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\begin{document}

\title{EFFECT OF CENTRALLY AND PERIPHERALLY ACTING GABAB AGONISM ON THE COUGH
REFLEX}



\author[1]{Huda Badri}%
\author[1]{Carmen Farrelly}%
\author[1]{Dimitra Denton}%
\author[1]{Imran Satia}%
\author[1]{Kimberley Holt}%
\author[1]{Rachel Dockry}%
\author[2]{Graeme Wilkinson}%
\author[2]{Alison Holt}%
\author[3]{Brendan Canning}%
\author[4]{Jaclyn Smith}%
\affil[1]{The University of Manchester Faculty of Biology Medicine and Health}%
\affil[2]{AstraZeneca Medimmune Cambridge}%
\affil[3]{Johns Hopkins Asthma and Allergy Center}%
\affil[4]{The University of Manchester}%


\vspace{-1em}



  
  \date{May 16, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Background: Currently there are no effective licensed anti-tussive
therapies. Understanding how the neuronal mechanisms mediating the cough
reflex in animal models translate to humans is important for the
development of effective therapies. Pre-clinical studies suggest that
the activation of GABAB receptors in both the peripheral and central
nervous systems inhibit cough. Objective: To compare the effect of
central and peripherally acting GABAB agonists (lesogaberan and
baclofen) on the cough reflex in healthy volunteers. Methods: We
performed a single center, double-blind, double-dummy, three-way
crossover trial in healthy controls comparing single doses of
lesogaberan (120mg MR), with baclofen (40mg) and placebos. Cough
responses to inhaled capsaicin were assessed at screening and 2h
post-dose on each study day. The primary endpoint was the maximum number
of coughs evoked at any concentration of capsaicin (Emax) and the
secondary endpoint was the concentration evoking 50\% of the maximal
response (ED50). Results: Fifteen patients enrolled onto the study
(median age 29 (IQR 25-44) years; 7 females, mean BMI 24.6(\selectlanguage{ngerman}±3.0).
Lesogaberan treatment produced a small, statistically significant
increase in Emax compared with placebo {[}mean 13.4coughs (95\%CI
10.1-17.9) vs. 11.8coughs (8.8-15.9), p=0.04{]}, but had no effect on
ED50 {[}geometric mean 47.4\selectlanguage{greek}µ\selectlanguage{english}M (95\%CI 24.4-91.7) vs 37.6 \selectlanguage{greek}µ\selectlanguage{english}M (95\%CI
19.2-73.5), p=0.37{]}. In contrast, baclofen had no significant effect
on Emax (11.1, 95\%CI 8.1-15.4) (p=0.23), but significantly increased
ED50 compared with placebo (geometric mean 75.2\selectlanguage{greek}µ\selectlanguage{english}M (95\%CI 37.2-151.8),
p=0.002). Conclusion: This data suggests the anti-tussive actions of
GABAB agonists, in healthy volunteers, occur in the central rather than
the peripheral nervous system.%
\end{abstract}%



\sloppy


Huda Badri PhD\textsuperscript{1,2}, Carmen LGibbard\textsuperscript{1},
Dimitra Denton PhD\textsuperscript{1}, Imran Satia
PhD\textsuperscript{1,3}, Rachel J Dockry PhD\textsuperscript{1},
Kimberley Holt MPhil\textsuperscript{1}, Greame Wilkinson
PhD\textsuperscript{4}, Alison Holt PhD\textsuperscript{4}, Brendan J
Canning PhD\textsuperscript{5}, Jacky A Smith PhD\textsuperscript{1}.

\textsuperscript{1}Division of Infection, Immunity and Respiratory
Medicine, The University of Manchester, Manchester Academic Health
Sciences Centre, Manchester, UK. \textsuperscript{2}North Manchester
General Hospital, Pennine Acute NHS Trust, UK; Department of Respiratory
Medicine \textsuperscript{3}Division of Respiratory Medicine, McMaster
University, Hamilton, Ontario, Canada,\textsuperscript{4}Emerging
Innovations Unit, Scientific Partnering and Alliances, IMED Biotech
Unit, AstraZeneca, Cambridge, United Kingdom. \textsuperscript{5}Former
employees at AstraZeneca, Alderley Park, UK. \textsuperscript{6}Johns
Hopkins Asthma and Allergy Ctr., Baltimore, MD, USA.

