Sir, the indications for the use of botulinum toxin (BT) in the head and neck region include hypersalivation, migraine, masseteric hypertrophy, hemifacial muscle spasm and for the treatment of rhytids.1,2 Although widely accepted as a safe drug, there are many side effects and interactions, and we hope this summary serves as a quick yet essential guide.

There are no absolute contraindications except a history of allergy to constituents of BT product. It should not be injected directly into infected skin or skin with psoriasis or eczema. Relative contraindications include avoiding injecting BT in patients who are breastfeeding, on contraceptives or pregnant unless clinically highly indicated. The evidence suggests that botulinum does not cross the placenta and systemic levels after cutaneous injections are extremely low.3 As a caution, BT injected into patients with neuromuscular or neurological disorders (eg myasthenia gravis) can result in severe muscle weakness.

With regards to drug interactions, antibiotics - through their blockade effect at the neuromuscular junction - gentamycin, amikacin, tobramycin and neomycin may result in exaggerated effects of botulinum toxin. Acetylcholinesterase inhibitors, prescribed for patients with myasthenia gravis, act as toxin antagonists and therefore may reduce the effect of botulinum toxin (common medication includes pyridostigmine). Aminoquinoline: these antimalaria medications have a negative effect on acetylcholine and therefore reduce nerve excitation. The result is that it has the potential to magnify the effect of BT. Cyclosporin: through an unknown mechanism, cyclosporin may potentiate the effects of BT.

Side effects can include:

  • Keloid scar at injection site

  • Ptosis - if an injection is too close to the eyebrow, toxin solution may diffuse to the levator muscles of upper eyelid causing obvious weakness

  • Dysphagia - if injection given to major salivary gland or to the sternocleidomastoid muscle. Diffusion of toxin into surrounding muscles can cause this issue4

  • Respiratory embarrassment - injections into both submandibular glands for excessive hypersalivation may result in toxin solution extruding out of the gland capsule and into surrounding muscles involved with breathing4

  • Facial weakness - caused by diffusion of toxin to facial nerve branches, in particular when injected into the masseter muscle

  • Pain, bleeding, swelling, bruising, infection

  • Headache

  • Paraesthesia

  • Aesthetic disenchantment.

The vast majority of BT injections in this region are safe but a full patient assessment and thorough medical history is essential. Risks must be clearly explained and documented in the medical notes.