chapter 37 antihistamines, decongestants, antitussives and expectorants - week 4 Flashcards
understanding common cold
- Most are caused by viral infection (rhinovirus or influenza virus).
- Virus invades tissues (mucosa) of upper respiratory tract, causing upper respiratory infection.
- Excessive mucus production results from the inflammatory response to this invasion.
- Fluid drips down the pharynx into the esophagus and lower respiratory tract, causing cold symptoms: sore throat, coughing, upset stomach.
- Irritation of nasal mucosa often triggers the sneeze reflex.
- Mucosal irritation also causes the release of several inflammatory and vasoactive substances, dilating small blood vessels in the nasal sinuses and causing nasal congestion.
treatment of common cold
- Involves combined use of antihistamines, nasal decongestants, antitussives, and expectorants
- Treatment is symptomatic only, not curative.
- Symptomatic treatment does not eliminate the causative pathogen.
- Difficult to identify whether cause is viral or bacterial
- Treatment is “empirical therapy,” treating the most likely cause
- Antivirals and antibiotics may be used, but a definite viral or bacterial cause may not be easily identified.
pediatric concerns with the common cold treatments
In 2009, Health Canada issued recommendations that over-the-counter (OTC) cough and cold products not be given to children younger than 6 years of age.
Not effective in small children, and parents are advised to consult their pediatrician on the best ways to manage these illnesses.
antihistamines
Drugs that directly compete with histamine for specific receptor sites
Histamine antagonists
H1-antagonists (or H1-blockers)
H2-antagonists (or H2 -blockers)
anaphylaxis
Release of excessive amounts of histamine can leading to:
* Constriction of smooth muscle, especially in the stomach and lungs
* Increase in body secretions
* Vasodilatation and increased capillary permeability, movement of fluid out of the blood vessels and into the tissues, and drop in blood pressure and edema
histamine
Major inflammatory mediator in many allergic disorders
* Allergic rhinitis (e.g., hay fever and mould and dust allergies)
* Anaphylaxis
* Angioedema
* Drug fevers
* Insect bite reactions
* Urticaria (pale red, raised, itchy bumps)
h1- antagonists examples and properties
chlorpheniramine, fexofenadine (Allegra®), loratadine (Claritin®), cetirizine (Reactine®), desloratadine (Aerius®), diphenhydramine (Benadryl®)
- Antihistaminic
- Anticholinergic
- Sedative
h2 blockers or h2 antagonists
Used to reduce gastric acid in peptic ulcer disease
Examples: cimetidine, ranitidine (Zantac®), famotidine (Pepcid AC®), nizatidine (Axid®)
antihistamines mechanism of action
- Block action of histamine at H1-receptor sites
- Compete with histamine for binding at unoccupied receptors
- Cannot push histamine off the receptor if already bound
- The binding of H1-blockers to the histamine receptors prevents the adverse consequences of histamine stimulation.
* Vasodilation
* Increased gastrointestinal, respiratory, salivary, and lacrimal secretions
* Increased capillary permeability with resulting edema - More effective in preventing the actions of histamine than in reversing them
- Should be given early in treatment before all the histamine binds to the receptors
Histamine Versus Antihistamine Effects (cardiovasular)
Cardiovascular (small blood vessels)
Histamine effects:
dilation and increased permeability
(allowing substances to leak into tissues)
Antihistamine effects
dilates blood vessels
increases blood vessels permeability
Histamine Versus Antihistamine Effects (smooth muscles)
Smooth muscle (on exocrine glands)
Histamine effects: stimulation of salivary, gastric, lacrimal, and bronchial secretions
Antihistamine effects: reduction of salivary, gastric, lacrimal, and bronchial secretions
Histamine Versus Antihistamine Effects (immune sysem)
Immune system (release of substances commonly associated with allergic reactions)
Histamine effects: mast cells release histamine and other substances, resulting in allergic reactions
Antihistamine effects: bind to histamine receptors, thus preventing histamine from causing a response
anit histamines indications
Management of:
Nasal allergies
Seasonal or perennial allergic rhinitis (hay fever)
Allergic reactions
Motion sickness
Parkinson’s disease
Vertigo
Sleep disorders
Also used to relieve symptoms associated with the common cold
Sneezing, runny nose
Does not cure common cold
anithistamines contraindications
- Known drug allergy
- Acute-angle glaucoma
- Cardiac disease, hypertension
- Kidney disease
- Bronchial asthma, chronic obstructive pulmonary disease (COPD)
- Not to be used as sole drug therapy during acute asthmatic attacks
- salbutamol or epinephrine
- Peptic ulcer disease
- Seizure disorders
- Benign prostatic hyperplasia
- Pregnancy
antihistamine pediatric considerations
Fexofenadine hydrochloride is not recommended for children under 6 years of age or for those with kidney impairment.
Desloratadine is not recommended for children.
Loratadine is not recommended for children younger than 2 years of age.
antihistamines adverse effects
- Anticholinergic (drying) effects: most common
- Dry mouth
- Difficulty urinating
- Constipation
- Changes in vision
- Cardiovascular, central nervous system, gastrointestinal, and other effects
- Drowsiness
- Mild drowsiness to deep sleep
two types of anti histamines
Traditional: brompheniramine, chlorpheniramine, dimenhydrinate, diphenhydramine, and promethazine
Nonsedating: loratadine, cetirizine, and fexofenadine
nonsedating antihistamines
- Developed to eliminate unwanted adverse effects, mainly sedation
- Work peripherally to block the actions of histamine; thus, fewer central nervous system adverse effects
- Longer duration of action (increases compliance with once-daily dosing)