- Journal List
- BMJ Clin Evid
- v.2011; 2011
- PMC3275147

Common cold
Bruce Arroll
Department of General Practice and Primary Health Care, Auckland, New Zealand
Abstract
Introduction
Each year, children suffer up to 5 colds and adults have two to three infections, leading to time off school or work, and considerable discomfort. Most symptoms resolve within 1 week, but coughs often persist for longer.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments for common cold? We searched: Medline, Embase, The Cochrane Library, and other important databases up to January 2010 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 21 systematic reviews and RCTs that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review we present information relating to the effectiveness and safety of the following interventions: analgesics or anti-inflammatory drugs, antibiotics, antihistamines, decongestants for short-term and for long-term relief, decongestants plus antihistamines, echinacea, steam inhalation, vitamin C, and zinc (intranasal gel or lozenges).
Key Points
Transmission of common cold infections is mostly through hand-to-hand contact rather than droplet spread. Several types of virus can cause symptoms of colds.
- Each year, children suffer up to 5 colds and adults have two to three infections, leading to time off school or work and considerable discomfort. Most symptoms resolve within 1 week, but coughs often persist for longer.
Nasal and oral decongestants reduce nasal congestion over 3 to 10 hours, but we don't know how effective decongestants are for longer-term relief (>10 hours).
Antibiotics don't reduce symptoms overall, and can cause adverse effects and increase antibiotic resistance.
- Antibiotics may improve symptoms after 5 days compared with placebo in people with nasopharyngeal culture-positive Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae, but it is difficult to identify which people may have these infections.
Vitamin C seems unlikely to reduce the duration or severity of cold symptoms compared with placebo.
- We don't know whether zinc gel or lozenges, echinacea, steam inhalation, or analgesics or anti-inflammatory drugs reduce the duration of symptoms of colds.
Antihistamines may slightly reduce runny nose and sneezing, but their overall effect seems small. Some antihistamines may cause sedation or arrhythmias.
We found insufficient evidence to assess whether decongestants plus antihistamines are effective in reducing cold symptoms.
About this condition
Definition
Common colds are defined as upper respiratory tract infections that affect the predominantly nasal part of the respiratory mucosa. Because upper respiratory tract infections can affect any part of the mucosa, it is often arbitrary whether an upper respiratory tract infection is called a "cold" or "sore throat" ("pharyngitis" or "tonsillitis"), "sinusitis", "acute otitis media", or "bronchitis" (see figure 1 in review on sore throat). Sometimes all areas (simultaneously or at different times) are affected during one illness. Symptoms include sneezing, rhinorrhoea (runny nose), headache, and general malaise. In addition to nasal symptoms, half of sufferers experience sore throat, and 40% experience cough. This review does not include treatments for people with acute sinusitis (see review on acute sinusitis), acute bronchitis (see review on acute bronchitis), or sore throat (see review on sore throat). One prospective US study (1246 children enrolled at birth) found that children who had frequent colds when aged 2 or 3 years were twice as likely to experience frequent colds at year 6 compared with children who had infrequent colds at 2 or 3 years (RR 2.8, 95% CI 2.1 to 3.9).
Incidence/ Prevalence
Upper respiratory tract infections, nasal congestion, throat complaints, and cough are responsible for 11% of general practice consultations in Australia. Each year, children suffer about 5 such infections and adults two to three infections. One cross-sectional study in Norwegian children aged 4 to 5 years found that 48% experienced more than two common colds annually.
Aetiology/ Risk factors
Transmission of common cold infection is mostly through hand-to-hand contact, with subsequent passage to the nostrils or eyes — rather than, as commonly perceived, through droplets in the air. Common cold infections are mainly caused by viruses (typically rhinovirus, but also coronavirus and respiratory syncytial virus, or metapneumovirus and others). For many colds, no infecting organism can be identified.
Prognosis
Common colds are usually short lived, lasting a few days, with a few lingering symptoms lasting longer, especially cough. Symptoms peak within 1 to 3 days and generally clear by 1 week, although cough often persists. Although they cause no mortality or serious morbidity, common colds are responsible for considerable discomfort, lost work, and medical costs.
