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An H1 antihistamine is a histamine antagonist which serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions, through action at the H1 receptor. Only agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines - other agents may have antihistaminergic action but are not true antihistamines. Image File history File links Broom_icon. ...
A histamine antagonist is an agent which serves to inhibit the release or action of histamine. ...
This article or section does not cite any references or sources. ...
Allergy is an abnormal reaction to a substance foreign to the body that is acquired, predictable and rapid. ...
// H1 receptors Distribution Smooth muscle Endothelial cells Adrenal medulla Heart CNS Effects of Histamine at H1-receptors Vasodilation of small bloods vessels - flushing Increase Capillary Permeability - leaky endothelial cells - oedema Vasoconstriction of large vessels Contraction of smooth muscle - bronchial muscle H1-receptors Activates phospholipase C Mediated by a pertussis toxin...
In common use, the term "antihistamine" refers only to H1-receptor antagonists, also known as H1-antihistamines. It has been discovered that these H1-antihistamines are actually inverse agonists at the histamine H1-receptor, rather than antagonists per se. [1] In pharmacology, an inverse agonist is an agent which binds to the same receptor binding-site as an agonist for that receptor but exerts the opposite pharmacological effect. ...
Antagonists will block the binding of an agonist at a receptor molecule, inhibiting the signal produced by a receptor-agonist coupling. ...
Pharmacology
In allergic reactions an allergen (a type of antigen) interacts with and cross-links surface IgE antibodies on mast cells and basophils. Once the mast cell-antibody-antigen complex is formed, a complex series of events occurs that eventually leads to cell degranulation and the release of histamine (and other chemical mediators) from the mast cell or basophil. Once released, histamine can react with local or widespread tissues through histamine receptors. An allergen is any substance (antigen), most often eaten or inhaled, that is recognized by the immune system and causes an allergic reaction. ...
For the server security software, see Microsoft Forefront. ...
Each antibody binds to a specific antigen; an interaction similar to a lock and key. ...
Mast cells A mast cell (or mastocyte) is a resident cell of areolar connective tissue (loose connective tissue) that contains many granules rich in histamine and heparin. ...
Categories: Wikipedia cleanup | Biology stubs | Blood and immune system cells ...
The degranulation process in a Mast cell. ...
The histamine receptors are a class of G-protein coupled receptors with histamine as their endogenous ligand. ...
Histamine, acting on H1-receptors, produces pruritus, vasodilatation, hypotension, flushing, headache, tachycardia, bronchoconstriction, increases vascular permeability, potentiates pain, and more. [2] An itch (Latin: pruritus) is an uncomfortable sensation felt on an area of skin that causes a person or animal to desire to scratch that area. ...
Vasodilation is where blood vessels in the body become wider following the relaxation of the smooth muscle in the vessel wall. ...
In physiology and medicine, hypotension refers to an abnormally low blood pressure. ...
For a person to flush is to become markedly red in the face and often other areas of the skin, from various physiological conditions. ...
A headache (cephalalgia in medical terminology) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ...
This article or section does not cite any references or sources. ...
Bronchoconstriction is the constriction of the airways in the lungs due to the tighting of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. ...
Vascular permeability characterizes the capacity of a blood vessel wall to pass through small molecules (ions, water, nutrients) or even whole cells (lymphocytes on their way to the site of inflammation). ...
“Hurting†redirects here. ...
While H1-antihistamines help against these effects, they only work if taken before contact with the allergen. In severe allergies, such as anaphylaxis or angioedema, these effects may be so severe as to be life-threatening. Epinephrine, often in the form of an autoinjector (Epi-pen), is required by people with such hypersensitivities. Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. ...
Angioedema (BE: angiooedema), also known by its eponym Quinckes edema, is the rapid swelling (edema) of the skin, mucosa and submucosal tissues. ...
Adrenaline redirects here. ...
A 0. ...
Clinical use of antihistamines
Indications H1-antihistamines are clinically used in the treatment of histamine-mediated allergic conditions. Specifically, these indications may include: [3] Antihistamines can be administered topically (through the skin, nose, or eyes) or systemically, based on the nature of the allergic condition. Rhinitis is the medical term describing irritation and inflammation of the nose. ...
