The Common Cold

Disease and Therapy , Knowledge Base / September 28, 2016

1. Introduction:

The common cold is a self-limiting contagious, upper-respiratory tract (nose and throat) viral infection. Despite there being no treatment for common cold, OTC medicines are often used for symptomatic relief.

Although cold weather in itself is not a cause, common cold occurs mainly during the winter months. Possible reasons for this include prolonged time spent indoors and low humidity, which causes dry nasal passages presenting a more susceptible environment for viral infection.

2. Epidemiology:

Common cold is the most frequently occurring ailment worldwide. Children could suffer a total of 8 to 10 colds per year, while adolescents and adults may suffer a total of 2 to 4.

Cold symptoms usually appear 2 to 3 days after exposure to the virus, and clear up within one week. They could, however, in some cases persist for up to 2 weeks.

Common cold viruses are spread through direct contact with the tiny respiratory droplets released from infected individuals as they cough, sneeze, or speak. They can also be spread through indirect contact, when an individual touches a contaminated object, transferring the virus to their mouth, nose, or eyes.

3. Etiology:

There are more than 200 types of viruses responsible for common cold, the most common being rhinoviruses – causing 50% of cases; and corona viruses – causing around 20%.

4. Pathophysiology:

The appearance of the symptoms of cold is due to the body’s response to the infection. When a nasal cell is infected by a cold virus, parts of the immune system are accordingly activated, accompanied by certain nervous system reflexes.

As the rhinoviruses enter the nasal epithelium, they bind to the intercellular adhesion molecule (ICAM-1), producing inflammation and other immunologic responses that are characteristic of the common cold. Several inflammatory mediators are released upon infection, including histamine, kinins, prostaglandins and interleukins. These substances play a role in protecting the body from the infection through dilatation and leakage of blood vessels, increasing mucus gland secretion, initiating sneeze and cough reflexes, and stimulating pain nerve fibers. These changes are actually what lead to the development of the symptoms of cold.

5. Signs and Symptoms:

a) Sore Throat:

It often is the first sign of a common cold infection – the throat feels itchy and sore.

b) Nasal Congestion:

Most patients experience rhinorrhea, which presents initially as a clear watery fluid, followed by the production of thicker, yellow or green mucus. Nasal congestion occurs due to dilatation of blood vessels, leading to swelling of the nasal mucosa and narrowing of the nasal passages. Increased mucus production further increases the feeling of stuffiness.

c) Sneezing:
It occurs due to blockage and irritation of nasal passages.

6. Complications:

a) Cough:

A cough may occur due to either irritation of the pharynx which produces a dry, tickly cough; or due to irritation of the bronchus, caused by postnasal drip.

b) High Temperature:

In most cases fever will not be present; and when present, it most likely is indicative of flu rather than a cold.

c) Aches and Pains (headache):

They are experienced due to inflammation and congestion of nasal passages and the sinuses. The occurrence of a persisting pain above or below the eyes (frontal headache) may be due to sinusitis, which are hollow cavities around cheek bones and eyes that function to warm, moist and filter the air.

Sinusitis occurs when the mucosal lining of the sinuses become inflamed and swollen. This leads to a lack of drainage of the increased mucus produced within, along with the development of a secondary bacterial infection, causing a build-up of pressure and pain. The pain produced is felt behind the eye and usually affects only one side (unilateral). The headache may be associated with rhinorrhoea or nasal congestion. The affected sinus often feels tender when pressure is applied and usually becomes worse on bending over or lying down.

d) Ear Ache:

Ear ache is a common complication of colds, especially in children. When nasal catarrh is present, the ear can feel blocked due to the blocking of the Eustachian tube connecting the middle ear to the back of the nasal cavity. The middle ear normally contains air, so when the Eustachian tube is blocked the ear can no longer be cleared by swallowing and may thus feel uncomfortable and deaf. This situation often resolves spontaneously, however, decongestants and inhalations can be helpful.

The situation worsens when the middle ear fills up with fluid becoming an ideal site for a secondary bacterial infection, where the ear becomes acutely painful and may require antibiotics. Such an ear infection is known as acute otitis media. Acute otitis media is common in young children, and treatment can be carried out via paracetamol and ibuprofen.

e) Asthma:

It can be triggered by a respiratory viral infection. Most asthma patients learn to start or increase their usual medication in anticipation of such an attack.

7. Exclusion for Self-Care:

The following conditions call for exclusion of self-care and necessitate referral to a professional.

  • Fever 38.5°C
  • Chest pain
  • Shortness of breath
  • Concurrent underlying chronic cardiopulmonary diseases, e.g. asthma, congestive heart failure or chronic obstructive pulmonary diseases.
  • AIDS or chronic immunosuppressive therapy.
  • Frail or aged patients.
  • Worsening of symptoms or development of additional symptoms during self-treatment.

8. Treatment of Common Cold:

Goal of Treatment:

To relieve the symptoms of cold.