Aims of intervention
To relieve symptoms, shorten the illness, or reduce complications; to reduce infectivity to others, with minimal adverse effects from treatments.
Outcomes
Symptom severity: includes cure rate, time away from work or school, and symptom duration; occurrence of complications; adverse effects of treatment.
Methods
Clinical Evidence search and appraisal January 2010. The following databases were used to identify studies for this systematic review: Medline 1966 to January 2010, Embase 1980 to January 2010, and The Cochrane Database of Systematic Reviews 2009, Issue 4 (1966 to date of issue). An additional search within The Cochrane Library was carried out for the Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA). We also searched for retractions of studies included in the review. Abstracts of the studies retrieved from the initial search were assessed by an information specialist. Selected studies were then sent to the contributor for additional assessment, using predetermined criteria to identify relevant studies. Study design criteria for inclusion in this review were: published systematic reviews of RCTs and RCTs in any language, at least single blinded, and containing >20 individuals of whom >80% were followed up. We required 7 days of follow-up to include studies; however, we report outcomes within the studies at shorter timeframes than these. We excluded all studies described as "open", "open label", or not blinded unless blinding was impossible. We included systematic reviews of RCTs and RCTs where harms of an included intervention were studied applying the same study design criteria for inclusion as we did for benefits. In addition we use a regular surveillance protocol to capture harms alerts from organisations such as the US FDA and the UK MHRA, which are added to the reviews as required. Where possible, we have excluded RCTs undertaken solely in people with experimentally induced colds, although meta-analyses in some systematic reviews do include such RCTs. We have also excluded RCTs that only assessed the outcome of bacteriological clearance. We performed a broad search for RCTs of any decongestant, analgesic, or anti-inflammatory in people with common cold, and included any RCTs of sufficient quality. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table). The categorisation of the quality of the evidence (high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com).
Table
GRADE Evaluation of interventions for Common cold.
| Important outcomes | Complications, Symptom severity | ||||||||
| Studies (Participants) | Outcome | Comparison | Type of evidence | Quality | Consistency | Directness | Effect size | GRADE | Comment |
| What are the effects of treatments for common cold? | |||||||||
| at least 10 (at least 3592) | Symptom severity | Antihistamines versus placebo | 4 | –1 | 0 | –2 | 0 | Very low | Quality point deducted for incomplete reporting of results. Directness points deducted for inclusion of experimentally induced colds and for unclear clinical importance of results |
| 7 (703) | Symptom severity | Decongestants for short-term relief versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for incomplete reporting of results. Directness point deducted for unclear clinical importance of results |
| at least 3 (at least 659) | Symptom severity | Decongestants for long-term relief versus placebo | 4 | –2 | 0 | 0 | 0 | Low | Quality points deducted for incomplete reporting of results and weak methods (randomisation not reported) |
| 3 (461) | Symptom severity | Decongestants plus antihistamines versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for incomplete reporting of results. Directness point deducted for unclear clinical importance of results |
| 2 (254) | Symptom severity | Analgesics or anti-inflammatory drugs versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for weak methods in 1 RCT. Directness point deducted for small number of analgesics assessed |
| at least 10 (at least 1630) | Symptom severity | Echinacea versus placebo | 4 | –1 | 0 | –2 | 0 | Very low | Quality point deducted for incomplete recording of results. Directness points deducted for clinical heterogeneity between RCTs (including statistical heterogeneity in 1 analysis), significance of results depending on the analysis undertaken, and for the use of additional supplements in some RCTs |
| 2 (146) | Symptom severity | Steam inhalation versus sham inhalation | 4 | −3 | 0 | 0 | 0 | Very low | Quality points deducted for sparse data, uncertainty about the validity of control, and unclear symptom score indices |
| 10 (at least 1212) | Symptom severity | Zinc lozenges versus placebo | 4 | –1 | –1 | 0 | 0 | Low | Quality point deducted for inclusion of people with experimentally induced colds. Consistency point deducted for heterogeneity between RCTs |
