Drugs used for the temporary relief of the symptoms and allergy caused by allergic rhinitis, hay fever and allergy symptoms.
July 11, 2011 – 12:27 pm
TABLE. Relative Adverse-Effect
Profiles of Antihistamines
Relative Sedative Effect
Relative Anticholinergic Effect
Low to none
Low to none
Low to none
class, peripherally selective
Low to none
Low to none
Low to moderate
Low to none
Low to none
Low to none
Low to none
Low to none
Low to none
Low to none
TABLE. Oral Dosages of Commonly Used
Antihistamines and Decongestants
Dosage and Intervala
4 mg every 6 h
6-12 yr: 2 mg every 6 h
2-5 yr: 1 mg every 6 h
8-12 mg daily at bedtime or 8-12 mg
every 8 h
6-12 yr: 8 mg at bedtime <6 yr: Not recommended Clemastine fumarateb 1.34 mg every 8 h 6-12 yr: 0.67 mg every 12 h Diphenhydramine hydrochlorideb 25-50 mg every 8 h 5 mg/kg/day divided every 8 h (up to 25 mg per dose) Peripherally selective (second-generation) antihistamines Loratadineb 10 mg once daily 6-12 yr: 10 mg once daily 2-5 yr: 5 mg once daily Fexofenadine 60 mg twice daily or 180 mg once daily 6-11 yr: 30 mg twice daily Cetirizineb 5-10 mg once daily >6 yr: 5 mg once daily infants
60 mg every 4-6 h
6-12 yr: 30 mg every 4-6 h
2-5 yr: 15 mg every 4-6 h
120 mg every 12 h
Note: Fexofenadine and
cetirizine are available by prescription only.
aDosage adjustment may be needed in
renal/hepatic dysfunction. Refer to manufacturers’ prescribing information.
bAvailable in liquid form.
c0.25 mg/kg orally demonstrated to
available: 240 mg once daily (60-mg immediate-release with 180-mg
TABLE. Duration of Action of Topical
Up to 4
Up to 12
TABLE. Dosage of Nasal Corticosteroids
Dosage and Interval
>12 yr: 1 inhalation (42 mcg) per
nostril 2-4 times a day (maximum, 336 mcg/day)
6-12 yr: 1 inhalation per nostril 3 times/day
>12 yr: 1-2 inhalations once
daily 6-12 yr: 1 inhalation per nostril (42 mcg) twice daily to start
>6 yr: 2 sprays (64 mcg) per
nostril in AM and PM or 4 sprays per nostril in AM (maximum, 256 mcg)
Adults: 2 sprays (50 mcg) per
nostril twice daily (maximum, 400 mcg)
Children: 1 spray per nostril 3
times a day
Adults: 2 sprays (100 mcg) per
nostril once daily; after a few days decrease to 1 spray per nostril
Children > 4 yr and adolescents:
1 spray per nostril once daily (maximum, 200 mcg/day)
>12 yr: 2 sprays (100 mcg) per
nostril once daily
>12 yr: 2 sprays (110 mcg) per
nostril once daily (maximum, 440 mcg/day)
June 18, 2011 – 7:31 am
Traditionally all H1 antagonists were considered to act via the mechanism of competitive inhibition at the H1 receptor. Recently, the concept of reversed or inverse agonist has been introduced to explain the action of antihistamines. The idea is based on the existence of histamine receptors, at equilibrium, existing in both active and inactive forms. Histamine stabilizes the histamine receptor’s conformation, resulting in a predominantly activated state, whereas antihistamines are thought to be agonists of the inactive conformation at the receptor site. Stimulation by antihistamines at the receptor thus results in the abolition of the effects of histamine. Important regarding this concept is that antihistamines induce the downregulation of histamine receptor activity, both in the presence and the absence of histamine. Most, but not all, first-generation antihistamines have a structural resemblance to histamine in that they contain a substituted ethylamine moiety. It was previously felt that this structural similarity was necessary for competitive inhibition. However, with the development of newer agents, it has been shown that antihistamine activity can occur without an obvious shared structural relationship between histamine and its antagonist. The proposed difference between the mechanisms of action of antihistamines with an ethylamine moiety (thus exhibiting a structural resemblance to histamine) and those without this entity is that the former group may actually bind to the same site on the histamine receptor as histamine, whereas the latter group binds to the seven-chain, G protein-coupled histamine receptor at other sites to sterically hinder the binding of histamine. In addition, the absence of structural similarities adds credence to the inverse agonist hypothesis.
