Utrecht, The Netherlands—Researchers looking at the effectiveness of a procedure to lower blood pressure (BP) in resistant hypertension came up with a surprising conclusion: As many as 20% of the patients seeing specialists for the condition weren’t taking any of their blood pressure medications.

The study, published in the American Heart Association’s journal Hypertension, found, in fact, that only one in five of the patients were taking all of their prescribed drugs. 

“Another twenty percent are not taking any of their blood pressure medications,” pointed out senior author Peter Blankestijn, MD, PhD, professor of nephrology and hypertension at the University Medical Center Utrecht in the Netherlands. “People mistakenly thought to have resistant hypertension—which is high blood pressure despite taking three or more medications—end up seeing specialists and undergoing extra tests because we don’t understand why they are so difficult to treat.”

The Dutch researchers had set out to determine if blood pressure could be lowered with renal denervation in addition to hypertension medication. In the procedure, a catheter is inserted into one of the blood vessels in the groin and advanced through blood vessels until it enters the artery feeding the kidney. Radio waves or ultrasound then are used to destroy sections of the nerves sending messages between the brain and the kidneys.

“There is much evidence to suggest that these nerves play a role in high blood pressure,” Blankestijn explained. “In the 1930s and 1940s, the nerves were sometimes cut during surgical procedures. Now the nerve destruction can be done in a much less invasive way. Several devices are being studied as possible treatments for resistant hypertension.”

The study found renal denervation as therapy for resistant hypertension was not superior to usual care, and it also uncovered some disturbing information about medication adherence among resistant-hypertension patients.

For the study, Dutch researchers randomly assigned 95 patients—average age 62 years, 42.1% male—to undergo renal denervation without a medication change; a control group of 44 patients—average age 60 years, 29.5% male—continued their usual drug therapy.

Daytime systolic blood pressure was measured and blood was drawn to determine effectiveness and medication adherence at the beginning of the study and 6 months later.

Results indicate that, in addition to 20% of patients taking all their medication and 20% none, 31% either improved or lessened their medication compliance. After 6 months, average daytime systolic blood pressure fell two points (mm Hg) more in control patients than in those who had renal denervation, but remained abnormally high in both groups.

Among patients with similar blood levels of medication at each assessment, meanwhile, systolic blood pressure fell 3.3 points more in those who received the procedure than in controls.

“Objective assessment of medication use shows that medication adherence is extremely poor when patients are unaware of monitoring,” study authors note. “Changes over time in adherence are common and affect treatment estimates considerably. Objective measurement of medication adherence during follow-up is strongly recommended in randomized trials."

“Adherence to medication greatly affects the ability to assess the value of another treatment, so researchers need to measure adherence and do what they can to improve it,” Blankestijn added.

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