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August 1, 2010



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Separating Fact from Fiction on the Use of Oral Zinc for the Treatment of Colds

Changes in our society, changes in our environment, and changes in our development and utilization of prescription and nonprescription medications have made management of the common cold a greater challenge for pharmacists and other health care professionals. Globalization of our world has made its inhabitants more susceptible to a variety of viral contagions. Population increases and ineffective personal hygiene have enabled viruses to spread with greater ease. Airtight planes, trains, and crowded office buildings have become havens for viral transmission. Medications previously targeted to suppress bacterial and viral infections have become impotent due to emerging resistance and previously unknown adverse effects. Consequently, pharmacists and other health care professionals have a more difficult time trying to answer that age-old question: “So, what do you have for a cold?”

Since there is no established treatment for the common cold, clinicians are faced with the challenge of determining the most appropriate approach to mitigating the symptoms associated with colds. Remedies that once worked with some assurance for the management of symptoms associated with the common cold may no longer be effective, may no longer be available, or may no longer be safe. Thus, pharmacists and other health care professionals need to revisit the modalities that once were the remedies of first choice and to reconsider the remedies that were once passed over. This monograph provides insight and guidelines into renewed approaches to the management of the common cold, with emphasis on zinc, which has been the subject of much discussion, both fact and fiction.

EPIDEMIOLOGY OF THE COMMON COLD

It is estimated that individuals in the United States suffer more than one billion colds annually.1 Although the common cold is usually mild, with symptoms lasting one to two weeks, it is a leading cause of doctor visits and of school and job absenteeism. Indeed, acute upper respiratory infection is the second most common diagnosis in physicians’ offices and the most common discharge diagnosis in emergency departments.2,3

Colds are most prevalent among children and seem to be related to youngsters’ relative lack of resistance to infection and to contact with other children in day-care centers and schools. Children have about six to ten colds a year. In families with children in school, the number of colds per child can be as high as 12 a year. Day-care attendance is another major risk factor. During the first years of life, boys seem to have more respiratory infections than girls, but this difference is reversed later in life. Adults average about two to four colds a year. Women, especially those aged 20 to 30 years, are more likely to have more colds than men, possibly because of their closer contact with children.4

The occurrence of the common cold may be associated with seasonality. In temperate regions of the northern hemisphere, the frequency of respiratory infections increases rapidly in the autumn, remains fairly high throughout the winter, and decreases again in the spring. In tropical areas, most colds arise during the rainy season.

Seasonal changes in relative humidity may affect the prevalence of colds. The most common cold-causing viruses survive better when the humidity is low; lower humidity is seen in the colder months of the year. Cold weather also tends to dry out the linings of the nasal passages, making them more susceptible to viral infection.

PATHOPHYSIOLOGY OF THE COMMON COLD

More than 200 different viruses are known to cause the symptoms of the common cold. Some, such as the rhinoviruses (which are the most prevalent cause of colds), seldom produce serious illnesses. Others, such as parainfluenza and respiratory syncytial viruses, produce mild infections in adults but can precipitate severe lower respiratory infections in young children. Coronaviruses also play a role in the pathophysiology of the common cold. These viruses are found in 7% to 18% of adults with upper respiratory infections.5-7

The symptoms associated with the common cold, which may include nasal drainage, cough, headache, muscle aches, sore throat, hoarseness, fever, and sneezing, vary with their viral cause. Fever is an infrequent finding during rhinovirus infections in adults, but it is fairly common in children with upper respiratory infections of any cause.8 Symptoms usually begin one to two days after viral contact and are usually mild. Most episodes begin with a scratchy, tickling, or soreness of the throat. Throat discomfort progresses until it becomes moderately painful but usually resolves by the second or third day. Nasal symptoms often accompany sore throat. Initially, the patient notices a copious, thin discharge that persists for two or more days. Then the consistency of the discharge usually thickens and may become purulent. Typically, the nose is partially or totally blocked. The nasal discharge and nasal blockage gradually improve by the fourth or fifth day. The occurrence of coughing heralds the next stage. The cough may be productive initially, gradually becoming tight, dry, and nonproductive.8