First-generation antihistamines have classically been separated into categories based on the atom linking the ethylamine grouping to aromatic substituents (Fig. 1). For example, if the link is via oxygen, the drugs are classified as ethanolamines; if via carbon, they are called alkylamines; and if via nitrogen, they are called ethylenediamines. Certain biological activities have been attributed to these differences, but clinically it is unclear whether or not these are significant. For example, it is said that alkylamines cause less drowsiness in general than do ethanolamines.
All first-generation H1 receptor antagonists are rapidly absorbed and reach peak serum concentration within 3 h when given in liquid form. All are extensively metabolized in the liver, and little, if any, of these drugs are excreted unchanged in the urine. All of these agents are metabolized through the hepatic cytochrome P450 system. Rates vary from patient to patient and are age dependent, with children having shorter, and the elderly having longer elimination half-lives. Severe hepatic dysfunction can prolong the half-life and require dosing adjustments.
An important principle of the pharmacodynamic activity of these drugs is that their tissue effect is delayed relative to peak serum levels and can extend far beyond the life of the drug in the serum. For example, hydroxyzine can suppress histamine-induced wheal and flare for as long as 60 h despite maintaining a negligible serum concentration at this time.
Table Characteristics of Representative First-Generation H1 Antagonists Based Upon Chemical Classification
antimuscarinic effects. Can be potent sedatives, but sedative potential
varies, with clemastine producing the least amount. Low incidence of
gastrointestinal side effects. Can have some anti-motion sickness activity.
Diphenhydramine and clemastine both available over the counter.
moderate incidence of drowsiness.
anticholinergic effect. No antiemetic or antimotion sickness activity. Little
gastrointestinal side effects. All available over the counter. Occasional
paradoxical central nervous system stimulation, especially in children.
moderate sedation. Slight anticholinergic effect. Some local anesthetic
is sold over
the counter and is the oldest antihistamine preparation available today. As a
group, may have more frequent gastrointestinal side effects.
has highest sedative activity in group. Meclizine and cyclizine relatively
low sedative activity with main use being for vertigo, anti-motion sickness,
and antiemetic activity. Hydroxyzine has significant anticholinergic
moderate sedation. Little anticholinergic activity, antiemetic activity, and
anti-motion sickness activity. Cyproheptadine has potent antiserotonin
effect. As a class, has relatively high incidence of paradoxical central
nervous system stimulatory activity.
sedating. Strong antiemetic,
activity. Main clinical use is as
The tissue effect, however, is delayed compared to peak serum concentrations. For example, with hydroxyzine, maximal suppression of wheal and flare does not occur until 7 h after peak serum concentrations have been achieved. Based on these pharmacody-namic observations, it can be concluded that it is best to administer H1 antagonists before allergen exposure.
Table Pharmacokinetic and Pharmacodynamic Characteristics of Selected First-Generation H1 Antagonists
at which peak serum oncentration is reached
after oral dose (h)
Approximate half-life (h)
Approximate duration of biological activity
(suppression wheat and flare)
Route of metabolism
First-generation antihistamines have a number of pharmacological activities unrelated to their antihistaminic properties. They can exert antimuscarinic, anti-aadrenergic, antidopaminergic, antiserotonergic, local anesthetic, antiemetic, and anti-motion sickness activity.
By far the most common significant side effect of first-generation antihistamines is drowsiness. All first-generation antihistamines cross the blood-brain barrier. The exact mechanism of production of drowsiness by these drugs is unknown, but may include antihistaminic, anticholinergic, antiserotonergic, and antiadrenergic activities. It should be noted that the antihistaminic activity does not necessarily correlate with the sedative potential, suggesting that this is not the sole cause of this side effect. The degree of sedation depends on many factors, including age, the pattern and quality of nocturnal sleep, and concurrent medication. First-generation antihistamines clearly potentiate the activity of other sedative drugs such as alcohol.
Of importance is the fact that the subjective degree of drowsiness does not necessarily correlate with the objective measurement of central nervous system impairment. For example, drowsiness can occur without impairment and impairment without drowsiness. Although drowsiness can be overcome by the exertion of will, impairment of cognitive functions and psychomotor performance cannot, and will persist until the effect of the drug abates.
