|Routes||IM (approved), SC, intradermal, into glands|
|Molecular mass||147,336.839 Da|
|(what is this?)|
|PDB structures||RCSB PDB PDBe PDBsum|
|Gene Ontology||AmiGO / EGO|
Botulinum toxin is a neurotoxic protein produced by the bacterium Clostridium botulinum and related species. It is the most acutely lethal toxin known, with an estimated human median lethal dose (LD-50) of 1.3–2.1 ng/kg intravenously or intramuscularly and 10–13 ng/kg when inhaled. Botulinum toxin (BTX) can cause botulism, a serious and life-threatening illness in humans and animals. Forms of botulinum toxin types A and B are available commercially for research and various medical and cosmetic procedures. Therapeutic indications include upper motor neuron syndrome, focal hyperhidrosis, blepharospasm, strabismus, and chronic migraine as well as a widely used cosmetic treatments. The U.S. Food and Drug Administration requires drug products containing the toxin that are sold in the U.S. to carry a mandatory boxed warning, which since 2009 has included the caution that effects of locally administered botulinum toxin may spread from the injection area to other areas of the body, causing symptoms similar to those of botulism poisoning; the warning was the result of documented deaths associated with its therapeutic uses, especially unapproved (off-label) use in children.
- 1 History
- 2 Toxin production
- 3 Organism and toxin susceptibilities
- 4 Biochemistry and mechanism of toxicity
- 5 Botulinum poisoning and treatment
- 6 Medical and cosmetic uses
- 7 Manufacturers
- 8 Adverse events, reactions, and deaths
- 9 Global warning label requirements
- 10 Possible use in bioterrorism
- 11 Therapeutic research
- 12 See also
- 13 References
- 14 External links
|This section requires expansion with: further historical highlights and first therapeutic demonstrations. (February 2015)|
Justinus Kerner described botulinum toxin as a "sausage poison" and "fatty poison" (from Latin botulus meaning "sausage"), because the bacterium that produces the toxin often caused poisoning by growing in improperly handled or prepared meat products. Kerner, a physician, first conceived a possible therapeutic use of botulinum toxin,[clarification needed] and coined the name botulism. In 1897, Emile van Ermengem found the producer of the botulin toxin was a bacterium, which he named Clostridium botulinum. P.T. Snipe and Hermann Sommer purified the toxin for the first time In 1928. In 1949, Arnold Burgen's group experimentally discovered that botulinum toxin blocks neuromuscular transmission through decreased acetylcholine release.
Botulism toxins are produced by bacteria of the genus Clostridium, namely Clostridium botulinum, C. butyricum, C. baratii and C. argentinense, which are widely distributed, including in soil and dust. As well, the bacteria can be found inside homes on floors, carpet, and countertops even after cleaning. Some food products such as honey can contain amounts of the bacteria.
Food-borne botulism results, indirectly, from ingestion of food contaminated with Clostridium spores, where exposure to an anaerobic environment allows the spores to germinate, after which the bacteria can multiply and produce toxin. Critically, it is ingestion of toxin rather than spores or vegetative bacteria that causes botulism. Botulism is nevertheless known to be transmitted through canned foods not cooked correctly before canning or after can opening, and so is preventable. Infant botulism cases arise chiefly as a result of environmental exposure and are therefore more difficult to prevent. Infant botulism arising from consumption of honey can be prevented by eliminating honey from diets of children less than 12 months old.
Therapeutic and weaponisable forms of the toxin are sourced from strains of Clostriudium where both the growth and toxin isolation are under specialized conditions.
Organism and toxin susceptibilities
|This section requires expansion with: modern content and referencing on antibiotic susceptibilities. (February 2015)|
Proper refrigeration at temperatures below 3 °C (38 °F) retards the growth of Clostridium botulinum. The organism is also susceptible to high salt, high oxygen, and low pH levels. The toxin itself is rapidly destroyed by heat, such as in thorough cooking. The spores that produce the toxin are heat-tolerant and will survive boiling water for an extended period of time.
The botulinum toxin is denatured and thus deactivated at temperatures greater than 80 °C (176 °F). As a zinc metalloprotease (see below), the toxin's activity is also susceptible, post-exposure, to inhibition by protease inhibitors, e.g., zinc-coordinating hydroxamates.