Beyond overall skin structure, refer below to: See-also. ...
Contact dermatitis is a term for a skin reaction resulting from exposure to allergens or irritants. ...
Angioedema (BE: angiooedema), also known by its eponym Quinckes edema, is the rapid swelling (edema) of the skin, mucosa and submucosal tissues. ...
An itch (Latin: pruritus) is a sensation felt on an area of skin that makes a person or animal want to scratch it. ...
Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. ...
Beyond overall skin structure, refer below to: See-also. ...
For other uses, see Nose (disambiguation). ...
For other uses, see Eye (disambiguation). ...
The authors of the American College of Chest Physicians Updates on Cough Guidelines (2006) recommend that for cough associated with the common cold, first-generation antihistamine-decongestants are more effective than newer, nonsedating antihistamines. First generation antihistamines include Diphenhydramine (Benadryl); Carbinoxamine (Clistin); Clemastine (Tavist);Chlorpheniramine (Chlor-Trimeton)and Brompheniramine (Dimetane). However, it is important to note that a 1955 study of "antihistaminic drugs for colds," carried out by the U.S. Army Medical Corps, reported that "there was no significant difference in the proportion of cures reported by patients receiving oral antihistaminic drugs and those receiving oral placebos. Furthermore, essentially the same proportion of patients reported no benefit from either type of treatment."[4] Diphenhydramine hydrochloride (trade name Benadryl, as produced by J&J, or Dimedrol outside the U.S. & Canada. ...
Adverse drug reactions Adverse drug reactions are most commonly associated with the first-generation H1-antihistamines. This is due to their relative lack of selectivity for the H1-receptor. An adverse drug reaction (abbreviated ADR) is a term to describe the unwanted, negative consequences sometimes associated with the use of medications. ...
The most common adverse effect is sedation; this "side effect" is utilized in many OTC sleeping-aid preparations. Other common adverse effects in first-generation H1-antihistamines include: dizziness, tinnitus, blurred vision, euphoria, uncoordination, anxiety, insomnia, tremor, nausea and vomiting, constipation, diarrhea, dry mouth, and dry cough. Infrequent adverse effects include: urinary retention, palpitations, hypotension, headache, hallucination, and psychosis. [3] Over-the-counter substances, also abbreviated OTC, are drugs and other medical remedies that may be sold without a prescription and without a visit to a medical professional, in contrast to prescription only medicines (POM). ...
Tinnitus (IPA pronunciation: or ,[1] from the Latin word for ringing[2]) is the perception of sound in the human ear in the absence of corresponding external sound(s). ...
Euphoria (Greek ) is a medically recognized emotional state related to happiness. ...
what up?? Anxiety is a physiological state characterized by cognitive, somatic, emotional, and behavioral components (Seligman, Walker & Rosenhan, 2001). ...
This article is about the sleeping disorder. ...
For other uses, see Nausea (disambiguation). ...
Constipation or irregularity, is a condition of the digestive system where a person (or animal) experiences hard feces that are difficult to egest; it may be extremely painful, and in severe cases (fecal impaction) lead to symptoms of bowel obstruction. ...
Types 5-7 on the Bristol Stool Chart are often associated with diarrhea Diarrhea (in American English) or diarrhoea (in British English) is a condition in which the sufferer has frequent watery, loose bowel movements (from the Greek word διάÏÏοια; literally meaning through-flowing). Acute infectious diarrhea is a common cause...
This article does not cite any references or sources. ...
In physiology and medicine, hypotension refers to an abnormally low blood pressure. ...
A headache (cephalalgia in medical terminology) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ...
A hallucination is a sensory perception experienced in the absence of an external stimulus, as distinct from an illusion, which is a misperception of an external stimulus. ...
Psychosis is a generic psychiatric term for a mental state often described as involving a loss of contact with reality. Stedmans Medical Dictionary defines psychosis as a severe mental disorder, with or without organic damage, characterized by derangement of personality and loss of contact with reality and causing deterioration...
