Thursday January 13 2011
Longer-term effects of combined drugs have not yet been tested
A newly published study has suggested that “a combination of drugs is better than a single one in treating high blood pressure”, BBC News reported.
This randomised controlled trial found that starting patients on a combination of hypertension drugs gives a faster and greater reduction in blood pressure than either of the drugs on their own, without any more side effects. The drugs, amlodipine and aliskiren, work to lower blood pressure in different ways.
Doctors currently start patients with high blood pressure on one drug and may add others later if needed. The authors of this well-designed trial suggest that clinical practice should now be changed and that patients with high blood pressure be started on two drugs rather than one. However, although the results of this study are significant, it looked only at two specific types of drug, so cannot make comparisons of the effectiveness of treatment with other classes of blood pressure drug, whether used alone or in combination. Longer-term effects and adverse outcomes beyond 32 weeks (such as stroke, heart attack or early death) have not yet been examined.
People who are concerned about their blood pressure or its treatment should visit their GP.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge, the British Hypertension Society, the University of Glasgow, Novartis Pharma AG, Switzerland, and Ninewells Hospital and Medical School, Dundee. It was funded by Novartis Pharma AG and two of the study’s authors are employees of this company. The study was published in peer-reviewed medical journal The Lancet.
The study was mostly reported accurately by the BBC, however, the statement that the combined treatment had fewer side effects is incorrect. The proportion of people who withdrew due to side effects was actually the same for combined treatment and the group taking aliskiren plus placebo, but higher (18%) for those taking amlodipine. The claim by the Daily Express that the pill could “prevent 5,000 strokes a year” is not supported by the study, which looked at the effect of different treatments on blood pressure measurements, not on strokes or other cardiovascular outcomes.
What kind of research was this?
This randomised controlled trial investigated whether starting patients on a combination of high blood pressure (hypertension) drugs is more effective and causes no more side effects than either of the drugs on their own. This type of study design is thought to be the best for assessing the effectiveness of medical treatments.
Several different types of drugs are used in the treatment of high blood pressure. The two types tested in this trial were aliskiren, a type of drug known as a renin inhibitor, and amlodipine, a class of drug called a calcium channel blocker. The two drugs treat blood pressure in different ways.
The current practice is to start patients on one of the drugs, and then introduce another drug if required. However, the authors say that short-term studies have suggested that using a combination of drugs at the beginning of treatment may be better than one alone. They wanted to test whether this is the case.
What did the research involve?
Researchers recruited 1,254 patients from 10 different countries between November 2008 and 2009. Participants had to be at least 18 years old and have high blood pressure, which was defined as seated (resting) systolic pressure of between 150 and 180mmHg and diastolic blood pressure of less than 110mmHg. Blood pressure is a measure of the force of your blood in the blood vessels as the heart beats.
A blood pressure reading constitutes two measurements: systolic (when the heart pumps and the pressure is at its highest) and diastolic (when the heart relaxes and the pressure is lowest). Both are recorded during a single heartbeat. When interpreting blood pressure, both systolic and diastolic levels need to be taken into consideration together, as both are indicators of cardiovascular health.
The patients were asked to stop taking any existing treatments for hypertension at least two weeks before the trial began. Those taking treatments but whose systolic blood pressure did not meet the inclusion criteria (ie. was not between 150 and 180mmHg) were asked to stop taking them at least four weeks before starting the trial medication.
Patients were randomly assigned to one of three different groups for the first phase of the trial, which lasted 16 weeks. One group was treated with 150mg daily of aliskiren plus a placebo (dummy) drug, one group received 5mg of amlopidine plus a placebo and the third received both drugs, at the same doses. At eight weeks, all doses were doubled. The placebo drugs were used so that patients would not know which group they were in or whether they were taking one medication or two.
From 16 to 32 weeks, all patients received a combination of 300mg aliskiren plus 10mg amlodipine. From 24 weeks, depending on their blood pressure measurement, patients also received a diuretic drug called hydrochlorothiazide if needed, or placebo if not.
The researchers compared the effect of treatment with one and two drugs on systolic blood pressure, at 8, 16 and 24 weeks.
The trial sponsor (Novartis Pharma AG) was involved in some aspects of the study, including drawing up the detailed protocol, provision of drugs and data collection.
What were the basic results?
A summary of the main results:
- Patients given combination treatment from the start of the trial had a 6.5mmHg greater reduction in average systolic blood pressure than patients taking only one drug (95% Confidence Interval [CI] 5.3 to 7.7). Average reductions from the start of the trial to weeks 8-24 were 25.3mmHg in the initial combination group and 18.9mmHg in each of the single drug groups.
- At 24 weeks, when all patients were on combination treatment, those who had initially started on the combined treatment still had lower blood pressure, but with an average difference of only 1.4mmHg from people who had started on single medication. This was only of borderline significance (95% CI –0.05 to 2.9, p=0.059 [significance is at p<0.05]). Average systolic blood pressure reductions from the start of the trial to 24 weeks were 27.4mmHg in the combination group and 25.9mmHg in each of groups initially treated with a single drug.
- Side effects caused 85 patients (14%) to withdraw from the group taking both drugs from study start, 45 (14%) from the aliskiren group and 58 (18%) from the amlodipine group. The most common side effects were swelling of the lower legs and symptoms of low blood pressure.
- There was no difference in the proportions requiring add-on diuretic blood pressure treatment after week 24 (27% of those treated initially with combination; 26% treated initially treated with a single drug).
How did the researchers interpret the results?
The authors conclude that starting treatment for high blood pressure with two drugs is more effective than starting with one and should therefore be recommended.
This high quality study has several strengths, including its relatively large size and that most of the participants in each of the three groups completed the trial. The researchers found that taking a combination treatment for high blood pressure from the start was more effective and had a similar number of side effects than taking just one drug, and then adding a second later. The blood pressure of patients who were started on only one drug never improved as much, on average, as those who were started on two drugs. However, the difference between the groups at the end of the trial when all were on both treatments was then only 1.4mmHg, and this was only of borderline significant difference. It should be noted that:
- The final effects on blood pressure of the different treatments were measured at 24 weeks. The results may have been different if the study had gone on longer, with the blood pressure of those started on only one drug decreasing to comparable levels to those who were started on the combination treatments.
- The study looked at the effectiveness of two specific drugs. It is uncertain if the results apply to other types of drug in the same class or to other classes of blood pressure drug.
- The study was in a defined, predominantly white population, with average systolic blood pressure of over 160. It is uncertain if the results would be the same in other groups.
- More than half of the patients had previously been treated for high blood pressure, although they were taken off previous treatments. It is uncertain if the results of the trial are applicable to patients who have not been treated with blood pressure medication before.
- Finally, the trial does not look at outcomes such as the effect of different drug regimens on heart disease, stroke and premature death. A far longer, larger study would be needed to do this.
These appear to be robust findings. Changes to treatment recommendations usually require strong evidence that a treatment method is better than the one currently in use. It is therefore likely that these results will be considered together with other evidence on the subject. Further research will be needed to gather enough evidence to show whether combination treatment should automatically be given to patients diagnosed with hypertension.