Full-course drug challenge test in the diagnosis of delayed allergic reactions to penicillin

Simplifying the drug provocation test in non-immediate hypersensitivity reactions to amoxicillin in children: The experience of a tertiary care allergy unit

BACKGROUND

Mild non-immediate reactions (NIR) to beta-lactams (βLs) are the most common manifestation of adverse drug reactions in children, and the drug provocation test (DPT) remains the gold standard for diagnosis. However, there are still controversies about the protocol that should be used, especially regarding the administration of doses and the DPT length.

OBJECTIVE

This study aimed to evaluate a pediatric population with a history of mild NIR to amoxicillin (AMX) or to amoxicillin-clavulanic acid (AMX/CL) who underwent a diagnostic workup including a DPT with the culprit drug, to understand if a graded DPT or, instead, a single full dose could be the most appropriate way of administration in clinical practice.

METHODS

The data of children were retrospectively analyzed for a 5-year period, with demographic and clinical characteristics collected. We reported the allergy workup and the results of the DPT performed with the administration of incremental doses and a prolonged DPT at home for a total of 5 days.

RESULTS

Three hundred fifty-four patients were included. Overall, 23/354 (6.5%) DPTs were positive: 11/23 patients showed a reaction after 2-8 h after the last dose on the 1st or 2nd day (1 reacted 30 min after the last dose), 1/23 reacted with urticaria 30 min after the first dose, 11/23 reacted at home on the 5th day of the DPT.

CONCLUSION

This paper indirectly suggests that a single therapeutic dose administered on the 1st day of a DPT could be safe in the diagnostic workup of mild NIR to AMX/CL. Moreover, this could be less time-consuming as patients would spend less time in the hospital, also considering the public health restrictions imposed during the COVID-19 pandemic.

Single-dose prolonged drug provocation test, without previous skin testing, is safe for diagnosing children with mild non-immediate reactions to beta-lactams

INTRODUCTION

Mild non-immediate reactions (NIRs) to beta-lactams (BLs) are the most frequent manifestation of drug allergy in children. The diagnostic approach is complex as the utility of skin tests (STs) and lymphocyte transformation tests (LTTs) is controversial. Drug provocation test (DPT) is the gold standard, although no standardized protocols exist. We aimed to investigate the utility of DPT in a unique dose without previous STs, and LTTs in the diagnosis of NIRs to BLs in children.

METHODS

We prospectively evaluated children 0-14 years old referred to the Regional University Hospital of Málaga during 2017-2020 reporting NIRs to BLs. We performed a DPT with a unique dose followed by regular treatment at home. If positive, STs and LTTs were done after the reaction had disappeared.

RESULTS

We included 194 children, having 24 (12.4%) a positive DPT. The main culprit was AX (70.1%) followed by AX-clavulanic acid (CLV) (26.8%) and the main symptoms maculopapular exanthema (MPE) (49.5%) and delayed-urticaria (48.5%). A decrease (p = 0.013) in the interval of days between drug administration and onset of symptoms was observed in positive DPT compared with the original reaction (3.5 vs 6 days), with no differences in the overall percentage of MPE and delayed-appearing urticaria (p = 0.551). No severe reactions occurred during DPT. Moreover, STs were positive in 13.33% and LTTs in 52.9%.

CONCLUSIONS

Single-dose DPT without previous STs is a safe and useful way to assess NIRs to BLs in children. LTT has shown to be useful, confirming a T-cell mechanism involved in these reactions.

Frequency of severe reactions following penicillin drug provocation tests: A Bayesian meta-analysis

BACKGROUND

Patients with a penicillin allergy label tend to have worse clinical outcomes and increased healthcare use. Drug provocation tests (DPT) are the gold-standard in the diagnostic workup of penicillin allergy, but safety concerns may hinder their performance. We aimed to assess the frequency of severe reactions following a DPT in patients with reported allergy to penicillins or other β-lactams.

METHODS

We performed a systematic review, searching MEDLINE, Scopus, and Web of Science. We included primary studies assessing participants with a penicillin allergy label who underwent a DPT. We performed a Bayesian meta-analysis to estimate the pooled frequency of severe reactions to penicillin DPTs. Sources of heterogeneity were explored by subgroup and metaregression analyses.

