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Botulinum Toxin Adverse Events
Raffaela Pero, Sonia Laneri and Giovanna Fico
Additional information is available at the end of the chapter
© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
RaaelaPero, SoniaLaneri and GiovannaFico
Additional information is available at the end of the chapter
Botulinum toxin acts at the neuromuscular junction (motor plaque) blocking the release
and eects of acetylcholine (ACh), a neurotransmier of both the central nervous system
(CNS) and the peripheral nervous system (SNP). By inhibiting the release of acetylcholine,
botulinum toxin interferes with the nervous impulse and causes a characteristic accid
paralysis of the muscles. This eect is used to decrease wrinkles of the facial skin and chin
providing a smooth appearance and for the treatment of a variety of human syndromes
characterized by hyperfunction of selected nerve terminals. Side eects of this treatment
are rare, but are essentially related to the active ingredient of the drug or to medical mal-
practice. These adverse events and their possible therapy are discussed in this chapter.
Keywords: botulinum toxin, adverse events, therapy, esthetic, motor endplate
Botulinum toxin is a neurotoxic protein produced by the anaerobic bacterium Clostridium
botulinum. There are seven types of distinct botulinum toxin and are indicated with the alpha-
bet leers: A, B, C, D, E, F, and G .
Recently, a novel botulinum neurotoxin (BoNT/X) has been identied  and the rst botuli-
num-like toxin outside the Clostridia family has been described .
The currently used in esthetic medicine is botulinum toxin type A (BoNT-A). It is used for
wrinkles of expression and for those dynamic wrinkles linked to the hypertonia of mimic
muscles . Botulinum toxin acts at the level of the neuromuscular junction (motor end-
plate) blocking the release and eects of acetylcholine, an ester of acetic acid and choline,
responsible for neurotransmission both at the central nervous system (CNS) level and at the
© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
peripheral nervous system (SNP) level. The enzyme acetylcholineesterase, present in the pre-
synaptic nerve endings, continuously hydrolyses the acetylcholine which is then immediately
resynthesized and stored through an active transport mechanism by means of a specic car-
rier protein, within synaptic cholinergic vesicles of storage. Within these cytosolic vesicles,
acetylcholine is transported to the presynaptic region of the neuron (synaptic buon) where it
waits for the ionic signal (calcium ions) to release its role as a neurotransmier .
Acetylcholine is normally released into the synaptic space trough a potential action that, by fol-
lowing the axon of the neuron at the last termination level of the nal arborization of the axon,
determines the opening of voltage-dependent ion channels: the channels of calcium. The cal-
cium ions, present in the synaptic space, penetrate inside the synaptic buon and start the real-
izing process of ACh into the synaptic space where it acts on specic receptors (ACh receptors).
ACh receptors are located on the postsynaptic cell membrane of the muscle brocell, which are
of two types: nicotinic and muscarinic. Interacting with ACh receptors, the neurotransmier
achieves its eects by determining, at the postsynaptic level, the opening of sodium-potassium
ion channels through which the sodium ions penetrate into the muscle brocell which, thus, ini-
tiate muscle contraction. Immediately afterward, ACh is hydrolyzed by acetylcholinesterase. By
inhibiting the release of acetylcholine, botulinum toxin interferes with the nervous impulse and
causes a accid paralysis of the muscles. Botulinum toxin is in fact a real muscle relaxant .
Botulin toxin is a double-chain polypeptide consisting of a heavy chain and a light chain. The
former has a molecular weight of 100 KDa while the laer has a molecular weight of 50 KDa.
The heavy chain is linked to the light chain via sulde bridges. The two chains perform dier-
ent functions. The heavy chain binds to a receptor on the cell membrane of the synaptic buon,
the SV2 receptor, and begins the endocytosis phenomenon through which the botulinum toxin
enters into the synaptic buon. The heavy chain works like a sort of light chain conveyor .
Once penetrated into the synaptic buon, the botulinum toxin releases the light chain that
can perform its protease function capable of hydrolyzing the proteins of the SNARE complex
(SNAP-25, syntaxin, synaptobrevin) of the neuromuscular junction preventing the release of
ACh from synaptic vesicles .
The proteins of the SNARE complex play a crucial role in the release of ACh, because they
favor the fusion between the membrane of the synaptic vesicles in which the acetylcholine
and the membrane of the synaptic buon are stored. The protein that is hydrolyzed is SNAP-
25, and in this way, the fusion between the synaptic vesicle membrane in which the acetyl-
choline and the synaptic membrane are crammed is made impossible, and it is for this reason
that the acetylcholine cannot be released into the synaptic space of the motor plate and the
characteristic accid paralysis of the treated muscles is determined .