Paradoxical central nervous system stimulation can occur in some individuals, especially children. Other central nervous system side effects include dizziness, tinnitus, blurred vision, and tremors.
The next most common group of side effects produced by first-generation antihistaminics relate to their antimuscarinic activity. These include dryness of the mouth, urinary retention, blurring of vision, difficulty urinating, and constipation.
Other side effects are uncommon and include loss of appetite, nausea, abdominal pain, and diarrhea. Drug allergy to first-generation antihistamines is extremely rare but has been reported. Leukopenia, agranulocytosis, and hemolytic anemia have all been seen. Teratogenic effects have been noted in animals, but there has been no documentation of this in human beings.
Limitations to the use of the first-generation antihistamines result from their side effects, including sedation, dry mouth, urinary hesitancy, and, in children, paradoxical central nervous system stimulation.
May 6, 2011 – 8:59 am
Antihistamines have been employed in the treatment of allergic rhinitis since the discovery of the first histamine receptor antagonists in 1937. First-generation antihistamines — including diphenhydramine (Pfizer’s Benadryl, generics), chlorpheniramine (Schering-Plough’s Chlor-Trimeton, generics), and brompheniramine maleate (Wyeth’s Dimetane, generics) — are very effective in treating many common allergic rhinitis symptoms (e.g., rhinorrhea, sneezing, itchy nose, itchy eyes). However, first-generation antihistamines are highly lipophilic and can readily cross the blood-brain barrier. Once they penetrate the CNS, first-generation antihistamines bind H1 receptors, as well as cholinergic, dopamin-ergic, and serotonergic receptors, in the brain. This action triggers undesirable and troublesome CNS side effects, including fatigue, drowsiness, performance impairment, and anticholinergic effects (e.g., dryness of the mouth and eyes, constipation, increased ocular pressure).
Since 1981, numerous second-generation antihistamines (e.g., fexofenadine [Sanofi-Aventis’ Allegra / Telfast], cetirizine [Pfizer / UCB / Daiichi / / Sumitomo’s Zyrtec / Virlix / Cirrus, generics], desloratadine [Schering-Plough’s Clarinex / Aerius / Neoclarityn], levocetirizine (UCB’s Xyzal / Xusal]) have entered the market, and these agents have all but replaced first-generation antihistamines in the prescription allergic rhinitis market. Second-generation antihistamines are equally effective in controlling the common symptoms of allergic rhinitis, but they offer numerous advantages over their predecessors. Because second-generation antihistamines are larger molecules, possess a different ionic charge, and are more lipophobic than the first-generation agents, they do not cross the blood-brain barrier as readily as the original antihistamines. Thus, they lack the unwanted CNS effects of the first-generation agents. Additionally, second-generation antihistamines are highly specific for histamine H1 receptors, with little affinity for cholinergic, dopaminergic, and serotonergic receptors. As a result, they cause mild or no sedation, do not affect performance, and have no anticholinergic effects.
The discussion here focuses on four of the top-selling second-generation antihistamines — fexofenadine, cetirizine, desloratadine, and levocetirizine — as representatives of this crowded class. These four antihistamines offer comparable efficacy. Some of the product characteristics that differ between agents include the following: indications and age of patients for which each drug is approved; formulations in which the drug is available; and the potential to cause sedation.
There are four types of histamine receptors in the human body — H1, H2, H3, and H4 — although H1 is the receptor through which histamine exerts most of its effects in allergic disease. The H1 receptor demonstrates constitutive activity in the human body — even in the absence of ligand binding — because two states of the H1 receptor (the active state and the inactive state) exist in equilibrium. Histamine preferentially binds to the active form of the receptor, shifting the balance between the two receptor states toward the active form. The active form of the receptor then initiates a G protein-mediated signal transduction cascade that results in the degranulation of FceRI+ cells. Antihistamines bind to the inactive form of the H1 receptor and stabilize this conformation, thereby inhibiting the signal transduction cascade that ultimately results in degranulation of mast cells and basophils. H1 antihistamines, previously viewed as H1 receptor antagonists, have been reclassified as inverse agonists owing to enhanced understanding of their molecular pharmacology.
