“There is no question that obesity is the underlying cause,” said Dr Victoria Chan, registrar in the clinical medicine department at the hospital, and lead author of the study. “We have identified a new problem related, in part, to the increasing amount of fat in patients’ buttocks.”
Pharmaceutical companies design medications so that the proper dosage is absorbed into the blood stream from the muscle. Because fat tissue has significantly fewer blood vessels relative to muscle, less of the medication is absorbed into the blood stream and delivered to the appropriate part of the body.
Furthermore, if the medication is not absorbed into the blood stream, it remains in the fatty tissue where it can cause local infection and irritation.
Many medications are administered through injections into the muscles of the buttocks, including painkillers, vaccines, contraceptives and anti-nausea drugs. The upper, outer quadrant of the buttock is the preferred site for intramuscular injections, because there are relatively few major blood vessels, nerves and bones in this region that could be damaged by the needle. Yet the rich supply of microscopic blood vessels in muscle speeds drug absorption into the system.
The use of intramuscular injections has increased over the past 10 years, and new medications have been developed for delivery in this way. However this research has demonstrated that many of these injections are largely ineffective.