Biochemistry and mechanism of toxicity
|This section needs additional citations for verification. (February 2015)|
The toxin produced by Clostridum species is a two-chain protein composed of a 100-kDa heavy chain polypeptide joined via disulfide bond to a 50-kDa light chain polypeptide. The eight serologically distinct toxin types "possess different tertiary structures and significant sequence divergence," and are designated A to G; six of the eight have subtypes, and five further subtypes of target molecules of botulinum A have been described.[clarification needed] The A, B, and E serotypes cause human botulism, with the activities of types A and B enduring longest in vivo (from several weeks to months).
The terminals of specific axons must internalize the toxin to cause paralysis, and the heavy chain of the toxins is implicated in targeting the toxin to such axon terminals; following the attachment of the toxin heavy chain to proteins on the surface of the terminals, toxin molecules enter the neurons by endocytosis. The light chain, which has zinc metalloprotease activity, is released from the endocytotic vesicles and reaches the cytoplasm.[clarification needed] Specific serotypes of the toxin cleave synaptosomal-associated protein (25 kDa) (SNAP-25), a protein from the soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) family involved in vesicle fusion and mediating release of neurotransmitter, in particular acetylcholine, from axon endings.[non-primary source needed] Cleavage of the SNARE proteins inhibits release of acetylcholine. Hence, botulinum toxins A, B, and E specifically cleave SNAREs, preventing "neurosecretory vesicles" from docking/fusing with the interior surface of the plasma membrane of the nerve synapse, and so block release of neurotransmitter. In inhibiting acetylcholine release, nerve impulses are blocked, causing the flaccid (sagging) paralysis of muscles characteristic of botulism (versus the distinct spastic paralysis seen in tetanus).
Botulinum poisoning and treatment
If the symptoms of botulism are diagnosed early, an equine antitoxin, use of enemas, and extracorporeal removal of the gut contents can be used to treat the food-borne illness. Wound infections can be treated surgically. Information regarding methods of safe canning, and public education about the disease are methods of prevention. Tests to detect botulism include a brain scan, a nerve conduction test, and a tensilon test for myasthenia gravis to differentiate botulism from other diseases that manifest in the same way. Electromyography can be used to differentiate myasthenia gravis and Guillain-Barré syndrome, diseases that botulism often mimics. Toxicity testing of serum specimens, wound tissue cultures, and toxicity testing, and stool specimen cultures are the best methods for identifying botulism. Laboratory tests of the patient's serum or stool, which are then injected into mice, are also indicative of botulism. The faster way to detect botulinum toxin in people, however, is using the mass spectrometer technology, because it reduces testing time to three or four hours and at the same time can identify the type of toxin present.
The case fatality rate for botulinum poisoning between 1950 and 1996 was 15.5%, down from about 60% over the previous 50 years. Death is generally secondary to respiratory failure due to paralysis of the respiratory muscles, so treatment consists of antitoxin administration and artificial ventilation until the neurotoxins are excreted or metabolised. If initiated on time, these treatments are quite effective, although antisera can not affect toxin polypeptides that have already entered cells. Occasionally, functional recovery may take several weeks to months or more.
Two primary botulinum antitoxins are available for treatment of botulism.
- Trivalent (A,B,E) botulinum antitoxin is derived from equine sources using whole antibodies (Fab and Fc portions). This antitoxin is available from the local health department via the CDC in the USA.
- The second antitoxin is Heptavalent (A,B,C,D,E,F,G) botulinum antitoxin, which is derived from "despeciated" equine IgG antibodies, which have had the Fc portion cleaved off, leaving the F(ab')2 portions. This less immunogenic antitoxin is effective against all known strains of botulism where not contraindicated, and is available from the United States Army. On June 1, 2006, the US Department of Health and Human Services awarded a $363 million contract with Cangene Corporation for 200,000 doses of heptavalent botulinum antitoxin over five years for delivery into the Strategic National Stockpile beginning in 2007.
Medical and cosmetic uses
Although botulinum toxin is a lethal, naturally occurring substance, it can be used as an effective and powerful medication. Researchers discovered in the 1950s that injecting overactive muscles with minute quantities of botulinum toxin type-A would result in decreased muscle activity. Botulinum toxin type-A has this effect because it prevents the vesicle where the acetylcholine is stored from binding to the membrane where the neurotransmitter can be released. Botulinum toxin type-A thus blocks the release of acetylcholine by the neuron. This will effectively weaken the muscle for a period of three to four months.
