For adults with asthma that is poorly controlled on inhaled corticosteroids (ICS), guidelines suggest adding a long-acting beta2-agonist (LABA). The LABA can be taken together with ICS in a single (combination) inhaler. Improved symptom control can be assessed in the individual; however, the long-term risk of hospital admission or death requires evidence from randomised controlled trials. Clinical trials record these safety outcomes as non-fatal and fatal serious adverse events (SAEs), respectively.
To assess the risk of serious adverse events in adults with asthma treated with regular maintenance formoterol or salmeterol compared with placebo, or when randomly assigned in combination with regular ICS, compared with the same dose of ICS.
We included Cochrane reviews on the safety of regular formoterol and salmeterol from a June 2013 search of the Cochrane Database of Systematic Reviews. We carried out a search for additional trials in September 2013 and incorporated the new data. All reviews were independently assessed for inclusion and for quality (using the AMSTAR tool). We extracted from each review data from trials recruiting adults (participants older than 12 or 18 years of age).
We combined the results from reviews on formoterol and salmeterol to assess the safety of twice-daily regular LABA as a class effect, both as monotherapy versus placebo and as combination therapy versus the same dose of ICS.
We did not combine the results of direct and indirect comparisons of formoterol and salmeterol, or carry out a network meta-analysis, because of concerns over transitivity assumptions that posed a threat to the validity of indirect comparisons.
We identified six high-quality, up-to-date Cochrane reviews. Of these, four reviews (89 trials with 61,366 adults) related to the safety of regular formoterol or salmeterol as monotherapy or combination therapy. Two reviews assessed safety from trials in which adults were randomly assigned to formoterol versus salmeterol. These included three trials with 1116 participants given monotherapy (all prescribed background ICS) and 10 trials with 8498 adults receiving combination therapy. An additional search for trials in September 2013 identified five new included studies contributing data from 693 adults with asthma treated with combination formoterol/fluticasone in comparison with the same dose of inhaled fluticasone, as well as from 447 adults for whom formoterol monotherapy was compared with placebo.
No trials reported separate results in adolescents. Overall, risks of bias for the primary outcomes were assessed as low.
Death of any cause
None of the reviews found a significant increase in death of any cause from direct comparisons; however, none of the reviews could exclude the possibility of a two-fold increase in mortality on regular formoterol or salmeterol (as monotherapy vs placebo or as combination therapy versus ICS) in adults with asthma. Pooled mortality results from direct comparisons were as follows: formoterol monotherapy (odds ratio (OR) 4.49, 95% confidence interval (CI) 0.24 to 84.80, 13 trials, N = 4824), salmeterol monotherapy (OR 1.33, 95% CI 0.85 to 2.08, 10 trials, N = 29,128), formoterol combination (OR 3.56, 95% CI 0.79 to 16.03, 25 trials, N = 11,271) and salmeterol combination (OR 0.90, 95% CI 0.31 to 2.6, 35 trials, N = 13,447). In each case, we did not detect heterogeneity, and the quality of evidence was rated as moderate. Absolute differences in mortality were very small, translating into an increase of 7 per 10,000 over 26 weeks on any monotherapy (95% CI 2 less to 23 more) and 3 per 10,000 over 32 weeks on any combination therapy (95% CI 3 less to 17 more).
Very few deaths were reported in the combination therapy trials, and combination therapy trial designs were different from those of monotherapy trials. Therefore we could not use indirect evidence to assess whether regular combination therapy was safer than regular monotherapy.
Only one death occurred in the monotherapy trials comparing formoterol versus salmeterol, so evidence was insufficient to compare mortality.
Non-fatal serious adverse events of any cause
Direct evidence showed that non-fatal serious adverse events were increased in adults receiving salmeterol monotherapy (OR 1.14, 95% 1.01 to 1.28, I2 = 0%,13 trials, N = 30,196) but were not significantly increased in any of the other reviews: formoterol monotherapy (OR 1.26, 95% CI 0.78 to 2.04, I2 = 15%, 17 trials, N = 5758), formoterol combination (OR 0.99, 95% CI 0.77 to 1.27, I2 = 0%, 25 trials, N = 11,271) and salmeterol combination (OR 1.15, 95% CI 0.91 to 1.44, I2 = 0%, 35 trials, N = 13,447). This represents an absolute increase on any monotherapy of 43 per 10,000 over 26 weeks (95% CI 6 more to 85 more) and 16 per 10,000 over 32 weeks (95% CI 22 less to 60 more) on any combination therapy.
Direct comparisons of formoterol and salmeterol detected no significant differences between risks of all non-fatal events in adults (as monotherapy or as combination therapy).
Available evidence from the reviews of randomised trials cannot definitively rule out an increased risk of fatal serious adverse events when regular formoterol or salmeterol was added to an inhaled corticosteroid (as background or as randomly assigned treatment) in adults or adolescents with asthma.
An increase in non-fatal serious adverse events of any cause was found with salmeterol monotherapy, and the same increase cannot be ruled out when formoterol or salmeterol was used in combination with an inhaled corticosteroid, although possible increases are small in absolute terms.
However, if the addition of formoterol or salmeterol to an inhaled corticosteroid is found to improve symptomatic control, it is safer to give formoterol or salmeterol in the form of a combination inhaler (as recommended by the US Food and Drug Administration (FDA)). This prevents the substitution of LABA for an inhaled corticosteroid if symptom control is improved on LABA.
The results of three large ongoing trials in adults and adolescents are awaited; these will provide more information on the safety of combination therapy under less supervised conditions and will report separate results for the adolescents included.