Rocuronium‐induced anaphylaxis is probably not mitigated by sugammadex: evidence from an in vitro experiment

Jones and Turkstra raised the intriguing question of whether the administration of sugammadex (a selective binding agent that encapsulates rocuronium [1]) mitigates ongoing anaphylaxis due to rocuronium [2]. They speculated that sugammadex might remove free rocuronium molecules from the circulation, and hence slow down or halt the allergic reaction. This question cannot easily be answered by in vivo studies, as this would require a controlled and blinded administration of sugammadex/placebo to sufficient numbers of patients in whom the diagnosis of rocuronium allergy is not established at the time of the acute event. As the principle of in vitro activation of basophils closely mirrors the in vivo situation leading to allergic symptoms [3], we anticipated that the technique could help to elucidate on this issue. Following Local Ethics Committee approval and informed consent from the participants or their parents, activation of basophils was performed in three patients with skin-test documented rocuronium allergy. For a description and interpretation of skin tests and activation of basophils, the reader is referred elsewhere [3]. Briefly, aliquots of 100 μl whole heparinised blood of rocuronium-allergic patients (positive basophil activation test and skin test) were challenged at 37 °C with buffer as a negative control, anti-IgE (Pharmingen, BD Bioscience, Erembodegem, Belgium) as a positive control, serial dilutions of rocuronium (Esmeron, Organon, Brussels, Belgium, 0.2–2.0 × 103 μg.ml−1), serial dilutions of sugammadex (Bridion®; Merck Sharp & Dohme, Oss, The Netherlands) 0.2–2.0 × 103 μg.ml−1 and with a mixture of different concentrations of rocuronium and sugammadex. Flow cytometric analysis of basophils was performed using triple labelling with CD123-PE, HLA-DR-PerCP, CD63-FITC (BD Biosciences) and using monoclonal antihuman IgE (clone GE-1; Sigma-Aldrich Chemic GmBH, Steinheim, Germany), labelled with AlexaFluor 488 (Molecular Probes, Invitrogen, Paisley, UK). Samples were analysed on a flow cytometer (FACsCanto BD; Immunocytometry Systems, San Jose, CA, USA) and expressed as CD63-positive basophils. Samples were regarded as positive when CD63-reactive basophils were higher than 4% [3]. All patients were clearly responsive to positive control stimulation with anti-IgE and also to rocuronium. Stimulation with sugammadex alone did not activate the basophils. To establish whether encapsulation of rocuronium by sugammadex was able to inhibit basophil activation by the neuromuscular blocking agent, we stimulated the basophils for 15 min with a pre-incubated mixture of rocuronium and sugammadex in different concentrations. We found that sugammadex is able to prevent rocuronium from cross-linking IgE-receptors and activating mast cells, provided that the inhibitor and the culprit drug are pre-incubated in advance of cell stimulation (Fig. 2). From the figure, it appears that pre-incubation with sugammadex demonstrates a dose-dependent inhibition of rocuronium-induced cell activation. Note that a 5:1 ratio of sugammadex:rocuronium is needed to achieve effective prevention of rocuronium-induced activation of the basophils. Dose-dependent inhibition of rocuronium-induced basophil activation in three rocuronium-allergic patients. Solid line: pre-incubated mixture of rocuronium and sugammadex. Dotted line: addition of sugammadex after 3 min of activation with rocuronium. However, to be useful in the treatment of acute rocuronium-induced anaphylaxis, sugammadex should halt ongoing basophil activation, and not simply prevent triggering of the cell. Therefore, we set up a second in vitro experiment, resembling this clinical situation. Basophils were first activated with rocuronium and after 3 min, sugammadex was added in increasing concentrations to assess whether this could halt an ongoing reaction. In none of our patients could activation of the basophils be blocked completely by adding sugammadex, even in very high concentrations (Fig. 2). In conclusion, it appears that encapsulating rocuronium by sugammadex can prevent, but not stop, in vitro basophil activation by the neuromuscular blocking agent. Therefore, it seems unlikely that administration of sugammadex would mitigate rocuronium-induced anaphylaxis. No external funding and no competing interests declared. Previously posted at the Anaesthesia Correspondence website: http://www.anaesthesiacorrespondence.com.