Obesity complicates shots in buttocks, study finds

In most cases, the needle couldn't get past the layers of fat to reach muscle.
SCRIPPS HOWARD
That traditional shot in the behind may be doing less and less good as people become plumper, according to a new study presented Monday.
"Our study has demonstrated that a majority of people, especially women, are not getting the proper dosage from injections to the buttocks. There is no question that obesity is the underlying cause," said Dr. Victoria Chan, a researcher at the Adelaide and Meath Hospital in Dublin, Ireland.
Her study found that as few as one in 10 women and six in 10 men may be getting proper doses from injections because the needle can't reach the target zone.
She presented the findings during the annual meeting of the Radiological Society of North America being held in Chicago this week.
Many drugs and vaccines are typically administered through injections into the muscles of the buttocks, including painkillers, antibiotics and anti-nausea drugs.
The region is considered a good spot because it has relatively few major blood vessels, nerves or bones to be damaged by a needle, yet has many small blood vessels that speed absorption of drugs.
But the new study showed that "68 percent of intramuscular injections do not reach the muscles of the buttock," Chan said. "The amount of fat tissue overlying the muscles exceeds the length of the needles commonly used for these injections."
Why this is a problem
Since fat tissue has significantly fewer blood vessels compared with muscle, less of a medication is absorbed into the bloodstream and delivered to the desired part of the body.
Yet drug companies design their injections with doses based on the expectation that the needle will reach a muscle target.
Coming up short in fatty tissue "results in the patient either not receiving the maximum benefit of the drug, or receiving no benefit at all, because the drug levels are insufficient to have any effect," Chan said. In addition, medicine that's not absorbed into the bloodstream can linger in the fatty tissue, where it can cause irritation and localized infection.
The solution, unfortunately, Chan said, may be to use longer needles. "The more fat tissue there is in the buttock, the less likely the needle will reach the muscles underneath that fat."
The study involved 50 patients -- half men, half women, ranging in age from 21 to 87, who were scheduled to undergo computed tomography, or CT, scans of the stomach or pelvis for a medical condition.