The newer second-generation H1-antihistamines are far more selective for peripheral histamine H1-receptors and, correspondingly, have a far improved tolerability profile compared to the first-generation agents. The most common adverse effects noted for second-generation agents include: drowsiness, fatigue, headache, nausea and dry mouth. [3]
First-generation (non-selective, classical) These are the oldest antihistaminergic drugs and are relatively inexpensive and widely available. They are effective in the relief of allergic symptoms, but are typically moderately to highly potent muscarinic acetylcholine receptor-antagonists (anticholinergic) agents as well. These agents also commonly have action at α-adrenergic receptors and/or 5-HT receptors. This lack of receptor-selectivity is the basis of the poor tolerability-profile of some of these agents, especially compared with the second-generation H1-antihistamines. Patient response and occurrence of adverse drug reactions vary greatly between classes and between agents within classes. An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of the neurotransmitter acetylcholine. ...
An anticholinergic agent is a member of a class of pharmaceutical compounds which serve to reduce the effects mediated by acetylcholine in the central nervous system and peripheral nervous system. ...
Epinephrine Norepinephrine The adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines. ...
In the field of neurochemistry, 5-HT receptors are receptors for the neurotransmitter and peripheral signal mediator serotonin, also known as 5-hydroxytryptamine or 5-HT. 5-HT receptors are located on the cell membrane of nerve cells and other cell types in animals and mediate the effects of serotonin...
Classes The first H1-antihistamine discovered was piperoxan, by Jeff Forneau and Daniel Bovet (1933) in their efforts to develop a guinea pig animal-model for anaphylaxis at Ryerson University.[5] Bovet went on to win the 1957 Nobel Prize in Physiology or Medicine for his contribution. Following their discovery, the first-generation H1-antihistamines were developed in the following decades. They can be classified on the basis of chemical structure, and agents within these groups have similar properties. Daniel Bovet (March 23, 1907 – April 8, 1992) was a Swiss-born Italian pharmacologist who won the 1957 Nobel Prize in Physiology or Medicine for his discovery of drugs that block the actions of specific neurotransmitters. ...
This article is about the species Cavia porcellus. ...
Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. ...
Ryerson University is a public university located in downtown Toronto, Canada. ...
Emil Adolf von Behring was the first person to receive the Nobel Prize in physiology or Medicine, for his work on the treatment of diphtheria. ...
| Class | Description | Examples | | Ethylenediamines | Ethylenediamines were the first group of clinically-effective H1-antihistamines developed. | | | Ethanolamines | Diphenhydramine was the prototypical agent in this group. Significant anticholinergic adverse effects, as well as sedation, are observed in this group but the incidence of gastrointestinal adverse effects is relatively low. [3] [6] | | | Alkylamines | The isomerism is a significant factor in the activity of the agents in this group. E-triprolidine, for example, is 1000-fold more potent than Z-triprolidine. This difference relates to the positioning and fit of the molecules in the histamine H1-receptor binding site. [6] Alkylamines are considered to have relatively fewer sedative and gastrointestinal adverse effects, but relatively greater incidence of paradoxical CNS stimulation. [3] | | | Piperazines | These compounds are structurally-related to the ethylenediamines and the ethanolamines; and produce significant anticholinergic adverse effects. Compounds from this group are often used for motion sickness, vertigo, nausea and vomiting. The second-generation H1-antihistamine cetirizine also belongs to this chemical group. [6] | | | Tricyclics and Tetracyclics | These compounds differ from the phenothiazine antipsychotics in the ring-substitution and chain characteristics. (Nelson, 2002) They are also structurally-related to the tricyclic antidepressants (and tetracyclics), explaining the antihistaminergic adverse effects of those three drug classes and also the poor tolerability profile of tricyclic H1-antihistamines. The second-generation H1-antihistamine loratadine was derived from compounds in this group. | | Mepyramine[1] is a first generation antihistamine. ...
Antazoline is an antihistamine used to relieve nasal congestion and in eye drops, usually in combination with naphazoline, to relieve the symptoms of allergic conjunctivitis. ...
An anticholinergic agent is a member of a class of pharmaceutical compounds which serve to reduce the effects mediated by acetylcholine in the central nervous system and peripheral nervous system. ...
Diphenhydramine hydrochloride (trade name Benadryl, as produced by J&J, or Dimedrol outside the U.S. & Canada. ...