Although as noted previously the common cold is usually a self-limited viral illness of short duration, the infection is sometimes accompanied by a bacterial complication. In children, the most common bacterial complication is acute otitis media, which occurs in about 20% of children with viral upper respiratory infections.9 Clinical studies suggest that respiratory viruses play a crucial part in the development of acute otitis media, and the detection rates of different viruses in the middle-ear fluid suggest that at least some viruses actively invade the middle ear and contribute to the inflammatory process.10,11

    Myths About the Common Cold
 

Cold weather causes the common cold.
Cold weather has never been positively linked to being a cause of the common cold. Some theories suggest that the increase in the occurrence of the common cold during colder months is due to more people gathering indoors, with compromised air circulation and quality, enabling cold viruses to more likely spread.

Eating chicken soup is a
popular way to cure the common cold.
Although eating a bowl of chicken soup certainly does feel soothing on a dry, scratchy throat, it cannot cure a cold. However, chicken is a good source of protein, and the broth contains water and electrolytes, which will help individuals to stay well hydrated and nourished.

Drinking milk causes increased
nasal mucus during a cold.
Milk and mucus may look slightly similar, but there is no evidence that drinking milk will increase the amount of mucus.

People should starve a cold.
Cold sufferers should not starve a cold; in fact, that could only make the cold worse. Patients should eat a healthy, well-balanced diet in order to remain well nourished in order to effectively fight a cold.

Only people with a weak
immune system can catch a cold.
Anyone can catch a cold once exposed to the virus. In fact, nearly 95% of adults with healthy immune systems have caught a cold when exposed to the virus.

DISEASE PROGRESSION

The pathogenesis of the common cold involves a complex interplay between replicating viruses and the host’s inflammatory response. The detailed pathogenetic mechanisms of the various respiratory viruses can be very different from each other, as indicated by the fact that the primary site of replication of influenza viruses is the tracheobronchial epithelium, whereas rhinovirus replication starts predominantly in the nasopharynx.12,13

It is interesting to note that even blowing one’s nose can be the cause of further replication. The authors of one study concluded that blowing the nose creates such extreme intranasal pressure that it may propel fluid from the nasal cavity to the paranasal sinuses.14

TRADITIONAL PRESCRIPTION APPROACHES TO THE MANAGEMENT OF THE COMMON COLD

The symptomatic treatment of colds has been aimed at relieving the most disturbing symptoms of the illness, and hundreds of different preparations are available.15 Systematic reviews have shown that antibiotics do not have a major role in the treatment of the common cold.16,17 Antibiotics are ineffective at reducing the symptom duration and severity of symptoms. The risk of adverse gastrointestinal effects, the cost of treatment, and increased resistance are other reasons why antibiotics are not an effective option for the common cold.

Theoretically, corticosteroids may be able to effectively reduce the duration and severity of nasal symptoms, but results of clinical studies of either intranasal or oral steroids have shown no such clinical benefit.18 The use of intranasal steroids in children during rhinovirus infection could even increase the risk of acute otitis media.18

The use of antihistamines has been questioned in managing symptoms associated with the common cold. Although some randomized controlled trials of older first-generation antihistamines have shown positive results for mitigation of certain symptoms, a Cochrane review concluded that antihistamines do not alleviate cold-related sneezing or nasal symptoms to a clinically significant degree and do not affect subjective improvement in children or adults.19 Even if a slight clinical benefit exists, there are risks and adverse effects, especially with first-generation antihistamines.20 The results of several studies on the efficacy of local ipratropium in reducing rhinorrhea have provided mixed conclusions.21,22

Cough medications, both antitussives and mucolytic agents, are frequently used, although their efficacy has not been conclusively substantiated.23