In 1980, botulin toxin was rst described and used by ophthalmologists in humans for the
treatment of strabismus , while its esthetic use was rst reported in 1992 by Carruthers and
1.1. Commercial products of botulinum toxin
The most widespread toxin in the world has the trade name of Botox. Botox for esthetic use
• Vistabel® 50 U (corresponding to Botox® used in pathology); the storage of the solution
requires a temperature between 2 and 8°C, because the toxin is thermolabile. According to
the technical sheet, it is maintained for up to 4 hours. According to some scientic works,
in 12 hours, the eect is reduced to 50%. According to other works, the eect remains intact
for 6 weeks. When inserting the needle into the bole, the syringe must be sucked: this is
a sort of test to verify that the product is actually under vacuum and has therefore been
• Azzalure® 125 U (corresponding to the Dysport® used in pathology); and
• Bocouture® 50 U (corresponding to Xeomin® used in pathology) is a bare toxin (not a com-
plex protein like the previous ones). Units are not equivalent. The conversion rate is 2.5 (1 U
Vistabel or Bocouture = 2.5 U Azzalure). Bocouture not requires the cold chain; it is stored
at room temperature (0–25°) for 3 years and presents less risk of allergies as albumin is
absent in the commercial preparation .
1.2. Therapeutic uses of BTX
In the last 20 years, the therapeutic spectrum of botulinum toxin has greatly increased.
BoNT-A has been used for a wide range of established and emerging applications grouped
into the following categories:
• urological disorders,
• gastrointestinal/proctological disorders,
• pain, and
• symptomatic treatment of Parkinson’s disease (PD) [11–13].
1.3. Esthetic uses of BoNT-A
In 2002, AIFA authorized the esthetic use of BoNT-A with the following indication: “Temporary
improvement of vertical wrinkles, moderate to severe, between eyebrows to wrinkling, in adults
aged <65 years, when the severity of such wrinkles has an important psychological impact on
the patient.” Although this is the only indication for esthetic use approved by the regulatory
authority, many physicians use the toxin in o-label mode at injection sites other than those
approved, in particular for periocular and frontal wrinkles . Actually, botulinum toxin is
approved by the US Food and Drug Administration (FDA) for esthetic use in the treatment of:
• axillary hyperhidrosis,
• glabellar lines, and
• lateral canthal lines.
Botulinum Toxin Adverse Events 3
The dynamic rhytides of the upper third of the face are the best indication of botulinum toxin
These dynamic wrinkles depend on both the muscle factor and the photoaging. If the muscle
factor (young subject) predominates and if the skin is ne, you can hope for a good result;
if photoaging is predominant (older subject) and if the skin is thick, the result is less good.
Despite the apparent ease of injections, the correction of these glabellar wrinkles in particular
requires a good understanding of the anatomy and function of the fur muscles of the region.
It is necessary to respect the depression/elevator balance, which is not the same for each face,
and the type of frowning to choose the appropriate doses and to respect the recommended
injection points (Figure 1) .
2. Adverse eve nts
Side eects are essentially related to active ingredient of the drug and are referred to both
therapeutic and esthetic use.
2.1. Eects related to the drug
Regarding the side eects related to the drug, those most frequently reported are:
• injection of high doses of this drug (more than 200 units in every injection); and
• booster within less than 1 month is dangerous .
Side eects of this treatment are rare, but can include bruising, headache, allergic reactions
due to allergy to human albumin or sodium chloride present as an excipient in the drug, facial
and palpebral edema, injection site pain, eye pain, erythema, psoriasis, skin infections, vertigo,
nausea, fever, blepharitis, xerostomia, respiratory virosis, itching, asthenia, muscle weakness,
psychiatric disorders, and pneumonia ab ingestis ineectiveness of the drug (the formation of
antibodies against botulinum toxin neutralizes the eect of the toxin itself).
Figure 1. Fronto-orbital balance of the eyebrows: levator muscles and depressor muscles. The fronto-orbital balance
claries botulinum toxin action: relaxing of the frontalis muscle determines a strength increase of depressor muscles,
with possible ptosis. Instead, relaxing of the depressor muscles causes a strength increase of the frontalis.
In many cases, side eects can be minimized by lower injection doses .
2.2. Side eects of esthetic use
In esthetic, the dose of use is between 6 and 400 units; the maximum dose is between 400 and
600 U; the LD50 or toxic dose is between 2500 and 3000 U.
The most common reported side eects are mild and transient, and include injection site discom-
fort, erythema, bruising, temporary headaches, and rarely, prolonged migraine headaches .
