Optimizing adherence in hypertension: a comparison of outcomes and costs using single tablet regimens vs individual component regimens.

BACKGROUND: Several studies have demonstrated that the use of single tablet regimens (STRs) in hypertension is associated with improved outcomes and reduced healthcare costs compared with individual component regimens. The objective was to carry out a retrospective analysis of a UK general practice population to test these conclusions in a UK context.
METHOD: A retrospective cohort study was carried out using a primary care database (The Health Improvement Network; THIN), comparing 9929 hypertensive patients on STRs with 18,665 patients on individual component therapy. Data were collected for prescriptions, significant cardiovascular events, and out-patient referrals over a minimum follow-up period of 5 years after initiation of therapy. Current NHS costings were applied to the data, to arrive at an estimate of comparative resource use.
RESULTS: There were significantly more cardiovascular events in the individual component group than those treated with a single tablet regimen. Five year event rates: 8.3% vs 13.6%; Absolute Risk Reduction (ARR) =5.3%; Number needed to treat (NNT) =18.9. After correction for potential confounders, the hazard ratio was 0.74 (95%CI=0.70-0.77), p<0.0001. Hospital admission costs were lower in the STR group, but drug costs were higher. Overall, the mean annual management cost per patient was similar in the two groups (£191.49 vs £189.35). KEY LIMITATIONS: The study was based on a retrospective cohort and the result may therefore be influenced by unidentified confounders. It was not possible to identify the reasons for individual prescriptions, some of which may have been issued for reasons other than hypertension. Costings for some components of the outcome could not be assessed from the dataset and are therefore omitted from the analysis. Finally, no attempt was made to distinguish outcomes associated with individual classes of anti-hypertensives.
CONCLUSIONS: This study confirms the association observed by other authors that patients treated with STRs are less likely to experience serious cardiovascular events than those on individual component therapy. In a UK context this analysis has shown that potential hospital savings broadly offset the additional drug acquisition costs associated with STRs. These agents can therefore be considered cost neutral.