Statin usage in Australia and New Zealand, and problems with use of DDDs
There is a possible bias with the use of defined daily doses (DDDs)
when looking at statin usage, as used in Walley and colleagues’ analysis
of statin usage rates in Europe . This is because the DDD for
simvastatin is 15 mg/day, c.f. 10mg for atorvastatin
(http://www.whocc.no/atcddd/). Arguably, a more realistic DDD for
simvastatin should be 20mg/day – this is certainly our understanding of
relative potencies, and is in line with average daily doses for
simvastatin in Australia and New Zealand since the year 2000. The use of
15mg DDD for simvastatin will tend to overestimate patient-based usage for
statins across populations, by a factor of 20/15 = 1.33 of the simvastatin
proportion of total statin DDD. This means those countries with relatively
higher simvastatin use will have overstated statin use (e.g. Norway,
Sweden), compared with countries like Ireland with very little simvastatin
use compared to other statins.
We have adjusted for this anomaly, and think this means that France’s
usage rate in 2000 surpassed that of Norway, while Ireland’s rate
surpassed that of Germany (i.e. swapping rankings).
We have also made a crude estimate of usage rates in 2002, using Walley et
al’s "annual average increase 1998 to 2002 (%)", which we assume gives
exponential increases. If we were to assume the annual average increase
1998-2002 equally applied to the two years between 2000 and 2002, then
usage varies across countries even more. This is shown in the following
table and graph, where we have also included actual data for New Zealand
and Australia . New Zealand had DDD rates similar to England in 2000,
whereas Australia had uptake higher than anywhere in Europe.
However, since the lifting of prescribing restrictions for statins
for New Zealand in mid 2000, by November 2003 New Zealand’s DDD rates for
statins were equal with Australia, which we estimated to be at 74
DDDs/1000/day for both countries that month.
Of course, the use of DDDs depends upon the average daily dose of
statins used. In countries with higher average daily doses, this means
their DDDs (and “uptake”) will seem higher than other countries with the
same rates of usage per head of population. In terms of measuring uptake,
patient-based measures (e.g. patient-year equivalents from dispensing
data) may be more appropriate.
Public Health Physician
Pharmaceutical Management Agency (PHARMAC)
 Walley T, Folino-Gallo P, Schwabe U, van Ganse E; EuroMedStat group.
Variations and increase in use of statins across Europe: data from
administrative databases. BMJ. 2004;328:385-6.
 PHARMAC analysis of PBS data at
http://www.hic.gov.au/statistics/dyn_pbs/forms/pbs_tab1.shtml, and PHARMAC
New Zealand PharmHouse data, denominated by Australian and New Zealand
census data (with intercensal interpolations and extrapolations)
Competing interests: No competing interests