II. Indications
- Allergic Rhinitis
- Antiemetic
- Anaphylaxis (adjunct)
- Allergic Reaction
- Acute Urticaria
- Chronic Urticaria
- Antitussive (Cough Suppression)
- Drug-Induced Parkinsonism
- Anti-pruritic
- Suppresses itching, and reduces lesions
- Does not completely eradicate
- Hydroxyzine (Atarax) is most potent Antihistamine for Pruritus
-
Insomnia
- Not recommended (On Beers List, risk of Akathisia)
III. Mechanism
- See Histamine
- H1 Blockers
- First Generation Antihistamine have more potent Anticholinergic activity (sedation, Dry Mouth)
- Second Generation Antihistamines (e.g. Fexofenadine) are labeled as Non-Sedating Antihistamines
-
H2 Blockers (e.g. Cimetidine) are also Antihistamines
- Although primarily active in suppressing acid secretion from the Stomach, H2 Blockers have some H1 activity
-
Vertigo Management agents are also Antihistamines
- See Meclizine
- See Dimenhydrinate
-
Phenothiazines are also Antihistamines
- Antiemetics (e.g. Promethazine)
- Antipsychotics
IV. Types: Antihistamines (H1 Antagonists)
-
Ethanolamines (high Anticholinergic activity)
- Clemastine (Tavist)
- Carbinoxamine
- Dimenhydrinate (Dramamine)
- Diphenhydramine (Benadryl)
- Doxylamine (Unisom)
- Alkylamines (moderate Anticholinergic activity, low to moderate sedation)
- Brompheniramine (Dimetane, found mostly in combination products including Dimetapp)
- Chlorpheniramine (Chlor-Trimeton)
- Dexchlorpheniramine (Polaramine, Polmon)
-
Phenothiazine: Piperidines (moderate Anticholinergic activity, low to moderate sedation)
- Cyproheptadine (Periactin)
- Loratadine (Claritin) and its active isomer Desloratadine (Clarinex)
- Fexofenadine (Allegra)
-
Phenothiazine: Piperazines (moderate Anticholinergic activity, low to moderate sedation)
- Hydroxyzine (and its active metabolites, Cetirizine and Levocetirizine)
- Meclizine (Antivert)
- Intranasal Antihistamines
- Azelastine (Astelin) nasal spray
- Olopatadine (Patanol)
- Ocular Antihistamine
V. Adverse Effects
- See Anticholinergic Toxicity
- Sedation, or, in children, paradoxical excitability
- Worsens Benign Prostatic Hyperplasia
- Worsens Glaucoma
- Dizziness
- Respiratory depression
- Tachycardia
- Seizures
-
QTc Prolongation (and Torsades de Pointes)
- Especially with Hydroxyzine
-
Anticholinergic Symptoms
- Delirium (elderly)
- Hallucinations
- Blurred Vision
- Agitation
VI. Medications: First Generation Antihistamines (Sedating Antihistamines)
- See Meclizine
- See Dimenhydrinate
- See Doxylamine
-
Carbinoxamine (Palgic, Ryvent, pregnancy category C) - Regular Release Formulation
- Adult: 4 to 8 mg orally three to four times daily
- Child age 2 to 3 years: 2 mg orally three to four times daily
- Child age 3 to 6 years: 2 to 4 mg orally three to four times daily
- Child age 2 to 3 years: 4 to 6 mg orally three to four times daily
-
Chlorpheniramine (Chlor-Trimeton, Pregnancy Category B, approved for age over 6 years)
- Dosing: Regular Release Formulation
- Adult (age >=12 years): 4 mg orally every 4 to 6 hours
- Child (age 6 to 11 years): 2 mg orally every 4 to 6 hours
- Child (age 2 to 5 years): 1 mg orally every 4 to 6 hours (NOT fda approved)
- Dosing: Timed Release Formulation