STATUS OF NONPRESCRIPTION COLD MEDICATIONS

Over the past few years, nonprescription cold medications, especially those for children, have received unprecedented attention from regulators, health care professionals, the media, patients, and parents. As a result of this scrutiny and revised FDA provisos, nonprescription medications for the management of cold symptoms containing ingredients such as phenylpropanolamine and pseudoephedrine are either no longer available to consumers or only available “behind the counter.” In pharmacies throughout the US, this movement has placed pharmacists in the position of having to be extremely cognizant of educating and counseling patients about the appropriate use of nonprescription cold products. Indeed, it is estimated that over 40% of US households purchase these products annually.24 Over-the-counter cough and cold preparations include various combinations of antihistamines, decongestants, antitussives, and expectorants.

The conundrum for pharmacists is that no established or recognized protocol exists for identifying, classifying, and recommending these products. Consumers purchase about 95 million packages of such medication for use in children each year.24

Within the pediatric community, however, concern over the efficacy and safety of these products has been growing for more than two decades. In 2006, the American College of Chest Physicians found that “literature regarding over-the-counter cough medications does not support the efficacy of such products in the pediatric age group.” Meanwhile, from 2000 to 2007, US poison-control centers have reported more than 750,000 calls of concern related to cough and cold products.25 A report from the Centers for Disease Control and Prevention identified more than 1,500 emergency room visits in 2004 and 2005 for children younger than 2 years of age who had been given cough or cold products.26

COMPLEMENTARY AND ALTERNATIVE THERAPIES

As a result of the conflicting findings regarding traditional approaches to the nonprescription management of symptoms associated with the common cold and a hesitancy on the part of pharmacists to recommend these therapies, especially in special populations such as pediatric patients, elderly patients, and patients with conditions such as hypertension and diabetes, complementary and alternative therapies have come to the forefront. In the US, 36% of people use some form of complementary and alternative therapies, of which almost 10% are for managing cold symptoms.27Indeed, in a survey of patients on the use of complementary and alternative therapies, the prevention of colds and influenza and “immune boosting” were among the top-10 reasons they took vitamins, minerals, and herbal supplements.28

Since there are a plethora of complementary and alternative therapies for the management of symptoms associated with the common cold, this article will only discuss a few of the more commonly used options by patients that are often recommended by pharmacists: echinacea, vitamin C, and zinc.

Echinacea is a flowering plant that grows throughout the US and Canada. More than 800 products contain some form of the herbal in the US. Clinical studies on the benefits of echinacea in the management of syptoms associated with the common cold have had mixed results. Extracts of echinacea may increase the number of circulating white blood cells and may boost the activity of other immune cells. Yet a study published in 2005 in the New England Journal of Medicine found that echinacea was no more effective than placebo in preventing colds.29 The study also concluded that echinacea did not reduce the severity of cold symptoms. In addition, studies funded by the National Center for Complementary and Alternative Medicine did not find any benefit from echinacea for the common cold in either children or adults.30 A Cochrane review concluded that, despite some studies showing benefit, there was no solid evidence that echinacea products effectively treat or prevent the common cold.31The authors also cited concerns regarding the clinical studies evaluated, such as publication bias (ie, positive studies were more likely to be published), poor study quality, and variability of study results.

Even though a more recent meta-analysis on the use of echinacea for colds demonstrated that echinacea may prevent colds by more than half in comparison to placebo and may shorten the duration of a cold by an average of 1.4 days, the authors mentioned possible side effects, such as stomach discomfort and nausea.32 More long-term studies should be conducted to determine the safety and efficacy of echinacea for treating the common cold.

Vitamin C is often used to treat the common cold. Available in products such as tablets, fortified juices, cough drops, and tea, vitamin C functions as an important antioxidant that helps keep the body strong and healthy. It is used to maintain bone, muscle, and blood vessels and assists in the formation of collagen. It also enhances the oral absorption of iron.

