PROlonged versus Single dose in PEnicillin oral Challenge Testing-2

Penicillin allergies are highly prevalent in the healthcare setting and are associated with second-line inferior antibiotics being prescribed. An incorrect penicillin allergy label leads to increased risk of resistant organisms, side effects from second-line antibiotics as well as increased medical costs. The gold standard for penicillin allergy testing is an oral challenge – either direct or following skin testing. What remains unknown is if a single dose is sufficient to determine if the patient has a delayed or unknown timing immune mediated penicillin allergy or if a prolonged oral challenge (5 days or more) is required. The PROSPECTOR pilot trial demonstrated the feasibility and safety of a placebo-controlled trial of single dose penicillin challenge versus prolonged challenge (5-day). PROSPECTOR2 continues from the PROSECTOR pilot trial (ACTRN12623001242617) to assess the superiority of prolonged oral challenge versus single dose challenge for identifying immune-mediated penicillin allergy. The current Drug Allergy Practice Parameters recommend “against the routine use of multiple-day challenges in the evaluation of penicillin allergy”, providing a “strong recommendation” but with “low certainty of evidence”. The European guidelines reviewed the literature of over 6484 patients, demonstrating a 2.3% positive rate following the initial challenge and 5.5% during the varied prolonged challenges. They concluded there is no consensus on a preferred procedure and could not provide a recommendation for or against prolonged challenge. In Europe, a mixture of observational and retrospective studies has suggested that extended challenges ranging from 3 to 10 days may be superior to single dose challenges at excluding delayed immune reactions, however the reported prevalence of delayed reactions is highly variable (5-12% of patients) and many were reliant on patient self-reporting. In a recent retrospective single centre Danish experience of 3,179 low-risk patients, 2.6% were positive on day 1 of challenge and 7.2% on days 3-10. This is in contrast to the North American experience, where delayed prolonged challenges have been associated with low rates of delayed reactions (0-1.8%). Whilst a study of children demonstrated that delayed reactions may occur less than 7 days following a single challenge. Therefore, whilst oral challenge is the well-defined gold standard for penicillin allergo-immunological investigation, limited controlled evidence is available regarding the efficacy of single dose versus prolonged oral challenge.