Population Profiles of Drug Expenditure and Drug Use
illustrates the age/sex profile of the BC population in 1996 and 2002 and, on the right-hand scale, the total percentage change in the share of the population (male plus female) that fell in the age-specific cohort between 1996 and 2002. It illustrates the wave of baby-boomers, roughly aged 40–60 in 2002, followed by a decline in the population profile (the “baby bust” generation, or generation X), and then a second relatively large generation comprised of the boomers children (the echo generation) (Foot and Stoffman 1998
). Owing to aging of the boomers, the share of the population aged 45–60 grew significantly: rising from 18.8 percent in 1996 to 22.5 percent in 2002. In contrast, the share of the population younger than 10 declined from 13 percent in 1996 to 11.3 percent in 2002, and the population share aged 21–40 fell from 31.6 to 28.3 percent. Owing to increased longevity in BC, the share of the population aged 85 and older increased from 1.4 percent of the population in 1996 to 1.8 percent of the population in 2002.
Age/Sex Profiles of Population, 1996 and 2002
The effect of population aging on overall drug expenditures will depend on the gradient of age-specific drug expenditure—. Over the male and female age-specific drug expenditure profiles in both 2002 and 1996, average expenditures for an individual increased by roughly 3.5 percent per year of age from 35 to 65 years of age. Age-specific expenditures per capita fall beyond age 80, which may reflect a healthy-survivor selection bias. In addition to the slope in the age gradient, the other principle finding from is that, between 1996 and 2002, age-specific drug expenditures increased by between 60 and 90 percent for adults over age 30 and increased by 20–60 percent for younger populations.
Age/Sex Profiles of Expenditures per Capita, 1996 and 2002
Factors contributing to the age/sex profiles of drug expenditures are illustrated in . Each graph in illustrates the age-specific levels of a variable for males and females as well as the percentage change in these variables for all persons of given ages (male and female combined). The scale of the percentage change measures is found on the right side of each graph; moreover, it is identically scaled across all graphs in , allowing ready comparison of the differences in growth across ages and across variables.
The profile of “use” of any drug treatment shows that the share of an age/sex cohort that receives one or more prescription drugs increases slightly with age and is notably higher for females, particularly those of childbearing age. While not shown in the figure, secondary analysis illustrated that use in drugs from ATC categories G (“genito urinary system and sex hormones”) and N (“nervous system”) explain virtually all of the gender difference between ages 13 and 73. In both 1996 and 2002, greater than 75 percent of females over age 17 filled one or more prescriptions; only males over age 55 filled prescriptions at a rate of 75 percent or more. The rate of drug use among adults over age 50 increased by 2–5 percent between 1996 and 2002, while use fell for younger cohorts, particularly children under 13 years of age.
Conditional on use of at least one drug of any kind, the average number of distinct therapeutic categories from which patients received prescriptions increased with age and was consistently higher for females beyond childhood. The average child that was exposed to any drug therapy filled prescriptions from approximately 1.5 different therapeutic categories. Rising steadily with age, the average number of categories of drug received by prescription users was above three for residents aged 50 and older and above four for residents aged 80 and older. Between 1996 and 2002, this age/sex-specific profile rose only slightly, with the rate of change slightly greater for older adults.
The age/sex profile of prescriptions filled per patient per therapeutic category had a moderate, positive slope between ages 15 and 65. Beyond age 65, this positive age-gradient increases substantially, particularly for females. The number of prescriptions per patient per therapeutic category increased between 1996 and 2002 at rates ranging from 20 to 31 percent across adult cohorts. The change was more rapid for males than females. Whereas males and females age 23–64 filled comparable numbers of prescriptions per course of therapy in 1996, male prescription users age 23–64 filled a larger number of prescriptions per therapeutic category than their female contemporaries did in 2002.
