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OTC cold remedies contain a selection of different active ingredients. Alan Nathan explains the purpose of each and discusses evidence for their effectiveness

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Colds normally present as a complex or sequence of symptoms. Proprietary products marketed for their treatment usually contain several ingredients, each intended to alleviate a different symptom. Most systemic products for colds contain combinations of two or more of the following:

• Sedating antihistamine
• Sympathomimetic decongestant
• Expectorant
• Cough suppressant
• Analgesic/antipyretic.

In addition, a number of volatile substances are included in products to be inhaled for the relief of cold symptoms. Several complementary medicines are also promoted as cold treatments.

Analgesics are also used for their antipyretic action, although raised temperature is not a usual feature of the common cold in adults but may occur in children. Several cold remedies also contain cough suppressants and expectorants, which will be dealt with in a future article.

Antihistamines

Compounds included in cold treatments are:

• Chlorphenamine
• Diphenhydramine
• Doxylamine
• Promethazine
• Triprolidine

Action

An antimuscarinic side-effect of sedating antihistamines is drying up of nasal secretions, which is exploited to counteract rhinorrhoea.

Side-effects and cautions

Sedation, dry mouth, urinary retention, constipation and blurred vision. Antihistamine-containing products should be used with caution in the elderly as they are more susceptible to these side-effects, and should not be recommended to patients with glaucoma or prostate problems. Suppression of rhinorrhoea provokes congestion, so antihistamines are usually co-formulated with sympathomimetics to offset this effect, as well as sedation.

Efficacy

There is no evidence that any antihistamine is preferable to another in the treatment of rhinorrhoea. Three systematic reviews^1,2,3 have concluded that antihistamines alone are of little clinical benefit in colds, but antihistamine- decongestant combinations may have a beneficial effect on general recovery as well as on nasal symptoms.

Systemic sympathomimetic decongestants

Compounds

Pseudoephedrine, phenylephrine and ephedrine.

Action

Sympathomimetics stimulate alpha-adrenoceptors causing constriction of mucosae and blood vessels in the nasal passages, which become swollen and dilated during a cold, thus improving air circulation and mucus drainage.

Side-effects and cautions

Sympathomimetics are CNS-stimulating agents so should not be used near bedtime. Their vasoconstricting action tends to raise blood and intra-ocular pressure and they should be used with caution in patients with any kind of cardiovascular condition or glaucoma. They also interfere with metabolism, including glucose metabolism, and should be used with caution in patients with thyroid problems or diabetes. Products containing sympathomimetics are not licensed for use in children under 12 years.

Efficacy

See above.

Local sympathomimetic decongestants

Compounds

Oxymetazoline and xylometazoline are used as nasal drops and sprays.

Action and uses

When used topically inside the nose, the vasoconstricting action of sympathomimetic decongestants restricts their absorption, confining activity to the area of application, so they can generally be used by patients for whom systemic decongestants are contraindicated. They have a rapid and potent action and an application is effective for up to 12 hours.

Cautions

The likelihood of interactions is low, but patients taking monoamine oxidase inhibitors should not use topical decongestants. If used for prolonged periods, topical decongestants cause a rebound effect, and the congestion can return worse than before. To prevent this, they should not be used for more than seven days. They are not licensed for use in children under 12 years but saline nasal drops, which help liquefy mucus to aid its removal, are available for children.

Efficacy

A systematic review4 found that in the common cold a single dose of nasal decongestant, either oral or topical, is moderately effective for the short-term relief of congestion in adults, but there was no evidence to show benefit over a longer period.

Inhalants

Constituents

Inhalant preparations contain up to six volatile ingredients, with combinations differing between products. The most frequently included constituent is menthol, and other popular ingredients include:

• Eucalyptus oil
• Benzoin
• Camphor
• Methyl salicylate
• Thymol
• Pine oil
• Peppermint oil.

Other ingredients include creosote: clove oil, aniseed oil, juniper berry oil, turpentine oil, and cajuput oil. Concentrations of constituents vary widely between products.

Action

All inhalants have a pungent, aromatic odour. There is no objective evidence that they improve cold symptoms, but products containing these substances have been popular for generations and they undeniably produce a temporary sensation of clearing the nasal passages. Inhalants are presented as steam inhalations, as oils that can be inhaled directly or via steam inhalations, salves for application applied around the throat and upper chest or used in
steam inhalations, and pastilles. The theoretical basis for use of steam inhalations is that steam may help congested mucus drain better and heat may destroy cold virus.

Caution

Excessive use of inhalants without steam may exacerbate congestion, through reducing clearance of mucus by impairing the action of cilia in the upper respiratory tract.

Efficacy

A Cochrane Review⁵ could not recommend inhalants in the routine treatment of common cold symptoms until more double-blind RCT trials had been conducted.

Complementary medicines

Of the complementary medicines promoted as ‘cold cures’, objective evidence for their usefulness has been provided for only the following:

Zinc

A Cochrane Review found that zinc, given within 24 hours of the onset of symptoms, reduces the duration and severity of the common cold in healthy people.⁶

Echinacea

Limited evidence that some preparations of echinacea may improve cold symptoms compared with placebo.⁷

Vitamin C

Limited evidence that vitamin C slightly reduces the duration of cold symptoms.⁸

References

1. De Sutter AI, Lemiengre M, Campbell H. Antihistamines for the common cold. Cochrane Database Syst Rev. 2009
2. De Sutter AI, van Driel ML, Kumar AA, Lesslar O, Skrt A. Oral antihistamine-decongestant-analgesic combinations for the common cold. Cochrane Database Syst Rev. 2012
3. D’Agostino RB, Weintraub M, Russell HK, et al. The effectiveness of antihistamines in reducing the severity of runny nose and sneezing: a meta-analysis. Clin Pharmacol Ther 1998; 64:579–96
4. Taverner D, Latte GJ. Nasal decongestants for the common cold. Cochrane Database Syst Rev. 2009
5. Singh M, Singh M. Heated, humidified air for the common cold. Cochrane Database Syst Rev. 2013.
6. Zinc for the common cold. Cochrane Database Syst Rev. 2013 Jun 18;6:CD001364.
7. Linde K, Barrett B, Wolkart K, et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev. 2006 Jan 25;(1):CD000530
8. Hemila H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013 Jan 31;1:CD000980