In cosmetic applications, injection of a small dose of botulinum toxin can be used to prevent development of wrinkles by paralyzing facial muscles.[better source needed] As of 2013, it is the most common cosmetic operation, with 6.3 million procedures in the United States, according to the American Society of Plastic Surgeons. Qualifications for Botox injectors vary by county, state and country. Botox cosmetic providers include dermatologists, plastic surgeons, aesthetic spa physicians, dentists, nurse practitioners, nurses and physician assistants. The wrinkle-preventing effect of Botox normally lasts about three to four months, but can last up to six months.[better source needed] Following treatment, visible results of Botox Cosmetic are usually seen within 3–5 days, however it can take up to 2 weeks to see full results.  The global market for botulinum toxin products, driven by their cosmetic applications, is forecast to reach $2.9 billion by 2018; they are a component of the facial aesthetics market that is forecast to reach $4.7 billion ($2 billion in the U.S.) in the same timeframe.
- cervical dystonia (spasmodic torticollis), a neuromuscular disorder of the head and neck;
- blepharospasm, uncontrolled muscle contraction or twitch of the eyelid;
- severe primary axillary hyperhidrosis, a condition of excessive sweating;
- chronic migraine, defined by patient history, and high frequency of occurrence;
- strabismus, improper alignment of the eyes (heterotropia; colloquially "crossed eyes"); and
- temporary cosmetic treatment of glabellar lines.
Other adult uses of botulinum toxin type A not specifically approved by the FDA (off-label uses) include:
- oesophageal achalasia, failure of smooth muscle relaxation such that the oesophageal sphincter fails to open when needed;
- bruxism, parafunctional teeth grinding/jaw clenching. by injection into masticating muscles (e.g., the masseter;
- chronic focal neuropathies;
- Idiopathic and neurogenic detrusor overactivity
- vaginismus to reduce the spasm of the vaginal muscles
- movement disorders associated with injury or disease of the central nervous system, including trauma, stroke, multiple sclerosis, Parkinson's disease, or cerebral palsy
- focal dystonias affecting the limbs, face, jaw, or vocal cords
- obesity, i.e., as an aid in weight loss, by increasing the gastric emptying time.
- detrusor sphincter dyssynergia and benign prostatic hyperplasia;
- vocal cord dysfunction, including spasmodic dysphonia and tremor;
- painful bladder syndrome;* Anal fissure
- gastric cancer 
- Allergic rhinitis
Uses of botulinum toxin type A in pediatric cases, based on adult evidence, include:
- Pediatric cerebral palsy, for spasm of the limbs, which has lead to patient deaths;
- Pediatric incontinence, including incontinence due to overactive bladder, and incontinence due to neurogenic bladder
Emerging uses for botulinum toxin type A include chronic musculoskeletal pain, temporomandibular joint pain disorders, diabetic neuropathy, generalized wound healing, excessive salivation, and jaw reduction.
In the United States, botulinum toxin products are manufactured by a variety of companies, for both therapeutic and cosmetic use. Allergan, Inc., a principal U.S. supplier through their Botox products, reported in its company materials in 2011 that it could "supply the world's requirements for 25 indications approved by Government agencies around the world" with less than one gram of raw botulinum toxin. Myobloc or Neurobloc, a botulinum toxin type B product, is produced by Solstice Neurosciences, a subsidiary of US WorldMeds. Dysport, a therapeutic formulation of the type A toxin manufactured by Galderma in the United Kingdom, is licensed for the treatment of focal dystonias and certain cosmetic uses in the U.S. and worldwide.
After the three primary U.S. manufacturers, there many reports of other sources of production. Xeomin, manufactured in Germany by Merz), is also available for both therapeutic and cosmetic use in the U.S. Lanzhou Institute of Biological Products in China is reported to manufacture a BTX-A product; BTX-A is also sold as Lantox and Prosigne on the global market. Neuronox, a BTX-A product, was introduced by Medy-Tox Inc. of South Korea in 2009; Neuronox is also markets as Siax in the U.S.
