Extended maintenance intervals during long-term venom immunotherapy (VIT)

RATIONALE: VIT may be discontinued after 5 years, but prolonged treatment is preferred in many cases. Maintenance intervals are often extended to 6-12 weeks. Our aim was to study the feasibility, safety and efficacy of a trial of extended intervals of 12-20 weeks during long-term VIT. METHODS: Consenting patients with at least 5 years of VIT had their interval increased to 12-16 weeks. If sting challenge 2 years later caused no systemic reaction their interval was increased by another 4 weeks with repeat sting challenge 2 years later. RESULTS: Recruitment for the study was difficult, patients often choosing to avoid sting challenge by discontinuing VIT, or continuing our standard 6-8 week intervals. Of 24 patients who consented, sting challenge could not be done in 9 cases: 3 had poor compliance; 2 began ß-blockers, 1 refused sting challenge, 1 chose discontinuing VIT and 2 died of unrelated causes. Two patients enrolled last year and are not yet due for sting challenge. There were no systemic reactions induced by 22 sting challenges in 13 patients: 9 on a 12 week interval, 12 on a16 week interval, and 1 on a 20 week interval. No adverse reactions occurred to injections in any of the 24 patients, even when the interval exceeded 20 weeks due to poor compliance. CONCLUSIONS: This preliminary study suggests that extended maintenance intervals may be a safe alternative to discontinuing VIT, but it may lead to poor compliance. Further studies are needed to confirm the efficacy of extended intervals especially in high-risk patients.