Carbinoxamine is an antihistamine. ...
This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ...
Clemastine is an over-the-counter antihistamine sold in the United States under the name Tavist. ...
This article does not cite any references or sources. ...
In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bonds between atoms, but in which the atoms are arranged differently (analogous to a chemical anagram). ...
A diagram showing the CNS: 1. ...
Pheniramine maleate is an antihistamine used to treat allergic conditions such as hay fever or urticaria. ...
Chlorphenamine (INN) or chlorpheniramine (USAN, former BAN), commonly marketed as its salt chlorphenamine maleate (CPM), is first-generation antihistamine used in the prevention of the symptoms of allergic conditions such as rhinitis and urticaria. ...
Dexchlorpheniramine maleate (Polaramine®, Schering) is an antihistamine used to treat allergic conditions such as hay fever or urticaria. ...
Categories: Stub | Antihistamines ...
Triprolidine hydrochloride is an over-the-counter antihistamine. ...
An anticholinergic agent is a member of a class of pharmaceutical compounds which serve to reduce the effects mediated by acetylcholine in the central nervous system and peripheral nervous system. ...
Cetirizine hydrochloride (IPA sɛ.ˈtɪɹ.ɪ.ˌzin) is a major metabolite of hydroxyzine, and a racemic selective H1 receptor antagonist used in the treatment of allergies, hay fever, angioedema, and urticaria. ...
Cyclizine is an antihistamine drug used to treat nausea, vomiting and dizziness associated with motion sickness, vertigo and post-operative following administration of general anaesthesia and opioids. ...
This article belongs in one or more categories. ...
Hydroxyzine is a piperazine derivative that is used as an antihistamine (especially for itches), anti-emetic (nausea reducing), and anxiolytic (anxiety reducing) drug. ...
Meclizine (proposed INN is meclozine) is an antihistamine, considered to be an antiemetic. ...
Phenothiazines are the largest of the 5 main classes of antipsychotic drugs. ...
The term antipsychotic is applied to a group of drugs used to treat psychosis. ...
Chemical structure of the tricyclic antidepressant amitriptyline. ...
There are also several chemically unrelated tetracyclic antibiotics based on Tetracycline. ...
Promethazine is a first-generation H1 receptor antagonist antihistamine and antiemetic medication. ...
Alimemazine (INN), also known as trimeprazine (former BAN and USAN; trade names Nedeltran, Panectyl, Repeltin, Therafene, Theralen, Theralene, Vallergan, Vanectyl, or Temaril), commonly provided as a tartrate salt, is a phenothiazine derivative that is used as an antipruritic (it prevents itching from causes such as eczema or poison ivy, by...
Cyproheptadine (usually as cyproheptadine hydrochloride, trade name Periactin) is an antihistaminic and antiserotonergic agent. ...
Azatadine is an antihistamine. ...
Ketotifen fumarate (Zaditor®) is an H1-antihistamine available in two forms. ...
Common structural features - Two aromatic rings, connected to a central carbon, nitrogen or CO
- Spacer between the central X and the amine, usually 2-3 carbons in length, linear, ring, branched, saturated or unsaturated
- Amine is substituted with small alkyl groups eg CH3
X = N, R1 = R2 = small alkyl groups
X = C
X = CO Image File history File links Antihistamine. ...
- Chirality at X can increase both the potency and selectivity for H1-receptors
- For maximum potency, the two aromatic rings should be orientated in different planes.
- for example, tricyclic ring system is slightly puckered and the two aromatic rings lie in different geometrical planes, giving the drug a very high potency.
Second-generation and third-generation (selective, non-sedating) Second generation antihistamines are newer drugs that are much more selective for peripheral H1 receptors in preference to the central nervous system histaminergic and cholinergic receptors. This selectivity significantly reduces the occurrence of adverse drug reactions compared with first-generation agents, while still providing effective relief of allergic conditions. A diagram showing the CNS: 1. ...
