Patient reports of benefits are inaccurate in asthma trials
MedWire News: Patient reports cannot be relied on to assess the effectiveness of asthma interventions, suggest results from a randomized, placebo-controlled trial that show the strength of the placebo effect.
Many studies of asthma interventions have reported a strong placebo effect and the repeated lung-function assessments usually performed over a short period of time in such trials make asthma an "excellent model" for the study of placebo effects, write Michael Wechsler (Harvard Medical School, Boston, Massachusetts, USA) and colleagues.
However, most studies to date "have generally not controlled for the effects of variability that can occur over the period of observation without treatment," the investigators say.
To address this, Wechsler and colleagues assigned 39 patients with asthma to blinded treatment with an albuterol inhaler, a placebo inhaler, sham acupuncture, or no intervention, in which patients were asked to wait for several hours and then sent home. Each patient received all four interventions in a random order, with 3 to 7 days between interventions and the sequence of four interventions repeated three times.
As expected, albuterol treatment increased lung function, measured by forced-expiratory volume over 1 second (FEV1) by 20%, whereas a placebo inhaler, sham acupuncture, and no intervention each increased lung function by approximately 7%.
Despite this, when patients were asked what effect each intervention had on their symptoms, the benefits were similar with reported improvements of 50% with albuterol, 45% with a placebo inhaler, 46% with sham acupuncture, all of which were significantly greater than the 21% benefit perceived with no intervention.
Writing in the New England Journal of Medicine, the researchers conclude that "although placebos remain an essential component of clinical trials to validate objective findings, assessment of the course of the disease without treatment, if medically appropriate, is essential in the evaluation of patient-reported outcomes."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
By Philip Ford