\textbf{Corresponding author:}

Professor Jacky Smith

2\textsuperscript{nd} floor Education and Research Centre

Manchester University Foundation NHS Trust

Wythenshawe Hospital.

Southmoor Rd,

Manchester, M23 9LT

United Kingdom

Tel: +44 (0)161 291 5863

Email: Jacky.smith@manchester.ac.uk

\textbf{Word Count:} 2015 words

\textbf{Data Sharing:} Data available on request from the authors

\textbf{Conflict of interest statement:}

JAS is an inventor on a patent describing methods for detecting cough
from sound recordings, licensed to Vitalograph Ltd. JAS has received
funding for consultancy and research funds from Afferent
Pharmaceuticals, Merck Inc., Bayer, Bellus, GSK, Xention Ltd, Ario
Pharma Ltd, Glenmark, Almirall, AstraZeneca, Axalbion, Patara, Verona
Pharma, NeRRe Pharmaceuticals, Menlo Pharmaceuticals, Attenua Inc. BJC
is on the board of a pharmaceutical company. GW and AH were previous
employees of AstraZeneca. HB, CLG, IS, DV, RJD, KH, have no conflicts of
interests.

\textbf{Funding:}

This study was funded by an MRC `Mechanism of human disease' grant in
collaboration with AstraZeneca (Grant Ref: MR/K015141/1). JAS is funded
by the NIHR Manchester Biomedical Research Centre, a Wellcome
Investigator in Science Award and is an NIHR Senior Investigator. HB is
funded by a North West Lung Centre Pickering Fellowship. I.S currently
supported by the European Respiratory Society RESPIRE 3 Marie Curie
Fellowship Award (EU Horizon 2020 713406). I.S also reports grants from
BMA James Trust Award, North West Lung Centre Charity, personal fees
from Educational Talks for GPs, Travel Award for Conference Meetings,
outside the submitted work.

\textbf{Author contribution to manuscript:}

J.A.S, G.W, A.H., and B.J.C, study concept. H.B., J.A.S., CLG, D.D.,
I.S., K.H., and R.J.D study design, protocol, set up of study,
recruitment, data collection and analysis. Manuscript written by H.B.
and J.A.S but all authors contributed and reviewed the article.

\textbf{ABSTRACT} \emph{(250 words)}

\textbf{Background and Purpose} : There are no effective, licensed,
anti-tussive therapies. Understanding how the neuronal mechanisms
mediating the cough reflex in animal models translate to humans is
important for the development of effective therapies. Pre-clinical
studies suggest that the activation of GABA\textsubscript{B} receptors
in both the peripheral and central nervous systems inhibit cough. This
study compares the effect of central and peripherally acting
GABA\textsubscript{B} agonists (lesogaberan and baclofen) on the cough
reflex in healthy volunteers (HV).

\textbf{Experimental Approach:} Single center, double-blind,
double-dummy, three-way crossover trial in HV comparing single doses of
lesogaberan, with baclofen and placebos. Cough responses to inhaled
capsaicin were assessed at screening and 2h post-dose on each study day.
The primary endpoint was the maximum number of coughs evoked at any
concentration of capsaicin (Emax) and the secondary endpoint was the
concentration evoking 50\% of the maximal response (ED50).

\textbf{Key Results:} Fifteen HV were enrolled (median age 29 (IQR
25-44) years; 7 females, mean BMI 24.6(\selectlanguage{ngerman}±3.0). Lesogaberan (120mg MR)
treatment produced a small, statistically significant increase in Emax
compared with placebo {[}mean 13.4coughs (95\%CI 10.1-17.9) vs.
11.8coughs (8.8-15.9), p=0.04{]}, but had no effect on ED50 {[}geometric
mean 47.4\selectlanguage{greek}µ\selectlanguage{english}M (95\%CI 24.4-91.7) vs 37.6 \selectlanguage{greek}µ\selectlanguage{english}M (95\%CI 19.2-73.5), p=0.37{]}.
In contrast, baclofen (40mg) had no significant effect on Emax (11.1,
95\%CI 8.1-15.4) (p=0.23), but significantly increased ED50 compared
with placebo (geometric mean 75.2\selectlanguage{greek}µ\selectlanguage{english}M (95\%CI 37.2-151.8), p=0.002).

\textbf{Conclusion and Implications:} This data suggests the
anti-tussive actions of GABA\textsubscript{B} agonists, in HV, occur in
the central rather than the peripheral nervous system.