The degranulation of mast cells and basophils initiates a host of physiological changes leading to allergic rhinitis’s early-phase symptoms (e.g., sneezing, itching, rhinor-rhea, ocular irritation). However, antihistamines are less effective at controlling nasal congestion, as histamine is not the primary mediator of this symptom. Instead, mediators such as kinins, prostaglandins, leukotrienes, and, in the late-phase allergic response, leukocyte infiltration are more intimately involved in nasal congestion.
Numerous in vitro and in vivo studies have shown that antihistamines possess a range of anti-inflammatory properties, including down-regulation of adhesion protein expression, inhibition of eosinophil and other inflammatory cell migration
and activation, and inhibition of the generation and activity of various proinfiammatory cytokines and mediators. However, further studies are needed to determine the clinical relevance of these anti-inflammatory effects in allergic rhinitis patients during natural exposure to allergens at typical therapeutic doses of oral antihistamines.
Most second-generation antihistamines are delivered orally; the exceptions are azelastine (MedPointe’s Astelin, Viatris’ Allergodil / Rhinolast / Afluon) and levocabastine (Janssen Cilag’s [a Johnson & Johnson subsidiary] Livostin), which are administered intranasally. Because of patient preference for oral formulations, azelastine and levocabastine are used far less frequently than oral antihistamines for the treatment of allergic rhinitis.
April 13, 2011 – 6:08 am
Immediate and delayed reactions to airborne allergens, beginning with
the generation and presence of specific antigen-responsive IgE antibody
receptors on mast cells of the nasal mucosa
• An antigen-antibody chemical union initiates a cascade of events in
the mast cell culminating in its degranulation and production of a
melange of inflammatory mediators including histamine, heparin,
leukotrienes, prostaglandins, proteases and platelet activating factor
• An immediate symptomatic response occurs followed by a more
prolonged, persistent late phase reaction. This involves the
infiltration into the reactive region of eosinophils, neutrophils,
basophils and mononuclear cells
• May be seasonal or perennial depending on climate and individual response and the offending antigens
• Seasonal responses usually to grasses, trees and weeds
• Perennial responses usually house dust mites, mold antigens and animal body products
System(s) affected: Pulmonary, Skin/Exocrine, Hemic/Lymphatic/lmmunologic
Genetics: Complex, but strong genetic determination present
Incidence/Prevalence in USA: 10-25% of the population affected
• Onset usually in first 4 decades with declining tendency with advancing age
• Mean age onset approximately 10 years
Predominant sex: Male = Female
• Nasal stuffiness and congestion
• Rhinorrhea usually clear
• Pruritus of nose, eyes and palate
• Sneezing, often paroxysmal
• Injection and watering of eyes
• Postnasal drainage
• Mouth breathing
• Fatigue or malaise
• Dark circles under eyes, “allergic shiners”
• Transverse nasal crease from rubbing nose upwards
• Inhalant allergens:
– Perennial: house dust mites, molds, animal dander.
– Seasonal: tree, grass and weed pollens
– Occupational: latex, plant products (such as baking flour), sensitizing chemicals
• Family history
• Repeated exposure to offending antigen
• Exposure to multiple offending allergens
• Presence of other allergies, e.g., atopic dermatitis, asthma, urticaria
• Non-compliance to appropriate therapeutic measures
• Nonallergic rhinitis with eosinophilia syndrome (NA-RES)
• Vasomotor rhinitis
• Chronic sinusitis
• IgA deficiency with recurrent sinusitis
• Nasal polyps and tumor
• Reactive rhinitis of recumbency
• Cribriform plate defect with cerebrospinal fluid leakage (rule out by testing watery discharge for sugar)
• Foreign body
• Hormonal: pregnancy, thyroid disorder, oral contraceptives
– Rebound effect associated with continued use of topical decongestant drops and sprays
– Aldosterone converting enzyme inhibitors
– Chronic aspirin use
• Septal/anatomical obstruction
• Chronic rhinitis digitorum
• CBC with differential. May have slight increase in eosinophils but often normal with uncomplicated rhinitis.
• Nasal probe smear with cytologic exam for eosinophils
• Increase IgE level. Determine specific allergen sensitivity with allergen skin testing or RAST.
