6% Abstracts

44 IDENTIFICATION OF STRATEGIES TO ENSURE PATIENTS CONTINUE

TAKING STUDY MEDICATION - RESULTS FROM THE LIPID STUDY

W. Hague, S. Dunn and R.J. Slmes for the LIPID Study Group University of Sydney

Sydney, Australia

LIPID is a large multicentre randomised double-blind placebo-controlled study to determine whether long-term cholesterol reduction can reduce coronary mortality in patients with coronary artery disease. 9,014 patients from 85 centres throughout Australia and New Zealand are being followed for a minimum of 5 years.

Previous work presented has provided results of study centre strategies associated with increasing patients taking study medication. The current work describes a retrospective pilot study undertaken to determine patient attitudes to study management practices which were associated with continuing study medication.

For the three LIPID centres selected for this study, a written questionnaire was sent to all patients who had permanently discontinued study medication and an equal number of sex- matched patients still receiving study medication (104 in total). From the 75 responses received, there were no significant differences (chi square test, p > 0.05) between the two groups with respect to previous clinical trials participation, recruitment method, study understanding, perceived expectations and benefits from participation, staff relations, problems keeping appointments/attending clinics, support by family/friends or receipt of the study newsletter. However, patients who felt that being part of an important study (p=O.O06) was a benefit, were willing to participate in a similar study (p<O.OOl) or were employed (p=O.O4), were more likely to still be taking study medication whereas those who had concerns with respect to the treatment blind (p=O.O06), possible side effects (p=O.OOl), that they were taking too many tablets (p=O.O07) or reported poor dietary compliance @=0.02) were more likely to have discontinued study medication. Work is ongoing on a multivariate model.

This work has led to a modified patient questionnaire being sent to 1,000 patients from the 60 centres agreeing to participate.

45 PILL COUNTING AND ATTAINMENT OF BLOOD PRESSURE

GOALS IN TIIE AFRICAN AMERICAN STUDY OF KIDNEY DISEASE AND HYPERTENSION (AASK)

Paul Greene, Deborah Brooks, Jennifer Gassman, Tom Greene, Yvette Hall, John Kusek, Robert Phillips,

Delia Smith, Beth Wilkening, and the AASK Study Group National Institutes of Health

Bethesda, Maryland

The AASK is an ongoing NM-sponsored 21-center clinical trial testing the effects of blood pressure (BP) control on the progression of kidney disease. In this 3x2 factorial design study, participants are randomized to 1 of 3 blinded antihypertensive regimens and to either low BP (MAP x 92 mmI-Ig) or usual BP (MAP 102 to 107 mrnHg), where MAP = l/3 systolic BP + 2/3 diastolic BP; e.g., a 120/78 BP is a MAP of 92. In the 478 patients with 2 3 months of follow-up, the MAP measurements at the latest protocol visit are 95.3 +. 12.4 (mean + s.d.) for the low BP goal and 104.9 f 9.8 for the usual goal. These follow-up MAP measurements are lower and less variable than these patients’ pre-randomization MAP measurements (111.8 f. 16.0).

Abstracts 69s

Study coordinators at AASK hospitals and African American medical schools have been successful in getting participants to bring pill bottles in, accomplishing 93% completeness of data collection for blinded antihypertensives and 7 1% completeness of data collection for all antihypertensives for current visits.

When adherence is defined as a pill count 80 to 110% of prescribed, 70% of 336 adherent patients reached goal at their most recent visit vs 50% of 110 non-adherent patients with pill count < 80% 0, = .OOl). Consistent with this fmdmg, the mean MAP for adherent participants is lower than that for non-adherent participants in the low BP group (93.3 vs 101.0) and in the usual BP group (103.7 vs 107.3). The mean difference in MAP between low and usual blood pressure groups is 10.4 mmHg for adherent participants but is only 6.3 for non-adherent participants.

Medication adherence measured by pill count is associated with better blood pressure control. AASK team members are currently implementing behavioral strategies to promote medication adherence in order to increase the proportion of participants at BP goal, to decrease variability in BP within each group, and to enhance separation between low and usual BP groups, thereby leading to greater power to test the AASK hypothesized relationship between level of MAP and progression of kidney disease.

46 LOGISTIC REGRESSION UPON A CONTINUOUS COVAIUATB

WITH A CHANGEPOINT

David F. Signorini University of Edinburgh

Edinburgh, United Kingdom

When predicting outcome after severe head trauma, one of the most important factors is the age of the injured person. In previous models this has often been included as a continuous variable in a logistic regression (1). Semi-parametric models suggest, however, that age is not a significant risk factor until somewhere between 35 and 55 years, after which time the relative risk increases approximately linearly on the logistic scale. These models do not, however, give a clear indication of where the relationship changes.

This problem of detecting and estimating changepoints is well known and researched in both time series and linear regression (2), but very little work has been published on the logistic regression case.

This paper explores several methods of estimating both the changepoint and its accuracy, using a data set of approximately 1000 patients collected over the last seven years. The results of maximum likelihood, Bayesian and semi-parametric approach are compared, both using the real data set and via simulation.

References 1. Titterington DM, Murray GD, Murray LS, et al. (1981). Comparison of

discrimination techniques applied to a complex data set of head injured patients. JRSS B 144:145-175.

2. Stephens DA. (1994) Bayesian retrospective multiple-changepoint identification. JRSS C 43:159-178.