Botulinum Toxins: Clinical Pharmacology, Resistance, Regimens, and Results

The introduction of Botulinum A toxin chemodenervation by Alan Scott revolutionized the treatment of spastic and paretic disorders of the eyelids and the extraocular muscles. This specific, local treatment has shown that patients want and will respond to temporary, targeted, graded relief of spasticity. The spectrum of disorders treated by Botulinum toxins continues to enlarge. One reason for the success of this therapy is that the side effects are generally local (ptosis and diplopia with eyelid injections, untargeted muscle paresis: bleeding and ocular perforation with retrobulbar injections, difficulty swallowing with dysphonia treatment). Ocular local side effects lasting over 180 days are about 1% of all side effects with ptosis less long lasting than vertical deviation. Systemic side effects are mostly noted with quantitative testing such as single fiber EMG at remote sites and autonomic side effects such as dysphagia, dry mouth, sluggish pupillary responses, reduction in variability of he heart rate, and impaired emptying of the gall bladder. Other than hypersensitivity and perhaps pregnancy, there are few contraindications to Botulinum toxin therapy but patients with disorders of neuromuscular transmission should be evaluated for the possibility of enhanced toxicity. Aminoglycoside antibiotics, clindomycin, and cyclosporine may potentiate general anesthetic induced neuromuscular relaxation resulting in residual paralysis following surgery.