The subjective recording in diary cards of symptoms of itch, sneeze, nose running, and blockage, with the use of a rating scale to indicate the level of severity, is usual for clinical trials in allergic rhinitis. The primary outcome measure is usually a composite score that enables a single total symptoms score endpoint. It is appreciated, however, that rhinitis has a greater effect on the individual than is reflected purely by the recording of anterior nasal symptoms. Nasal obstruction is troublesome and may lead to sleep disturbance in addition to impaired daytime concentration and daytime sleepiness. These impairments affect school and work performance. Individuals with rhinitis find it socially embarrassing to be seen sneezing, sniffing, or blowing their nose. To capture these and other aspects of the disease-specific health-related quality of life, questionnaires such as the Rhinoconjunctivitis Quality of Life Questionnaire have been developed and validated for clinical trial use. The adoption of health-related quality of life questionnaires into clinical trials broadens the information obtained regarding the effect of the therapeutic intervention and helps focus on issues relevant to the individual patient. It must be appreciated that it is not only the disease that may adversely affect health-related quality of life; administered therapy, although intended to be beneficial, may also cause health impairment. Adverse-event monitoring is thus essential in clinical trials.

The first-generation H₁-histamines, because of their effect on central H₁-receptors, are classically associated with central nervous system (CNS) effects such as sedation. Although this is not always perceived by the patient, it is clearly evident with objective performance testing, and positron emission tomography scanning has directly demonstrated the central H₁-receptor occupancy. The second-generation H₁-antihistamines have reduced central H₁-receptor occupancy and considerably reduced or absent CNS sedative effects. Therefore, the CNS effects are entirely avoidable, and the first-generation H₁-antihistamines should no longer be used in the management of allergic rhinitis. The considerably rarer but potentially very serious cardiac arrhythmogenic effects of H₁-antihistamines are appreciated to be molecule-specific rather than class-specific. The in vitro screening of new compounds to eliminate the further development of those with cardiotoxicity ideally will lead to this adverse effect being historic. The incorporation of electrocardiogram recording in clinical trials provides direct information relating to prolongation of QT interval corrected for heart rate.

Although administered at low doses, intranasal steroids still have the potential for systemic absorption and adverse consequences. However, it is appreciated that meaningful differences exist in the bioavailability of different steroid molecules, and although a small but statistically significant effect on growth in children has been identified with the long-term use of intranasal beclomethasone when administered twice daily for 1 year, this is not evident with all intranasal steroids. In addition, twice-daily intranasal steroid administration may have more effect—from the endocrinologic perspective—than once-daily administration in the morning, which coincides better with the natural diurnal variation in cortisol. Thus, once-daily intranasal steroid administration is preferable, and when used in studies in children, measurement of height change during the study period is an important outcome variable together with other indices of systemic steroid bioavailability (eg, tests of hypothalamic-pituitary-adrenal axis function). These considerations have even greater relevance if children are concurrently also receiving inhaled steroids for asthma, because the total steroid load will be greater.