The key difference between antihistamines and decongestants is that antihistamines inhibit histamines to alleviate allergy symptoms such as itching, sneezing, and runny nose, while decongestants narrow blood vessels in the nasal passage to reduce the swelling and congestion to relieve nasal congestion and stuffy nose.
Antihistamines and decongestants are the two main medications commonly used to treat symptoms associated with allergies, colds, and respiratory conditions. These drugs target different aspects of these conditions to offer therapeutic effects for individuals experiencing specific symptoms. Antihistamines work by inhibiting histamines. Antihistamines are available in different generations; second-generation drugs are preferred due to their reduced sedating effect. In contrast, decongestants activate the α- adrenergic receptors to narrow the blood vessels in the nasal passage reducing swelling and congestion. However, topical decongestants should be used for shorter durations due to rebound congestion and damage to the nasal cavity upon prolonged use. Understanding their mechanism of action and differences allows individuals to make informed decisions regarding their use and find effective relief.
CONTENTS
1. Overview and Key Difference
2. What are Antihistamines
3. What are Decongestants
4. Similarities – Antihistamines and Decongestants
5. Antihistamines vs Decongestants in Tabular Form
6. Summary – Antihistamines vs Decongestants
What are Antihistamines?
Antihistamines are a group of medications commonly used to treat the symptoms of histamine-mediated allergies. Histamine is an endogenous chemical messenger that acts against allergens by promoting gastric acid secretion, inflammatory responses, dilating blood vessels, and affecting muscle contraction in the intestine and lungs. Histamine promotes vascular permeability, leading fluid movement from the capillaries to surrounding tissues resulting in swelling and blood vessel dilation. There are two major classes of histamine receptors: H1 and H2 receptors. Antihistamines that target H1 receptors are primarily used to treat allergies and allergic rhinitis. H2 receptors are commonly used to treat gastrointestinal conditions such as gastroesophageal reflux disease, peptide ulcers, and gastritis.
Figure 01: Common Chemical Structure for Antihistamines
H1 blockers are further categorized into first-generation agents and second-generation agents. The first-generation H-1 antihistamines bind with central and peripheral histamine receptors and readily cross the blood-brain barrier. In contrast, second-generation H-1 antihistamines selectively bind with peripheral histamine-1 receptors and do not cross the blood-brain barrier. Examples of H1-antihistamines include diphenhydramine, cetirizine, chlorpheniramine, and cyclizine. Examples of H-2 antihistamines include cimetidine, famotidine, and nizatidine. The duration of the action of first-generation and second-generation H1-antihistamines is about 4-6 hours and 12-24 hours, respectively.
What are Decongestants?
Decongestants are prescribed to relieve the symptoms of allergies, colds, and respiratory conditions. They provide short-term relief for nasal congestion by narrowing the blood vessels in the nasal passage. The vasoconstriction of the decongestant within the nasal mucosa is attributed to the activation of alpha (α)- adrenergic receptors. However, these agents are ineffective against rhinorrhea, pruritus, or sneezing. Therefore, to improve the effectiveness of decongestants, they are frequently combined with other agents, such as antihistamines. Decongestants are available as nasal sprayers, drops, tablets or capsules, liquid or syrups, and flavored powders. The most common side effects of decongestants include insomnia, irritability, palpitations, and elevated blood pressure.
Topical intranasal decongestants are used for allergic rhinitis. They include catecholamines or imidazoline derivatives with a more rapid onset of action than systemic decongestants. However, long-term use of topical decongestants leads to withdrawal symptoms such as rebound nasal congestion. Sometimes, the prolonged use of decongestants may lead to the development of rhinitis medicamentosa, which is challenging to treat.
What are the Similarities Between Antihistamines and Decongestants?
- Antihistamines and decongestants can relieve symptoms associated with allergies, colds, and respiratory conditions.
- Both drugs are available over the counter without a prescription.
- They are commonly combined, aiming to relieve multiple symptoms simultaneously.
- Both antihistamines and decongestants offer temporary relief from symptoms rather than treating the underlying cause.
What is the Difference Between Antihistamines and Decongestants?
Antihistamines and decongestants are commonly used to treat allergies, colds, and symptoms related to respiratory conditions. However, there is a distinct difference between antihistamines and decongestants with respect to their mechanism of action, duration of use, and side effect profiles. Antihistamines work by blocking the H-1 and H-2 histamine receptors. There are two classes of antihistamines available: namely, first-generation and second-generation. First-generation drugs are associated with sedative effects. In contrast, decongestants activate the α- adrenergic receptors to narrow the blood vessels in the nasal passage with no sedative effect. However, the long-term use of topical decongestants is not recommended due to the rebound congestion and damage to the nasal cavity.
Therefore, this difference between antihistamines and decongestants should be considered carefully when deciding the right choice for managing allergy symptoms.
Below is a summary of the difference between antihistamines and decongestants in tabular form for side-by-side comparison.
Summary – Antihistamines vs Decongestants
Antihistamines and decongestants are primarily used to treat the symptoms of allergies, colds, and respiratory conditions. Antihistamines block the histamine receptors and are available as first-generation and second-generation drugs, with second-generation drugs being less sedating. In contrast, decongestants narrow the blood vessels in the nasal passage, relieving nasal congestion and stuffiness. They work by activating the α- adrenergic receptors. Decongestants can be taken orally and applied topically, but topical use should be limited to short-term use to avoid rebound congestion. Therefore, understanding the difference between antihistamines and decongestants is essential when choosing the appropriate medication for symptom relief.
Reference:
1. Church, MartinK, and DianaS Church. “Pharmacology of Antihistamines.” Indian Journal of Dermatology, vol. 58, no. 3, 2013, p. 219.
2. Taverner, David, and G. Jenny Latte. “Nasal Decongestants for the Common Cold.” Cochrane Database of Systematic Reviews, 2007.
Image Courtesy:
1. “Antihistamine” By Wolfmankurd – Inkscape (CC BY-SA 3.0) via Commons Wikimedia