title: Histamine 2 blocker potentiates the effects of histamine 1 blocker in suppressing histamine-induced wheal.
abstract: BACKGROUND
  Histamine is responsible for the wheal and flare reaction in various allergic conditions. Classical antihistamines are the drugs which block the H 1 receptors and are widely used in various allergic conditions, whereas H 2 blockers are mainly used for acid peptic disease. Although H 1 receptor-mediated actions of histamine are primarily responsible for vasodilatation, vasopermeability, and itching, it has been observed that combined blocking of both H1 and H2 receptors may provide better relief.
  
  
  OBJECTIVE
  To compare the efficacy of levocetirizine (H1 blocker) versus levocetirizine and ranitidine (H2 blocker) in suppressing histamine-induced wheal.
  
  
  METHODS
  Fifteen volunteers were given a single dose of levocetirizine 5 mg on day 1 and a single dose of levocetirizine 5 mg with ranitidine 150 mg twice a day on day 7. A pretest was performed by intradermal histamine prick test. After administration of the drugs, the prick test was repeated at 1 hour, 2, 3, 6, and 24 hours, and the size of the wheal measured and statistically analyzed.
  
  
  RESULTS
  At 1 hour, there was no statistically significant difference in the wheal size between levocetirizine alone and the combination of levocetirizine and ranitidine. Levocetirizine with ranitidine resulted in statistically significant reduction of wheal size at 2, 3, 6, and 24 hours when compared with levocetirizine alone.
  
  
  CONCLUSIONS
  H2 blocker potentiates the effects of an H1 blocker in suppressing histamine-induced wheal.
authors.affiliation: Department of Dermatology, PSG Hospitals, Coimbatore, India.
authors.forename: N B
authors.initials: NB
authors.lastname: Dhanya
authors.forename: Reena
authors.initials: R
authors.lastname: Rai
authors.forename: C R
authors.initials: CR
authors.lastname: Srinivas
mesh_terms: D000293:Adolescent; D000328:Adult; D017332:Cetirizine / Q000008:administration & dosage; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D005260:Female; D006632:Histamine / Q000633:toxicity; D039563:Histamine H1 Antagonists, Non-Sedating / Q000008:administration & dosage*; D006635:Histamine H2 Antagonists / Q000008:administration & dosage*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011899:Ranitidine / Q000008:administration & dosage; D014581:Urticaria / Q000139:chemically induced* / Q000188:drug therapy* / Q000382:microbiology; D055815:Young Adult
chemical_list: D039563:Histamine H1 Antagonists, Non-Sedating; D006635:Histamine H2 Antagonists; C472067:levocetirizine; D006632:Histamine; D011899:Ranitidine; D017332:Cetirizine