Allergy to Neuromuscular Blocking Agents and Pholcodine Exposure

The main objective of this study is to compare pholcodine exposure in patients having presented with a perianaesthetic anaphylactic reaction to a NMBA (cases) to pholcodine exposure in matched anaesthetised patients with injection of NMBA, who did not present with an anaphylactic reaction (controls). The secondary objectives of the study are: * To compare anti-pholcodine IgE, anti-ammonium IV IgE and total IgE levels between the case and control groups. * To study the concordance between exposure to pholcodine in cases and controls, by means of a patient self-questionnaire on the one hand and, on the other hand, by a computerized drug history, supplemented where relevant by the drug master file. * To study the impact of taking 1, 2 or 3 sources in account for pholcodine exposition. * To study the association between exposure to pholcodine and the presence/levels of pholcodine-specific IgE, reflecting sensitisation to pholcodine. * To study NMBA and pholcodine cross-sensitisation by testing skin reactions to pholcodine in case patients allergic to (at least) one NMBA.