Introduction

A number of factors may contribute to lack of adequate control in asthma, including poor treatment adherence, psychosocial problems and steroid resistance. Patient self-report and the use of pharmacy prescription refill records are the most commonly used methods to measure patient adherence, however, the reliability of these methods is questionable (McNabb, 1997). The aim of the present study was to use plasma and urine monitoring to assess patient adherence to oral prednisolone and high dose inhaled steroids at a special clinic for patients with difficult to control asthma. Plasma prednisolone values and morning urine cortisol suppression were measured in the case of prednisolone while in the case of inhaled therapy the urine test alone was performed. In all cases the data were compared with patients' self report of adherence to their prescribed therapy.

Method

Patients attending the clinic were invited to participate in the study, which was approved by the University Ethical Committee. They were instructed to bring a sample from their first passage of morning urine to the clinic; a blood sample was also taken for patients prescribed prednisolone. The patients were also interviewed: demographic, asthma control and self-reported adherence data were collected. Prednisolone and cortisol concentrations were measured by HPLC (Adair et al., 1992). Morning urinary cortisol/creatinine ratio has been shown to be as sensitive as 24-hour urinary cortisol in detecting endogenous cortisol suppression (Mclntyre et al ., 1995). Patients who were prescribed high dose inhaled steroids were considered adherent if their morning urinary cortisol was suppressed. Patients who were prescribed oral prednisolone were considered adherent if prednisolone was detected in their plasma, and their morning urinary cortisol was suppressed.

Results

The study is ongoing with a target sample size of 100 patients. A total of 36 patients have been recruited into the study to date. Of these 7 (58%) out of 12 patients taking oral prednisolone were found to be non-adherent and 13 (54%) out of 24 taking high dose inhaled steroids were found to be non-adherent using the plasma / urine monitoring i.e. a total of 20 patients (56%) were found to be non-adherent with their therapy, even though they were in a difficult to control asthma population. Data on self-reported non-adherence indicated that only 10 (28%) patients admitted that they sometimes forgot or skipped taking their medication or ran out of their medication.

Discussion

In patients with difficult asthma it is very important to determine what factors are causing the poor control. Our preliminary results from 36 patients indicates that there is a high percentage of non-adherence with prescribed steroid therapy as measured by plasma / urine sampling. This poor adherence is often not admitted by patients when asked directly about their medication taking behaviour. The plasma / urine monitoring is therefore effective in determining adherence and will facilitate the successful identification of non-adherent patients and thereby allow healthcare providers to target such patients for adherence counselling.

References

Adair C, McCallion O, McElnay JC, Scott MG, et al. (1992) A pharmacokinetic and pharmacodynamic comparison of plain and enteric-coated prednisolone tablets. British Journal of Clinical Pharmacology. 33:495-499.

Mc Intyre H, Bowler S, Mitchell C. (1995) Measuring the systemic effects of inhaled beclomethasone: timed morning urine collections compared with 24 hour specimens. Thorax. 50: 1280-1284.

McNabb WL (1997) Adherence in diabetes: can we define it and can we measure it? Diabetes Care. 20: 215 � 218.