Adverse events, reactions, and deaths
|This section needs additional citations for verification. (February 2015)|
|This section requires expansion with: coverage of allergic reactions, and of non-cosmetic adverse events/reactions, especially in treatment of limb spasticity where the most serious adverse reactions, including deaths, have occurred. (February 2015)|
Off-target, or side effects, that have been reported are consistent with the mechanism of the protein toxin's function, and its known modes of action; there are, consequently, two major areas of off-target effects: allergic reaction, and paralysis of the wrong muscle group.
Adverse events or reactions from cosmetic use include facial paralysis resulting in inappropriate facial expression, drooping eyelid, and double vision, bruising, swelling, or redness at the site of injection, headaches, dysphagia, flu-like syndromes, blurred vision, dry mouth, fatigue, and allergic reactions. Cosmetic treatments are of limited duration; they can be as short as six weeks, but can last from 2–3 months; hence paralysis side-effects can have the same durations. The results of inappropriate facial expression, drooping eyelid, and double vision are foremost,[better source needed] but the list extends to uneven smiling, and loss of the ability to close ones eyes; at least in some cases, these effects are reported to dissipate in the weeks after treatment. Bruising at the site of injection is not a side effect of the toxin but rather of the mode of administration, and is reported as preventable if the clinician applies pressure to the injection site; when it occurs, it is reported in specific cases to last 7–11 days. When injecting the masseter muscle of the jaw, loss of muscle function can result in a loss or reduction of power to chew solid foods.
Individuals who are pregnant, have egg allergies, or a neuromuscular disorder are advised to avoid botulinum toxin drugs, and breastfeeding mothers are advised to consult their doctors.[better source needed]
The psychological and emotional consequences associated with cosmetic treatments is not yet well documented, and reports are not yet consistent. A study of treatment of glabellar lines with consequent reduction of ability to frown correlated with a "more positive mood[s]",[non-primary source needed] while a study on the treatment of "crow's feet" or "laughter lines" suggested the opposite effect as a consequence of the impact of the treatment on the patient's ability to smile.[better source needed][disputed ]
Links to deaths
The FDA has formally linked complications from use of botulinum drug products to patient deaths. In September 2005, the Journal of American Academy of Dermatology communicated information from the FDA reporting 28 deaths between 1989 and 2003 associated with the use of botulinum toxin products, though none attributed to cosmetic use.
In January 2008, a petition filed by Public Citizen with the FDA requested regulatory action concerning the possible spread of the effects of botulinum toxin injectable products, including Botox and Myobloc, from the site of injection to other parts of the body.
On February 8, 2008, the FDA announced its conclusion that this class of drugs had "been linked in some cases to adverse reactions, including respiratory failure and death, following treatment of a variety of conditions using a wide range of doses," due to its ability to spread to areas distant from the site of the injection. The communication was a result of ongoing FDA safety reviews of the on-market product, and found adverse reactions associated with uses that were both FDA-approved and non-approved, the most severe being in children with cerebral palsy treated for limb spasticity (not approved for either adult or pediatric use).
On April 30, 2009, based on a continuing safety evaluation of on-market botulinum toxin products, the FDA reported its conclusion that the prescribing information for Botox, Botox Cosmetic, and Myobloc must be updated to ensure their continued safe use. On July 31, 2009, FDA, under the authorities granted by the Food and Drug Administration Amendments Act of 2007, approved revisions to the prescribing information (see following).
As well, on April 30, the FDA announced an update to its mandatory boxed warnings for four on-market products—Botox, Botox Cosmetic, Myobloc, and Dysport—and on July 31, it approved revisions to the prescribing information for the four drugs. In the revisions, it made clear that the effects of botulinum toxin may spread from the area of injection to other body areas, causing symptoms similar to those of botulism, including potentially life-threatening swallowing and breathing difficulties resulting in patient death. Most accumulated adverse reactions were again reported for pediatric palsy patients (off-label use, see above), though adverse reaction reports were also fielded for adult patients involved in both approved and unapproved uses; the FDA emphasized that at recommended/approved doses there were few serious adverse reactions for common, standard treatments for focal hyperhidrosis, blepharospasm, or strabismus, or for cosmetic/dermatologic treatments, e.g., for glabellar lines (i.e., when label instructions were followed). The FDA further emphasized that the activity units of each product do not interconvert, specifically that "different botulinum toxin products are not interchangeable, because the units used to measure the products are different," and required a change in the established drug names of older drugs, from:
- Botox and Botox Cosmetic to onabotulinumtoxinA,
- Dysport to abobotulinumtoxinA (already in place, so no change), and from
- Myobloc to rimabotulinumtoxinB,
A further FDA communication aimed at health care professionals reiterated the approved drugs for each adult indication:
- cervical dystonia: OnabotulinumtoxinA (Botox), AbobotulinumtoxinA (Dysport), and RimabotulinumtoxinB (Myobloc);
- blepharospasm, severe primary axillary hyperhidrosis, strabismus: OnabotulinumtoxinA (Botox); and
- temporary cosmetic treatment of glabellar lines: OnabotulinumtoxinA (Botox), AbobotulinumtoxinA (Dysport).