\textbf{Key Words:}

\textbf{GABA\textsubscript{B}, Lesogaberan, Baclofen, Cough, Capsaicin.}

\textbf{Abbreviations:}

GABA: Gamma aminobutyric acid

CNS: Central Nervous system

PNS: peripheral Nervous System

ED50: capsaicin dose inducing half-maximal response

Emax: maximum cough response evoked by any concentration of capsaicin



\textbf{INTRODUCTION}

Cough is the commonest presenting symptom in physician consultations,
yet effective licensed therapies remain an unmet clinical need (1). Most
consultations for cough are likely to be a consequence of coughing
associated with viral respiratory infections which typically resolve
spontaneously however it is estimated that around 10\% of the general
population suffer from chronic coughing defined as a persistent cough of
more than 8 weeks duration (1).

Gamma aminobutyric acid (GABA) is the main inhibitory neurotransmitter
in the nervous system, with GABA\textsubscript{B} receptors found in the
brain, airways and the gastrointestinal tract. Animal studies have
demonstrated the presence of peripheral GABA\textsubscript{B} receptors
in the upper airways, the trachea and the lower oesophageal sphincter
(2). Pre-clinical studies of central and peripheral
GABA\textsubscript{B} agonists suggest that they are potent antitussive
agents (3, 4). Interestingly GABA\textsubscript{B} agonists i.e.
baclofen have also been shown to reduce cough responses to inhaled
irritants such as capsaicin (5). It is unclear whether this is a central
nervous system (CNS) or peripheral nervous system (PNS) effect and
whether this change in experimentally evoked cough responses results in
reduction of cough frequency in patients. Human data exits on the use of
central GABA\textsubscript{B} agonists (baclofen) as an antitussive
agents (5-8). However, CNS side effects such as drowsiness and even
seizures have limited the use of baclofen in clinical practice.
Lesogaberan is a novel predominantly peripherally acting
GABA\textsubscript{B} receptor agonist, which is devoid of CNS side
effects due to its uptake by GABA transporters (GAT) in the CNS, its
effect on the human cough reflex is unknown.

We hypothesized that GABA\textsubscript{B} receptors were capable of
inhibiting cough in both the central and peripheral nervous system, and
therefore predicted that both a peripherally acting
GABA\textsubscript{B} receptor agonist (lesogaberan), and a centrally
acting GABA\textsubscript{B} receptor agonist (baclofen) would both
significantly inhibit cough responses to inhaled capsaicin compared to
matched placebo therapy. We therefore performed a trial in healthy
controls comparing the effect of single doses of lesogaberan (120mg MR),
with baclofen (40mg) and matched placebos on cough responses to inhaled
capsaicin.

\textbf{METHODS}

The study was performed in accordance with the Declaration of Helsinki,
Good Clinical Practice, and applicable regulatory requirements. The
local ethics board approved this study (Liverpool East, REC reference:
14/NW/1497), registered in the ISRCTN registry (ISRCTN82391675)and
patients provided written consent.

\textbf{Study design}

We carried out a single center, randomized double-blind,
placebo-controlled, double dummy, three-way crossover trial in healthy
volunteers comparing the effects of a single dose of lesogaberan 120mg
Modified Release (MR), baclofen 40mg and matched placebos on evoked
cough responses to capsaicin (Figure1; Study overview). Participants
were dosed with either lesogaberan plus baclofen placebo, lesogaberan
placebo plus baclofen or lesogaberan placebo plus baclofen placebo.
Capsaicin cough challenge was performed at screening and then repeated
on each study day at 2h post dosing which was the peak serum
concertation (C\textsubscript{max}) for both therapies. The washout
period between doses was [?]7 days.

\textbf{Participants}

Volunteers with any clinically significant disease or diagnosis
(including a history of lower or upper respiratory tract infection
within the preceding 4 weeks) were excluded. Current smokers or
ex-smokers with \textgreater{}10 pack year history and volunteers with
\textless{}6 months abstinence were excluded. Pregnant or breastfeeding
women were also excluded. We recruited 15 healthy volunteers from a
database of previous volunteers.