Third generation antihistamines are the active enantiomer (levocetirizine) or metabolite (desloratadine & fexofenadine) derivatives of second-generation drugs intended to have increased efficacy with fewer adverse drug reactions. Indeed, fexofenadine is associated with a decreased risk of cardiac arrhythmia compared to terfenadine. However, there is little evidence for any advantage of levocetirizine or desloratadine, compared to cetirizine or loratadine respectively. In chemistry, enantiomers (from the Greek á¼Î½Î¬Î½Ï„ιος, opposite, and μÎÏος, part or portion) are stereoisomers that are nonsuperimposable complete mirror images of each other, much as ones left and right hands are the same but opposite. ...
A metabolite is the product of metabolism. ...
Efficacy is the ability to produce a desired amount of a desired effect. ...
An adverse drug reaction (abbreviated ADR) is a term to describe the unwanted, negative consequences sometimes associated with the use of medications. ...
Cardiac arrhythmia is any of a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal. ...
Cetirizine hydrochloride (IPA sɛ.ˈtɪɹ.ɪ.ˌzin) is a major metabolite of hydroxyzine, and a racemic selective H1 receptor antagonist used in the treatment of allergies, hay fever, angioedema, and urticaria. ...
Loratadine is a drug used to treat allergies. ...
Systemic, second-generation Acrivastine is a medication used for the treatment of allergies and hay fever. ...
Astemizole is a second generation antihistamine that has a long duration of action. ...
Cetirizine hydrochloride (IPA sɛ.ˈtɪɹ.ɪ.ˌzin) is a major metabolite of hydroxyzine, and a racemic selective H1 receptor antagonist used in the treatment of allergies, hay fever, angioedema, and urticaria. ...
Loratadine is a drug used to treat allergies. ...
Mizolastine is an antihistamine. ...
Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. ...
Cardiac arrhythmia is any of a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal. ...
Fexofenadine hydrochloride (brand names include Allegra® and Telfast®) is an antihistamine drug used in the treatment of hayfever and similar allergy symptoms. ...
Topical, second-generation Azelastine hydrochloride is an antihistamine and mast cell stabilizer available as a nasal spray (Astelin®) for hay fever and as eye drops (Optilar®) for allergic conjunctivitis. ...
Levocabastine is a selective second-generation H1-receptor antagonist used for allergic conjunctivitis. ...
Olopatadine hydrochloride is an antihistamine and mast cell stabilizer, usually sold as a prescription eye drop (0. ...
Systemic, third generation Xyzal Levocetirizine (as levocetirizine dihydrochloride) is a third generation non-sedative antihistamine, developed from the second generation antihistamine cetirizine. ...
Desloratadine is a drug used to treat allergies. ...
Fexofenadine hydrochloride (brand names include Allegra® and Telfast®) is an antihistamine drug used in the treatment of hayfever and similar allergy symptoms. ...
Common structural features Structure of these drugs varies from case to case. There are no common structural features.
References - ^ Leurs R, Church MK, Taglialatela M (2002). "H1-antihistamines: inverse agonism, anti-inflammatory actions and cardiac effects". Clin Exp Allergy 32 (4): 489-98. PMID 11972592.
- ^ Simons FE (2004, Nov 18). "Advances in H1-antihistamines". N Engl J Med 351 (21): 2203-17. PMID 15548781 Abstract.
- ^ a b c d e Rossi S (Ed.) (2004). Australian Medicines Handbook 2004. Adelaide: Australian Medicines Handbook. ISBN 0-9578521-4-2
- ^ Hoagland, R.J., Deitz, E.N., Myers, P.W., Cosand, H.C., "Antihistaminic drugs for colds: Evaluation Based on a Controlled Study." Journal of the American Medical Association 143(2), pp. 157-160
- ^ Forneau E, Bovet D (1933). Recherches sur l'action sympathicolytique d'un nouveau derive du dioxane. Arch Int Pharmacodyn 46, 178-91.
- ^ a b c Nelson, WL (2002). In Williams DA, Lemke TL (Eds.). Foye's Principles of Medicinal Chemistry (5 ed.). Philadelphia: Lippincott Williams & Wilkins. ISBN 0-683-30737-1
The Australian Medicines Handbook or AMH is a medical reference text commonly used in practice by health professionals (particularly general practitioners and pharmacists) in Australia. ...
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