These have been extended, through later announcement, to include:
- adult headache prevention in cases of chronic migraine: OnabotulinumtoxinA (Botox),
which is defined for patients having a history of migraine, and experiencing a headache on most days of the month."
In the 2009 communication to professionals, the FDA reiterated the foregoing adverse reaction observations and the possibility of "unexpected loss of strength or muscle weakness," leading to:
- double vision, blurred vision or drooping eyelids;
- dysphonia (hoarseness, trouble talking), dysarthria (trouble enunciating words), or trouble swallowing;
- trouble breathing; or
- loss of bladder control
and that "swallowing and breathing difficulties can be life-threatening" (i.e., that there have been "deaths related to the effects of spread of botulinum toxin"). The communication to professionals reiterated that pediatric spasticity patients were at greatest risk from existing treatment practices, but also that approved and lower doses used to treat cervical dystonia and adult spasticity were also seen among the "cases of toxin spread," so that in all cases of drug administration, patients and their caregivers needed to:
"Pay close attention for any signs or symptoms of adverse events. [and] Seek immediate medical attention… [in the case of] difficulty swallowing or talking, trouble breathing, or muscle weakness…"
and that these events may occur "as late as several weeks after treatment."
Global warning label requirements
In January 2009, the Canadian government warned that botulinum toxin products can have the adverse effect of spreading to other parts of the body, which could cause muscle weakness, swallowing difficulties, pneumonia, speech disorders and breathing problems.
In April 2009, the FDA updated its mandatory boxed warning cautioning that the effects of the botulinum toxin may spread from the area of injection to other areas of the body, causing symptoms similar to those of botulism, and that these adverse reactions, which were more likely in cases ignoring approved use guidance and label directions, could result in patient death (see above).
Possible use in bioterrorism
The effects of botulinum toxin are distinguishable from those involving nerve agents insofar as botulism symptoms develop relatively slowly (over several days), while nerve agent effects are generally much more rapid, and can be instantaneous. Evidence suggests that nerve exposure (simulated by injection of atropine and pralidoxime) will increase mortality by enhancing botulin toxin's mechanism of toxicity.
With regard to detection, current protocols using NBC detection equipment (such as M-8 paper or the ICAM) will not indicate a "positive" when samples containing botulinum toxin are tested. To confirm a diagnosis of botulinum toxin poisoning, therapeutically or to provide evidence in death investigations, botulinum toxin may be quantitated by immunoassay of human biological fluids; serum levels of 12–24 mouse LD50 units/mL have been detected in poisoned patients.
Alan Scott and Edward Schantz were the first to work on a standardized botulinum toxin preparation for therapeutic purposes, beginning in the late 1960s. Scott, working at Smith-Kettlewell Institute in 1963, used botulinum toxin type A (BTX-A) in monkey experiments. In 1980, Scott used BTX-A in a first human treatments of blepharospasm ("uncontrollable blinking") and strabismus, a condition in which the eyes are not properly aligned with each other ("crossed eyes"). In 1993, Scott, P.J. Pasricha, and colleagues showed botulinum toxin could be used for the treatment of achalasia, a spasm of the lower esophageal sphincter. In 1994, K.O. Bushara and D.M. Park were the first to demonstrate a non-muscular use of BTX-A in humans, with a demonstration that injections could inhibit conditions resulting in sweating.[non-primary source needed]
Blepharospasm and strabismus
In the early 1980s, university-based ophthalmologists in the USA and Canada further refined the use of botulinum toxin as a therapeutic agent. By 1985, a scientific protocol of injection sites and dosage had been empirically determined for treatment of blepharospasm and strabismus. Side effects in treatment of this condition were deemed to be rare, mild and treatable. The beneficial effects of the injection lasted only 4–6 months. Thus, blepharospasm patients required re-injection two or three times a year.