\textbf{Capsaicin evoked cough responses}

Participants inhaled four breaths of doubling concentrations of
capsaicin (0.97-1,000\selectlanguage{greek}µ\selectlanguage{english}M: Stockport Pharmaceuticals Ltd, Stockport, UK)
at 30 second intervals using a dosimeter (KoKo dosimeter; DeVilbiss
Healthcare Inc., Somerset, PA). Only the coughs evoked in the first 15
seconds post each inhalation were counted. The challenge continued until
the maximum tolerated dose or the final concentration was inhaled. The
maximum number of coughs evoked at any concentration (Emax) and the
concentration evoking 50\% of the maximal response (ED50) were
calculated.

\textbf{Blinding and Randomization}

Randomization of participants was carried out using a computer generated
scheme (Almac, Craigvon, UK) independent of the study site and
procedures. Blinded study medication was supplied to the pharmacy where
it was dispensed; un-blinding was by way of un-blinding scratch cards.
Matched placebos for both Lesogaberan and Baclofen were manufactured and
thus each study treatment consisted of 2 capsules Lesogaberan
120mg/matched Lesogaberan placebo plus Baclofen 40mg/matched Baclofen
placebo. Each subject received (in a random, double-blinded fashion) (i)
Lesogaberan plus Baclofen Placebo, (ii) Lesogaberan Placebo plus
Baclofen and (ii) Lesogaberan Placebo plus Baclofen Placebo.

\textbf{Outcomes}

The primary outcome was the effect of lesogaberan vs baclofen vs placebo
on cough responses (Emax), with the secondary outcome being the effect
on cough sensitivity (ED50) to inhaled capsaicin.

\textbf{Statistical methods}

Generalized Estimating Equation (GEE) models were used to analyze the
data (IBM SPSS statistics version 22). The GEE model was generated using
a Poisson distribution for Emax and linear for logED50. The exchangeable
correlation matrix was then selected and Wald's estimate for mean and
95\% Confidence intervals generated.

The power calculation was based on previous cough challenge data, where
one doubling dose of the challenge agent is generally accepted to be a
clinically relevant difference in cough reflex sensitivity. Thus, with
15 participants treated, this study had approximately 90\% power to
detect a one doubling dose change in cough reflex sensitivity of 0.3 for
lesogaberan compared with placebo, assuming a standard deviation of \selectlanguage{ngerman}±
0.29 (9).

\textbf{RESULTS}

\textbf{Participants}

Nineteen healthy volunteers were recruited, 4 of which failed screening
(see consort, Figure2) leaving 15 completing the study. There were 8
males in the study, the median age was 29 years (IQR 25-44 years), mean
BMI was 24.6 kg/m\textsuperscript{2} (SD±3.0). Median FEV1 percent
predicted was 96\% (IQR 89-117). All the volunteers were never smokers.

\textbf{Capsaicin evoked cough responses}

Rather than reducing cough responses, lesogaberan treatment was
associated with a small, increase in the maximal cough response (Emax
mean 13.4 coughs, 95\% CI 10.1-17.9) compared with placebo (11.8 coughs,
95\%CI 8.8-15.9; p= 0.04), but had no effect on ED50 (geometric mean
47.4 \selectlanguage{greek}μ\selectlanguage{english}M CI 24.4-91.7 vs placebo 37.6 CI 19.2-73.5 p=0.37). In contrast,
baclofen had no significant effect on Emax (11.1, CI8.1-15.4; p=0.23),
but ED50 was significantly increased compared with placebo (geometric
mean 75.2\selectlanguage{greek}μ\selectlanguage{english}M 95\%CI 37.2-151.8 p=0.002), i.e. approximately 1 doubling
dose higher, indicating that the volunteers tolerated higher doses of
capsaicin without coughing. There was no evidence of any period effect
for either Emax (p=0.39) or ED50 (p=0.41) in these GEE models. There
were too few subjects in this study for sequence effect to be assessed
as in some cases only 2 subjects had the same sequence of treatment
periods.

\textbf{Adverse events}

There were very few adverse events in this study, and all were
considered minor. The most common adverse events were dizziness,
headache and light headedness. (Table1) These observations were
consistent with the known side effect profile of baclofen. In addition,
there was no significant change in the subject's spirometry pre/ post
dosing and pre/post capsaicin cough challenge.