RESULTS

We included 112 primary studies which included a total of 26,595 participants. The pooled frequency of severe reactions was estimated at 0.06% (95% credible interval [95% CrI] = 0.01%-0.13%; I2  = 57.9%). Most severe reactions (80/93; 86.0%) consisted of anaphylaxis. Compared to studies where the index reaction was immediate, we observed a lower frequency of severe reactions for studies assessing non-immediate index reactions (OR = 0.05; 95% CrI = 0-0.31). Patients reporting anaphylaxis as their index reaction were found to be at increased risk of developing severe reactions (OR = 13.5; 95% CrI = 7.7-21.5; I2  = 0.3%). Performance of direct DPTs in low-risk patients or testing with the suspected culprit drug were not associated with clinically relevant increased risk of severe reactions.

CONCLUSIONS

In patients with a penicillin allergy label, severe reactions resulting from DPTs are rare. Therefore, except for patients with potentially life-threatening index reactions or patients with positive skin tests-who were mostly not assessed in this analysis -, the safety of DPTs supports their performance in the diagnostic assessment of penicillin allergy.

Delabeling Delayed Drug Hypersensitivity: How Far Can You Safely Go?

Delayed immune-mediated adverse drug reactions (IM-ADRs) are defined as reactions occurring more than 6 hours after dosing. They include heterogeneous clinical phenotypes that are typically T-cell-mediated reactions with distinct mechanisms across a wide spectrum of severity from benign exanthems through to life-threatening cutaneous or organ-specific diseases. For mild reactions such as benign exanthem, considerations for delabeling are similar to immediate reactions and may include a graded or single-dose drug challenge with or without preceding skin or patch testing. Evaluation of challenging cases such as the patient who is on multiple drugs at the time a severe delayed IM-ADR occurs should prioritize clinical ascertainment of the most likely phenotype and implicated drug(s). Although not widely available and validated, procedures such as patch testing, delayed intradermal skin testing, and laboratory-based functional drug assays or genetic (human leukocyte antigen) testing may provide valuable information to further help risk stratify patients and identify the likely implicated and/or cross-reactive drug(s). The decision to use a drug challenge as a diagnostic or delabeling tool in a patient with a severe delayed IM-ADR should weigh the risk-benefit ratio, balancing the severity and priority for the treatment of the underlying, and the availability of alternative efficacious and safe treatments.

The negative predictive value of 5-day drug provocation test in nonimmediate beta-lactam allergy in children

BACKGROUND

Extending the drug provocation test (DPT) period is recommended for patients with suspected nonimmediate beta-lactam antibiotic (BLA) allergy and negative DPT. No consensus has been reached regarding the duration of prolonged provocation.

OBJECTIVE

We aimed to determine the negative predictive value (NPV) of the 5-day extended DPT.

METHODS

Parents of patients with suspected nonimmediate mild cutaneous reactions with BLAs who had been subjected to 5-day DPT with culprit drugs were questioned by telephone interview about reexposure to the tested drug. Patients with reported reaction during reexposure were reevaluated. Skin tests and serum-specific immunoglobulin E (IgE) analysis were not performed before first DPT.

RESULTS

A total of 355 patients had negative results in 5-day DPT. The median age at DPT was 4.2 years, and 52.9% were male. The families of 255 patients (72%) could be contacted. Of these 255 patients, 179 (70%) had used the same drug, and reactions were reported for 6 (3.4%) of those patients, who were subsequently reevaluated. Five of the 6 patients had DPT with amoxicillin-clavulanate and 1 with cefixime. When detailed history was taken, 2 of the 5 patients with amoxicillin-clavulanate reaction were found to have used the drug unintentionally after their reaction to reexposure and did not have any symptoms. One of the patients underwent allergy workup and tested negative, and the other 2 refused the test. The patient with reported cefixime reaction underwent repeated allergy workup and tested negative. Therefore, the NPV of 5-day prolonged DPT was 98.9%.

CONCLUSION

The 5-day prolonged DPT has high NPV and seems appropriate in duration for children with suspected nonimmediate-BLA allergy.

