Botulinum toxin is the purified form of a poison created by the bacterium Clostridium botulinum. These bacteria grow in improperly canned food and cause botulism poisoning. Minute amounts of the purified form can be injected into muscles to prevent them from contracting; it is used in this way to treat a wide variety of disorders and cosmetic conditions.
Botulinum toxin was developed to treat strabismus (cross-eye or lazy eye), and was shortly thereafter discovered to be highly effective for many forms of dystonia. Spasticity can also be effectively treated with botulinum toxin. Injected into selected small muscles of the face, it can reduce wrinkling. Other conditions treated with botulinum toxin include:
- back pain
- excess saliva production
- eyelid spasm
- hemifacial spasm
- palatal myoclonus
- spastic bladder
- uncontrollable eye blinking
It is important to note that as of early 2004, the only Food and Drug Administration-approved uses for botulinum toxin are for certain forms of dystonia, hemifacial spasm, strabismus, blepharospasm (eyelid spasms), and certain types of facial wrinkles. While there is general recognition that certain other conditions can be effectively treated with botulinum toxin, other uses, including for headache or migraine, are considered experimental.
A solution of botulinum toxin is injected into the overactive muscle. The toxin is taken up by nerve endings at the junction between nerve and muscle. Once inside the cell, the toxin divides a protein. The normal job of this protein is to help the nerve release a chemical, a neurotransmitter, which stimulates the muscle to contract. When botulinum toxin divides the protein, the nerve cannot release the neurotransmitter, and the muscle cannot contract as forcefully.
The effects of botulinum toxin begin to be felt several days after the injection. They reach their peak usually within two weeks, and then gradually fade over the next 2–3 months. Since the effects of the toxin disappear after several months, reinjection is necessary for continued muscle relaxation.
In the United States, purified botulinum toxin is available in two commercial forms: Botox and MyoBloc. The recommended doses of the two products are quite different, owing to the differing potencies of the two products. The size of the muscle and the degree of weakening desired also affect the dose injected. For Botox, the maximum recommended dose for adults is 400–600 units in any three-month period, while for MyoBloc it is 10,000–15,000 units. The maximum dosage may be reached in the treatment of spasticity or cervical dystonia, while much smaller amounts are used in the treatment of facial lines, strabismus, and hemifacial spasm.
When injected by a trained physician, botulinum toxin is very safe. The toxin remains mainly in the muscle injected, spreading only slightly to surrounding muscles or beyond. Botulism poisoning, which occurs after ingesting large amounts of the toxin, is due to the effects of the poison on the breathing muscles. In medical use, far less toxin is injected, and care is taken to avoid any chance of spread to muscles needed for breathing. Injection into the shoulders or neck may weaken muscles used for swallowing, which patients need to be aware of. Some patients may need to change to a softer diet to make swallowing easier during the peak effect of their treatment.
Repeated injections of large amounts of botulinum toxin can lead to immune system resistance. While this is not a dangerous condition, it makes further treatment ineffective.
Patients with neuromuscular disease should not receive treatment with botulinum toxin without careful consultation with a neurologist familiar with its effects.
Botulinum toxin can cause a mild flu-like syndrome for several days after injection. Injection of too much toxin causes excess weakness, which may make it difficult to carry on normal activities of daily living. In some patients, toxin injection may cause blurred vision and dry mouth. This is more common in patients receiving MyoBloc than with Botox.
Brin, M. F., M. Hallett, and J. Jankovic, editors. Scientific and Therapeutic Aspects of Botulinum Toxin. Philadelphia: Lippincott, 2002.
WE MOVE. December 4, 2003 (February 18, 2004). <http://www.wemove.org>.
MD Virtual University. December 4, 2003 (February 18, 2004). <www.mdvu.org>.