\textbf{DISCUSSION}

This is the first human study to determine whether both peripherally
acting and centrally acting GABA\textsubscript{B} agonists modulate
cough responses to inhaled capsaicin compared with placebo. The data
suggests that the actions of GABA\textsubscript{B} agonists, in healthy
volunteers occur in the central rather than the peripheral nervous
system. Lesogaberan (peripherally acting GABA\textsubscript{B} agonist)
had no significant inhibitory effect on the cough reflex whereas
baclofen (centrally acting GABA\textsubscript{B} agonist) increased the
ED50. Interestingly, lesogaberan had a small but significant increase on
Emax i.e. the subjects coughed, slightly, more on this drug.

The dose response curve from our data (Figure 3) demonstrates a subtle
but significant right shift of the baclofen curve, suggesting a stronger
stimulus is required to evoke coughing when on baclofen treatment,
consistent with the existing literature. Dicpinigaitis et al, studied a
similar group pf subjects to those in this study (20 healthy volunteers,
mean age 30) who were dosed chronically with baclofen 10mg three times a
day (6) and following that study he went on to study 20mg dosing in a
similar group (7). In both of these studies the baclofen group
demonstrated a significant increase in the log C5 capsaicin
concentration. This is the concentration of capsaicin that induces 5
coughs which is broadly comparable to the ED50 in our study. There are
two small case series in the literature which have suggested baclofen
might also treat chronic cough. One was an open-label study evaluating a
4-week course of low-dose, oral baclofen against ACE inhibitor-induced
cough (8) suggesting that baclofen treatment caused a prolonged
antitussive effect. The other study reported suppression of cough and
capsaicin cough responses in two chronic cough patients after a 14-day
course of baclofen, 10mg; three times a day (5). Participants in both of
these studies did not report significant adverse effects, however, in
clinical practice patients report significant dizziness (up to 28\% of
patients) and drowsiness (up to 10\% of patients) which limits its use
(10).

It is worth noting that changes in experimentally evoked cough do not
necessarily equate to clinical anti-tussive effects on spontaneous
coughing. This was demonstrated by Belvisi et al., 2017 who studied the
effect of a potent TRPV1 antagonist (XEN-D0501) vs placebo on capsaicin
evoked cough and spontaneous 24-hour cough frequency (11). Despite
XEN-D0501 leading to significant reduction in the capsaicin Emax, there
was no improvement in objective cough frequency. In addition to this
some agents (such as morphine and gabapentin) that have been shown to
improve cough specific quality of life, and are currently used
off-license in a clinical setting, do not appear to modulate the C5
endpoint in cough challenge (12). However, it remains unclear which
challenge agents, methodology and endpoints are optimal at present. Thus
the main role of cough challenge seems to be in confirming target
engagement and understanding whether mechanisms translate from animal
studies to humans.

Interestingly, the data from this study suggests a difference between
the effects of lesogaberan in humans compared with a guinea pig model.
Canning et al., found that both lesogaberan and baclofen significantly
reduced citric acid evoked coughs in guinea-pigs (4). Possible
explanations for this include differences in the blood brain barrier
between species and also relatively higher levels of dosing in the
guinea pig, which may have saturated the GATs responsible for inhibiting
the CNS effects of lesogaberan.

Despite the relatively small number of subjects in this study,
statistically significant changes between the treatments were teased out
by the dose response inhalational capsaicin challenge, suggesting the
utility and power of this particular method and these endpoints when
assessing cough reflex responses. The small but statistically
significant increase in Emax with lesogaberan therapy is interesting,
paradoxical in the context of the inhibitory nature of
GABA\textsubscript{B} and difficult to explain. Our prediction was that
Emax would have reduced with lesogaberan, mirroring the changes in
animal studies. One potential explanation for the lack of reduction in
Emax with lesogaberan in healthy volunteers is that
GABA\textsubscript{B} is involved in endogenous inhibitory mechanisms
controlling cough. In the healthy state, these control mechanisms are
intact and thus additional GABA\textsubscript{B} agonism may have no
effect on cough responses, whereas in patients with chronic cough there
is increasing evidence that these descending inhibitory mechanisms may
be deficient (13-15) and in such circumstances
GABA\textsubscript{B}agonism could have an effect in chronic cough
patients not seen in healthy controls.

This study has some limitations. Firstly we used single doses of
lesogaberan and baclofen, as opposed to multiple dosing. However, we
were still able to replicate previous findings with baclofen after two
weeks of dosing. Another possible limitation of this study is that
capsaicin was used for the cough challenge, whereas the animal studies
used citric acid. This choice was made in light of the fact that all
previous human studies suggesting an effect of baclofen on cough
responses had all employed capsaicin challenge, furthermore this
particular challenge methodology has not been performed using citric
acid. An effect of lesogaberan on citric acid but not capsaicin evoked
cough cannot be excluded.