Recent developments in drug hypersensitivity in children

Introduction: Drug allergy is an important public health problem that causes 0.4-10.3% of hospital admissions in children. The epidemiology, clinical spectrum, diagnosis, and management of drug hypersensitivity reactions (DHRs) differ in pediatric and adult patients. However, the same algorithms used in adults have often been applied in the pediatric population due to a lack of evidence in the literature. Areas covered: In this review, we aimed to discuss recent developments in the area of pediatric DHRs based on the growing body of literature advancing our understanding of the epidemiology, clinical aspects, and diagnostic approaches to DHRs in children. Expert opinion: Misdiagnosis, under-diagnosis, and self-diagnosis are common problems related to drug allergies in children. Viral infections are particularly frequent in children and make diagnosis difficult. Identifying true DHR is a key step in the management of drug allergy in children. Therefore, a complete allergy work-up with standardized drug allergy tests is necessary. In order to eliminate non-standardized tests, future studies including larger numbers of children should be conducted to determine more accurate standardized tests for diagnosing DHRs in the pediatric population.

The Limited Value of Prolonged Drug Challenges in Nonimmediate Amoxicillin (Clavulanic Acid) Hypersensitivity

BACKGROUND

Misdiagnosis of amoxicillin (clavulanic acid) (AX(/CL)) hypersensitivity has serious consequences. A drug challenge (DC) is the final diagnostic to affirm or infirm AX(/CL) hypersensitivity. However, uncertainties remain whether a prolonged drug challenge (pDC) should benefit the diagnosis of a nonimmediate AX(/CL) hypersensitivity.

OBJECTIVE

To assess the added value of a standardized 7-day pDC in the diagnosis of nonimmediate or unclear penicillin hypersensitivity.

METHODS

A total of 132 patients with a history of a nonimmediate hypersensitivity reaction or an unclear reaction to AX(/CL) or an undefined penicillin with a negative diagnostic workup including a single-day DC (DC) with AX(/CL) were selected. In all these patients, an additional pDC with AX(/CL) was planned. Thirteen patients started the pDC immediately after the DC. To ensure that hypersensitivity symptoms manifesting during the pDC course do not result from the DC, in the remaining 119 patients, the pDC was scheduled after a washout of 1 week.

RESULTS

A total of 128 patients (12 without washout, 116 with washout) completed the pDC. Three patients reacted with a mild maculopapular exanthema. However, the value of a pDC was evidenced in only 1 patient who reacted during her pDC after an uneventful washout. In 2 patients pDC was cancelled because they reacted during the washout.

CONCLUSIONS

A pDC is of limited added value to the diagnostic algorithms of nonimmediate hypersensitivity reaction or unclear hypersensitivity reactions to AX(/CL). In our hands, the traditionally recommended diagnostic algorithm that offers a 1-day DC as a final diagnostic in patients with negative workup for AX(/CL) is appropriate.

Provocation Tests in Nonimmediate Hypersensitivity Reactions to β-Lactam Antibiotics in Children: Are Extended Challenges Needed?

BACKGROUND

β-Lactam antibiotics are the most common trigger of reactions in children with most of them being nonimmediate (85.5%), but proven allergy after the allergological workup is between 7% and 10%. There is no agreement on how to perform the provocation tests in these types of hypersensitivity reactions.

OBJECTIVE

To determine whether or not repeated doses of the β-lactams are required to reproduce a nonimmediate reaction in children.

METHODS

This is a retrospective observational study. We included children under 14 years who were referred for a nonimmediate reaction to β-lactams. All patients underwent a 1-day hospital provocation and were kept under observation at home during the following days for at least the time elapsed between the first dose and the symptoms of the index reaction. If no reaction was triggered, the patient resumed the provocation at home with 2 daily therapeutic doses for an equal of interval time.

RESULTS

Ninety-seven patients were included in the study. A positive reaction was recorded in 14 of them (14.4%). The short hospital provocation triggered 3 immediate reactions and 8 delayed reactions. The home rechallenge developed 1 immediate reaction and 2 delayed reactions.

CONCLUSIONS

Nonimmediate reactions to β-lactams in children may be triggered with a 1-day provocation test. We suggest to perform a 1-day provocation test followed by an observational period of at least the time interval of the index reaction. If this challenge is negative, an extended home provocation could subsequently be carried out.

Efficacy and Safety of 5-Day Challenge for the Evaluation of Nonsevere Amoxicillin Allergy in Children

BACKGROUND

Penicillin allergy is the most frequent drug allergy, among which aminopenicillins are reputed for causing delayed rashes in children, particularly in the context of viral infections. Despite a negative allergy evaluation, a significant proportion of individuals continue to avoid penicillin antibiotics for fear of an allergic reaction.

