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Oregon Evidence-based Practice Center . Drug Class Review: Newer Antihistamines: Final Report [Internet]. Portland (OR): Oregon Health & Science University; 2006 Apr.

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

Cover of Drug Class Review: Newer Antihistamines

Drug Class Review: Newer Antihistamines: Final Report [Internet].

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Literature Search

To identify articles relevant to each key question, we searched the Cochrane Library (3rd Quarter 2005), MEDLINE (1966 to August Week 4 2005), EMBASE (1991 to August Week 4, 2005), the two dossiers we received from pharmaceutical companies for fexofenadine HCL (Allegra ®) and desloratadine (Clarinex®), and reference lists of review articles. The complete search strategy for electronic searches is in Appendix A. All citations were imported into an electronic database (EndNote 9.0)

Study Selection and Inclusion Criteria

1. Populations

Adult or pediatric outpatients with the following conditions were included in this review:

  • Seasonal allergic rhinitis
  • Perennial allergic rhinitis
  • Urticaria, including both acute and chronic urticaria

Subgroups of interest included, but were not limited to, different races, ages (older adult versus younger adult), concomitant use of other medications (in consideration of drug-drug interactions), persons with various comorbidities (pregnancy and consideration of drug-disease interactions), and sex.

2. Interventions

Drug included in this review are listed below. This review is restricted to drugs currently available on the U.S. and Canadian markets. No new oral antihistamines were identified that have become available in the U.S. or Canada in the last 12 months.

  • Cetirizine hydrochloride (Zyrtec®, Reactine®)
  • Loratadine (Claritin®)
  • Fexofenadine hydrochloride (Allegra®)
  • Desloratadine (Clarinex®)

3. Outcomes

The following were the primary outcomes for this review:

Efficacy and effectiveness outcomes

  • Symptoms (e.g., nasal congestion, rhinorrhea, sneezing, itching and pain from skin irritations)
  • Functional capacity (e.g., physical, social and occupational functioning, quality of life)
  • Time to relief of symptoms (e.g., time to onset, duration of relief)
  • Duration of effectiveness (e.g., switch rate)

Safety outcomes

  • Overall adverse effects
  • Withdrawals due to adverse effects
  • Serious adverse events or withdrawals due to specific adverse events (e.g., central nervous system effects, sedation, gastrointestinal effects, dry mouth, urinary retention)

4. Settings

Studies had to occur in an outpatient setting, including the emergency department. There were no restrictions on the geographic location of studies.

5. Study design

Efficacy and effectiveness

  1. For efficacy and effectiveness we included randomized controlled trials (RCTs), controlled clinical trials, and systematic reviews of fair or better quality.
  2. Both direct and indirect comparisons were included (head-to-head, placebo-controlled, and active-controlled trials).
  3. Studies of any duration of follow-up were included.
  4. Studies in artificial environments (e.g., antigen exposure chambers) were included.
  5. Studies published only as abstracts were not included as these studies generally have insufficient information describing the intervention and quality of the trial is difficult to assess.


  1. For the review of safety and adverse events, we included studies with any design, including RCTs, controlled clinical trials, pre-versus post-design studies, and observational studies (cohort studies with or without a comparison group, case series, and case reports). Clinical trials are often not designed to assess adverse events, and may select low-risk patients (in order to minimize dropout rates) or utilize inadequately rigorous methodology for assessing adverse events. Observational studies designed to assess adverse event rates may include broader populations, have longer follow-up, or examine larger sample sizes.
  2. To be included, reports about overall safety or adverse events had to report total withdrawals, withdrawals due to specific adverse events (e.g., central nervous system effects, sedation, gastrointestinal effects, dry mouth, urinary retention, etc.); or the frequency and severity of these specific adverse events.

Data Abstraction

Two reviewers abstracted the following data from included trials: study design, setting, population characteristics (including sex, age, race/ethnicity, diagnosis); eligibility and exclusion criteria; interventions (dose and duration); comparison group treatment; numbers screened, eligible, enrolled, and lost to follow-up; methods of outcome ascertainment; and results for each outcome. Any discrepancies in abstraction were resolved through discussion and consensus was achieved. We recorded intention-to-treat results if available and if the trial did not report high overall loss to follow-up.

Validity Assessment

We assessed the internal validity (quality) of trials based on the predefined criteria listed in Appendix B. These criteria are based on those developed by the US Preventive Services Task Force and the National Health Service Centre for Reviews and Dissemination (UK).23; 24 We rated the internal validity of each trial based on the methods used for randomization, allocation concealment, and blinding; the similarity of compared groups at baseline; maintenance of comparable groups; adequate reporting of dropouts, attrition, crossover, adherence, and contamination; loss to follow-up; the use of intention-to-treat analysis, and the funding source and role of the funder. Trials that had a fatal flaw in one or more categories were rated poor quality and were excluded from the review; trials that met all criteria were rated good quality; the remainder were rated fair quality.

The "fair quality" category is broad; studies with this rating vary in their strengths and weaknesses: the results of some fair quality studies are likely to be valid, while others are only probably valid. A "poor quality" trial is not valid—the results are at least as likely to reflect flaws in the study design as the true difference between the compared drugs. Poor quality studies are listed in Appendix C and are generally excluded from consideration in the results.

External validity of trials was assessed based on whether the publication adequately described the study population, how similar patients were to the target population in whom the intervention will be applied, and whether the treatment received by the control group was reasonably representative of standard practice.

Appendix B also shows the criteria we used to rate observational studies of adverse events. These criteria reflect aspects of the study design that are particularly important for assessing adverse event rates.

Overall quality ratings for each individual study were based on ratings of the internal and external validity of the trial. A particular randomized trial might receive two different ratings: one for efficacy and another for adverse events. The overall strength of evidence for a particular key question reflects the quality, consistency, and power of the set of studies that addressed a specific key question.

Data Synthesis

We summarized our results in evidence tables and in a narrative summary (see Table 18).

Copyright © 2006, Oregon Health & Science University, Portland, Oregon.
Bookshelf ID: NBK10359


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