Although vitamin C has been widely studied in the management of symptoms associated with the common cold and also as a preventive measure, data on its actual benefit have been inconsistent. A Cochrane review showed that taking 200 mg or more of vitamin C daily does not significantly decrease the severity or duration of symptoms when initiated after the onset of cold symptoms.33

Furthermore, studies have demonstrated that higher doses of vitamin C necessary for the prevention and/or treatment of colds have been associated with the occurrence of kidney stones, nausea, and diarrhea.34 In addition, healthy adults who take large doses of vitamin C may experience a decline in blood levels of vitamin C when they abruptly discontinue high-dose therapy and then resume a normal vitamin C intake. To avoid this potential complication, high doses of vitamin C should be gradually cut back to normal doses.

Data regarding the prophylactic use of vitamin C have also been varied. Thirty trials involving 9,676 cold episodes showed a modest but statistically significant decrease in the duration of the cold with vitamin C taken before the onset of symptoms: an 8% decrease in adults and a 13.5% decrease in children.33

THE STORY BEHIND ZINC

Zinc is an essential mineral found in almost every cell. Zinc stimulates the activity of approximately 100 enzymes, supports a healthy immune system, is needed for wound healing, helps maintain senses of taste and smell, and is required for DNA synthesis. The typical daily intake of zinc in the Western diet is approximately 10 mg, which is two thirds of the recommended dietary allowance (RDA). Low zinc intake is often seen in the elderly, alcoholics, people with anorexia, and individuals on restrictive weight-loss diets.

As with echinacea and vitamin C, the use of zinc for the treatment of the common cold has produced conflicting clinical results. Some experts believe that patients do not need to take zinc supplementation for the common cold, since colds generally resolve on their own within 7 to 10 days. Yet others believe that taking zinc supplementation at the first sign of a cold significantly reduces the duration of the cold and mitigates symptoms. Other questions that arise about zinc supplementation include what is the minimum dosage required for zinc to have a beneficial effect, what is the length of time needed for effective zinc administration, and what formulation of zinc is most appropriate for specific patient populations, such as children, the elderly, and patients with conditions such as diabetes.

ZINC’S MECHANISM OF ACTION

The exact biochemical, immunologic, or virologic basis for the action of zinc in the common cold has not been elucidated. However, a leading hypothesis is that Zn2+ is a competitive inhibitor of intercellular adhesion molecule-1 (ICAM-1) in both rhinovirus particles and the nasal epithelium.35-37 At least one clinical trial of zinc in the common cold correlated plasma levels of zinc and pro-inflammatory cytokines.38

Rhinoviruses are transmitted to a susceptible host by either direct contact or large particle aerosols.39 Entry of rhinoviruses into the nasal epithelium is mediated by binding to ICAM-1.35,40 ICAM-1 also plays a role in inflammatory processes and in the T-cell-mediated host defense system.41 ICAM-1 is used as a receptor for leukocyte function-associated antigen (LFA-1) to bind with leukocytes and initiate and sustain inflammation.35,41

HISTORY OF ZINC SUPPLEMENTATION IN CLINICAL STUDIES

Numerous studies on the efficacy and safety of zinc supplementation in the management of the common cold have been conducted, with some indicating there is a benefit to zinc supplementation and others indicating there may not be any benefit.38,43-48 The results of some of the older, more anecdotal studies evaluating the use of zinc for cold symptoms are difficult to compare with those of the newer, more evidence-based clinical trials. Several of these older negative studies contained some methodological flaws.49,50 Criticisms of these studies include small sample size, too low a zinc dosage (4.5 mg), inadequate blinding of subjects, chiefly subjective self-reported data, and the use of flavoring agents that theoretically could inactivate zinc salts.

The proposed benefit of zinc gluconate tablets for the management of symptoms associated with the common cold was first clinically hypothesized in a 1984 study.51 Even though the authors speculated that the zinc ion delivered in tablet form could both shorten the duration of colds as well as reduce symptoms, the acceptance of zinc gluconate tablets among the medical community for the management of symptoms associated with the common cold was mitigated by the unpalatable taste of the tablets. Since that time, numerous attempts have been made to add ingredients to make the tablets taste better.