Drugs that may alter lab results:
• Corticosteroids will ablate eosinophilia
Disorders that may alter lab results:
• Secondary infections may alter differential and decrease nasal eosinophils
• Parasitic infestations with more marked eosinophilia
• Nasal washing/scraping
– Eosinophils predominate
– May see mast cells
• Nasal mucosa
– Submucosal edema but intact without evidence of destruction
– Eosinophilic infiltration
– Granulocytes to lesser extent
– Increased amount of tissue waterwith poor staining of ground substance
– Congested mucous glands and goblet cells
• Skin tests using suspected antigens. Either technique manifests a
positive reaction by inducing an expanding wheal and flare reaction.
Special training recommended and available treatment for anaphylaxis
– Prick or puncture: a superficial injury to the epidermis with application of diluted test antigen
– Intradermal: Introduction of diluted material between layers of skin raising a 4 mm wheal using a 25 or 27 gauge needle
• Radioallergosorbent test (RAST)
– More expensive and used especially in cases where skin testing not practical, e.g., in atopic dermatitis and dermatographia
– For deficits and baseline evaluation
– Rhinoscopy: particularly useful to visualize intra-nasal anatomy,
posterior pharyngeal structures including adenoids and larynx
Sinus radiographs when indicated. Check for complete opacity, fluid
level and mucosal thickening. Sinus imaging using CT may be preferable.
Appropriate diagnostic prick test kits available.
Appropriate Health Care
• Patient education, assurance and understanding important
• Limit exposure to offending allergen
• Try to establish specific cause(s) — history and appropriate skin testing
• Intensity of treatment determined by severity of disease
• Allergen immunotherapy (allergy shots/desensitization)
– Usually reserved for seasonal allergies uncontrollable with drugs and not responding to environmental adjustment.
– Specific allergen extract is injected subcutaneously in increasing doses to patient tolerance as determined by local reaction
– Patient response should be evaluated each season or year
Septoplasty when deviation significant enough to interfere with benefits of medication.
No specific restrictions. Emphasize avoiding activity in areas of allergen exposure.
No special diet unless concomitant food reactions suspected and evaluated
Drug(s) of Choice
Most patients present because of inability to control symptoms with
avoidance of allergens or with over the counter medications.
Antihistamines (second generation have a favorable side effects profile)
are considered first line therapy for most patients. Topical nasal
corticosteroids are usually considered second line therapy, but should
be used in patients with more severe nasal symptoms. Consider allergen
immunotherapy when usual pharmaceutical therapy fails or in patients
with comorbidities or complications. Cromolyn is sometimes surprisingly
helpful but a patient may have already tried this OTC agent.
• Antihistamines (H1 antagonists):
– First generation: side effects include sedation, performance impairment, anticholinergic effects. Includes 5 major classes:
• Ethanolamines — diphenhydramine (Benadryl), clemastine (Tavist)
• Alkylamine — chlorpheniramine, brompheniramine
• Ethylenediamines — tripelennamine (PBZ)
• Piperazines — hydroxyzine (Atarax)
• Phenothiazines — promethazine (Phenergan), methdilazine (Tacaryl)
– Second generation (considered non-sedating)
• Loratadine (Claritin)
• Desloratadine (Clarinex)
• Fexofenadine (Allegra)
• Cetirizine (Zyrtec)
– Intranasal: azelastine (Astelin)
– Oral, e.g., pseudoephedrine
– Topical drops or sprays, e.g., phenylephrine
– Topical ophthalmic for annoying conjunctival itching
• Mast cell stabilizers
– Cromolyn (Nasalcrom)
– Olopatadine (Patanol), cromolyn (Opticrom); topical ophthalmics for conjunctival itching
• Leukotriene antagonist
– Montelukast (Singulair)
• Beclomethasone (Beconase AQ, Vancenase AQ)
• Flunisolide (Nasalide, Nasarel)
• Triamcinolone (Nasacort)
• Budesonide (Rhinocort)
• Mometasone (Nasonex)
– Fluticasone (Flonase)
– Systemic. Only in urgent, selected cases and only for short-term use.
• Physiologic saline solution may be comforting
• Antihistamines may precipitate urinary retention in males with prostatism and/or hypertrophy
• Decongestants if congestion is a “rebound” phenomenon
• Discourage decongestants if hypertension a problem
• The elderly often require less aggressive treatment and will more frequently present with non-allergic rhinitis
• Warn patients that first generation antihistamines are associated with somnolence and may impair performance
Significant possible interactions: Refer carefully to manufacturer’s literature for interactions
Combinations with decongestants
• Initiate patient education, supplementing with available videotapes and/or literature
• Avoidance — most patients with inhalant allergy have problems controlling their symptoms totally with allergen avoidance
• Air conditioning and limited outside exposure during season helpful
• Instructions as to the best housekeeping tactics and control for dust mites in patients sensitive to this allergen helpful
• Exposure to all animal contacts minimized. Discourage house pets.
