title: Inhibition of cough reflex sensitivity by diphenhydramine during acute viral respiratory tract infection.
abstract: BACKGROUND
  Currently available over-the-counter cough remedies historically have been criticized for lack of scientific evidence supporting their efficacy. Although the first-generation antihistamine diphenhydramine is classified as an antitussive by the United States Food and Drug Administration, to the authors' knowledge it has never been shown to inhibit cough reflex sensitivity in subjects with pathological cough.
  
  
  OBJECTIVE
  To evaluate the effect of diphenhydramine on cough reflex sensitivity.
  
  
  METHODS
  Montefiore Medical Center, an academic medical center in New York City.
  
  
  METHODS
  Twenty two subjects with acute viral upper respiratory tract infection (common cold) underwent cough reflex sensitivity measurement employing capsaicin challenge on 3 separate days, 2 h after ingesting single doses of study drug (to coincide with peak blood concentrations), administered in randomized, double-blind manner: a multicomponent syrup containing diphenhydramine (25 mg), phenylephrine (10 mg), in a natural cocoa formulation; dextromethorphan (30 mg) syrup; and, placebo syrup. The standard endpoint of cough challenge was used: concentration of capsaicin inducing ≥5 coughs (C5).
  
  
  METHODS
  Effect on cough reflex sensitivity (C5).
  
  
  RESULTS
  A significant difference (p = 0.0024) was established among groups, with pairwise analysis revealing a significant increase in mean log C5 (0.4 ± 0.55 (SD); p < 0.01) for the diphenhydramine-containing medication versus placebo, but not for dextromethorphan versus placebo.
  
  
  CONCLUSIONS
  Our results provide the initial evidence of the ability of diphenhydramine to inhibit cough reflex sensitivity in subjects with acute pathological cough. Timing of cough reflex sensitivity measurement may not have allowed demonstration of maximal antitussive effect of dextromethorphan.
authors: Department of Medicine, Albert Einstein College of Medicine and Montefiore Medical Center, 1825 Eastchester Road, Bronx, NY, 10461, USA, pdicpin@gmail.com.
authors: Peter V
authors: PV
authors: Dicpinigaitis
authors: Sean
authors: S
authors: Dhar
authors: Amber
authors: A
authors: Johnson
authors: Yvonne
authors: Y
authors: Gayle
authors: John
authors: J
authors: Brew
authors: Wilson
authors: W
authors: Caparros-Wanderley
mesh_terms: D000328:Adult; D000996:Antitussive Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002211:Capsaicin / Q000009:adverse effects / Q000037:antagonists & inhibitors; D003371:Cough / Q000139:chemically induced / Q000150:complications* / Q000188:drug therapy* / Q000517:prevention & control; D003915:Dextromethorphan / Q000494:pharmacology / Q000627:therapeutic use; D004155:Diphenhydramine / Q000494:pharmacology* / Q000627:therapeutic use*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D012018:Reflex / Q000187:drug effects*; D012141:Respiratory Tract Infections / Q000150:complications* / Q000188:drug therapy; D055815:Young Adult
chemical_list: D000996:Antitussive Agents; D003915:Dextromethorphan; D004155:Diphenhydramine; D002211:Capsaicin