In conclusion, this data suggests GABA\textsubscript{B} receptor
agonists are inhibitory of the human cough reflex in health, but only
through their activity in the central nervous system. It remains to be
seen whether peripheral GABA\textsubscript{B} agonists have any effect
on the sensitized cough reflex in chronic cough patients.

\textbf{REFERENCES}

1. Centre for Disease Control and Prevention U. National Ambulatory
Medical Care Survey: Physician office visits. CDC website. 2015:Tables
1, 11, 6.

2. Bettler B, Kaupmann K, Mosbacher J, Gassmann M. Molecular structure
and physiological functions of GABA(B) receptors. Physiol Rev.
2004;84(3):835-67.

3. Bolser DC, Aziz SM, DeGennaro FC, Kreutner W, Egan RW, Siegel MI, et
al. Antitussive effects of GABAB agonists in the cat and guinea-pig.
British journal of pharmacology. 1993;110(1):491-5.

4. Canning BJ, Mori N, Lehmann A. Antitussive effects of the
peripherally restricted GABAB receptor agonist lesogaberan in guinea
pigs: comparison to baclofen and other GABAB receptor-selective
agonists. Cough. 2012;8(1):7.

5. Dicpinigaitis PV, Dobkin JB, Rauf K, Aldrich TK. Inhibition of
capsaicin-induced cough by the gamma-aminobutyric acid agonist baclofen.
Journal of clinical pharmacology. 1998;38(4):364-7.

6. Dicpinigaitis PV, Dobkin JB. Antitussive effect of the GABA-agonist
baclofen. Chest. 1997;111(4):996-9.

7. Dicpinigaitis PV, Rauf K. Treatment of chronic, refractory cough with
baclofen. Respiration; international review of thoracic diseases.
1998;65(1):86-8.

8. Dicpinigaitis PV. Use of baclofen to suppress cough induced by
angiotensin-converting enzyme inhibitors. The Annals of pharmacotherapy.
1996;30(11):1242-5.

9. Hilton EC, Baverel PG, Woodcock A, Van Der Graaf PH, Smith JA.
Pharmacodynamic modeling of cough responses to capsaicin inhalation
calls into question the utility of the C5 end point. J Allergy Clin
Immunol. 2013;132(4):847-55 e1-5.

10. Excellence NIfHaC. British National Formulary. 2020(29th October
2020).

11. Belvisi MG, Birrell MA, Wortley MA, Maher SA, Satia I, Badri H, et
al. XEN-D0501, a Novel Transient Receptor Potential Vanilloid 1
Antagonist, Does Not Reduce Cough in Patients with Refractory Cough. Am
J Respir Crit Care Med. 2017;196(10):1255-63.

12. Morice AH, Menon MS, Mulrennan SA, Everett CF, Wright C, Jackson J,
et al. Opiate therapy in chronic cough. Am J Respir Crit Care Med.
2007;175(4):312-5.

13. Mazzone SB, Cole LJ, Ando A, Egan GF, Farrell MJ. Investigation of
the neural control of cough and cough suppression in humans using
functional brain imaging. J Neurosci. 2011;31(8):2948-58.

14. Mazzone SB, McGovern AE, Cole LJ, Farrell MJ. Central nervous system
control of cough: pharmacological implications. Curr Opin Pharmacol.
2011;11(3):265-71.

15. Hilton E, Satia I, Holt K, Woodcock AA, Belcher J, Smith JA. The
Effect of Pain Conditioning on Experimentally Evoked Cough: Evidence of
Impaired Endogenous Inhibitory Control Mechanisms in Refractory Chronic
Cough. The European respiratory journal. 2020.

\textbf{FIGURE LEGENDS}

Figure 1. Three-way crossover study randomizing participants to receive
lesogaberan, baclofen and their matched placebos in a double-bind,
double dummy design.

Figure 2. Consort diagram showing patient flow through the study.

Figure 3. Cough responses to capsaicin challenge showing dose response
curves when subjects were treated with lesogaberan= lesogaberan plus
baclofen placebo, baclofen= baclofen plus lesogaberan placebo and
placebo=lesogaberan placebo and baclofen placebo.

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