| 3 (451) | Symptom severity | Intranasal zinc gel versus placebo | 4 | 0 | 0 | –2 | 0 | Low | Directness points deducted for wide range of doses used in RCTs, inclusions of slightly different population, and varying significance of results depending on analysis undertaken |
| at least 7 (at least 3294 cold episodes) | Symptom severity | Vitamin C versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for analysis by cold episodes not people. Directness point deducted for wide range of treatment protocols in RCTs |
| at least 6 (at least 1482) | Symptom severity | Antibiotics versus placebo | 4 | –1 | 0 | –1 | 0 | Low | Quality point deducted for incomplete reporting of results (and unclear in 1 review). Directness point deducted for inclusion of people with additional bacterial infection |
We initially allocate 4 points to evidence from RCTs, and 2 points to evidence from observational studies. To attain the final GRADE score for a given comparison, points are deducted or added from this initial score based on preset criteria relating to the categories of quality, directness, consistency, and effect size. Quality: based on issues affecting methodological rigour (e.g., incomplete reporting of results, quasi-randomisation, sparse data [<200 people in the analysis]). Consistency: based on similarity of results across studies. Directness: based on generalisability of population or outcomes. Effect size: based on magnitude of effect as measured by statistics such as relative risk, odds ratio, or hazard ratio.
Glossary
| Low-quality evidence | Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. |
| Very low-quality evidence | Any estimate of effect is very uncertain. |
Notes
The information contained in this publication is intended for medical professionals. Categories presented in Clinical Evidence indicate a judgement about the strength of the evidence available to our contributors prior to publication and the relevant importance of benefit and harms. We rely on our contributors to confirm the accuracy of the information presented and to adhere to describe accepted practices. Readers should be aware that professionals in the field may have different opinions. Because of this and regular advances in medical research we strongly recommend that readers' independently verify specified treatments and drugs including manufacturers' guidance. Also, the categories do not indicate whether a particular treatment is generally appropriate or whether it is suitable for a particular individual. Ultimately it is the readers' responsibility to make their own professional judgements, so to appropriately advise and treat their patients. To the fullest extent permitted by law, BMJ Publishing Group Limited and its editors are not responsible for any losses, injury or damage caused to any person or property (including under contract, by negligence, products liability or otherwise) whether they be direct or indirect, special, incidental or consequential, resulting from the application of the information in this publication.
Notes
Acute sinusitis
Acute bronchitis
Sore throat
References
- BMJ Clin Evid. 2011; 2011: 1510. »
- Antihistamines
Antihistamines
Summary
Antihistamines may slightly reduce runny nose and sneezing, but their overall effect seems small. Some antihistamines may cause sedation or arrhythmias.
Benefits and harms
Antihistamines versus placebo:
We found two systematic reviews (search date not reported, 9 RCTs, 1757 adults; 7 RCTs in adults with naturally acquired colds, 2 RCTs in adults with experimentally induced colds; and search date 2003, 32 RCTs, 8228 adults and children with naturally acquired colds, 702 with experimentally induced colds) and one subsequent RCT.
Symptom severity
Compared with placebo Antihistamines may be marginally more effective at reducing symptoms of runny nose and sneezing at 2 days, but we don't know whether they are more effective at reducing cough frequency or at increasing the speed of recovery (very low-quality evidence).
Adverse effects
Further information on studies
The effects of antihistamines were small. On a severity scale ranging from 0 (no symptoms) to 3 or 4 (severe symptoms), antihistamines reduced the score from baseline by about 0.25 (95% CI 0.10 to 0.40; results presented graphically) for runny nose on days 1 and 2, 0.15 (95% CI 0 to 0.30) for sneezing on day 1, and 0.30 (95% CI 0.15 to 0.45) for sneezing on day 2.
The RCTs identified by the second review assessed a wide variety of antihistamines, including cetirizine, chlorphenamine, clemastine, doxylamine succinate, loratadine, promethazine hydrochloride, and terfenadine. Decongestants used in combination with antihistamines included phenylpropanolamine and pseudoephedrine.
