Background: gamma-Aminobutyric acid (GABA) is a central inhibitory neurotransmitter that also exists in peripheral tissues, including the lung. The GABA-agonist baclofen has been shown, in animal studies, to inhibit cough via a central mechanism, but has not been investigated in humans (to our knowledge).

Study objective: To evaluate the antitussive effect of baclofen in normal human subjects.

Design: Randomized, double-blind, placebo-controlled study.

Setting: Academic medical center.

Participants: Twenty healthy, adult volunteers.

Interventions: Subjects underwent cough challenge with inhaled capsaicin before and after a 14-day course of baclofen, 10 mg three times daily, or placebo. Capsaicin cough threshold (C5) was defined as the concentration of inhaled capsaicin inducing five or more coughs.

Results: Subjects receiving baclofen (n=10) demonstrated a significant elevation of capsaicin cough threshold compared with placebo subjects (n=10). Mean delta log C5 after treatment was 0.48+/-0.19 (SEM) for the baclofen group, and -0.06+/-0.12 for the placebo group (p=0.024). Six of 10 subjects receiving baclofen, but none of the 10 subjects receiving placebo, demonstrated a fourfold or greater increase in capsaicin cough threshold (p=0.0054).

Conclusion: The antitussive activity of low-dose, oral baclofen demonstrated in this study supports further investigation of this drug, or other GABA-agonists, for a potential therapeutic role in the treatment of pathologic cough.