botulinum toxin is an injectable muscle relaxant, commonly known by one of its trademarked brand names,
botox.
botulinum toxin is responsible for causing botulism, the paralysing and potentially fatal foodborne illness. the name botulinum is derived from the latin word botulus (sausage) because the illness was once believed to originate from sausages. we now know that the botulinum toxin is produced by clostridium botulinum bacteria.
c. botulinum produces eight types of toxins, labelled from a to g. since the 1950s, research has focused on developing the muscle-relaxing properties of botulinum-a, and more recently botulinum-b, for therapeutic use.
how do botulinum toxins work?
botulinum-a and botulinum-b block nerve signals in the muscles. in order to contract, a muscle must receive a signal from peripheral nerve endings. this signal is the neurotransmitter, acetylcholine, which binds the receptors with the muscle, initiating muscle contraction.
botulinum toxin inhibits the release of acetylcholine and therefore also inhibits muscle contraction.
more specifically, botulinum-a and botulinum-b target a group of proteins called snare (soluble nsf attachment protein receptor). the function of snare is to release neurotransmitters from their storage vesicles by helping vesicle membranes fuse with the cell membrane. because snare is also involved in the release of other neurotransmitters, botulinum toxins have additional effects. for example, by preventing the release of glutamate and substance p, botulinum toxin lessens the sensation of pain.
muscle weakness is typically seen within two to four days, and maximal weakness or paralysis is noted around ten days. the effects of botulinum toxins are not permanent, because the affected nerves sprout new endings. after around three months, a working connection between the nerve and muscle is re-established. however, an element of atrophy (muscle wasting) occurs with each injection. this incremental atrophy explains why the interval needed for a second treatment can gradually lengthen following repeated injections.
what are the differences between the different types of botulinum-a?
in new zealand, there are three commercially available brands of botulinum-a:
●
botox (onabotulinumtoxina)
● dysport (abobotulinumtoxina)
● xeomin (incobotulinumtoxina).
each form has a unique molecular structure but shares the same core elements of the botulinum-a. the majority of research for cosmetic uses of botulinum-a have been based on onabotulinumtoxina.
it is important to note that there is no standardised international unit that can be used to compare or to measure the amount of botulinum toxin administered. this means the effect of one unit of
botox is different than one unit of dysport. the approximate conversion factor is 1:2.5 to 1:5 between
botox and dysport; and 1:1 between
botox and xeomin.
myobloc (rimabotulinumtoxinb) is a commercially available brand of botulinum-b. myobloc is used mainly in other medical specialties outside of
dermatology.
can botulinum-a reverse the effects of ageing?
the appearance of
ageing skin arises from a combination of factors. rhytides (wrinkles) are caused by altered
pigmentation, redundant and sagging skin, and loss of soft tissue. rhytides caused by muscle movements are called dynamic rhytides, while those rhytides that do not change with muscle movement are called static rhytides.
as an injectable muscle relaxant, botulinum-a is effective in treating dynamic rhytides and is currently fda-approved for the treatment of rhytides occurring in the upper face
● forehead lines
horizontal lines across the forehead result from contraction of the frontalis muscle. this is the
facial muscle involved when you express worriedness; hence the name ‘worry lines’.
the vertical lines between the eyebrows result from contraction of procerus and corrugator supercilii muscles. these are the
facial muscles involved in frowning; hence the name ‘frown lines'.
● crow’s feet
horizontal lines branching out from the outer corners of the eyes result from contraction of the orbicularis oculi muscle. this is the
facial muscle involved in the
facial expression when smiling, and the resulting lines are named after their resemblance to crow’s feet.
are there other approved uses for botulinum-a?
the other major use of botulinum-a in
dermatology is for treatment of localised hyperhidrosis. hyperhidrosis is a condition of excess and uncontrollable sweating. botulinum-a injected into the skin of the axillae and palms targets the eccrine sweat glands to prevent sweating. it is used off-label to treat the auriculotemporal syndrome.
botulinum-a is also approved for the following uses:
● overactive bladder causing symptoms of urinary incontinence, urgency, and frequency
● prevention of migraines
● blepharospasm (abnormal contraction of eyelid muscles)
● cervical dystonia (painful spasms of neck muscles)
● focal spasticity (localised groups of overactive muscles).
what are the contraindications to receiving botulinum-a injections?
botulinum-a is contraindicated in individuals with:
● pre-existing medical conditions that cause muscle weakness, including motor neurone disease (amyotrophic lateral sclerosis) and myasthenia gravis
● infection overlying the injection site
● previous allergic or hypersensitive
● reactions to botulinum-a.
botulinum-a should also be avoided during pregnancy and while breastfeeding.
certain medications that enhance the effects botulinum-a should be avoided. these medications include tetracycline antibiotics and aminoglycoside antibiotics.
blood thinners — including aspirin, warfarin and dabigatran — increase the risk of significant
bruising from injection sites.
what are the adverse effects of botulinum-a injections?
the most common adverse effects of botulinum-a are related to the injection, rather than to the botulinum toxin itself. these adverse effects include pain,
bruising,
swelling, and redness at the injection site.
● an uncommon side-effect of botulinum-a is the unintended weakness of the surrounding muscles (occurring in fewer than 10% of treatments). this weakness results from the spread of the toxin from the injection site into adjacent muscle groups.
●
the eyelids (
ptosis), brows, and lips can be affected.
● the weakness can persist for up to 12 weeks.
● medicated α-adrenergic eye drops can be prescribed for treatment of droopy eyelids and eyebrows.
● the hand muscles can be unintentionally affected when treating palmar hyperhidrosis, resulting in temporary weakness or reduced dexterity.
● some people note a mild headache, usually two to four hours after injection into forehead muscles, which can be treated with paracetamol (acetaminophen).