Comment
Some non-sedating antihistamines are associated with arrhythmias and adverse interactions with other drugs. The FDA has released a warning that respiratory depression, leading to death in some cases, has been reported when promethazine hydrochloride was given to children aged <2 years. The FDA recommends not using promethazine hydrochloride in children aged <2 years, and that parents and carers seek a doctor's advice about giving promethazine hydrochloride in any form to children aged 2 years and older.
Substantive changes
No new evidence
- BMJ Clin Evid. 2011; 2011: 1510. »
- Decongestants for short-term relief
Decongestants for short-term relief
Summary
Nasal and oral decongestants reduce nasal congestion over 3 to 10 hours, but we don't know whether they are effective in the longer term (>10 hours).
Phenylpropanolamine has been associated with an increased risk of haemorrhagic stroke.
Benefits and harms
Decongestants for short-term relief versus placebo:
We found one systematic review (search date 2006, 6 RCTs, 642 adults with naturally acquired colds; see further information on studies) and one subsequent RCT. We found one further case-control study that reported on adverse effects.
Symptom severity
Compared with placebo for short-term relief A single dose of a decongestant (oral norephedrine, topical oxymetazoline, oral pseudoephedrine, nasal xylometazoline) may be marginally more effective than placebo at reducing congestion at 3 to 10 hours (low-quality evidence).
Adverse effects
Further information on studies
The review found no RCTs in children. This Cochrane review has been withdrawn as it is awaiting update. We will report the updated review in a future issue of this Clinical Evidence review.
Comment
We found one further systematic review (search date 2007, 7 crossover RCTs, 113 people), which found that a single dose of phenylephrine significantly reduced nasal airway resistance compared with placebo at 30 to 90 minutes. However, the review did not report clinical outcomes but reported nasal airways resistance as measured by a modified Butler-Ivy airflow device, so we have not reported it further.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Decongestants for long-term relief
Decongestants for long-term relief
Summary
We don't know whether nasal decongestants are effective in the longer term (>10 hours).
Benefits and harms
Decongestants for long-term relief versus placebo:
We found one systematic review (search date 2006, 7 RCTs, 734 adults with naturally acquired colds; see further information on studies) and one subsequent RCT.
Symptom severity
Compared with placebo for long-term relief We don't know whether decongestants are more effective at improving nasal congestion at up to 5 days (low-quality evidence).
Adverse effects
Further information on studies
This Cochrane review has been withdrawn as it is awaiting update. We will report the updated review in a future issue of this Clinical Evidence review.
The RCT also reported subjective symptom scores measured by visual analogue scale (VAS; 100-mm scale where 0 = nose completely clear and 100 = nose completely blocked). The RCT reported that "a pooled analysis of days 1 and 3 data showed a VAS score decrease of 7.0% (P = 0.072) for the 0.5- to 3-hour interval and 8.0% (P = 0.43) for the 0.5- to 4-hour interval on pseudoephedrine. Pseudoephedrine was associated with a 1.4 times (mean change from baseline pseudoephedrine, –0.43; placebo, –0.18; P = 0.059) greater reduction in mean nasal congestion using daily diary categorical scale scores when compared with placebo".
Comment
See harms on decongestants for short-term relief.
See comment on decongestants for short-term relief.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Decongestants plus antihistamines
Decongestants plus antihistamines
Summary
We don't know whether decongestants plus antihistamines reduce cold symptoms or cold duration as we found insufficient RCT evidence.
Benefits and harms
Decongestants plus antihistamines versus placebo:
We found one systematic review (search date 2003; see further information on studies), which included RCTs that compared antihistamines in combination with decongestants with or without other agents versus placebo. We have only reported on RCTs that compared the effects of decongestants plus antihistamines alone versus placebo and reported on our outcomes of interest. The review did not separately pool data on decongestants plus antihistamines alone so we have reported included RCTs separately. The review included three RCTs of sufficient quality.
