Background -Corticosteroid trials are an important part of the assessment of patients with chronic airways obstruction, but false negative results will occur if the treatment is not taken. To determine compliance low dose phenobarbitone has been used as a marker. Methods -Thirty six patients referred to a chest clinic for assessment oftheir airways obstruction were studied. They were instructed to take eight capsules (each containing 5 mg prednisolone and 0-5 mg phenobarbitone) per day for two weeks. The response was assessed by home peak flow monitoring and clinic spirometric tests. Plasma phenobarbitone levels were measured after the trial to enable calculation of the dose to plasma concentration ratio (level to dose ratio, LDR) and the result was compared with the reference range for fully compliant individuals. Results -Five patients defaulted from follow up, 23 had LDR values within the expected range, and eight had low LDR values consistent with poor compliance. The nine patients with steroid responsive disease (>20% improvement in peak flow or spirometric parameters) all had LDR values in the expected range. Conclusion -Excluding those who defaulted whose compliance must be questionable, eight (26%) patients did not fully comply with the steroid trial. Not all patients who fail to respond to a two week home steroid trial have a steroid "unresponsive" disease.

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