Effect of a short course of prednisone in the prevention of early relapse after the emergency room treatment of acute asthma. BACKGROUND. Relapse after the treatment of acute asthma in the emergency room is common (occurring in 25 to 30 percent of cases) and is not accurately predicted by any available measurements. We studied the usefulness of prednisone in reducing this high rate of relapse. METHODS. One hundred twenty-two patients treated in the emergency room for acute exacerbations of asthma were assigned in a randomized, double-blind fashion to receive at discharge either prednisone for eight days (the dose being tapered from 40 to 0 mg per day) or matching placebo. Ninety-three were subsequently discharged from the emergency room and participated in the trial. On days 1, 7, and 14 after discharge, the patients were assessed during home visits with spirometry and diary-card review; they were contacted by telephone on day 21. Relapse was defined as an unscheduled medical visit occasioned by the patient's perceived need for further asthma treatment. RESULTS. The overall risk of relapse was significantly lower in the prednisone group (P less than 0.05), with a significantly reduced rate of relapse during the first 10 days of follow-up (3 of 48, as compared with 11 of 45 in the placebo group; P less than 0.05). Thereafter (days 11 through 21), there was no further significant difference in relapse rates between treatment groups (five in the prednisone group and six in the placebo group). During the first week after discharge, patients receiving prednisone reported significantly lower mean (+/- SD) daily symptom scores for shortness of breath (1.4 +/- 0.4 vs. 2.5 +/- 0.4, P less than 0.01) and less frequent use of an inhaled bronchodilator (5.2 +/- 0.5 vs. 6.9 +/- 0.2 puffs per day, P less than 0.05) than patients receiving placebo. Subsequently, symptom scores and bronchodilator use were similar in the two groups. CONCLUSIONS. A short course of prednisone reduced early relapse rates after the treatment of acute asthma in the emergency room, an effect limited to the period of steroid administration. 