Several years after the 1984 study by Eby and colleagues, Al-Nakib and colleagues found that zinc gluconate lozenges in a flavored sugar base that released 23 mg of elemental zinc were effective for the prophylaxis and treatment of induced rhinovirus colds in a small group of volunteers.52 Subsequently, a number of investigators conducted trials in patients with experimentally induced and natural colds using other flavoring agents with strong complexing components, such as citric acid, tartaric acid, or mannitol/sorbitol. However, these formulations resulted in highly bound zinc complexes that released very little ionic zinc in the mouth, and the trials were unable to demonstrate treatment effects different from those of placebo lozenges.53-55

Additional studies through the years have affirmed the efficacy and safety of zinc.37,38,46,47,56 In one study comparing the use of zinc acetate and zinc gluconate in patients with the common cold, the duration of illness was much shorter in the group receiving zinc gluconate lozenges (providing 13.3 mg of zinc) than in the group receiving zinc acetate lozenges (providing 5 or 11.5 mg of zinc).57

ZINC FORMULATIONS/ROUTES OF ADMINISTRATION

Of the many oral formulations of zinc available, which include zinc gluconate, zinc acetate, zinc carbonate, and zinc sulfate, only zinc acetate and zinc gluconate have been shown to have antiviral properties.58,59 A formulation containing zinc gluconate glycine is also available.

The effectiveness of products containing ionic zinc for reducing the severity and duration of common cold symptoms has been shown to be dependent on the formulation of zinc and its route of administration.40 As previously noted, research has shown that efficacy is contingent on the use of an ionic form of zinc and that the Zn2+ ions must be delivered to the nasal mucosa to reach and maintain contact with ICAM-1 receptor sites.40 Zinc ions are readily absorbed into the mucous membranes of the oropharyngeal cavity when applied directly to those tissues.35

   

Discrepancies in Clinical Studies on the Efficacy of Zinc Supplementation
 

Just about every clinical trial assessing the safety and efficacy of zinc lozenges for managing cold symptoms has had some methodological flaws. These flaws include inadequate sample size, use of too low a zinc dosage, inadequate blinding of subjects, and the use of chiefly subjective self-reported data. Some trials have been criticized for using formulations with excipients or flavoring agents that theoretically could inactivate zinc salts. Most studies do not detail how patient adherence was guaranteed. Most studies do not confirm the diagnosis of the common cold by using virologic testing. Furthermore, most studies have not specifically excluded allergy sufferers; allergy symptoms (eg, hay fever) often mimic the common cold.

An ongoing debate centers around the notion that chemically different lozenge formulations have caused the different results in the clinical trials to date. This hypothesis is supported by the fact that different lozenge formulations do in fact produce markedly different zinc ion availability in saliva. However, the optimum degree of ionization for a therapeutic benefit is unknown. Greater degrees of ionization may produce unpleasant taste and other side effects. The rationale behind using zinc as a lozenge and not systemically is partly because lozenges are less likely to result in higher serum concentrations with resulting adverse effects. It is generally thought that for zinc to be effective, the product should deposit in the oral, pharyngeal, and nasal mucosa.

Maintaining the ionic availability of zinc has been a challenge to the formulation of effective zinc products.40 Flavorings and chelating agents have been added to some products to mask the rather unpleasant metallic taste.40 However, as mentioned previously, masking the unpleasant taste may reduce the concentration of ionic zinc in some products, thereby reducing their efficacy. More recently developed oral zinc products have been formulated to provide high levels of ionic zinc and tissue affinity in a pleasant-tasting base.