• Avoid environmental irritants, e.g., smoke and fumes
• Air cleaners
• Use of allergy control covers especially on mattresses and pillows
• Secondary infection
• Otitis media
• Nasopharyngeal lymphoid hyperplasia
• Decreased pulmonary function
• Continue to suspect effects of medications
• Facial changes
• Maximal, beneficially acceptable control of symptoms should be the goal
• Treatment tailored to each individual case.
• Immune system changes overtime often associated with lessening of
symptoms of allergic rhinitis. Therefore early, adequate control
• Other IgE mediated conditions, e.g., asthma and atopic dermatitis
• Consider allergy as principle cause of persistent rhinitis
• Family understanding and involvement important
• Environmental control requires a cooperative effort and may include
carpet and drape removal, removal of house plants, pet control, etc.
• Increased medication side effects
• Number and specific types of allergens causing symptoms may change
• Symptoms may decrease by 4th-5th decade (not a hard rule)
Physiological changes of pregnancy may aggravate all types of
rhinitis including allergic, vasomotor, nonallergic rhinitis with
eosinophilia and chronic irritable airways
• Hay fever
• IgE mediated rhinitis
International Classification of Diseases
477.9 Allergic rhinitis, cause unspecified
April 13, 2011 – 5:34 am
(Bidhist tablets, extended-release 6 mg (as maleate))
Brompheniramine competitively antagonizes histamine at H1-receptor
sites. It is indicated in the relief of sneezing, itchy and watery eyes,
itchy nose or throat, and runny nose because of hay fever (allergic
rhinitis) or other respiratory allergies. VaZol is also indicated for
temporary relief of runny nose and sneezing caused by the common cold;
and treatment of allergic and nonallergic pruritic symptoms.
Brompheniramine is an alkylamine antihistaminic (H1-receptor
antagonist) agent used in allergic symptoms of rhinitis (4 to 8 mg p.o.
t.i.d.). Brompheniramine is absorbed well from the gastrointestinal
tract, exerts its effects in 15 to 30 minutes, and the peak of action is
seen in 2 to 5 hours. It is extensively (95%) metabolized in the liver,
and 5% of it is excreted unchanged by the kidneys. Clinical
manifestations of overdose may include either those of CNS depression
(sedation, reduced mental alertness, apnea, and cardiovascular collapse)
or of CNS stimulation (insomnia, hallucinations, tremors, or
convulsions). Anticholinergic symptoms, such as dry mouth, flushed skin,
fixed and dilated pupils, and GI symptoms, are common, especially in
children. Monoamine oxidase inhibitors inhibit the metabolism of
brompheniramine, prolonging its effects. Because brompheniramine has
strong anticholinergic effects, it should be used cautiously in patients
with narrow-angle glaucoma, or in those with pyloroduodenal obstruction
or urinary bladder obstruction from prostatic hypertrophy or narrowing
of the bladder neck.
(Lodrane liquid 4 mg brompheniramine / 60 mg pseudoephedrine, Lodrane 12 D tablets 6 mg)
The combination is a respiratory agent. Brompheniramine: competitively antagonizes histamine at H1-receptor sites. Pseudoephedrine: causes
vasoconstriction and subsequent shrinkage of nasal mucous membranes by
alpha-adrenergic stimulation, which promotes nasal drainage. They are
indicated in temporary relief of symptoms associated with seasonal and
perennial allergic rhinitis and vasomotor rhinitis, including nasal
(Rondec-DM liquid 4 mg brompheniramine, 45 mg pseudoephedrine, 15 mg dextromethorphan)
Brompheniramine: competitively antagonizes histamine at H1-receptor sites.
Pseudoephedrine: Causes vasoconstriction and
subsequent shrinkage of nasal mucous membranes by alpha-adrenergic
stimulation, which promotes nasal drainage.
Dextromethorphan: Suppresses cough by central action on the cough center in medulla.
The combination is recommended for the relief of cough and upper
respiratory tract symptoms (including nasal congestion) associated with
allergy or common cold.
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