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QUESTION: In patients with a common cold, do zinc acetate lozenges reduce the duration and severity of symptoms?
Randomised (allocation concealed*), blinded (patients and outcome assessors),* placebo controlled trial with 12 days follow up.
Detroit Medical Center, Detroit, Michigan, USA.
50 volunteers (mean age 37 y, 63% men) who were recruited within 24 hours of developing symptoms of the common cold and had ≥2 of the following 10 symptoms: cough, headache, hoarseness, muscle ache, nasal drainage, nasal congestion, scratchy throat, sore throat, sneezing, or fever. Exclusion criteria were pregnancy, immunodeficiency disorder, chronic illness, or previous use of zinc lozenges to treat the common cold. 48 patients (96%) completed the trial.
25 patients were allocated to zinc lozenge, containing 12.8 mg of zinc acetate to be taken every 2 to 3 hours while awake as long as they had cold symptoms. 23 patients were allocated to placebo to be taken in the same way as the zinc lozenges. All patients were instructed to take no other cold preparations during the study period.
Main outcome measures
The primary outcome was the average duration of cold symptoms. Secondary end points were plasma concentrations of zinc and pro-inflammatory cytokines.
Mean overall duration of cold symptoms was shorter in the zinc group than in the placebo group (table). The specific symptoms that were of shorter duration in the zinc group were cough (3.1 v 6.3 d, p=0.001) and nasal discharge (4.1 v 5.8 d, p=0.025). Patients in the zinc group had decreased total severity scores for all symptoms (2.7 v 5.4, p=0.002). The difference in pro-inflammatory cytokine concentrations was greater in the zinc group than in the placebo group, but this difference was not significant. Plasma zinc concentration was higher in the zinc group (between group difference in mean change from baseline 3.7 μmol/l, 95% CI 2.2 to 5.0).
In patients with a common cold, zinc acetate lozenges reduced the duration and severity of cold symptoms.
Evidence of the efficacy of treatments for the common cold is important given the morbidity and costs to society resulting from coryzal illness. Zinc has antiviral properties in vitro, and zinc lozenges were proposed to treat colds after the report of the trial by Eby et al in 1984.1 A recent meta-analysis suggests, however, that there is not enough evidence of efficacy and that any benefit will probably be modest.2
The study by Prasad et al provides important additional evidence and suggests that zinc lozenges may provide benefit for both symptom duration and symptom severity. Nevertheless, several limitations are inherent in this study, particularly its size. The trial was underpowered to detect important apparent differences in blinding,3 which is especially difficult with zinc. The trial also uses a university volunteer sample, which makes the results difficult to extrapolate to routine settings. Furthermore, the benefit in terms of symptom severity is modest: by day 4, the difference in scores was <3 (equivalent to 3 symptoms being rated mild rather than moderate out of a total of 10 symptoms) and most benefit occurred after day 4 when symptoms are mild. Large, adequately blinded trials in representative primary care settings are needed to establish more firmly the place of zinc in treatment of the common cold.
Source of funding: in part, the George and Patsy Eby Research Foundation.
For correspondence: Dr A S Prasad, Department of Medicine, Division of Hematology-Oncology, Wayne State University, University Health Center 5-C, 4201 St Antoine, Detroit, MI 48201, USA. Fax + 1 313 745 4440.