Fat people don't get the full benefit of intra-muscular injections as fatty tissues often exceed the needle length. The remedy could be a longer needle, says a scientist.

Victoria Chan, M.B of the Adelaide and Meath Hospital in Dublin and colleagues studied 50 patients, equally divided between men and women, who were at their institution for a CT scan of their abdomen and pelvis, reports health portal MedPageToday.

With their consent, they gave the patients intra-muscular injection -- which included a small air bubble - in the upper quadrant of the buttocks, using a standard 23-gauge needle.

Two independent radiologists analysed CT scans to fix the position of the bubble, Dr Chan said. The analysis found that among the women, 23 of 25 injections - or 92 percent - failed to reach muscle.

Among men, 11 of 25 injections - or 44 percent - missed the mark. Overall, the failure rate of the injections was 68 percent.

The take-home message for clinicians is that a longer needle may be needed, Dr Chan said - especially for women, who typically have more fat and less muscle in their buttocks than men.

Many medications are administered through injections into the muscles of the buttocks, including painkillers, vaccines, contraceptives and anti-nausea drugs.

"The more fat tissue there is in the buttock, the less likely the needle will reach the muscles underneath that fat," Dr. Chan said.

The details of the study were presented at a conference of the Radiological Society of North America.