A recent study on the safety of botulinum toxin described that the treatment-related adverse
• eylid ptosis,
• brow ptosis,
• eye sensory disorders in the upper face,
• lip asymmetries, and
• imbalances in the lower face .
Eyelid ptosis is due to the interference with the function of the upper eyelid levator muscle. It
can mainly occur when there is an excessive diusion of the toxin to the frontalis muscle. It is
therefore necessary to avoid high dosage, to inject slowly and rmly to press the eyeball with
a free nger to prevent any possible diusion of the drug into the orbital area. Eyelid ptosis
appears after the 2nd day and can last from 1 to 2 months. Therapy is based on the admin-
istration of an eyedrop (Iopidine®) based on apraclonidine (α-adrenergic) which causes, in
addition to mydriasis, the contraction stimulation of the Muller muscle of the upper eyelid,
resulting in elevation of the lash margin (Figure 2) .
Eyelid ptosis is connected with the unwanted diusion of the product toward the eyelid lift
if the corrugator has been injected too low and too far outside. This complication is always
feared, even if exceptional for an experienced operator, and hardly dissipates before 4–6
weeks. A possible asymmetry of the eyebrows can be corrected secondarily if it is an excessive
and/or asymmetrical lift, while the lowering is more dicult to modify. The frontal muscle
should not be injected too low, especially in men who already have eyebrows and a fairly low
forehead [22, 23].
Lateral brow ptosis is due to chemodenervation of the frontal leaet and therefore the orbicu-
laris muscle of the eyes (pars superior) pulls down the lateral third of the eyebrow.
Medial brow ptosis can occur after excess of dosage or injections too low in the frontal muscle.
Prevention consists of the injections at least 2 cm above the orbital rim.
Lateral brow elevation (mephisto sign) is caused by a compensatory contraction of the lateral
portion of the frontal muscle. The remedy consists in the botulinum toxin treatment of the
external portion of the frontalis muscle [24, 25].
A full blockage of the frontal mimic muscles can be avoided with intradermal injections to
obtain a beer distribution of botulinum toxin and with lower concentration in the underly-
ing muscular tissue .
Botulinum Toxin Adverse Events 5
A scleral show, greater evidence of sclera, can be veried after a functional decit of the eye’s
orbicularis (pars inferior) following interference with the function of this muscle.
Ectropion, anomalous reversal toward the outside of the lower eyelid, is due to functional decit
of the orbicularis muscle of the eye (pars inferior) for chemodenervation of the orbicularis muscle.
A strabismus, deviation of the visual axes, is caused by the malfunction of the extrinsic ocu-
lomotor muscles (lateral rectus) with consequent inability of binocular representation at the
Diplopia is caused by the involvement of the lateral rectus muscle through the diusion of
the toxin inside of the secondary orbitary cavity with inoculation too deep and close to the
margin orbital. Temporary monolateral ocular bandage may be useful (Figure 3) [27–29].
Smile asymmetry is due to the toxin diusion into the nearby zygomaticus major muscle and
asymmetry of mouth mobility is caused by the blockage of the zygomatic muscle with ptosis
of the lip (Figure 4).
Diculty in whistling occurs after a functional decit of the orbicular muscle of the mouth.
Incidence may be reduced using diluted doses of botulinum toxin [30, 31].
Figure 2. Schematic representation of eyelid ptosis complication of BoNT-A administration: uilateral eyelid ptosis.
Botulinum toxin is often interesting to mitigate the fold of the marionee, which gives the face
a sad and aged appearance, injecting the depressor of the corner of the mouth, which lowers
the labial commissures. The injection must be low to prevent the lips from spreading to the
At the neck, the araction through the posterior platysmal cords of the area in which the
falling cheeks are delineated can be aenuated by the Nefertiti lift, injecting two or three
small doses along the posterior platysmal chord and the mandibular edge. The anterior and
posterior platysmal chords can be mitigated by small doses of botulinum toxin, injected every
2 cm, pinching and aracting the rope forward [33, 34].
All of these events resolved spontaneously maybe dose-dependent and were aributed to
local diusion of BoNT into adjacent areas .
Serious adverse events related to the cosmetic use of botulinum toxin include thyroid eye
disease in a patient with Graves hyperthyroidism, sarcoidal granuloma, pseudoaneurysm of
the frontal branch of the superior temporal artery, and respiratory damage [36–39].
2.3. Side eects of therapeutic use
Recent studies demonstrate that BoNT tracking is not restricted to the neuromuscular junc-
tion, but also involves internalization of the toxin by spinal cord motor neurons and fast
axonal retrograde transportation. Toxin’s eect is sometimes observed beyond the site of local
injection. Major adverse events can include:
Figure 3. Schematic representation of diplopia complication of BoNT-A.