Symptom severity
Compared with placebo Decongestants plus antihistamines may be more effective at improving some overall symptoms scores at up to 5 days. However, results were inconsistent between studies, and the clinical importance of some improvements is unclear (low-quality evidence).
Adverse effects
Further information on studies
This Cochrane review has been withdrawn as it is awaiting update. We will report the updated review in a future issue of this Clinical Evidence review.
In reviewing the evidence on decongestants plus antihistamines (including RCTs that had also included other additional treatments as part of the combination therapy), the review noted that in most trial reports there was insufficient data to judge the effect size and thus the clinical importance. The review concluded that decongestants plus antihistamines might lead to some general improvement and relief from a blocked or runny nose, although there is not enough evidence to be certain.
Comment
None.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Analgesics or anti-inflammatory drugs
Analgesics or anti-inflammatory drugs
Summary
We don't know whether analgesics or anti-inflammatory drugs reduce the duration of symptoms of colds.
Benefits and harms
Analgesics or anti-inflammatory drugs versus placebo:
We found one systematic review (search date 2009) on non-steroidal anti-inflammatory drugs (NSAIDs). The review included 6 RCTs comparing NSAIDs versus placebo and pooled data. However, three RCTs were in people with experimentally induced colds. We have not reported these RCTs further. Of the remaining three RCTs, one did not report on efficacy outcomes. We have therefore reported the two remaining RCTs separately below.
Symptom severity
Analgesics or anti-inflammatory drugs compared with placebo We don't know whether ibuprofen or loxoprofen are more effective than placebo at improving symptom scores or at reducing the duration of cold (low-quality evidence).
Adverse effects
Further information on studies
None.
Comment
None.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Echinacea
Echinacea
Summary
We don't know whether echinacea is more effective than placebo at reducing the severity or duration of cold symptoms.
Benefits and harms
Echinacea versus placebo:
We found two systematic reviews (search dates 2007 and 2006). The reviews had different inclusion criteria, performed a different analysis, and came to differing conclusions. The first review excluded combinations of echinacea with other herbs, included RCTs that reported on severity of symptoms or duration, and did not pool data because of clinical heterogeneity between included RCTs (preparation used, trial design, and outcomes reported). It included 14 RCTs on treatment. The second review included RCTs in which echinacea had been used with or without a supplement, all of which reported on cold duration. In the analysis of effects on cold duration, it included 4 RCTs that were included in the first review, two RCTs that were excluded by the first review because of methods used, and included one RCT not included in the first review. The second review pooled data and came to slightly different conclusions to the first review (see further information on studies).
Symptom severity
Compared with placebo We don't know whether echinacea is more effective at reducing cold symptoms or at reducing the duration of cold (very low-quality evidence).
Adverse effects
Further information on studies
The second review, which pooled data, also performed a sensitivity analysis of RCTs in which no supplement had been given with echinacea. It found no significant difference between groups in cold duration (3 RCTs, 915 people; WMD –1.57 days, 95% CI –4.34 days to +1.19 days, P = 0.27). The authors of the first review noted that the second reviewhad come to more favourable conclusions on the effects of echinacea than it had. The authors of the first review noted that the second review had included trials on highly variable echinacea products and pooled data, whereas they had chosen not to because of the clinical heterogeneity between trials.
Comment
Echinacea is not a single product. There are >200 different preparations based on different plants, different parts of the plant (roots, herbs, whole plant), and different methods of extraction. The weakness of trial methods and differences in interventions make it difficult to draw conclusions about effectiveness. Large RCTs may be difficult because echinacea is not patentable, and each producer controls a small share of the market. The authors of the first systematic review received personal information about several unpublished studies that they were not able to include.
Isolated cases of anaphylaxis have been reported in people taking echinacea.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Steam inhalation
Steam inhalation
Summary
We don't know whether steam inhalation reduces the duration of symptoms of colds.
