Rationale: Airway hyperresponsiveness to adenosine monophosphate (AMP) has been validated as a surrogate marker for airway inflammation. We wished to know whether an abbreviated challenge at the final threshold dose would produce the same fall in FEV1 as a full, conventional dose-response challenge.
Methods: Seventeen patients with mild-to-moderate asthma (mean FEV1, 75.5% predicted) attended for a full dose-response protocol, where the highest concentration of AMP to produce > 20% fall in FEV1 was noted, along with the maximum percentage fall and recovery time. Patients returned within 2 days for a further challenge, when they received only the highest concentration (as a single bolus) reached on the previous visit.
Results: The mean (± SEM) percentage fall in FEV1 after the full challenge was 25.5 ± 1.3%, and after the abbreviated challenge was 9.4 ± 2.4%. The mean recovery after the full challenge was 28.13 ± 4.65 min, and after the abbreviated test was 10.81 ± 4.27 min.
Conclusion: An abbreviated challenge using a single bolus dose of AMP grossly underestimates bronchial hyperresponsiveness. Although the pharmacologic half-life of AMP is short (90 s), the lesser response and shortened recovery with the abbreviated challenge suggest a more prolonged physiologic half-life, which in turn may have implications for abbreviated challenge protocols