Twelve randomised controlled trials (325 patients) were included, of which 8 (199 patients) were placebo-controlled.
It was difficult to compare the different studies due to the diversity of the study designs. Studies were conducted over a 15-year period, during which time there have been considerable changes in asthma medications, the doses and duration of therapy, and the evaluation and treatment of gastroesophageal reflux. The participants also differed among the studies. Methodological flaws included the use of open studies and untreated controls; small sample sizes; and a lack of confirmation of gastroesophageal reflux with objective testing. None of the studies were graded as quality A. Eight studies were graded B (199 patients) and 4 studies were graded C (126 patients).
The number of studies (the corresponding number of patients was reported in brackets) showing improvement and no improvement in the outcomes were, respectively, as follows.
For grade B studies:
asthma symptoms, 3 (121) and 4 (64) studies;
asthma medication use, 2 (103) and 4 (64) studies;
PEF, 2 (38) and 5 (107) studies;
spirometry, 0 (0) and 6 (174) studies.
For improved gastroesophageal reflux (4 studies; 101 patients):
asthma symptoms, 2 (66) and 1 (20) studies;
asthma medication use, 1 (48) and 2 (38) studies;
PEF, 2 (38) and 2 (63) studies;
spirometry, 0 (0) and 4 (101) studies.
For grade C studies:
asthma symptoms: 4 (126) and 0 (0) studies;
asthma medication use, 2 (81) and 1 (30) studies;
PEF, 0 (0) and 1 (30) studies;
spirometry, 1 (15) and 2 (92) studies.
For all studies (12 studies; 325 patients):
asthma symptoms, 7 (247) and 4 (64) studies;
asthma medication use, 4 (184) and 5 (94) studies;
PEF, 2 (38) and 6 (137) studies;
spirometry, 1 (15) and 8 (266) studies.