Botulinum Toxin (BTX)(Table 6-21) - Purified protein toxin produced from Clostridium botulinum; seven serotypes which differ slightly in clinical effect and mechanism of action, but all block neuromuscular transmission causing temporary paralysis of striated muscle
- BTX specifically inhibits acetylcholine (ACh) release by cleaving proteins in the SNARE complex (required for Ach release)
- BTX type A light chain cleaves SNAP25 (synaptosome-associated protein), key protein for successful docking and release of ACh from vesicles within nerve endings
- BTX type B light chain cleaves synaptobrevin or VAMP (vesicle-associated membrane protein)
- BOTOX (type A): FDA-approved for glabellar rhytides and hyperhidrosis; each vial contains 50 or 100 units of vacuum-dried BTX A neurotoxin; smaller volume with higher dose keeps delivery precise with little diffusion
- Instructions recommend reconstitution with sterile, non-preserved saline, but preserved saline results in less pain on injection and does not reduce stability of toxin
- Contraindication: any neuromuscular disorder, infection/inflammation at injection site, known hypersensitivity to product or any of the contents, pregnancy (category C - safety for use during pregnancy has not been established) or breastfeeding
- Most effective in reducing dynamic facial lines (vs. static lines) (Table 6-21)
- Glabellar rhytides (procerus, corrugator supercilii):
- Stay 1 cm above orbital rim
- If BTX diffuses to levator palpebrae muscle, eyelid ptosis may occur
- Horizontal forehead lines (frontalis muscle):
- If weaken frontalis muscle significantly but eyebrow depressors not weakened concomitantly, will have unopposed action of depressors with lowering of the brow and an angry expression
- If patient narrow brow (<12 cm) between temporal fusion lines at mid brow level, receive fewer injection site (four instead of five)
- Crow’s feet (orbicularis oculi):
- Weakening of orbicularis oculi muscle by three injection sites
- Do not inject while patient is still smiling as toxin may affect ipsilateral zygomaticus complex, causing ptosis of upper lip
- Perioral rhytides (orbicularis oris):
- Vertical lines radiating outward from vermilion border due to overactive orbicularis oris
- Goal to produce mild weakening of muscle (avoiding paresis, which would interfere with speech); small doses 1–2 units per lip quadrant sufficient (total eight injection sites)
- Bunny lines (nasalis):
- Inject anterior to nasofacial groove on lateral wall of nose to soften ‘bunny lines’ (radial lines fanning obliquely across radix of nose); inject superficial to angular vein
- Avoid injecting nasofacial groove as this can affect levator labii superioris and levator superior alaeque nasi
- Depressor anguli oris (DAO):
- Contraction causes downward turn of corner of mouth, creating negative facial expression
- Inject 3–5 units at level of mandible (posterior margin), close to anterior margin of masseter; complications include asymmetric smile and flaccid cheek
- Patients using perioral muscles intensely are not good candidates for DAO injections
- Complications:
- Brow ptosis may occur while glabellar complex being treated if BTX inadvertently affects frontalis muscle; may also occur if frontalis muscle being treated in patient with already low-set eyebrows
- Quizzical appearance may appear when horizontal forehead lines are treated without treatment of most lateral frontalis fibers, which results in upward pull from the nontreated fibers
- Upper eyelid ptosis occurs typically with treatment of glabellar complex; toxin diffuses through orbital septum affecting upper eyelid levator muscle; appears as early as 48 h and as late as 14 days after treatment, lasts 2–12 weeks; avoid complication by injecting small volume with high concentration and always inject 1 cm above orbital rim; can treat with apraclonidine 0.5% eye drops, which is an α-adrenergic agonist and may lift lid by 1–2 mm (compensates for weakness of levator palpebrae superioris by causing Muller’s muscle to contract)
| | | | | | | Table 6-21 Muscles Treated with BTX | | | Muscle | | Resulting Rhytides | | Comments | | | Nasalis | | Bunny lines (radial lines across radix of nose) | | Avoid angular vein | | | Orbicularis oculi | | Crow’s feet (horizontal to oblique lines radiating from lateral canthus) | | | | | Frontalis muscle | | Horizontal forehead lines | | Complications: quizzical appearance, brow ptosis | | | Procerus, corrugator supercilii | | Glabellar lines | | Complications: eyelid ptosis, brow ptosis (latter rare) | | | | | | | |
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