The Effects of Mandatory Prescribing of Thiazides for Newly Treated, Uncomplicated Hypertension: Interrupted Time-Series Analysis

Background: The purpose of our study was to evaluate the effects of a new reimbursement rule for antihypertensive medication that made thiazides mandatory first-line drugs for newly treated, uncomplicated hypertension. The objective of the new regulation was to reduce drug expenditures. Methods and Findings: We conducted an interrupted time-series analysis on prescribing data before and after the new reimbursement rule for antihypertensive medication was put into effect. All patients started on antihypertensive medication in 61 general practices in Norway were included in the analysis. The new rule was put forward by the Ministry of Health and was approved by parliament. Adherence to the rule was monitored only minimally, and there were no penalties for non-adherence. Our primary outcome was the proportion of thiazide prescriptions among all prescriptions made for persons started on antihypertensive medication. Secondary outcomes included the proportion of patients who, within 4 mo, reached recommended blood-pressure goals and the proportion of patients who, within 4 mo, were not started on a second antihypertensive drug. We also compared drug costs before and after the intervention. During the baseline period, 10% of patients started on antihypertensive medication were given a thiazide prescription. This proportion rose steadily during the transition period, after which it remained stable at 25%. For other outcomes, no statistically significant differences were demonstrated. Achievement of treatment goals was slightly higher (56.6% versus 58.4%) after the new rule was introduced, and the prescribing of a second drug was slightly lower (24.0% versus 21.8%). Drug costs were reduced by an estimated Norwegian kroner 4.8 million (€0.58 million, US$0.72 million) in the first year, which is equivalent to Norwegian kroner 1.06 per inhabitant (€0.13, US$0.16). Conclusions: Prescribing of thiazides in Norway for uncomplicated hypertension more than doubled after a reimbursement rule requiring the use of thiazides as the first-choice therapy was put into effect. However, the resulting savings on drug expenditures were modest. There were no significant changes in the achievement of treatment goals or in the prescribing of a second antihypertensive drug. Atle Fretheim and colleagues found that the prescribing of thiazides in Norway for uncomplicated hypertension more than doubled after a rule requiring their use as first-choice therapy was put into effect. Background.: High blood pressure (hypertension) is a common medical condition, especially among elderly people. It has no obvious symptoms but can lead to heart attacks, heart failure, strokes, or kidney failure. It is diagnosed by measuring blood pressure—the force that blood moving around the body exerts on the inside of arteries (large blood vessels). Many factors affect blood pressure (which depends on the amount of blood being pumped round the body and on the size and condition of the arteries), but overweight people and individuals who eat fatty or salty food are at high risk of developing hypertension. Mild hypertension can often be corrected by making lifestyle changes, but many patients also take one or more antihypertensive agents. These include thiazide diuretics and several types of non-thiazide drugs, many of which reduce heart rate or contractility and/or dilate blood vessels. Why Was This Study Done?: Antihypertensive agents are a major part of national drug expenditure in developed countries, where as many as one person in ten is treated for hypertension. The different classes of drugs are all effective, but their cost varies widely. Thiazides, for example, are a tenth of the price of many non-thiazide drugs. In Norway, the low use of thiazides recently led the government to impose a new reimbursement rule aimed at reducing public expenditure on antihypertensive drugs. Since March 2004, family doctors have been reimbursed for drug costs only if they prescribe thiazides as first-line therapy for uncomplicated hypertension, unless there are medical reasons for selecting other drugs. Adherence to the rule has not been monitored, and there is no penalty for non-adherence, so has this intervention changed prescribing practices? To find out, the researchers in this study analyzed Norwegian prescribing data before and after the new rule came into effect. What Did the Researchers Do and Find?: The researchers analyzed the monthly antihypertensive drug–prescribing records of 61 practices around Oslo, Norway, between January 2003 and November 2003 (pre-intervention period), between December 2003 and February 2004 (transition period), and between March 2004 and January 2005 (post-intervention period). This type of study is called an “interrupted time series”. During the pre-intervention period, one in ten patients starting antihypertensive medication was prescribed a thiazide drug. This proportion gradually increased during the transition period before stabilizing at one in four patients throughout the post-intervention period. A slightly higher proportion of patients reached their recommended blood-pressure goal after the rule was introduced than before, and a slightly lower proportion needed to switch to a second drug class, but both these small differences may have been due to chance. Finally, the researchers estimated that the observed change in prescribing practices reduced drug costs per Norwegian by US$0.16 (€0.13) in the first year. What Do These Findings Mean?: Past attempts to change antihypertensive-prescribing practices by trying to influence family doctors (for example, through education) have largely failed. By contrast, these findings suggest that imposing a change on them (in this case, by introducing a new reimbursement rule) can be effective (at least over the short term and in the practices included in the study), even when compliance with the change is not monitored nor noncompliance penalized. However, despite a large shift towards prescribing thiazides, three-quarters of patients were still prescribed non-thiazide drugs (possibly because of doubts about the efficacy of thiazides as first-line drugs), which emphasizes how hard it is to change doctors' prescribing habits. Further studies are needed to investigate whether the approach examined in this study can effectively contain the costs of antihypertensive drugs (and of drugs used for other common medical conditions) in the long term and in other settings. Also, because the estimated reduction in drug costs produced by the intervention was relatively modest (although likely to increase over time as more patients start on thiazides), other ways to change prescribing practices and produce savings in national drug expenditures should be investigated. Additional Information.: Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040232.