Although differences in age-distribution seems to be an important variable in the explanation of differences statin consumption, it does not fully outweigh the inter-county variation of statin consumption in Norway. Variations in prevalences of use, and treatment intensity in terms of PDD and choice of statin also affect the total consumption.
Not surprisingly, the estimated PDDs for all statins were higher than the DDDs – up to twice the DDD for atorvastatin. The official DDDs for all statins have remained unchanged since 1994 and have not been adjusted to the new clinical documentation published over the last decade [10]. As indicated from all statin prescriptions dispensed for the first time in 2004; extensive use of atorvastatin, combined with a systematically higher PDD for all relevant statins in the high-consumption county Hedmark, influences total level of, and thereby variation in, statin consumption.
A limitation with this study is the lack of information on statin use in relation to other relevant patient characteristics such as cardiovascular morbidity and risk factors, including clinical measurements. However, the tendency of an overall more aggressive cholesterol treatment in the high-consumption county, Hedmark, is in line with previous findings from our population-based study in Hedmark and the average-consumption county, Oppland: a higher proportion of the statin users in Hedmark achieved the nationally recommended TC target [4]. Although we do not know to what extent LLDs dispensed actually are ingested, patterns of the number of tablets dispensed per day were similar between the counties in our present study. Thus, the success in achieving TC target in Hedmark may most likely be attributed the use of higher dosages, rather than increased continuity of use.
Overall achievement of TC target among statin users in our previous study in Hedmark and Oppland were, however, suboptimal. Only 40–60% of the statin users achieved the recommended TC target, consistent with results from other population-based studies in Norway from the same period [11, 12]. Although the presentation of tablet strength according to the first statin prescription dispensed do not take into account a future uptitration of the dose among incident users, it still seems to be a potential for optimising dosing of statins. For example, in our study, only 20–30% of all simvastatin users were on doses corresponding to the dose (40 mg) used in recent pivotal trials, such as the Heart Protection Study [13].
The observed variations in prevalences of statin use in our present study, may be explained by previous findings of a varying threshold for the initiation of statin therapy for primary prevention between the high- and average-consumption counties Hedmark and Oppland. Interestingly, this previous study identified a gap between current practice and guideline recommended level of statin use for primary prevention in both counties [4]. In this situation, the variation in prevalence of statin use today may be small compared with a "scenario" of full implementation of guidelines in either of the regions.
The prevalence patterns of statin use, however, were similar in the counties: increasing with age, peaking in the age group 70–79 years in both sexes. A third of all 70- to 79-year-old men in the high-consumption county, Hedmark, had at least one statin prescription dispensed in 2004. As a comparison, a quarter of all 75-year-old men reported use of a statin in this county in 2000–1 [4]. The age pattern of current statin use seems to be oriented towards more extensive use among elderly people, compared with the situation in the 1990s, where the peak of statin use was observed in individuals aged ten year younger [14–16]. This shift could be explained by several factors:
1. First, statin therapy would normally be a lifelong treatment. Naturally, the age of middle-aged patients, in whom the efficacy was initially documented and therefore recommended in the 1990s, will increase over time. Most patients seems adhere to treatment for many years in Norway [17, 18] and other populations with comparable reimbursement systems, such as in Denmark [19, 20].
2. Second, recent statin trials have extended our knowledge of the benefit of statin use in elderly people up to about 80 years of age, in secondary prevention of CVD in particular [13, 21]. Hence, current Norwegian guidelines now discuss statins for secondary prevention up to this age [22]. The high prevalence in this age group in our study may reflect recommendations being adopted in clinical practice. Corresponding age trends are seen in Denmark: the 75–84 year olds had the highest relative increase in statin use in a study of myocardial infarction (MI) patients in the period 1995–2002 [23].
In our study we found a markedly lower statin use among those aged 80+ compared with the 70–79 year olds in all three regions. These figures are parallel to findings from Norwegian hospitals. The majority of all MI patients aged up to 80 years were discharged with a statin, compared with one in ten of those aged 80 and above [17]. Documentation of beneficial effects of statins in very old people is limited, and our observations may reflect the scepticism among Norwegian doctors to prescribe statins based on extrapolation from evidence among younger individuals.