OBJECTIVE

To evaluate the safety and efficacy of a 5-day challenge to amoxicillin and the proportion of subsequent use of amoxicillin.

METHODS

Pediatric patients with a history of a reaction to amoxicillin were prospectively recruited in the study. All patients were challenged, and those with negative immediate challenges underwent an ambulatory 5-day challenge to amoxicillin to rule out nonimmediate reactions. Patients were called 2 years after their initial allergy evaluation to assess subsequent amoxicillin use and tolerance.

RESULTS

One hundred thirty children with a history of amoxicillin allergy underwent a graded drug provocation test (DPT) to amoxicillin. Three patients had a positive immediate challenge, 3 had a positive nonimmediate challenge, and 2 were equivocal. Of the 122 patients with a negative challenge, 114 (93.4%) were reached 2 years after their initial allergy evaluation: 75 had used antibiotics since, of which only 1 (1.3%) had refused to reuse amoxicillin because of fear of an allergic reaction. Finally, the 5-day DPT resulted in a 24.1% decrease in future penicillin avoidance compared with classical single-dose graded DPT performed for 1 day in a historical cohort (P < .0001).

CONCLUSION

The 5-day challenge is a safe and effective way to rule out nonimmediate amoxicillin allergy, and it ensures better compliance with future penicillin use.

Pro and Contra: Provocation Tests in Drug Hypersensitivity

Drug provocation test (DPT) is the controlled administration of a drug to diagnose immune- or non-immune-mediated drug hypersensitivity and the last step for accurate recognition of drug hypersensitivity reactions when the previous diagnostic evaluations are negative or unavailable. A DPT is performed only if other conventional tests fail to yield conclusive results. In each clinical presentation, "to provoke or not to provoke" a patient should be decided after careful assessment of the risk-benefit ratio. Well-defined benefits of DPT include confirmative exclusion of diagnoses of drug hypersensitivity and provision of safe alternatives. However, disadvantages such as safety, difficulty in interpretations of results, lack of objective biomarkers, risks of resensitization, efficiency in daily practice, and lack of standardized protocols, are poorly debated. This review summarizes the current published research concerning DPT, with particular emphasis on the advantages and disadvantages of DPT in an evidence-based manner.

Impact of an extended challenge on the effectiveness of β-lactam hypersensitivity investigation

BACKGROUND

Drug provocation tests (DPTs) are the gold standard in the diagnosis of β-lactam hypersensitivity. However, no consensus exists on the need for extended provocation tests, even though the effectiveness of the short DPT is relatively low and there has been an increase in the relative incidence of nonimmediate hypersensitivity reactions.

OBJECTIVE

To evaluate the effectiveness of a 7-day (extended) DPT compared with a 1-day-only (short) DPT in the management of hypersensitivity reactions to β-lactam antibiotics.

METHODS

Patients referred to the allergy clinic of the Sheba Medical Center for suspected β-lactam hypersensitivity from January 2008 to December 2012 underwent in vivo skin tests and an immediate short DPT with the culprit drug. Unless an immediate reaction was clearly documented, patients were offered a 7-day, extended DPT. Long-term effectiveness, calculated as the subsequent use of the tested antibiotic, and satisfaction levels were assessed with a telephone questionnaire.

RESULTS

Of 49 negative DPT results, 26 (53%) were long and 23 (47%) were short. A total of 78% of the patients who underwent the long DPT reported that they used the drug compared with 61% of those who underwent only the short DPT (P = .049). Most patients were very satisfied with the drug allergy evaluation process.

CONCLUSIONS

An extended DPT protocol increased the effectiveness of the allergy workup in our center without compromising patient satisfaction and safety, and it should be recommended to patients with a history of nonimmediate reaction to β-lactam.

Direct oral provocation tests in non-immediate mild cutaneous reactions related to beta-lactam antibiotics

BACKGROUND

Skin testing has a limited role in the diagnosis of non-immediate beta-lactam hypersensitivity in children. The aim of this study was to report the results of oral provocation tests performed without skin tests in children with non-immediate mild cutaneous reactions without systemic symptoms caused by beta-lactam antibiotics.

METHODS

Oral provocation tests with suspected antibiotics were performed to patients with non-immediate mild cutaneous reactions without systemic symptoms caused by beta-lactam antibiotics. Skin tests were not performed before provocation tests. A total of five doses were administered with half-an-hour intervals in increasing doses. Provocation was continued for 5 days.