- Adult (age >=12 years): 8 mg orally every 8 hours OR 12 mg orally every 12 hours
- Child (age 6 to 11 years): 8 mg orally every 12 hours (NOT fda approved)
- Dosing: Regular Release Formulation
-
Clemastine (Tavist)
- Dosing: Allergic Rhinitis
- Adult (age >=12 years): 1.34 mg orally twice daily (maximum 8.04 mg/day)
- Child (age 6 to 11 years): 0.67 mg orally twice daily (maximum 4.02 mg/day)
- Dosing: Urticaria or Angioedema
- Adult (age >=12 years): 2.68 mg orally two to three times daily (maximum 8.04 mg/day)
- Child (age 6 to 11 years): 1.34 mg orally twice daily (maximum 4.02 mg/day)
- Dosing: Allergic Rhinitis
-
Cyproheptadine (Periactin)
- Dosing: Allergic Rhinitis or Urticaria
- Adult (age >14 years): Start 4 mg orally three times daily (maximum 32 mg/day)
- Child (age 7 to 14 years): Start 4 mg orally three times daily (maximum 16 mg/day)
- Child (age 2 to 6 years): Start 2 mg orally three times daily
- Dosing: Serotonin Syndrome
- See Serotonin Syndrome
- Start 12 mg orally for first dose
- Next: 2 mg orally every 2 hours until symptoms resolve
- Next 8 mg every 6 hours until syndrome completes
- Dosing: Allergic Rhinitis or Urticaria
-
Diphenhydramine (Benadryl, Pregnancy Category B, approved for age over 6 years)
- Adult (age >=12 years): 25-50 mg PO/IV/IM every 6 hours (maximum: 300 to 400 mg/day)
- Child (age <12 years): 5 mg/kg/day divided four times daily (12.5 mg/5 ml)
- Age 2 to 5 years: 6.25 mg every 4 hours as needed
- Age 6 to 12 years: 12.5 mg every 4 years as needed
-
Hydroxyzine (Atarax, Vistaril)
- Dosing: Pruritus
- Adult: 25 to 100 mg orally or IM three to four times daily as needed
- Child (age 4 to 6 years): 50 mg/day divided four times daily as needed
- Child (age >=6 years): 50 to 100 mg/day divided four times daily as needed
- Dosing: Anxiety
- Adult: 50 to 100 mg orally three to four times daily as needed
- Dosing: Pruritus
VII. Resources
- (2017) Antihistamines, LiverTox, Bethesda
VIII. References
- Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 146-7
Images: Related links to external sites (from Bing)
Related Studies
Definition (NCI) | Any agent that binds to the histamine H1 receptor, thereby antagonizing histamine mediated allergic reactions, such as bronchoconstriction, vasodilation and up-regulated capillary permeability. |
Definition (NCI_NCI-GLOSS) | A type of drug that blocks the action of histamines, which can cause fever, itching, sneezing, a runny nose, and watery eyes. Antihistamines are used to prevent fevers in patients receiving blood transfusions and to treat allergies, coughs, and colds. |
Definition (MSH) | Drugs that selectively bind to but do not activate histamine H1 receptors, thereby blocking the actions of endogenous histamine. Included here are the classical antihistaminics that antagonize or prevent the action of histamine mainly in immediate hypersensitivity. They act in the bronchi, capillaries, and some other smooth muscles, and are used to prevent or allay motion sickness, seasonal rhinitis, and allergic dermatitis and to induce somnolence. The effects of blocking central nervous system H1 receptors are not as well understood. |
Concepts | Pharmacologic Substance (T121) |
MSH | D006634 |
