Prednisone Pretreatment Leads to Histaminic Airway Hyporeactivity Soon after Resolution of the Immediate Allergic Response

We assessed the effect of prednisone pretreatment (50 mg/day for three days) on the development of the early increase in histamine reactivity that occurs soon after resolution of the immediate response in allergic humans. Four allergic subjects who were known to develop only isolated immediate responses upon Kentucky bluegrass inhalation, as well as four mild allergic asthmatic subjects known to develop typical dual phase responses, were evaluated. All testing was done more than nine weeks after the grass pollen season had ended. Allergen inhalation produced an immediate response in all subjects. However, upon resolution of the immediate response to allergen in these pretreated subjects, the PC200 His in all dual responding asthmatics and in three of the four isolated immediate responders had substantially increased above baseline values. We conclude that prednisone pretreatment leads to histaminic hyporeactivity soon after resolution of the immediate allergic response in both dual responding asthmatics and isolated immediate responders. It would seem that this prednisone effect is independent of its potential influence on the influx of inflammatory cells into diseased airways. (Chest 1989; 95:314-19) PC200His = dose of histamine that doubled SRaw; EOR=early onset increase in airway reactivity.