RESULTS

A total of 119 patients with a median age of 4.3 (IQR: 2-7.5) years, of whom 58% were males, were included in the study. Amoxicillin-clavulanic acid was the most frequently responsible agent in 87 (73.1%) patients, and most common type of rash was maculopapular in 74 (62.2%) patients. Four patients (3.4%) had an urticarial reaction during the provocation test.

CONCLUSION

We did not experience any severe reactions during oral provocation test without previous skin tests performed to children with non-immediate mild cutaneous reactions without systemic symptoms. Omitting skin tests before oral provocation test in this group of children can help decreasing the burden of allergy clinics and alleviating the discomfort of children.

Amoxicillin allergy in children: five-day drug provocation test in the diagnosis of nonimmediate reactions

BACKGROUND

The drug provocation test (DPT) is the gold standard to rule out drug hypersensitivity. There are standardized DPT protocols to diagnose immediate reactions to drugs, but not for nonimmediate reactions.

OBJECTIVE

The aim of this study was to show the sensitivity and specificity of an allergy work-up that included a 5-day DPT in children with histories of nonimmediate reactions to amoxicillin through focusing on a pediatric population with histories of immediate and nonimmediate reactions to amoxicillin.

METHODS

Two hundred consecutive patients with histories of amoxicillin reactions referred to the Allergy Unit of Anna Meyer Children's Hospital for suspected drug allergy from 2008 to 2011 underwent in vivo tests with the culprit drug according to European Academy of Allergy and Clinical Immunology guidelines. Moreover, most of those children, regardless of the skin tests results, were challenged with amoxicillin for a total of 5 days.

RESULTS

In 4 years, 200 patients were evaluated for a history of drug hypersensitivity to amoxicillin. The majority of patients (76%) had a history of mild nonimmediate reactions. All 200 patients underwent skin tests, and 9 of 200 tested positive. A total of 177 DPTs were performed with amoxicillin for 5 days in each child. Diagnosis of amoxicillin allergy was confirmed by a DPT in 17 patients (9.6%); 14/17 had history of nonimmediate reactions; 4/14 (26.6%) reacted on day 5.

CONCLUSION

According to our results, a long-term DPT protocol increases the sensitivity of the allergy work-up, and it should be recommended for patients with a history of amoxicillin nonimmediate reaction.

Antibiotic allergy

Although allergy to β-lactam and non-β-lactam antibiotics is commonly claimed, true allergy to these drugs is often absent. Reactions to antibiotics can be classified according to the interval between the last administration of the drug and the onset of symptoms, but except for immediate reactions occurring within an hour of exposure, which are almost always either IgE-mediated or due to direct stimulation of mast cells, reactions occurring later than 1 hour probably have multiple mechanisms, including being IgE-mediated or involving cell-mediated reactions. The latter are likely caused by drug-specific T lymphocytes. The diagnosis of antibiotic allergy can be difficult.

Skin testing only with penicillin G in children with a history of penicillin allergy

BACKGROUND

The absence of commercially available penicilloyl-polylysine (PPL) for most of the last decade severely hampered the practice of penicillin allergy evaluation because skin testing without PPL is reported to have a poor negative predictive value (NPV).

OBJECTIVE

To determine the safety and NPV of skin testing without PPL using only penicillin G followed by a 3-dose graded challenge to the incriminated penicillin in children with a history of penicillin allergy.

METHODS

Patients evaluated for a history of penicillin allergy at the CHU Sainte-Justine Allergy Clinic between December 2006 and December 2009 were skin tested only with penicillin G and underwent a 3-dose graded challenge to the culprit penicillin if the skin test result was negative.

RESULTS

Among 563 patients skin tested to penicillin G, 185 (33%) had a positive skin test result. These patients had a shorter interval between the initial reaction and skin testing compared with patients with a negative skin test result (P = .03). A total of 375 of 378 patients (99%) with a negative skin test result were challenged and 18 (4.8%) reacted, translating into a NPV of 95.2% (95% confidence interval [CI], 92.5%-97.1%). Three of 17 patients with a history of anaphylaxis and a negative skin test result reacted to challenge (NPV, 82.4%; 95% CI, 59.0-93.8%). All challenge reactions were mild and resolved promptly with treatment.