SnomedCT | 349955005, 373228009 |
English | Antihistaminics, H1, H1 Antihistaminics, H1 Receptor Blockaders, Histamine H1 Receptor Blockaders, Receptor Blockaders, H1, Histamine H1 Receptor Antagonists, Antagonists, Histamine H1, Antagonists, Histamine H1 Receptor, Blockaders, Histamine H1 Receptor, H1 Antagonists, Histamine, Histamine H1 Blockers, Antihistamine, Histamine H1 Antagonists, HISTAMINE RECEPTOR ANTAGONISTS H1, BLOCKADERS HISTAMINE H1 RECEP, ANTIHISTAMINICS H 01, H1 RECEPT BLOCK, HISTAMINE H1 ANTAG, HISTAMINE H1 RECEPT ANTAG, HISTAMINE ANTAGONISTS H 001, RECEPT BLOCK H1, HISTAMINE H1 RECEPT BLOCK, HISTAMINE RECEPTOR BLOCKADERS H1, HISTAMINE H1 BLOCK, ANTAG HISTAMINE H1 RECEPT, ANTAG HISTAMINE H1, H1 blockers, histamine H1 receptor blockaders, antihistaminic h1, h1 antihistamine, h1 blockers, antihistamine h1, antihistamines h1, h1 blocker, antihistamine, H1 antihistamine, H1 antihistamine (product), H1 antihistamine (substance), H-1 Receptor Antagonist, Histamine-1 Receptor Antagonist |
French | Antagonistes des récepteurs histaminergiques H1, Antihistamines H1, Antihistaminiques des récepteurs H1, Anti-histaminiques H1, Anti-histamines H1, Antihistaminiques H1, Antagonistes H1 |
Swedish | Histamin H1-blockerare |
Czech | histamin H1 - antagonisté, histaminové H1-receptory - blokátory |
Finnish | Histamiini-H1-salpaajat |
German | Antagonisten, Histamin H1-Rezeptor-, Antagonisten, Histamin H1-, Histamin-H1-Rezeptor-Antagonisten, Histamin-H1-Rezeptorblocker, H1-Rezeptorblocker, Histamin H1-Blocker, ANTIHISTAMINIKA H 01, HISTAMIN REZEPTORENBLOCKER H1, HISTAMIN REZEPTOREN ANTAGONISTEN H1, HISTAMIN ANTAGONISTEN H 001, Antihistaminika, H1-, Histamin-H1-Antagonisten |
Russian | ANTIGISTAMINNYE H1 SREDSTVA, BLOKATORY GISTAMINOVYKH H1-RETSEPTOROV, GISTAMINA H1 ANTAGONISTY, ANTIGISTAMINNYE SREDSTVA, GISTAMINOVYKH H1-RETSEPTOROV ANTAGONISTY, GISTAMINOVYKH H1-RETSEPTOROV BLOKATORY, ANTIGISTAMINNYE SREDSTVA KLASSICHESKIE, PROTIVOGISTAMINNYE SREDSTVA, АНТИГИСТАМИННЫЕ H1 СРЕДСТВА, АНТИГИСТАМИННЫЕ СРЕДСТВА, АНТИГИСТАМИННЫЕ СРЕДСТВА КЛАССИЧЕСКИЕ, БЛОКАТОРЫ ГИСТАМИНОВЫХ H1-РЕЦЕПТОРОВ, ГИСТАМИНА H1 АНТАГОНИСТЫ, ГИСТАМИНОВЫХ H1-РЕЦЕПТОРОВ АНТАГОНИСТЫ, ГИСТАМИНОВЫХ H1-РЕЦЕПТОРОВ БЛОКАТОРЫ, ПРОТИВОГИСТАМИННЫЕ СРЕДСТВА |
Japanese | 古典的抗ヒスタミン薬, ヒスタミンH1拮抗剤, ヒスタミンH1遮断薬, ヒスタミンH1受容体拮抗薬, ヒスタミンH1受容体遮断剤, 抗ヒスタミン剤H1, 古典的抗ヒスタミン剤, ヒスタミンH1受容器遮断薬, ヒスタミンH1アンタゴニスト, ヒスタミンH1受容体遮断薬, H1受容体拮抗薬, H1ブロッカー, H1受容体拮抗剤 |
Croatian | HISTAMIN H1 ANTAGONISTI |
Polish | Antagoniści histaminy H1, Leki przeciwhistaminowe H1, Antyhistaminiki H1, Leki antyhistaminowe H1, Blokery receptora H1 histaminy, Antyhistaminiki klasyczne |
Portuguese | Bloqueadores dos Receptores Histamínicos H1, Antagonistas dos Receptores H1 de Histamina, Antagonistas dos Receptores Histamínicos H1, Bloqueadores dos Receptores H1 de Histamina, Anti-Histamínicos H1 |
Spanish | Bloqueadores de los Receptores Histamínicos H1, Antagonistas de los Receptores Histamínicos H1, Bloqueadores de los Receptores H1 de Histamina, antihistamínico H1 (producto), antihistamínico H1 (sustancia), antihistamínico H1, Antagonistas del Receptor H1 de Histamina, Antihistamínicos H1 |
Italian | Antagonisti dell'istamina H1 |