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Int J Clin Pharm. 2015 Jun;37(3):471-4. doi: 10.1007/s11096-015-0081-8. Epub 2015 Feb 12.

Inhibition of cough reflex sensitivity by diphenhydramine during acute viral respiratory tract infection.

Author information

1
Department of Medicine, Albert Einstein College of Medicine and Montefiore Medical Center, 1825 Eastchester Road, Bronx, NY, 10461, USA, pdicpin@gmail.com.

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.

SETTING:

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).

MAIN OUTCOME MEASURE:

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.

TRIAL REGISTRATION:

ClinicalTrials.gov NCT02062710.

PMID:
25673148
PMCID:
PMC4409637
DOI:
10.1007/s11096-015-0081-8
[Indexed for MEDLINE]
Free PMC Article

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