Antihistamines

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Antihistamines

• Serotonin Agonists

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Histamine Antagonists

• H 1 receptors
• inhibit smooth muscle contraction
• decrease wheal, flare,and itch
• decrease secretions salivary and lachrymal
• CNS sedation

• H 2 receptors
• inhibit gastric acid secretion
• decrease content and volume of gastric juice
• fasting, food stimulated and nocturnal

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H 1 antagonists

• Relief of manifestations of immediate-type
  hypersensitivity reactions
• allergic rhinitis
• cold remedies
• newer agents selective for peripheral H 1
  receptors
• less sedation (dose dependant)

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Antihistamine Products

• sedating
• diphenhydramine (Benadryl)
• chlorpheniramine (Chlor-Trimeton)

• non-sedating
• fexofenadine (Allegra)
• loratadine (Claritin)
• cetirizine (Zyrtec)
• metabolite sedating

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Sedation

• dose related even for newer agents
• most common ingredient in OTC sleep aids

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Childrens Formulations

• Most available as syrups
• Allegra
• 30 mg tab
• Claritin
• 10 mg Redi-tab (fast dissolve)

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Role of Antihistamines in the Treatment of
Allergic Rhinitis
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Nasal Steroids vs. Antihistamines
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UCDHS Adult Allergic Rhinoconjunctivitis
Guidelines
January 2001
HealthNet Nasonex, Nasacort Pacificare
Rhinocort, Nasonex, Nasarel WHA Rhinocort,
Nasonex, Nasacort AQ Approved UCDMG PT Committee
January 2001
Reviewed by T. Albertson S. Teuber, M. E.
Gershwin, R. Mowers, J. Fischer
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other routes of administration

• azelastine (Astelin)
• nasal spray
• allergic rhinitis
• decrease side effect profile
• Bitter amine taste
• sedation (systemic absorption)

• olopatadine (Patanol)
• emedastine (Emadine)
• ophthalmic antihistamine H 1
• allergic conjuctivitis and itching
• headache, taste perversion, abnormal dreams

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H 2 Antagonists

• Therapeutic Indications
• duodenal and gastric ulcer
• gastroesophageal reflux disease (GERD)
• erosive esophagitis
• hypersecratory conditions
• heart burn, indigestion, sour stomach
• multidrug regimen for the eradication of H.Pylori
  in peptic ulcer disease

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UC Davis Primary Care Adult Tx GERD
Drug AWP/ea Protonix 40 mg 3.00 Aciphex 20
mg 3.70 Prevacid 30 mg 3.88 Nexium 20
mg 3.99 Prilosec 20 mg 4.15
Beck IT et al. The Second Canadian Consensus
Conf. on Management of Patients with GERD. Can J
Gastroenterol 199711 suppl B 7-20. Katz PO.
Treatment of GERD Use of Algorithms. Am J
Gastroenterol 199994(11)suppl3-10.
Reviewed by T. Albertson, J. Lee, J. Fischer, R.
Mowers UCDMC PT Committee January 2002
June 2001
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Adverse Reactions

• low incidence of side effects
• headache and fatigue - 1
• cimetidine
• highest incidence of gynecomastia (1- 4)
• P450 drug interactions
• decrease digoxin levels
• increase flecainide activity

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Serotonin 5-HT1 agonists

• Treatment of Migraine with or without aura.
• Acute treatment of Cluster headaches.
• Drugs are combination of 5-HT (1A, 1B, 1D, 1E,
  1F, 7)
• No activity at 5HT 2-4 receptors, adrenergic,
  muscarinic, dopaminergic

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Mechanism of Action

• Stimulation 5HT-1 receptors in extracerebral and
  intracranial blood vessels results in
  vasoconstriction. Also seen is an inhibition of
  neuropeptide release and decreased transmission
  in trigeminal pain pathways.
• It is thought cranial vessel dilation induced by
  release of vasoactive peptides from sensory nerve
  endings in an active trigeminal system my be a
  root cause of Migraine.

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Prototype agents

• sumatriptan (Imitrex)
• Tablets, nasal spray, injection
• rizatriptan (Maxalt)
• Several others

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Common adverse events

• Generally well tolerated
• Events with 5 rate paresthesia, nausea,
  dizzsiness, fatigue, dry mouth, headache,
  flushing
• Rare but serious events cardiac events with
  fatalities, cerebrovascular events with
  fatalities (hemorrhage, stroke, others)

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Rebound headache

• The risk of rebound headaches increases with the
  number of doses taken.
• Patient information
• Take as soon as possible
• Second dose may be taken if no response in 2
  hours
• Limit injections to 2 per 24 hours
• Contact MD before taking additional doses if no
  response

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• Other drugs for Migraine Treatment
• Ergot alkaloids such as dihydroergotamine
  (Migranal, DHE 45)
• Migraine Prophylaxis
• Beta blockers
• Calcium channel blockers
• NSAID
• Valproate