US company claims new opioid painkillers show lack of dependance

Pain Therapeutics, a US-based medical research company, is to develop two new opioid painkillers, OxyTrex and MorViva, both of which it claims do not lead to the tolerance and dependance associated with other opioid painkillers.

Speaking at the 21st Annual Scientific Meeting of the American Pain Society in Baltimore, Maryland, the company's chief scientific officer, Grant Schoenhard said: "The company's new data present an intriguing challenge to the conventional view that opioid therapy is necessarily tied to drug dependence and tolerance."​

He added: "We have comprehensive animal data showing that chronic doses of oxycodone and morphine need not necessarily be associated with opioid tolerance, dependence or withdrawal."​

With repeat use, opioid drugs often lead to tolerance and physical dependence. Pain Therapeutics is developing an alternative drug to oxycodone, a widely used opioid painkiller chemically related to morphine, called OxyTrex, and an alternative drug to morphine called MorViva.

The company claims that these two drugs offer minimal opioid tolerance and physical dependence following chronic administration and have conducted two pre-clinical experiments to test the claims.

In the first experiment, two groups of healthy mice were given chronic doses of either morphine or MorViva over ten days. As expected, mice that received morphine quickly became tolerant to the drug and no longer responded to a standard assay of analgesia by day three.

Mice that received MorViva, however, did not show drug tolerance; these mice showed a continuous analgesic response during the entire seven day study (p<0.01).

Furthermore, when morphine tolerant mice were switched over to MorViva, these mice showed an analgesic response without subsequent redevelopment of tolerance (p<0.01). The company said that these results demonstrate the ability of MorViva to prevent and to reverse opioid tolerance in laboratory animals after chronic treatment.

In the second experiment, two groups of healthy mice were given chronic doses of either oxycodone or OxyTrex over seven days. Mice that received oxycodone quickly developed drug tolerance. In contrast, mice that received OxyTrex showed an absence of opioid tolerance.

In addition, OxyTrex was found to be more potent than oxycodone over the entire duration of the study.

At the end of each study mice were given naloxone to reverse the effects of both oxycodone and morphine. Mice that had been receiving oxycodone or morphine went into a classic opioid withdrawal behaviour, indicating the presence of physical dependence. Mice that had been receiving OxyTrex or MorViva did not do so, indicating the absence of physical dependence (p<0.01).

The research found that the drugs do not result in analgesic tolerance (p<0.01)and are more potent than oxycodone and morphine, respectively (p<0.01)

The company also claims that the drugs are effective for longer than oxycodone and morphine, and prevent withdrawal behaviour, indicating the lack of physical dependence.

Opioid painkillers are drugs derived from opium and the poppy plant. In the United States, opioid drugs exceed $3 billion in annual sales and account for over five percent of all prescription drug sales.