou Gehrig disease) or in those taking aminoglycoside antibiotics (including gentamicin, kanamycin, neomycin, streptomycin, and tobramycin).

One other important issue in the use of BTX in the treatment of spasticity is that of antibody formation. Because the immune system identifies BTX as a foreign substance, it produces antibodies that bind to and inactivate BTX, making it useless for spasticity reduction. Once a person forms antibodies to a particular type of BTX (A or B), any injections with that type of BTX are no longer effective. Repeated, high-dose injections are more likely to cause antibody formation than are less frequently repeated, low-dose injections. Therefore, the smallest amount of BTX necessary to achieve therapeutic benefit should be used, and the interval between treatment sessions should be as long as possible. Patients need to understand this important limitation on BTX therapy.

The effects of BTX are usually greatest for 2 to 6 weeks following treatment and usually fade completely after 3 to 6 months. In most situations, BTX is not injected again into the same muscle any sooner than 3 months after the last injection to decrease the possibility of antibody formation. In general, BTX cannot be used to treat widespread severe spasticity, since the amount of drug required to bring about meaningful functional improvements would likely lead to antibody formation, resistance to BTX, and eventual loss of response.

	Phenol and Alcohol