Prescribing patterns of antilipemic drugs and prevalence of hypercholesterolemia in the Nova Scotia population more than 65 years old

The Impact of US FDA and Health Canada Warnings Related to the Safety of High-dose Simvastatin

Introduction

Between 2010 and 2012, the US Food and Drug Administration and Health Canada issued warnings to healthcare professionals emphasizing the increased risk of muscle problems with high-dose simvastatin.

Objective

To measure the impact of the Health Canada safety warning regarding dose-dependent adverse effects of simvastatin on prescribing of low, medium, and high doses of simvastatin.

Methods

An interrupted time-series design was used to evaluate the impact of a Health Canada safety warning on 7 November 2012 regarding the safety of high-dose simvastatin. Monthly prescription records were analyzed for beneficiaries of the Nova Scotia Seniors’ Pharmacare Program aged 65 years or older who had received > 1 prescription of simvastatin between 1 January 1997 and 31 March 2015. Autoregressive Integrated Moving Average models were used to test changes in the proportion of beneficiaries dispensed a low dose (< 40 mg), medium dose (40 mg to < 80 mg), or high dose (≥ 80 mg) of simvastatin over time.

Results

There were 219 monthly periods, of which 29 periods occurred after the Health Canada warning. On average during the pre-warning periods there were 2944 simvastatin users per month, of whom 71% were dispensed a low dose, 26% a medium dose, and 2% a high dose. The proportion of beneficiaries dispensed low-dose simvastatin increased by 0.9% (one-sided p value 0.035; 90% CI 0.07–1.65), the proportion dispensed medium-dose simvastatin decreased by 0.7% (one-sided p value 0.0496; 90% CI −1.48 to −0), and there was no significant change in the proportion dispensed high-dose simvastatin (−0.15% change, one-sided p value 0.205; 90% CI −0.45 to 0.15).

Conclusions

The Health Canada Health Care Professional warning had a small effect on increasing the proportion of beneficiaries dispensed low and medium doses of simvastatin but not high doses of simvastatin. Nevertheless, there remain seniors in Nova Scotia receiving high-dose simvastatin for whom the benefit/risk potential may need to be re-evaluated.

Comparison of different methods to estimate prevalence of drug use by using pharmacy records

Several methods to estimate prevalence of drug use are available, which may complicate a valid comparison of these estimates. Standardization may contribute to more valid comparisons. We compared different methods to estimate prevalence of drug use by using pharmacy records. Data were obtained from the Dutch population-based PHARMO-database comprising medication histories of 300,000 subjects. Five point prevalences and a 1-year prevalence of cholesterol-lowering drug use were estimated in 1995. Four point prevalences differed in data handling before estimating prevalence (e.g., correction for irregular drug use or construction of episodes of drug use). The numerator of the fifth point prevalence estimate represented the number of defined daily doses (DDDs) instead of the number of patients filling a prescription. The first four point prevalences ranged from 11.0-12.1 per thousand. Prevalence ratio (male:female) was 1.2 for these methods. The fifth method resulted in an estimate similar to the other point prevalences (11.9 DDDs/1000 inhabitants). However, the prevalence ratio was 1.4 due to larger average number of DDDs prescribed to men. One year-prevalence was 4-5 per thousand higher than point prevalences. The comparison of these methods indicated that the choice of prevalence measure (point versus period prevalence) substantially influenced the prevalence estimate, whereas the influence of data handling was negligible. For standardization purposes in drug utilization research, we recommend estimating point prevalence instead of period prevalence. The various methods of data handling before estimating point prevalence yielded similar results and therefore we cannot recommend one specific method. However, defined daily doses should not be used to estimate (point) prevalences of drug use because this measure is significantly influenced by prescribed dosage regimens.