Tolerance of the venom immunotherapy switch from a highly purified aluminium hydroxide adsorbed hymenoptera venom extract to a nonpurified aqueous venom extract.

Background
European guidelines caution against switching from purified aluminium-hydroxide-adsorbed (AHA) venom extracts to non-purified aqueous extracts, and supporting data are lacking.Objective
To assess feasibility and short-term safety of switching from Alutard® (AHA) to Venomil® (non-purified aqueous) in routine care.Methods
Retrospective single-centre case series (March 2021-August 2024). Fifteen patients with hymenoptera venom allergy (13 bee, 2 wasp) on maintenance Alutard® were switched to Venomil®. Starting doses and escalation were individualised. Primary outcome was tolerability during switch; secondary outcomes were visits required to re-establish maintenance dosing.Results
Before switching, 10/15 were on 100 μg and 5/15 on 200 μg. Starting Venomil® doses were 20 μg (7/15), 30 μg (1/15), or 50 μg (6/15); 1 patient underwent ultra-rush re-induction after a systemic field sting on 100,000 SQU Alutard®. Fourteen of 15 patients tolerated the switch without systemic events; 1 bee-venom patient developed a Mueller grade II reaction during escalation toward 100 μg but subsequently reached 200 μg with gradual outpatient increments. Among those without events, 9/13 reached 100 μg on day 1 and 4/13 by day 7; achieving 200 μg typically required 3-4 visits.Conclusions
In a real-world setting with product constraints, switching from purified AHA to a non-purified aqueous extract was feasible and generally well tolerated when dosing was individualised and monitored. Prospective, standardised studies with sting-challenge endpoints are warranted.