Drugs potentially affecting the extent of airways reversibility on pulmonary function testing are frequently consumed despite guidelines

Terry E Jones,¹ AnneMarie Southcott,² Sean Homan<sup>3

1</sup>Pharmacy Department, The Queen Elizabeth Hospital, Woodville South, SA, ²Respiratory and Sleep Medicine, Western Health, Footscray, VIC, ³Respiratory Unit, The Queen Elizabeth Hospital, Woodville South, SA, Australia

Background: The increase in forced expiratory volume in one second (FEV₁) effected by a bronchodilator is routinely assessed when patients undertake pulmonary function testing (PFT). Several drug classes can theoretically affect the magnitude of the increase in FEV₁. Withholding periods are advised for many but not all such drugs. Anecdotally, many subjects presenting for PFT are found to have taken drugs that might affect the test. We did an audit of patients presenting for PFT to assess the frequency with which FEV₁ reversibility might be affected by drugs.
Methods: One hundred subjects presenting to the laboratory for PFT were questioned about recent drug consumption by an independent pharmacy intern. Reversibility of FEV₁ was assumed to have been affected if drugs of interest were consumed within defined withholding periods or two half-lives for drugs without such data.
Results: Sixty-three subjects were prescribed drugs likely to affect FEV₁ reversibility. Thirty-six subjects consumed at least one such drug within the withholding period. Half (18) of these patients consumed β-blockers with or without β-agonists. Sixty-five subjects did not recall receiving any advice about withholding drugs prior to the test and only 10 recalled receiving advice from their clinician or pulmonary function technician.
Conclusion: Subjects presenting for PFT are infrequently advised to withhold drugs that may affect FEV₁ reversibility, and consequently, often take such drugs close to the time of the test. Therefore, it is likely that the increase in FEV₁ is frequently affected by interference from drugs and this might impact on diagnosis and/or treatment options.

Keywords: lung function tests, beta-adrenergic agonists, beta-adrenergic antagonists, withholding periods, bronchodilators