The average cost per prescription filled increased with age up to age 70 for both the 1996 and 2002 age/sex profiles. Costs per prescription fell sharply with age beyond age 70. Given the profile of prescriptions per patient per category, it appears that older users of prescription drugs fill a greater quantity of less costly prescriptions per course of treatment. This may reflect the dispensation of “shorter” prescriptions for older populations. Age/sex-specific costs per prescription, which rose at rates of 17–50 percent, increased more rapidly than other factors contributing to age-specific expenditures per capita. Growth in costs per prescription was highest among children, and lowest among residents aged 67–84. Total price inflation between 1996 and 2002 for the drug products selected per prescription was approximately 0.9 percent for adults (of all ages) and 1.2 percent for children (average annual rates of 0.13 and 0.17 percent, respectively). This indicates that almost all of the change in costs per prescription stemmed from changes in the mix of products selected.
Causes of Change in Population-Wide Expenditures per Capita
The preceding profiles of drug expenditure and utilization measures combine to determine population-wide expenditures per capita. Prescription drug expenditures per BC resident increased by 86 percent from $186 in 1996 to $344 in 2002. Expenditures per female increased by 82 percent, from $213 to $389, and expenditures per male increased by 90 percent, from $158 to $300. lists the determinants of these changes in expenditure per capita for all prescription drugs, and for the fastest growing therapeutic categories.
Determinants of Change in Per Capita Prescription Drug Expenditures, 1996–2002
Population aging per se was sufficient to increase per capita drug expenditures by 6 percent (6 percent for females and 7 percent for males). Aging had a slightly larger impact on expenditures per male because the age gradient of expenditure per male was steeper over the range of ages for which population growth was most rapid. After accounting for aging, increases in age-specific drug expenditure along the demographic profile caused population-wide prescription drug expenditures per capita to increase by 75 percent between 1996 and 2002. Age-specific expenditures increased more rapidly for males (77 percent) than for females (73 percent).
The most significant determinant of drug spending at the population level—slightly more so for females than males—was changes in the age-specific mix of drugs prescribed per prescription. These changes were sufficient to increase the average expenditures per capita by 31 percent (29 percent for males and 32 percent for females). The second largest impact on per capita drug expenditures was the age-adjusted number of prescriptions filled per patient per therapeutic category, which increased population-wide per capita expenditures by 26 percent (29 percent for males and 23 percent for females). Changes in the age-specific rates at which residents used one or more prescription drugs had no measurable impact on population-wide drug expenditures, whereas the rise in age/sex-specific average numbers of categories used per “exposed” patient caused expenditures per capita to increase by 5 percent. Finally, drug price inflation (for existing products) increased expenditures per capita by 1 percent.
Causes of Change by Drug Category
In 1996 and 2002, over 75 percent of total drug expenditures were concentrated in the five fastest-growing broad therapeutic categories of drug treatment—. In descending order of expenditure, these categories were cardiovascular; nervous system; alimentary tract and metabolism; genitourinary system and sex hormones; and antiinfectives for systemic use.
Cardiovascular medicines were the largest drug category in terms of spending for males and second largest for females. Population aging caused per capita cardiovascular drug expenditures to rise by 10 percent between 1996 and 2002. This was slightly higher than the impact of aging on overall drug expenditures per capita because of the fact that there is a relatively steep age gradient in cardiovascular drug expenditures. Increases in the rate at which patients received cardiovascular drugs and increases in the quantity of prescriptions filled per recipient explained most of the expenditure change in this category. Given the breadth of the cardiovascular category, some of the increase in prescriptions filled per patient may reflect increased treatment of concomitant cardiovascular conditions (e.g., high cholesterol and hypertension).
Expenditure on nervous system treatments grew more quickly than overall drug expenditures, and accounted for 25 percent of total expenditures in 2002. Population aging had a relatively modest, 5 percent impact on nervous system drug expenditures because the age gradient was relatively flat for this therapeutic category. Most of the increase in nervous system drug expenditures resulted from age-adjusted increases in the number of prescriptions per recipient of therapy and changing mix of products selected.
Demographics played varying roles in the remaining top-selling therapeutic categories. While population aging had a pronounced impact on cardiovascular drug expenditure, it played a minor role in the antiinfective category. Aging had a small impact on genitourinary drug expenditure per female, but had a significant impact on expenditure per male in the same class. After adjusting for aging, the rate of use was the most significant determinant of increased spending on genitourinary drugs. Changes in the mix of drugs selected per prescription had the most significant impact on expenditures per capita for the remaining large therapeutic categories: alimentary tract and metabolism drugs; and antiinfectives for systemic use.