Non-pharmacological Therapy:

  • Drink lots of fluids, especially hot drinks (e.g. hot tea with honey and lemon).
  • Adequate rest and nutrition.
  • Chicken soup: Inhaling steam can ease nasal congestion and the fluid helps avoid dehydration. Studies have found that chicken soup has some anti-inflammatory properties.
  • The use of cool mist vaporizers or steamy showers in order to increase humidification. Inhaling steam from a humidifier or vaporizer can keep a sore throat moist and cut down on pain, while relieving nasal congestion.
  • The use of saline gargle helps keep the throat moist and reduce scratchy feeling.
  • Saline nasal sprays or drops soothe irritated nasal mucosal membranes and help reduce congestion.
  • Using nasal irrigation (washes).
  • Nasal strips for temporary relief from nasal congestion, especially night-time congestion. These are worn on the bridge of the nose in order to open nasal passages.
  • Menthol ointment: Relieves pain and the menthol aroma can help open clogged passages.

Pharmacological Therapy:

  • There is no direct cure for a cold.
  • Antibiotics are not prescribed as they do not work against viruses.
  • In cases where the cold leads to complications such as sinusitis, ear infection, tonsillitis or chronic bronchitis, antibiotics can then be prescribed.

OTC Treatment:

Over-the-counter (OTC) treatments for the common cold include the use of decongestants, anti-histamines, local anesthetics, systemic analgesics, and expectorants and antitussives. Treatment can include one or more of these drug classes, depending on the severity of the case and the symptoms experienced.

a) Decongestants:

Decongestants are adrenergic agonists or sympathomimetics. Decongestants are divided into several classes according to their site and method of action.

  • Systemic decongestants: Taken orally in the form tablets or syrups.
  • Local decongestants: Applied or administered topically in the form of sprays, gels, drops or inhalers.
  • Direct acting decongestants: such as phenylephrine, oxymetazoline, and tetrahydrozoline.
  • Indirect acting decongestants: such as ephedrine and pseudoephedrine.

The mode of action of nasal decongestants involves the constriction of the dilated blood vessels of the nasal mucosa. As a result, the nasal membranes are effectively shrunk so that the drainage of mucus and air circulation is improved; hence the feeling of nasal stuffiness is relieved.

Decongestants are prescribed for the relief of nasal congestion associated with sinusitis or Eustachian tube congestion.

Overdosage of systemic decongestants can lead to cardiovascular collapse, shock and coma.

Adverse effects of decongestants are mainly related to systemic decongestants. They include:

  • Cardiovascular stimulation:
    • Elevated blood pressure
    • Tachycardia
    • Palpitation
    • Arrhythmias
  • CNS stimulation:
    • Restlessness
    • Insomnia
    • Tremors
    • Hallucinations
  • May affect diabetic control because they can increase blood glucose levels.
  • More pronounced in children and elderly people.
  • Rebound congestion (rhinitis medicamentosa). It can also occur with topical decongestants applied for longer than 5 days. Benzalkonium chloride, used as preservative, may be one of the causes contributing to such a problem. In this case, replace the topical decongestant with topical normal saline solution.

Decongestants are contraindicated in cases of hypersensitivity, idiosyncrasy, and concomitant administration with monoamine oxidase inhibitors (MAOIs). Interaction can occur up to two weeks after the patient has stopped taking MAOIs. Such an interaction is also possible with topically applied decongestants or sympathomimetics.

Generally, decongestants should be used with caution in patients with diabetes, heart disease, hypertension, hyperthyroidism, increased intraocular pressure or prostatic hypertrohpy. It is best to avoid taking the dose near bed time, due to CNS stimulation that could lead to insomnia.

b) Anti-histamines (H1-receptor antagonists):

A histamine antagonist is a drug that blocks the action of histamine on histamine receptors. Commonly, the term antihistamine refers only to H1 antihistamines. H1 antihistamines are actually reverse agonists, rather than antagonists. They are used to treat allergic reactions.

Histamine, acting on H1-receptors, produces pruritus, vasodilation, hypotension, flushing, headache, tachycardia, bronchoconstriction, increased vascular permeability, potentiation of pain, etc…Many of which are common symptoms experienced in common cold and allergic reactions.

A common side effect of H1 antihistamines is sedation, which is experienced mainly with 1st generation antihistamines. 2nd generation antihistamines, however, do not cross the blood brain barrier and hence do not cause drowsiness.

For cough associated with common cold, it is recommended that 1st generation antihistamine-decongestants be used, since they are believed to be more effective than newer, non-sedating types.

1st generation H1-antihistamines are widely available and relatively inexpensive. They are effective in relief of allergic symptoms. They commonly referred to as non-selective antihistamines since they possess anticholinergic, alpha-adrenergic and serotonergic effects as well. This lack of receptor selectivity is the basis of the poor tolerability profile of some of these agents, and the occurrence of adverse effects – mostly related to anti-cholinergic action (drowsiness, constipation, blurred vision, dry mouth and urinary retention).They also cross the blood-brain barrier which is responsible for their sedating effect. H1 antihistamines are indicated in common cold also for their anticholinergic effect, which functions to reduce rhinorrhea (runny nose) and sneezing. Examples include drugs such as chlorpheniramine and promethazine.

