Hair analysis of formoterol as a novel tool to assess long-term inhalation medication adherence: Data from the TRICOLON trial.

AIM: The aim of this paper is to examine inhaled formoterol concentrations in hair and assess the potential of hair analysis as a tool for measuring long-term adherence, by validation with objective data from digital inhalers.

METHODS

Hair samples and digital inhaler data were collected from patients with COPD in 10 hospitals in the Netherlands as part of the TRICOLON trial. Hair samples were divided into three 1 cm segments, each representing 1 month of hair growth. Intra-patient variability was investigated. Correlations between formoterol concentrations and digitally measured inhalations were assessed. Hair colour, dyeing, sex, body mass index (BMI) and smoking status were examined for their association and effect modification.

RESULTS

Of the 96 patients who provided a hair sample, 49 had sufficient quality hair sample and digital data. Low intra-patient variability was observed (intraclass correlation coefficient .94, 95% CI 0.87-0.97). Over a 3-month period, a trend was observed in the correlation between the digitally recorded inhalations and hair formoterol concentration (correlation coefficient [r] = .25, p = .087). Regarding individual segments, a significant correlation was only found in the segment closest to the scalp (r = .30, p = .039). Higher formoterol concentrations were measured in dark hair and in those with a lower BMI. No effect modification by colour, dyeing, sex, BMI or smoking was observed.

CONCLUSION

Low intra-patient variability of hair formoterol concentrations was observed in patients with stable adherence. However, inter-patient variability and external factors may limit the correlation between formoterol concentrations in hair and adherence measured by a digital inhaler and thus the current utility of hair analysis as an adherence monitoring tool.