In 1986, Scott's micromanufacturer and distributor of Botox was no longer able to supply the drug because of an inability to obtain product liability insurance. Patients became desperate, as supplies of Botox were gradually consumed, forcing him to abandon patients who would have been due for their next injection. For a period of four months, American blepharospasm patients had to arrange to have their injections performed by participating doctors at Canadian eye centers until the liability issues could be resolved.
In December 1989, Botox, manufactured by Allergan, Inc., was approved by the US Food and Drug Administration (FDA) for the treatment of strabismus, blepharospasm, and hemifacial spasm in patients over 12 years old.
Botox is not been approved for any pediatric use. It has, however, been used off-label by physicians for several conditions. including spastic conditions in pediatric patients with cerebral palsy, a therapeutic course that has resulted in patient deaths. In the case of treatment of infantile esotropia in patients younger than 12 years of age, several studies have yielded differing results.[better source needed]
The cosmetic effect of BTX-A on wrinkles was originally documented by a plastic surgeon from Sacramento, California, Richard Clark, and published in the journal Plastic and Reconstructive Surgery in 1989. Canadian husband and wife ophthalmologist and dermatologist physicians, JD and JA Carruthers, were the first to publish a study on BTX-A for the treatment of glabellar frown lines in 1992. Similar effects had reportedly been observed by a number of independent groups (Brin, and the Columbia University group under Monte Keen. After formal trials, on April 12, 2002, the FDA announced regulatory approval of botulinum toxin type A (Botox Cosmetic) to temporarily improve the appearance of moderate-to-severe frown lines between the eyebrows (glabellar lines). Subsequently, cosmetic use of botulinum toxin type A has become widespread. The results of Botox Cosmetic can last up to four months and may vary with each patient. The US Food and Drug Administration approved an alternative product-safety testing method in response to increasing public concern that LD50 testing was required for each batch sold in the market.
Upper motor neuron syndrome
BTX-A is now a common treatment for muscles affected by the upper motor neuron syndrome (UMNS), such as cerebral palsy, for muscles with an impaired ability to effectively lengthen. Muscles affected by UMNS frequently are limited by weakness, loss of reciprocal inhibition, decreased movement control and hypertonicity (including spasticity). In January 2014, Botulinum toxin was approved by UK's Medicines and Healthcare Products Regulatory Agency (MHRA) for the treatment of ankle disability due to lower limb spasticity associated with stroke in adults. Joint motion may be restricted by severe muscle imbalance related to the syndrome, when some muscles are markedly hypertonic, and lack effective active lengthening. Injecting an overactive muscle to decrease its level of contraction can allow improved reciprocal motion, so improved ability to move and exercise.
As noted, Bushara and Park were the first to demonstrate a nonmuscular use of BTX-A while treating patients with hemifacial spasm at England in 1993, showing that botulinum toxin injections inhibit sweating, and so are useful in treating hyperhidrosis (excessive sweating).[non-primary source needed] BTX-A has since been approved for the treatment of severe primary axillary hyperhidrosis (excessive underarm sweating of unknown cause), which cannot be managed by topical agents.[when?]
BTX-A is commonly used to treat cervical dystonia, but it can become ineffective after a time. Botulinum toxin type B (BTX-B) received FDA approval for treatment of cervical dystonia on December 21, 2000. Trade names for BTX-B are Myobloc in the United States, and Neurobloc in the European Union.
Onabotulinumtoxin A (trade name Botox) received FDA approval for treatment of chronic migraines on October 15, 2010. The toxin is injected into the head and neck to treat these chronic headaches. Approval followed evidence presented to the agency from two studies funded by Allergan, Inc. showing a very slight improvement in incidence of chronic migraines for migraine sufferers undergoing the Botox treatment.
Since then, several randomized control trials have shown botulinum toxin type A to improve headache symptoms and quality of life when used prophylactically for patients with chronic migraine who exhibit headache characteristics consistent with: pressure perceived from outside source, shorter total duration of chronic migraines (<30 years), "detoxification" of patients with coexisting chronic daily headache due to medication overuse, and no current history of other preventive headache medications.
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