Benefits and harms
Steam inhalation versus sham inhalation:
We found one systematic review (search date 2005), which compared steam inhalation at 40 °C to 47 °C versus sham inhalation (air at 30 °C or higher). The review (6 RCTs, 319 people; 4 RCTs in people with naturally acquired colds, 2 in people with experimentally induced colds) could not perform a meta-analysis of all the RCTs because of heterogeneity in populations and methods used to assess symptoms, and poor reporting in some of the RCTs. We have reported the results from the meta-analysis, which pooled data from two RCTs in people with naturally acquired colds.
Symptom severity
Compared with sham inhalation We don't know whether steam inhalation is more effective than sham inhalation (air at 30 °C or higher) at reducing the proportion of people with symptoms of common cold immediately after treatment or at 4 days, as we found insufficient evidence from weak studies (very low-quality evidence).
Adverse effects
Further information on studies
None.
Comment
None.
Substantive changes
No new evidence
Zinc
Summary
We don't know whether zinc gel or lozenges reduce the duration of symptoms of colds.
Benefits and harms
Zinc lozenges versus placebo:
We found three systematic reviews (search dates 1997, 1998, and 2003), which compared zinc lozenges (gluconate or acetate) versus placebo for the treatment of naturally acquired colds. The reviews had different inclusion and exclusion criteria. The first and second reviews performed a meta-analysis, whereas the third review was narrative in character, and did not perform a meta-analysis. The third review identified 10 RCTs that were included in the two other reviews (including all the RCTs identified by both earlier reviews and 1 RCT excluded by the first review owing to poor methods, and 2 RCTs excluded by the second review because they involved people with experimentally induced colds). In addition, the third review identified two RCTs carried out subsequent to the earlier reviews, the results from which we report separately. We found one subsequent RCT. We found one further systematic review, which did not report numerical results of statistical analyses, so we have not reported it further here (see comments). One review identified case reports on adverse effects associated with zinc preparations (see further information on studies).
Symptom severity
Zinc lozenges compared with placebo We don't know whether zinc lozenges are more effective at reducing symptom duration (low-quality evidence).
Adverse effects
Intranasal zinc gel versus placebo:
We found one systematic review (search date 2007), which included three RCTs and pooled data. Two of the included RCTs used a high dose of zinc (daily dose 2.1 mg), whereas the third RCT used a lower dose (daily dose 0.044 mg). One review identified case reports on adverse effects associated with zinc preparations (see further information on studies).
Symptom severity
Zinc intranasal gel compared with placebo We don't know whether intranasal zinc is more effective at reducing the proportion of people with symptoms at 3 days (low-quality evidence).
Adverse effects
Further information on studies
Zinc lozenges versus placebo The results were statistically heterogeneous, which may be because the RCTs in the reviews used different zinc formulations, were undertaken in people with different types of virus, or because of unknown factors.
Intranasal zinc versus placebo: fixed effects analysis: The review found a significant difference between groups using a fixed effects analysis (3 RCTs, 451 people; RR 0.63, 95% CI 0.56 to 0.70). However, there was a large degree of heterogeneity among RCTs (P value not reported; I2 = 99.2%). With regard to the high degree of heterogeneity, one RCT using a high dose of intranasal zinc found a large treatment effect at 3 days (213 people; RR 0.32, 95% CI 0.24 to 0.42), whereas another high-dose RCT found a borderline effect (78 people; RR 0.78, 95% CI 0.61 to 1.00) and a third RCT using a lower dose of zinc found less effect (160 people; RR 0.96, 95% CI 0.91 to 1.02). Heterogeneity: The review reports that heterogeneity was caused in large part by the study with the large treatment effect. In addition, two RCTs only included people with symptoms for <24 hours, whereas the other RCT only included people with symptoms for 24–48 hours). The review also identified 10 case reports of permanent anosmia (see below).
Harms with intranasal zinc One report identified a series of 10 case reports of permanent anosmia (loss of smell) associated with intranasal zinc gluconate. The 10 people (aged 31–55 years) had immediate severe burning of the nose followed by severe hyposmia with parosmia or anosmia. The people had previously reported normal taste and smell and had no other causative history to account for the loss.
