HMG CoA reductase inhibitors, also called statins, are lipid-lowering drugs. Together with a diet, they are given as treatment for hypercholesterolemia and for cardiovascular disease risk reduction. The most common adverse effects of statins are muscle pain (myalgia) and increased muscle enzymes (myopathy), and raised liver enzymes. The uptake of statins in Australia has been substantial, amounting to a total yearly cost of more than $1,100m in 2005 (government and patient contribution combined) (Department of Health and Ageing, 2005).
The PBS qualifying criteria for statin benefits are complex. According to a flowchart, first lifestyle and dietary changes should be made for at least 6 weeks, and continued henceforth.
Statin therapy is then subsidised if fasting cholesterol exceeds a threshold level. The threshold depends on age and gender, family history, and conditions such as diabetes and coronary heart disease. In some cases statins are subsidised without raised cholesterol levels, for example in patients with symptomatic coronary heart disease or in diabetes patients over 60 years of age (Department of Health and Ageing, 2005).
Women and men differ in their life course of cholesterol profile and cardiovascular disease risk.
In both sexes the risk increases with age, but the increase occurs about 10 years later in women than in men. This is thought to be at least partly due to a (menopausal) reduction in circulating estrogens, resulting in an increase in LDL cholesterol. Ageing, hypertension and changes in body composition are also likely to contribute. The sharp increase in cardiovascular disease risk associated with menopause makes mid-age an interesting phase to study statin uptake by women; this section therefore focuses on the Mid-age cohort. The following sections address uptake of statins over time; characteristics of users, and adherence.
5.3.1. Uptake over time
Statin prescriptions were identified in the PBS by ATC coding: C10AA/C10B. Although uncommon in the Younger cohort, statin use was common and increasing between 2002 and 2005 in the Mid-age and Older cohorts, shown in Table 5-1. The pattern of increase in use in the Mid-age cohort, in percentages, is shown with the national statistics for all ages and both sexes, expressed as the number of defined daily doses per 1,000 people per day (Department of Health and Ageing, 2005) in Figure 5-1. Although on different scales, the patterns of increase are similar. This suggests that although a sharp increase in statin uptake by the Mid-age cohort can be expected on the basis of increased incidence of hypercholesterolemia in this
age group, part of the increase reflects a trend in the whole Australian population beyond the effects of ageing.
Table 5-1 Statin use in the three age cohorts, per year (column percentages)
2002 2003 2004 2005 Younger cohort (n=4,376)
Yes 0 0 1 1
No 100 100 99 99
Mid-age cohort (n=7,318)
Yes 10 12 14 16
No 90 88 86 84
Older cohort (n=5,752)
Yes 32 33 33 34
No 68 67 67 66
a)
b)
Figure 5-1 Statin claims over time; (a) among ALSWH participants and (b) national statistics
5.3.2. Longer-term use of statins
Characteristics of statin claimants at Survey 3 are shown in Table 5-2 for Mid-age women who consented to linkage to PBS data. Current claimants are women who were claiming statins at the start of PBS data collection in 2002, new claimants are those who first started claiming statins at least three months after the start of data collection. Non claimants are women who consented to linkage to PBS data but did not have a claim for statin medications between 2002 and 2005. Statin claimants had lower levels of education, were less likely to be employed and had more difficulty managing on their available income than non-claimants (P<0.001). There were no statistically significant differences in area of residence or marital status. Health and use of health services are shown in Table 5-3. As expected statin claimants were more likely to be postmenopausal, this includes surgical menopause such as having had a hysterectomy and/or oophorectomy. They were also more likely to have diabetes, hypertension or heart disease, and they had more yearly visits to a GP or specialist.
Table 5-2 Sociodemographics of Mid-age women according to statin claims
Statins
Characteristics at Survey 3
Non claimants
N=5,860
%
Claimants in 2002
N=544
%
New claimants 2002 - 2005
N=788
%
Level of education
No formal qualification 13 22 16 School or leaving certificate 48 50 53 Trade, apprenticeship, diploma or higher
education
39 28 31 Area of residence
Urban 37 38 39
Rural/remote 63 62 61
Marital status
Married/defacto 82 79 83
Separated/divorced/widowed 15 17 14
Single 3 4 3
Ability to manage on income
Impossible/difficult all the time 9 16 14 Not too bad/difficult some of the time 70 70 69
Easy 21 14 17
Employment No permanent paid work 41 58 48 Full or part time paid work 59 42 52
Table 5-3 Health and use of health services among Mid-age women according to Statin claims
Heart disease (angina, heart attack)
Yes 2 14 6
No 98 86 94
Number of yearly GP visits
Never, once or twice 46 21 32
3 to 6 42 51 48
7 to 24 11 24 19
More than 24 1 2.8 1
Number of yearly specialist visits
Never, once or twice 87 77 81
3 to 6 10 18 15
7 to 24 2 4 3
More than 24 0 1 0
* Statistically significantly different at P<0.0001
Statins are maintenance drugs; they have to be taken over a long period of time to be effective.
Generally, less than 50% of patients on long-term medication adhere adequately to prescriptions (N. H. Miller, 1997). Especially for drugs such as statins, that do not relieve symptoms but are taken exclusively for prevention of future morbidity, adherence is generally poor. This poor adherence leads to missed health benefits and subsequently increased disease related medical costs. We can infer non-adherence to medication from PBS data: that is, those women who do not fill repeat prescriptions are not adhering to recommended use patterns for statins. To determine adherence to statins in the Mid-age cohort, we identified new claimants of statins: a total of 788 women started claiming statins between 2002 and 2005. They were aged 55 [51 to 59] years at the time (median [range]). By the PBS requirements, they must all have had raised fasting cholesterol levels in spite of dietary measures, or they had significant cardiovascular risk factors. Risk factors include having symptomatic coronary heart disease, symptomatic cerebrovascular or peripheral artery disease, or having a first degree family member who died of coronary heart disease before the age of 45.
A majority of the initial statin prescriptions were issued by GPs (80%). The remainder of first prescriptions were issued by practitioners from a range of specialties such as cardiology, general medicine and endocrinology. Adherence was measured by determining the duration of continuous PBS claims. The period of continuous use was defined as the time from starting to claim statins, until failing to fill a script on time. ‘On time’ was defined as two weeks; because
each script lasts for a month, filling the next script after a break of more than two weeks means treatment coverage of less than two-thirds. The median number of days of continuous use was 137 (95% confidence intervals [125 to 157]) for new users. In other words, in less than five months half the women had failed to fill a script on time. Overall adherence is shown in Figure 5-2. A sharp decrease is seen at the start of claiming for statins; this corresponds with failure to fill the second (9%) script; 26% failed in timely script filling before the third script.
Figure 5-2 The declining percentage of Mid-age women who are still continuous users of statin medication