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Severe contact urticaria to guar gum included as gelling agent in a local anaesthetic

We report the first case of a life‐threatening immediate‐type hypersensitivity caused by Dynexan™, a local anaesthetic gel. After mucosal application by his dentist, a 63‐year‐old man rapidly developed urticaria, dyspnea and, at last, he collapsed and remained unconscious for 2 hr despite emergency care. While the standard prick tests were negative to all local anaesthetics tested including lidocaine, a 1‐fold positive reaction was detected to Meyprogat 60™, an ingredient of Dynexan™. As the gelling agent Meyprogat 60™ represents a derivative of guar (synonymous guar gum, guaran, E‐412), we subsequently tested different guar products derived from Cyamopsis tetragonoloba beans and, as control, the closely related locust bean gum E‐410. In the prick‐to‐prick tests, the guar‐derived food additive Provigel™ NAG 905 provoked a 1‐fold positive reaction. Native guar beans pounded and resuspended in water showed a 2‐fold positive reaction, whereas no reaction was found to derivatives of locust bean gum. Specific immunoglobulin E were negative in all cases. Despite the common use of guar as versatile food additive or gelling agent, this is the first case of a severe immediate‐type hypersensitivity after mucosal contact.