Validation of observed differences in the utilization of antihypertensive and antidiabetic drugs in Northern Ireland, Norway and Sweden.

The amount of antihypertensive and antidiabetic drugs based of defined daily doses per 1000 inhabitants per day varies two to three fold between Northern Ireland, Norway, and Sweden. We explored whether variations based on the universally applied defined daily doses might be accounted for by national differences in the actual average prescribed daily doses. Use of prescribed daily doses for antihypertensive drugs resulted in Northern Irish and Norwegian consumption figures which were respectively 40 and 21% lower than the Swedish one, compared to 38 and 25% when defined daily doses were used. The effect of population age-sex differences on the gross defined daily doses per 1000 inhabitants per day figures was determined by applying the Northern Irish or Norwegian age-sex group proportions to Swedish age-sex specific sales data. Taking population differences into account would have resulted in antihypertensive drug use being 21 rather than 38% less in Northern Ireland and 18 rather than 25% less in Norway. Also adjustment for prescribed daily doses left an unexplained difference of 23% between Sweden and Northern Ireland and 14% between Sweden and Norway. For oral antidiabetics use of prescribed daily doses resulted in a Northern Irish - Swedish difference of 62% compared to 67% when defined daily doses were used. Simultaneous adjustment for population differences and prescribed to defined daily dose variations left a 52% difference.