Botulinum toxin type B (BT-B) therapy failure due to formation of botulinum toxin type B antibodies (BT-B-AB) has only been reported in patients with botulinum toxin type A antibodies (BT-A-AB). We are reporting BT-B-AB-induced therapy failure in 2 patients with no previous exposure to botulinum toxin. In patient 1 complete therapy failure occurred after a single exposure to 14,400 mouse units (MU) BT-B (NeuroBloctrade mark). The mouse diaphragm assay (MDA) revealed a BT-B-AB titre in excess of 10 mU/ml. Doubling the BT-B dose did not elicit any effects. Application of 360 MU BT-A (Botox((R))) produced the original therapeutic effect, but the second BT-A application was followed by partial and the third by complete therapy failure. Doubling the BT-A dose did not elicit any effects. MDA testing showed a BT-A-AB titre in excess of 10 mU/ml. In patient 2 a single exposure to 7,200 MU BT-B lead to a complete therapy failure. MDA testing revealed a BT-B-AB titre in excess of 10 mU/ml. Doubling the BT-B dosedid not elicit any effects. Application of 180 MU BT-A (Botox) produced the original response on 3 consecutive applications. Antibody formation can occur after a single exposure to botulinum toxin. However, this is highly unusual. Since therapy failure occurred after the first-ever botulinum toxin exposure, short intervals between injections and use of booster injections can be excluded as causes for BT-B-AB formation in both patients. A more likely cause may be the substantially higher amount of antigenic protein administered in BT-B therapy compared to BT-A therapy. Further studies are necessary to compare the incidence of antibody formation in BT-B and BT-A therapy. Copyright (c) 2004 S. Karger AG, Basel.
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