Anesthesia drugs used for cutting pain during surgery may paradoxically increase pain and discomfort after the surgery, a team of researchers from Georgetown University Medical Center reported in the June 23 issue of the Proceedings of the National Academy of Sciences.

The study, funded by the National Multiple Sclerosis Society and the National Institutes of Health, revealed that “noxious” anesthesia drugs (the basic and commonly used drugs in the market) activate and then sensitize specific receptors on neurons in the peripheral nervous system, known as TRPV1 and TRPA1.

These receptors are often expressed together and are known to react to irritants like garlic and wasabi and they are also activated by the “noxious” drugs.

Gerard Ahern, an assistant professor in the department of pharmacology and lead author of the study along with his colleagues discovered that side effects of noxious drugs are caused by the way drugs affect nerve cell receptor TRPA1, a receptor highly activated when exposed to noxious drugs causing burning pain after the surgery.

During an experiment, the researchers tested noxious drugs on mice lacking TRPA1 receptors. They found that these mice did not feel any pain. Then they tested both noxious and sevoflurane drugs (drugs targeting brain and spinal cord with no side effects but considered not that effective) on normal mice. They found that those exposed to noxious drugs experienced pain and inflammation several hours after being exposed to the anesthetic.

These findings made Ahern state that “the choice of anesthetic appears to be an important determinant of post-operative pain. We hope these findings are ultimately helpful in providing more comfort to patients.”