Obesity influences effectiveness of injected drugs

November 27, 2005

The size of one’s backside is normally a sensitive subject, but at the RSNA meeting the topic was the focus of a scientific study presented Sunday. The study found that patients with large behinds do not receive the biggest benefit from vaccines and other injections into the buttocks.

The size of one's backside is normally a sensitive subject, but at the RSNA meeting the topic was the focus of a scientific study presented Sunday. The study found that patients with large behinds do not receive the biggest benefit from vaccines and other injections into the buttocks.

The study, by Victoria Chan and colleagues at the Adelaide and Meath Hospital in Dublin, Ireland, involved 60 obese men and women scheduled for CT scans of the abdomen and pelvis and who were receiving intramuscular medication. The team found that 68% of intramuscular injections did not reach the muscles of buttock.

The overall success rate of the injections was 32%. The success rate among men was 56% compared to only 8% among women. Compared to men, women typically have a higher amount of fat in their buttocks.

Medications are designed so that the proper dosage is absorbed into the blood stream from the muscle. Because fat tissue has far fewer blood vessels than muscle, less medication is absorbed into the blood stream and delivered to its intended anatomic target.

"The amount of fat tissue overlying the muscles exceeds the length of the needles commonly used for these injections," Chan said.

As a solution, Chan proposed using longer needs to increase the success rate of intramuscular injections.