Researchers have theorized that if rhinovirus replication takes place in the nasal mucosa, and zinc’s efficacy against the common cold resides in its ability to inhibit viral replication, intranasal administration of zinc may optimize the effectiveness of zinc on cold symptoms.60 Intranasal preparations of Zn2+ ions—nasal spray and gel formulations—have been evaluated to determine whether direct delivery of ionic zinc to the site of viral infection may be more effective than oral preparations.60,61 Evaluations of intranasal zinc gel in randomized, double-blind trials have been published.39,61,62 The intranasal gel formulation consisted of 33 mM ionic zinc in an emulsion with a pH of 7.2 and delivered 120 microliters per spray. The intranasal formulation was found to be no more effective than the oral formulation in managing cold systems.

SAFETY AND EFFICACY OF ORAL ZINC FORMULATIONS

Although the most common side effects associated with zinc lozenges are nausea, bad taste, diarrhea, vomiting, mouth irritation, and, rarely, mouth sores, the safety profile of zinc has been demonstrated in numerous studies.46,47 The results from one randomized, double-blind, placebo-controlled trial strongly supported the safety of zinc gluconate glycine lozenges in elderly individuals who were taking multiple medications for an array of medical conditions. Six days of multiple daily doses with zinc gluconate glycine lozenges produced no clinically significant changes in physical examination parameters or clinical laboratory values.47

Long-term use of oral zinc at dosages of 100 mg or more daily may cause a number of toxic effects, including severe copper deficiency, impaired immunity, cardiac arrhythmias, heart problems, and anemia.63-66 In addition, zinc at a dose of more than 50 mg daily may reduce levels of high-density lipoproteins.67 Pharmacists should educate and counsel patients on the possible long-term effects of high-dose, continued use of zinc supplementation. Chronic use of zinc above 100 mg daily should be discouraged unless done under medical supervision.

ZINC SUPPLEMENTATION IN SPECIAL POPULATIONS

The use of zinc supplementation in special populations, such as children, the elderly, and patients with diabetes, has been a subject of varied and continued interest.

Zinc gluconate glycine lozenges are highly recommended by clinicians for the treatment of the common cold in children and younger adults. A study by McElroy and Miller of 178 school-aged children given zinc lozenges prophylactically during the cold season demonstrated that 25% of the children did not experience a cold and 67% never had a cold or experienced only one cold.46 The investigators noted that the ease of use associated with the lozenges aided in patient adherence and positive outcomes.

Zinc gluconate glycine lozenges were also found to be safe and efficacious in elderly patients and in patients with diabetes.47,48 A randomized, double-blind, placebo-controlled, parallel-group trial enrolled men and women between 60 and 91 years of age who self-administered one zinc gluconate glycine or placebo lozenge every three to four hours for six days. The authors concluded that zinc gluconate glycine lozenges are safe and well tolerated by a geriatric population and are suitable for prophylactic or therapeutic use to reduce the duration or severity of the common cold.47

In a study by Di Silvestro of 40 postmenopausal women with type 2 diabetes, a three-week course of supplementation with zinc (30 mg/day) raised initially low plasma zinc values to above normal values without any harmful side effects and limited oxidative stress.56 This was an important finding since persons with diabetes often show signs of high degrees of oxidant stress and zinc deficiency.

  

Counseling Points
Concerning Zinc Supplementation
 

Pharmacists can respond to patients’ questions concerning the use of zinc for treating the common cold utilizing the following statements.

• Approximately half the studies of zinc show it is effective for treating cold symptoms. However, studies showing both positive and negative results have methodological flaws.

• Patients should begin zinc treatment within 24 hours of onset of cold symptoms.

• Certain zinc lozenges have been proven to be safe in children, the elderly, and patients with diabetes.

• The exact mode of zinc action is unknown, but several different mechanisms have been hypothesized.

• Zinc lozenges should be dissolved slowly in the oral cavity without being bitten or chewed. This will allow for a greater demulcent effect and permit the zinc to deposit in the oral, pharyngeal, and nasal mucosa.

• Pharmacists should discourage pregnant and lactating women from using zinc cold remedies unless future studies confirm their safety.

