Explanations for variations in clopidogrel prescribing in England

Background The National Audit Office (NAO) has produced prescribing indicators that Primary Care Trusts (PCTs) can use to judge their performance. One of the indicators is for the antiplatelet clopidogrel, measured as defined daily dose (DDD) per cardiovascular Specific Therapeutic Age Related Prescribing Unit (STAR-PU). Clopidogrel is used as an indicator because it is a more expensive medicine than the alternative (aspirin) and there may be scope for cost reduction. We aimed to establish if the NAO indicator for clopidogrel prescribing is a valid measure of prescribing performance. Methods Prescribing data for 152 PCTs and a range of explanatory variables were obtained. Correlation between variables was determined. A regression analysis was conducted to compare the dependent variable (prescribing) with the explanatory variables identified. Results The percentage of patients on the coronary heart disease register and Index of Multiple Deprivation explained 30 % of the variation in prescribing (DDD/STAR-PU) between PCTs. Even though DDD/STAR-PU is adjusted for age and sex other measures of need still have an impact on prescribing. Conclusions Using DDD/STAR-PU alone as a prescribing indicator might misidentify some PCTs, which are under- and over-using clopidogrel. Poor ranking against other PCTs using the NAO indicator should be fully explored taking into account other variables (cardiovascular morbidity and deprivation) before any corrective action is taken