Botulinum Toxin Adverse Events 7
• respiratory insuciency, and
• muscle weakness.
These systemic events are rare and observed only at high dosages or in patients with underly-
ing medical conditions predisposing to the complications [40–44].
Bahtia et al. reported on three patients in whom treatment of their dystonia with therapeutic
doses of botulinum toxin resulted in clinical muscle weakness distant from the site of injec-
tions. It may be speculated that repeated injections at intervals of 10–12 weeks as in their
patients may have an impact on toxin binding and diusion. In fact, according to authors, the
cause is most likely presynaptic inhibition due to systemic spread of the toxin . Even in the
case of repeated blepharospasm treatments with BoNT-A, an induction of acute myasthenic
crisis has been demonstrated .
Figure 4. Schematic representation of asymmetry of mouth mobility of BoNT-A administration.
Systemic adverse events have been reported at the time of botulinum toxin A injection
(6% injection episodes) and at follow-up (22% injection episodes) in children with cerebral
palsy (CP), and children in Gross Motor Function Classication System (GMFCS) levels IV
and V have increased rates of systemic adverse events .
Tugnoli et al. describes a rst case of generalized muscular weakness associated with signs of
systemic cholinergic autonomic impairment who was treated with 1400 U of BoNT-A for axil-
lary and palmar hyperhidrosis. The authors assert that this case is consistent with a mild but dif-
fuse Botulism-like syndrome, probably related to the high BoNT-A doses uses and to numerous
intradermal injections and the slight build of their patient .
All these data demonstrate the possible risk of unwanted adverse eects due to spreading of
the toxin .
2.4. Diusion and migration of BoNT
In the diusion phenomena, the concentration gradient and the BoNT molecular size deter-
mine the movement of the toxin beyond the immediate injection site through Brownian
motion even if these muscles are separated by fasciae. In migration instead, a haematic and
neuroaxonal transport of BoNT occurs, which is distant from the muscle and is related to
systemic side eects that may be fatal if left untreated [49, 50].
Experimental studies in rodents have shown that botulinum toxin receptors exist in the cen-
tral nervous system and a small amount of botulinum toxin crosses the blood-brain barrier.
This raises the possibility that botulinum toxin is transported retrogradely, similar to tetanus
toxin, and may cause centrally mediated side eects .
Botulinum toxin type-A can induce autonomic eects such as biliary colic, impairment of
gastrointestinal and cardiovascular autonomic pathways, and inhibition of autonomic cholin-
ergic pathways in the bladder. Cholinergic receptors in the pharyngeal and laryngeal sphinc-
ters are likely to be inhibited by systemic spread of BoNT and may be the main reason for
One of the suggested mechanisms for transport of the toxin from one part of the body (neck) to
a remote location (toes) is the vascular spread via absorption through the capillary system and
the retrograde axonal spread of the toxin. The injection of proximal upper extremity muscles
with BoNT-A can determine diusion of the toxin into the surrounding muscles resulting in
dysphagia. These data suggest a systemic spread even when toxin is injected in sites anatomi-
cally adjacent to the locus of the side eect. Retrograde axoplasmic spread of the toxin is the
second possible mechanism for the observed distant adverse events.
Recent studies show retrograde transport of enzymatically active toxin molecules via micro-
tubules in the axon to both sensory and motor regions in the spinal cord after intramuscular
and intraneural injections of BoNT-A. In fact, antinociceptive eect of BoNT-A may occur
through retrograde spread of BoNT-A from the sensory nerves in the periphery to the central
nervous system. Moreover, distant eects also may be caused by intrafusal uptake of the toxin
in the muscles spindles as well as neuroplastic changes post-BoNT-A injections. Diusion of
BoNT is aected by a variety of factors; however, dose, concentration, and volume probably
are the greatest contributors that increase the risk of diusion. In general, the BoNT reduction
in amplitude increased with increasing doses and with increasing concentration [55–57].
Botulinum Toxin Adverse Events 9
To limit diusion is target muscle localization using EMG and endoscopic or imaging guidance
2.5. Nonresponsiveness to treatment with BoNT
Nonresponsiveness to BoNT could be as a result of possible factors that include misdiag-
nosis, insucient dose, problems with toxin storage and preparation, and administration.
Another possible reason for lack of clinical eect is immunoresistance to BoNT, which refers
to ineectiveness of the toxin as a result of development of neutralizing antibodies against
the toxin .
