LONDON – AF-219, a promising targeted therapy for chronic cough derailed by taste disturbances, has been revived by new studies suggesting that there is a therapeutic window that preserves benefits but reduces the risk of the adverse effect, according to new data presented at the annual congress of the European Respiratory Society.
The median duration of chronic cough of the patients on which the new data is based was 13 years. For patients with this type of durable cough history, there is a major unmet need for effective agents, reported Dr. Jacky Smith, MB, ChB, PhD, and professor of respiratory medicine at the University of Manchester (England).
Dr. Jacky Smith
The P2X3 antagonist AF-219 “is showing real promise as an antitussive agent when used at low doses,” Dr. Smith said.
P2X3 receptors are expressed by afferent neurons on the vagus nerves and appear to be a strong trigger of cough when stimulated, according to previous work by Dr. Smith and others. AF-219 is an oral antagonist of P2X3 and produced a 75% reduction in cough frequency when administered in a dose of 600 mg twice daily in a previously reported double-blind, placebo-controlled pilot study (Abdulqawi R et al. Lancet. 2015;385:1198-205). “However, there was a small wrinkle. All of the patients had taste disturbances. At this dose, it was primarily loss of taste,” Dr. Smith explained. As P2X3 is also found on neurons mediating taste, the adverse event was consistent with the mechanism of AF-219.
A series of studies have since been conducted to show that much lower doses than the twice-daily 600 mg dose employed in the original trial provide an antitussive effect but impose a much reduced risk of affecting taste.
In the latest dose-ranging study, 30 patients, who on average were aged 60 years, were randomized in a crossover design to receive placebo or active therapy in sequential doses over 4 days each of 7.5 mg, 15 mg, 30 mg, or 50 mg twice daily. At the end of the initial 16-day study period and a washout of 14 to 21 days, the patients who were initially randomized to placebo were evaluated on the sequential doses of active therapy, and those previously treated with active therapy took placebo.
On placebo, there was no change in cough frequency. On active therapy, there were incremental reductions in cough at 7.5 and 15 mg, but the differences relative to placebo did not reach statistical significance. Significant reductions in cough frequency relative to placebo were reached on both the 30 mg (P = 0.001) and the 50 mg dose (P = 0.002). The reductions on these two doses, however, were not significantly different from each other, suggesting that 30 mg may be an adequate dose to achieve clinically relevant antitussive benefits.
Taste disturbances, which were reported in 6.7% of patients taking both the 7.5 mg and 15 mg dose, increased to 46.7% in those taking the 30 mg dose and then to 53.3% of those taking the 50 mg dose. Lack of taste was only reported by 6.7% of those taking the 50 mg dose and none of those taking lower doses. Other adverse events, such as nasal dryness and rhinitis, were infrequent (less than 10%) and not dose related.
“Significantly lower doses than we originally tested appear to provide near maximum antitussive effects but with a much reduced risk of changes in taste,” Dr. Smith reported.
She added that in this dose-ranging study, there was a correlation between increasing dose and increasing cough-specific measures of quality of life.
“These data support a separation of the dose response relationships for antitussive effects and taste disturbance,” Dr. Smith reported. “Studies of longer duration are needed to test sustained efficacy and tolerability.”