Comment
We found one further systematic review, which examined the effects of zinc lozenges, nasal sprays, or gels versus placebo. It did not report numerical results or statistical analysis. It included 14 RCTs, which were evaluated against 11 previously determined quality criteria (including validated case definition, double blinding, sample size calculation, etc.). In total, 4 RCTs fulfilled all the 11 quality criteria. Of these, one RCT found a positive effect with zinc nasal gel, while three RCTs found no effect with zinc lozenges or nasal spray. It concluded that the therapeutic effects of zinc lozenges have yet to be demonstrated.
The Cochrane review comparing zinc lozenges versus placebo has been withdrawn as it is awaiting update.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Vitamin C
Vitamin C
Summary
Vitamin C seems unlikely to reduce the duration or severity of cold symptoms compared with placebo.
Benefits and harms
Vitamin C versus placebo:
We found one systematic review (search date 2006). The review included RCTs of cold prophylaxis and treatment. We have only included data on treatment. The review included any RCTs using vitamin C (200 mg or more daily) compared with placebo in people with the common cold.
Symptom severity
Compared with placebo Vitamin C may be no more effective at reducing symptom severity or mean duration of symptoms (low-quality evidence).
Further information on studies
The RCTs included in the analysis used a variety of therapeutic protocols, ranging from a single dose at the onset of cold symptoms to continued treatment for 4 days using differing regimens. The review noted that RCTs in which vitamin C was used as treatment in doses up to 4 g daily did not demonstrate any benefit, but one large RCT reported an "equivocal" benefit from the use of a very high 8-g therapeutic dose at the onset of symptoms. However, there were methodological issues in this large RCT in that one of the two placebo groups had substantial baseline differences with the vitamin C groups, and that comparisons were restricted to the placebo group that had similar baseline data to the other vitamin C arms. Adverse effects Seven RCTs included in the review provided data on adverse effects. In these RCTs, 2490 people took >1 g daily of vitamin C during prophylaxis compared with 2066 people taking placebo. The review stated that no serious symptoms were reported. It found that 5.8% of people taking vitamin C reported symptoms that they attributed to the medication, compared with 6.0% taking placebo (no further details reported).
Comment
None.
- BMJ Clin Evid. 2011; 2011: 1510. »
- Antibiotics
Antibiotics
Summary
Antibiotics don't reduce symptoms overall, and can cause adverse effects and increase antibiotic resistance.
Antibiotics may improve symptoms after 5 days compared with placebo in people with nasopharyngeal culture-positive Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae, but it is difficult to identify which people may have these infections.
Benefits and harms
Antibiotics versus placebo:
We found three systematic reviews (search dates 2005, 6 RCTs; not reported, 12 RCTs; and 2005, 6 RCTs). The systematic reviews identified several RCTs in common. The second review included 4 RCTs identified by the first review and 8 RCTs excluded from the first review owing to poor methods. The third review identified 5 RCTs that were also included in one or both of the earlier reviews.
Symptom severity
Compared with placebo Antibiotics may be no more effective at increasing cure rate or general improvement at 5 to 7 days in people with colds. Antibiotics may be more effective at increasing the proportion of people with clearance of purulent rhinitis at 5 to 8 days in people with acute purulent rhinitis associated with an upper respiratory tract infection (low-quality evidence).
Adverse effects
Further information on studies
The relative risk (RR 1.01, 95% CI 0.90 to 1.13) surrounding clinical outcome reported by the second review does not match the absolute results reported; we have quoted it directly from the paper.
If people infected with H influenzae, M catarrhalis, or S pneumoniae could be identified at first consultation, then treating 4 of these people with antibiotic rather than placebo would result in an average of one more recovery at 5 days (NNT 4, CI not reported). However, there is currently no means of easily identifying people with these infections at first consultation.
Comment
We found no evidence of the size of the risk of antibiotic resistance or pseudomembranous colitis.
Clinical guide:
Because most common colds are viral, the potential benefit from antibiotics is limited. Until rapid identification of those people likely to benefit is possible, the modest effects seen in trials must be weighed against the adverse effects of antibiotics, costs, and potential for inducing antibiotic resistance.
Substantive changes
No new evidence
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