Monitoring adherence to drug treatment by using change in cholesterol concentration: secondary analysis of trial data.
OBJECTIVE
To estimate the accuracy of monitoring cholesterol concentration for detecting non-adherence to lipid lowering treatment.


METHODS
Secondary analysis of data on cholesterol concentration in the LIPID (long term intervention with pravastatin in ischaemic disease) study by using three measures of non-adherence: discontinuation of treatment, allocation to placebo arm, less than 80% of pills taken.


METHODS
Randomised placebo controlled trial in Australia and New Zealand.


METHODS
9014 patients with previous coronary heart disease.


METHODS
Pravastatin 40 mg or placebo daily.


METHODS
Sensitivity, specificity, area under the receiver operating characteristics (ROC) curve, post-test probability.


RESULTS
Monitoring of cholesterol concentration had modest ability for detecting complete non-adherence. One year after the start of treatment, half (1957/3937) of the non-adherent patients and 6% (253/3944) of adherent patients had a rise in concentration of low density lipoprotein cholesterol. Accuracy was reasonable (area under the curve 0.89). Cholesterol monitoring, however, had weak ability for detecting partial non-adherence. One year after the start of treatment, 16% (34/213) of partially adherent and 4% (155/3585) of fully adherent patients had a rise in concentration of low density lipoprotein cholesterol. Accuracy was poor (area under the curve 0.65). For typical pre-test probabilities of non-adherence ranging from low (25%) to high (75%), the post-test probabilities indicate continuing uncertainty after lipid testing. A patient with no change in low density lipoprotein cholesterol concentration has a post-test probability of being completely non-adherent of between 67% and 95% and a post-test probability of being partially non-adherent of between 48% and 89%. A patient with a decrease in concentration of 1.0 mmol/L has a post-test probability of being completely non-adherent of between 7% and 40% and a post-test probability of being partially non-adherent of between 21% and 71%.


CONCLUSIONS
Monitoring concentration of low density lipoprotein (or total) cholesterol has modest ability to detect complete non-adherence or non-persistence with pravastatin treatment and weak ability to detect partial non-adherence. Results of monitoring should be considered as no more than an adjunct to careful discussion with patients about adherence.
Screening and Test Evaluation Program, School of Public Health, University of Sydney, NSW 2006, Australia.
Katy J L
KJ
Bell
Adrienne
A
Kirby
Andrew
A
Hayen
Les
L
Irwig
Paul
P
Glasziou
D000924:Anticholesteremic Agents / Q000627:therapeutic use*; D015415:Biomarkers / Q000378:metabolism; D008078:Cholesterol, LDL / Q000378:metabolism*; D003327:Coronary Disease / Q000097:blood / Q000188:drug therapy*; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000627:therapeutic use*; D055118:Medication Adherence; D017035:Pravastatin / Q000627:therapeutic use*; D012372:ROC Curve
D000924:Anticholesteremic Agents; D015415:Biomarkers; D008078:Cholesterol, LDL; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D017035:Pravastatin