People treated with low-dose beta blockers after a heart attack may fare better than those given the standard dose of this commonly prescribed medication, a new study suggests.

Heart attack patients given just one-fourth of the dosage used in clinical trials lived just as long as patients on a higher dose, according to researchers at Northwestern University in Chicago.

And in some cases, those on a low dose lived even longer, with a 20 percent to 25 percent increase in survival. To maximize effectiveness, beta-blocker dosage should probably be personalized for individual patients, the study authors advised.

"We set out on a mission to show if you treat patients with the doses that were used in the clinical trials, they will do better. We expected to see patients treated with the lower doses to have worse survival," lead investigator Dr. Jeffrey Goldberger said in a university news release. "We were shocked to discover they survived just as well, and possibly even better."

Goldberger is a professor of medicine at Northwestern's Feinberg School of Medicine and a cardiologist at Northwestern Memorial Hospital. He also directs the cardiac arrhythmia program at Feinberg's Center for Cardiovascular Innovation.

Based on these findings, Goldberger said new studies should be conducted to determine the effects of different beta blockers and which are most effective for individual patients.

"There is probably not one right dose for every single patient," he said. "It doesn't make sense that the same dose will work for an 80-year-old frail man who had a small heart attack as a burly 40-year-old man with a huge heart attack," Goldberger explained.

The study included information on nearly 6,700 heart attack patients. Ninety percent of them were prescribed a beta blocker. Every patient on a beta blocker lived longer than those who were not given this medication, the investigators found.

Among those who received a full dose, nearly 15 percent died within two years, compared with just under 13 percent who got a half-dose of the drug. Meanwhile, 9.5 percent of the patients on a quarter-dose and 11.5 percent of those on a one-eighth-dose died during this time period, according to the study published Sept. 21 in the Journal of the American College of Cardiology.

"We now need to figure out how to dose it in individual patients. That's something no one has considered in the decades that we have been using this medication," Goldberger said.

"This huge gap in knowledge has been completely unexplored. Since this is medicine we use in every single heart attack patient, we ought to figure out how to use it properly," he said in the news release.

Roughly 90 percent of people treated for a heart attack are given a beta blocker, the study authors noted. This class of medication, which includes metoprolol (Toprol XL) and acebutolol (Sectral), is used to improve survival and prevent future heart attacks.

Beta-blockers work by blocking the effects of adrenaline on the heart. They also reduce irregular heartbeat and help prevent heart failure. Some patients are treated with low doses of the drug if there are greater concerns about possible side effects, such as fatigue, sexual dysfunction and depression, the study authors said.