Researchers from the Southeast Louisiana Veterans Health Care System and the Tulane University have come up with a new painkiller of the same strength as morphine but has fewer side effects and is not likely to be addictive.

In a study published in the journal Neuropharmacology, the researchers used rats to compare the efficacy and side effects of morphine to several variants of engineered endomorphin. Though based on peptides, the endomorphin variants targeted the same pain-relieving opioid receptor that morphine binds to.

Opium-based drugs are effective for chronic and severe pain so they are commonly prescribed. Unfortunately, they can also be highly addictive, resulting in abuse that kills thousands of Americans every year. Opioid overdose and abuse are due to patients building tolerance for the painkillers, in turn prompting the need for higher and more frequent dosages. Additionally, the drugs can lead to motor impairment and possibly fatal respiratory depression.

"It's unprecedented for a peptide to deliver such powerful pain relief with so few side effects," said James Zadina, lead investigator of the study. "These side effects were absent or reduced with the new drug."

Based on their findings, the researchers saw that the new drug offered longer-lasting pain relief without causing substantial slowing breathing in rats. For the same dose, morphine would have resulted in significant respiratory depression. Particularly important in older adults, motor coordination was dramatically impaired after morphine use but the same was not observed with the new endomorphin medication.

There was also less tolerance reported in the new drug and spinal glial cell activation was not produced. An inflammatory effect caused by morphine, spinal glial cell activation is a known contributor to tolerance development.

The researchers carried out several tests to assess the new drug's addictive qualities. Where rats were observed to spend more time in the spot where they were given their morphine dose, this was not seen in the endomorphin drug. Rats were also shown to make more effort to get their hands on morphine and not the endomorphin variant. As the tests were predictive of drug abuse in humans, they offered a look at how the new drug would affect people in terms of being addicted.

Within the next couple of years, the researchers are hoping to bring clinical trials to test the new endomorphin drug on humans.

Melita Fasold, Laszlo Hackler, Jenny Morgenweck and Mark Nilges also contributed to the study.

Photo : Eric Norris | Flickr