• Pharmacists can tell patients that short courses of zinc appear to be safe, but some mild side effects may occur. These effects are limited to the gastrointestinal tract and include bad taste, nausea, and stomachache.

APPROPRIATE ADMINISTRATION OF ORAL ZINC SUPPLEMENTATION

Oral zinc supplementation is most effective if taken at least one hour before or two hours after meals. However, if zinc supplements cause stomach upset, they may be taken with a meal. Certain foods such as bran and high fiber-containing foods may contribute to the diarrhea that is occasionally associated with zinc supplements. Patients should be encouraged to inform pharmacists and other health care professionals if they are taking zinc supplements with meals.

As previously noted, the average American typically consumes 10 mg of zinc a day, which is approximately one third less than the RDA. The recommended daily intake of zinc supplementation is noted in Table 1. It should be emphasized that the normal daily recommended intakes are expressed as an actual amount of zinc, and that the dosage forms, eg, zinc acetate or zinc gluconate, are commercially available in different strengths.

Table 1. RDA for Zinc Supplementation

Pediatric
• Infants birth to 6 months: 2 mg (AI)
• Infants 7 to 12 months: 3 mg (RDA)
• Children 1 to 3 years: 3 mg (RDA)
• Children 4 to 8 years: 5 mg (RDA)
• Children 9 to 13 years: 8 mg (RDA)
• Males 14 to 18 years: 11 mg (RDA)
• Females 14 to 18 years: 9 mg (RDA)

Adult
• Males 19 years and older: 11 mg (RDA)
• Females 19 years and older: 8 mg (RDA)
• Pregnant females 14 to 18 years: 12 mg (RDA)
• Pregnant females 19 years and older: 11 mg (RDA)
• Breastfeeding females 14 to 18 years: 13 mg (RDA)
• Breastfeeding females 19 years and older: 12 mg (RDA)

Source: National Institute of Medicine

THE ROLE OF PHARMACISTS

For clinicians, especially pharmacists, it is vastly important to have the proper mindset to wade through the clinical studies and anecdotal reports to determine whether oral zinc supplementation is appropriate for a given patient’s cold. In interpreting the results of these trials, pharmacists should recall that many studies of zinc for the common cold have been criticized due to small sample size, improper zinc dosage, inadequate blinding of subjects, and questionable endpoints. Some studies did not confirm the presence of the common cold by virological testing, and others did not exclude patients with allergic rhinitis. Pharmacists are likely to receive inquiries from patients regarding the safety and efficacy of zinc for the common cold. Pharmacists should reassure patients of zinc’s safety when used at dosages consistent with product labeling, particularly emphasizing that adverse effects are mild and are generally confined to the gastrointestinal tract.

Pharmacists should attempt to solicit information from patients regarding their medical history, including their current medication and dietary supplement intake, before making a recommendation regarding oral zinc supplementation. Patients particularly to be solicited include the elderly, children, and women who are pregnant or breastfeeding. Zinc formulations for the common cold have not been systematically studied in pregnant and lactating women.

Patients who might benefit from oral zinc supplementation should be counseled to begin zinc at the very first sign of cold symptoms, ideally within 24 hours of the onset of cold symptoms. Zinc supplementation should be continued until symptoms resolve or until otherwise advised by a physician. However, patients with cough or cold symptoms that last beyond 10 days should be referred for medical attention, especially if symptoms are accompanied by fever, persistent sore throat, weight loss, fatigue, or productive cough.

CONCLUSION

Pharmacists are likely to receive inquiries from patients regarding the safety and efficacy of zinc for the common cold. Evidence exists to support the therapeutic effect of zinc when started early in the course of a cold, ideally in the prodromal period. Pharmacists should reassure patients of zinc’s safety when used at dosages consistent with product labeling. In general, pharmacists and other health care professionals, as well as the patients they serve, should improve infection control efforts. Good personal hygiene, especially strict hand washing and avoiding self-inoculation with viruses that cause the common cold, may help curtail the spread of the common cold.

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