A Cochrane review 1 [Abstract] included 19 studies (6 paediatric, n=534, and 13 adult, n=476). None of the paediatric studies could be combined for meta-analysis. A single RCT in infants found that PPI (compared to placebo) was not efficacious for cough outcomes (OR 1.61, 95% CI 0.57 to 4.55, favouring placebo) but those on PPI had significantly increased serious adverse events (OR 5.56, 95% CI 1.18 to 26.25; number needed to treat for harm in 4 weeks was 11, 95% CI 3 to 232). In the 10 adult studies comparing proton pump inhibitors (PPIs) or cisapride to placebo, all but 2 studies showed no difference between improvement of cough scores in the active versus placebo arms. Pooled OR effect estimate for failure to cure between PPI and placebo groups was 0.46 and not statistically significant (95% CI 0.19 to 1.15; 4 studies, n=191). In pooled analysis for mean cough score at end of trial the effect of active drug was small and of borderline statistical significance (SMD -0.38, 95% CI -0.77, to 0; 4 studies, n=109). A pooled analysis of data from crossover studies was also not significant (SMD -0.29, 95% CI -0.62 to 0.04; 2 studies, n=70). In the single study comparing PPI to H2-antagonist, 70% of those on PPI improved versus 30% of participants on H2-antagonist. Data from the only study comparing H2-antagonist to placebo showed improvement in cough scores by intervention in all participants and the effect was significant by two weeks.
Comment: The quality of evidence is downgraded by limitations in study quality (inadequate or unclear allocation concealment), by inconsistency (heterogeneity in interventions and outcomes) and by possible indirectness (lack of standardised scales for cough symptoms, clinical heterogeneity of participants, aetiology of cough not always clear).
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