Frequency and predictors of tablet splitting in statin prescriptions: a population-based analysis

Abstract

Background: The price per milligram for most statin medications decreases at higher strengths, which provides an economic incentive to split tablets. We sought to determine the frequency with which statin tablets are split, and to evaluate factors associated with this practice.

Methods: We obtained prescription claims data for statins from the BC Ministry of Health for the period Jan. 1, 1996, to Dec. 31, 2006. We estimated the number of tablets per day, based on the ratio of the number of tablets to days-supply in each prescription, to estimate the frequency with which splitting occurred with each statin. We used multivariable logistic regression to assess patient and physician characteristics and the level of public drug plan coverage associated with tablet splitting. To estimate related cost savings, we used information on drug costs and quantities of dispensed statins reported by pharmacies.

Results: During the 11-year study period, we estimated that tablet splitting occurred in 2.6% of 7.2 million statin prescriptions. There was an increasing trend in the practice over time, to 4.5% of prescriptions in 2006. Lovastatin was the only scored tablet and was the most likely to be split, followed by rosuvastatin and atorvastatin. Fifty percent of the prescriptions in which tablet splitting occurred were prescribed by only 7.9% of the routine statin prescribers (i.e., > 10 statin prescriptions over the study period). Specialists were less likely than general practitioners to prescribe statins that were subsequently split (odds ratio [OR] 0.43, 95% confidence interval [CI] 0.40-0.46). Statin prescriptions that were fully covered by the public drug plan were half as likely as those with no such coverage to involve tablet splitting (OR 0.48, 95% CI 0.44-0.92). Having no public drug coverage, having a low annual household income and being female were patient factors found to be positively associated with tablet splitting. In 2006, the cost savings associated with tablet splitting was $2.3 million.

Interpretation: The frequency of tablet splitting in statin prescriptions in British Columbia was low but increased over time. It varied between patients, physicians and different levels of insurance coverage. In the final study year, 94.5% of the statin prescriptions were dispensed at strengths for which a tablet of twice the strength was available and could have been split, which suggests a potentially enormous cost savings.

Table 1

Statins and splitting combinations included in the analysis

Table 2

Tablets:days-supply ratios for statin prescriptions dispensed in British Columbia, 1996-2006

Table 3

Characteristics of new users dispensed statin prescriptions in British Columbia, by tablet-splitting status, 1998-2006

Table 4

Factors associated with tablet splitting

Table 5

Potential ingredient cost savings from splitting statin tablets in British Columbia, 2006

Figure 1

Proportion of statin prescriptions in British Columbia that involved tablet splitting, 1996-2006