CONCLUSION

Among children with a history of penicillin allergy, skin testing only with penicillin G followed by a 3-dose graded challenge to the incriminated penicillin is safe and yields a good NPV. This approach could be useful when PPL is unavailable.

Antimicrobial stewardship's new weapon? A review of antibiotic allergy and pathways to 'de-labeling'

PURPOSE OF REVIEW

The continued emergence of multiresistant pathogens and widespread antimicrobial use has led to a greater emphasis on antimicrobial stewardship programs. Concurrently, an increased awareness of the rising number of antibiotic allergy labels and impact on antimicrobial use has surfaced. The integration of antibiotic allergy de-labeling and antimicrobial stewardship programs may be a pathway worthy of further focus and investigation.

RECENT FINDINGS

Recent literature has evaluated the efficacy of antibiotic allergy management (historical de-labeling, in-vitro testing, skin prick testing, intradermal testing, and oral challenges) and impact of antibiotic allergy labels on patient outcome. The importance of true and perceived antibiotic allergy cross-reactivity in the setting of β-lactam allergies has been highlighted. The impact of dedicated antibiotic allergy de-labeling clinics, inpatient antibiotic allergy testing, and integrated antimicrobial stewardship programs has been recently appraised.

SUMMARY

More recent literature supports that appropriate antibiotic allergy in-vitro and in-vivo testing and subsequent antibiotic allergy de-labeling, particularly in regard to β-lactams, can decrease broad-spectrum antibiotic use, costs, patient length of stay, and mortality. Integration of antibiotic allergy management into the decision support systems of inpatient and outpatient antimicrobial stewardship programs represents an important opportunity to further improve measured outcomes from antibiotic utilization.

Antibiotic allergies in children and adults: from clinical symptoms to skin testing diagnosis

Hypersensitivity reactions to β-lactam and non-β-lactam antibiotics are commonly reported. They can be classified as immediate or nonimmediate according to the time interval between the last drug administration and their onset. Immediate reactions occur within 1 hour after the last drug administration and are manifested clinically by urticaria and/or angioedema, rhinitis, bronchospasm, and anaphylactic shock; they may be mediated by specific IgE-antibodies. Nonimmediate reactions occur more than 1 hour after the last drug administration. The most common manifestations are maculopapular exanthems; specific T lymphocytes may be involved in this type of manifestation. The diagnostic evaluation of hypersensitivity reactions to antibiotics is usually complex. The patient's history is fundamental; the allergic examination is based mainly on in vivo tests selected on the basis of the clinical features and the type of reaction, immediate or nonimmediate. Immediate reactions can be assessed by immediate-reading skin tests and, in selected cases, drug provocation tests. Nonimmediate reactions can be assessed by delayed-reading skin tests, patch tests, and drug provocation tests. However, skin tests have been well validated mainly for β-lactams but less for other classes of antibiotics.

Adverse reactions during drug challenges: a single US institution's experience

BACKGROUND

Drug challenge is a useful tool when diagnostic testing lacks predictive value for a questionable history of drug allergy. Placebo-controlled drug challenge studies demonstrate that a significant number of patients report purely subjective symptoms to placebo.

OBJECTIVE

To evaluate the safety and rate of adverse effects when performing drug challenges and to identify predictive factors for occurrences of subjective symptoms during drug challenges.

METHODS

We performed a 6-year, retrospective medical record review of patients who underwent drug challenges by members of the Allergy and Immunology Division after consultation deemed drug challenges to be appropriate. Statistical analysis was performed to compare the proportion of patients with subjective symptoms based on certain factors, including sex, age, number of listed drug allergies, interval from historical drug reaction to the drug challenge, and types of historical reaction.

RESULTS

A total of 114 patients underwent 123 drug challenges. Only 1 patient was deemed to have a true positive drug challenge result. Twenty patients reported subjective symptoms during graded challenge, all of which were not deemed a positive challenge. There was a significantly higher proportion of patients who reported subjective symptoms in females, those with a higher number of listed drug allergies, and those whose historical reactions were primarily subjective in nature.

CONCLUSION

Drug challenges are safe procedures in appropriately selected patients. A number of patients report subjective symptoms during drug challenges. Identifying patients at high risk for subjective symptoms may assist in determining whether placebo-controlled drug challenges should be performed.