Patient adherence to prescribed potassium supplement therapy

We have investigated whether patient adherence ratios calculated from prescription refill data for potassium supplement medications differ depending on the type of supplement. By using automated pharmacy claims records from a large managed care organization, an index of adherence to prescribed therapy was calculated for each patient as a ratio of total days of drug supplied to the total number of days between prescription refills. The mean patient adherence to prescribed therapy ratios were compared among different potassium drug regimens. There were 2289 patients eligible for analysis; 65.9% were women, and the mean age was 57.6 years. The mean patient adherence ratio for one brand of extended-release tablet, K-DUR, was 0.81 (a majority of the patients were receiving 20 mEq/day). This was higher than the combined mean patient adherence ratio for all other supplements (0.73); the combined mean ratio for all other extended-release tablets (0.74); the combined mean ratio for all other tablets and capsules (0.74); the combined mean ratio for liquids (0.50); the combined mean ratio for liquids and powders (0.63); and equivalent to the ratio for another extended tablet, Micro-K (0.82). Regression analysis showed that increased patient adherence was seen among patients taking K-DUR tablets as compared with those taking other potassium supplements. Increased adherence among patients taking K-DUR remained statistically significant after controlling for number of prescriptions filled, dose, age, sex, and health plan location. Pharmacy claims data can be used effectively to measure patient adherence with potassium supplement therapy. Future research should relate patient adherence ratios to clinical outcomes.