The formation of neutralizing antibodies to BoNT is increased by a short time period between
injections, the administration of booster injections, and the use of high BoNT doses. To pre-
vent antibody formation against BoNT, the practitioner can use a newer BoNT formulation
with the lowest protein content .
3. Contraindications and interactions with some medications
BoNT is contraindicated in patients with known peripheral motor neuropathies or neuro-
muscular disorders, such as Eaton-Lambert syndrome, multiple sclerosis, and myasthenia
gravis, because further chemodenervation may exacerbate muscle weakness. The cause is to
be found in a reduced release of acetylcholine in the neuromuscular endplate, due to the eect
of autoantibodies against the presynaptic channels of calcium .
The treatment can be performed in the 18–65 age range. Other contraindications are represented
• allergy to human albumin and/or sodium chloride,
• skin infections,
• presence of scleral show,
• senile ectropion,
• dysphagia, and
• psychiatric disorders.
Aminoglycoside antibiotics that can enhance the eect of botulinum toxin are netilmicin,
tobramycin, gentamicin, neomycin, amikacin, kanamycin, and streptomycin. Other drugs that
also interfere with neuromuscular transmission are muscle relaxants such as D-tubocurarine,
baclofen, thiocolchicoside, tizanidine, diazepam, dantrolene, and pridinol [62, 63].
4. Rehabilitation of the motor endplate
The rehabilitation of the motor endplate can be very useful in case of side eects following
treatment with botulinum toxin.
Radioiodinated botulinum toxin A (125I-BoNT/A-complex, 67 or 344 U free-125I-BoNT/A)
was injected into the gastrocnemius muscle of rats and measured in various tissues at dier-
ent time points. These “in vivo” studies allowed to establish that after 24 hours, the toxin is no
longer present in the inltrated muscle.
Thus, the side eects reported seem to be related to the damage caused by toxin caused and
not to the presence of it in the muscles. These eects can be visible after 10–12 days .
For this reason, it is useless to administer the antitoxin which exerts its action by binding to
the toxin still in circulation, complexing it and making it inactive. Furthermore, the healing
capacity depends on the regeneration of the aected synaptic terminations.
Because the light chain of botulinum toxin causes proteolysis of the SNAP 25 protein, reduc-
ing its endocellular pool, one must reestablish its own physiological endocellular pool.
In practice, it is necessary to stimulate the biosynthesis of the SNAP25 protein to favor the
structural and functional recovery of the motor endplate.
The aim of the therapy is to stimulate the biosynthesis of the SNAP 25 protein, consisting of
about 200 amino acids. So, we can correct side eects such as ectropion, diplopia, palpebral
ptosis, strabismus, scleral show, and asymmetries of smile and mouth mobility.
To improve the biosynthesis of the SNAP 25 protein, it is necessary to take:
a. A proteic diet (meat, sh);
b. Amino acids such as arginine and cysteine as they belong to the molecular composition
of the SNAP-25 protein. Then, we supplement other amino acids: arginine, bioargin, and
c. L-acetylcarnitine which is an agonist of the mitochondrial growth function and reparative
agents (NGF), expounds an antioxidant activity in the neurons of the central and periph-
eral nervous system. L-acetylcarnitine is structurally similar to acetylcholine and plays an
indispensable role for proper cellular energy, metabolism, and neurotransmission;
d. Alpha-lipoic acid (also called thioctic acid), a fat-soluble vitamin that participates in vari-
ous antioxidant mechanisms such as the regeneration of reduced glutathione (GSH) and
ascorbic acid; and
e. L-carnosine, a dipeptide composed of β-alanine and L-histidine; it has the ability to pro-
mote protein regeneration even in dicult situations such as in the late stage of the life
cycle. It has antioxidant properties.
This therapy is able to guarantee fast responses (7–10 days) and in 80% of cases [65–68].
Botulinum Toxin Adverse Events 11
The use of BoNts continues to steadily expand and multiply. New indications of clinical use of
BoNTs are continuously emerging in medical therapy and further applications will be devel-
oped in the future. Adverse events occur more frequently after the clinical use of the toxin, but
may also disclose after its esthetic use. The safe utilization of BoNTs requires knowledge of its
indications and pharmacology, anatomy of the treated muscles to avoid serious complications.
Raaela Pero1*, Sonia Laneri2 and Giovanna Fico3
*Address all correspondence to: email@example.com
1 Department of Molecular Medicine and Medical Biotechnology, University of Naples
“Federico II”, Naples, Italy
2 Department of Pharmacy, University of Naples “Federico II”, Naples, Italy
3 ASL Napoli 3 Sud, Naples, Italy
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