2nd generation H2-antihistamines are newer drugs that are much more selective for peripheral H1 receptors than central histaminergic and cholinergic receptors. This selectivity is mainly due to their inability to cross the blood-brain barrier; and it significantly reduces the occurrence of adverse reactions, including sedation, while still providing effective relief of allergic conditions. Examples include loratadine, cetirizine, and acrivastine.

Drug-drug interactions include alcohol intake, which increases drowsiness; concomitant administration of hypnotics and sedatives, potentiating the sedative effect; and Betahistine, for treatment of dizziness, which antagonizes the effect of antihistamines.

Caution should be advised in patients taking antihistamines who suffer from closed-angle glaucoma, since this can lead to increased intraocular pressure; in patients with prostatic obstruction, due to urinary retention; in patients with epilepsy, since high doses of anti-histaminic can induce convulsions; and in patients with liver disease.

c) Local Anesthetics:

Local anesthetics are available as lozenges, mouthwashes and sprays, used for temporary relief of sore throats. Examples include benzocaine and dyclonine hydrochloride. Some products contain local antiseptics, such as cetylpridinium chloride, menthol or camphor.

d) Systemic Analgesics:

Systemic analgesics are used for the relief of aches associated with common cold, examples of which include aspirin, acetaminophen, and NSAIDs (Ibuprofen).

Aspirin and aspirin-containing products are not to be used in children or teenagers since it has been associated with a rare and potentially life-threatening condition called Reye’s syndrome.

e) Expectorants and Antitussives:

Expectorants, or bronchomucotropic agents, are drugs used to assist in the removal of secretions or exudate from the trachea, bronchi or lungs. They exert their action by liquefying viscid mucus, thus act as decongestants. They are used in the treatment of cough to help expel exudates and secretions.

Expectorants include guaifenesin, which is used for symptomatic relief of dry, non-productive coughs in the presence of mucus in the respiratory tract.

Antitussives act on the CNS to raise the threshold of the cough center; act peripherally in the respiratory tract to reduce tassal impulses; or in both ways. They specifically inhibit or suppress the act of coughing, and act to control rather than eliminate the cough.

Antitussives are to be used only for dry unproductive cough, especially when sleep is disturbed. They should not be used at all to suppress productive coughing.

Examples of antitussives include:

  • Dextromethorphan:
    • It is a synthetic, non-narcotic codeine derivative.
    • Used to control non-productive coughs by soothing minor throat and bronchial irritations.
    • In rare cases, it may produce psychological, though not physical, dependence.
    • It should not be taken with MAOIs, TCAs, or SSRIs due to potential occurrence of serotonin syndrome.
    • It is frequently combined with guaifenesin.
  • Benzonatate (Tessalon Perles):
    • Works by anesthetizing the stretch receptors located in the respiratory passage and lungs, thus reducing the cough reflex at its source.
    • It is not an opioid, hence not prone to abuse
  • Terpin Hydrate Elixir with Codeine (ETH with Codeine):
    • Codeine is a narcotic antitussive, while the terpin hydrate is used primarily as a vehicle which has a mild expectorant effect as well.
    • The product contains 40% alcohol, which serves as the main bronchomucotropic agent.

f) Combinations:

Various combinations are available in the market containing decongestants and antihistamines, along with analgesics, expectorants, and antitussives.

Complementary Therapies:

a) Zinc:

Zinc appears to have antiviral properties, the proposed mechanism of action of which is competition with ICAM-1 receptors to prevent rhinovirus attachment and replication in nasal epithelial cells and reduction of inflammation.

It has been observed through studies that both duration and severity of cold symptoms were significantly reduced after using zinc acetate lozenges every 2 to 3 hours within 24 hours of developing common cold symptoms.

Side effects experienced with zinc therapy include gastric upset and bitter taste.

b) Vitamin C:

High-dose vitamin C therapy (over 1 gram per day) reduces the duration of colds by about half a day, which represents an approximate 15% reduction in duration.

Vitamin C strengthens connective tissue, hence increasing resistance to viral invasion. It also serves to strengthen the body’s immune system, neutralizing free radicals and killing viruses.

Caution should be advised that taking more than 2000 grams of vitamin C per day may lead to formation of kidney stones and development diarrhea.

c) Echinacea:

Echinacea is a dietary supplement promoted to aid in treatment of common cold as an immune-stimulant.

9. Cold or Flu?

There are several key differences between a cold and the flu, the most important of which is fever. High temperature or fever is rarely experienced in a common cold; while it is usual to experience an elevated temperature of 37.7C to 38.8C, or higher, which lasts from 3 to 4 days. Nasal congestion, sneezing, and a sore throat are all common and usual symptoms of the common cold, and sometimes occur in a fever as well. A mild to moderate cough can be experienced in a common cold, as well as, a hacking cough. Cough associated with fever is a common and more severe than that associated with a common cold.

Treatment for the flu involves seeing a doctor who would possibly prescribe an antiviral medicine.

10. Cold or Allergy?

In a cold, a slight sensation of ache and pain can be experienced, while none are felt in an allergy. Itchy eyes rarely or never occur in a cold, but are of common occurrence in allergy.

A common cold lasts 3 to 14 days, while an allergy can last for weeks.

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