NKTR-181: A Novel Mu-Opioid Analgesic with Inherently Low Abuse Potential.

The increasing availability of prescription opioid analgesics for the treatment of pain has been paralleled by an epidemic of opioid misuse, diversion, and overdose. The development of abuse-deterrent formulations (ADFs) of conventional opioids such as oxycodone and morphine represents an advance in the field and has had a positive but insufficient impact, as most opioids are still prescribed in highly abusable, non-ADF forms, and abusers can tamper with ADF medications to liberate the abusable opioid within. The abuse liability of mu-opioid agonists appears to be dependent on their rapid rate of entry into the central nervous system (CNS), whereas analgesic activity appears to be a function of CNS exposure alone, suggesting that a new opioid agonist with an inherently low rate of influx across the blood-brain barrier could mediate analgesia with low abuse liability, regardless of formulation or route of administration. NKTR-181 is a novel, long-acting, selective mu-opioid agonist with structural properties that reduce its rate of entry across the blood-brain barrier compared with traditional mu-opioid agonists. NKTR-181 demonstrated maximum analgesic activity comparable to that of oxycodone in hot-plate latency and acetic-acid writhing models. NKTR-181 was distinguishable from oxycodone by its reduced abuse potential in self-administration and progressive-ratio break point models, with behavioral effects similar to those of saline, as well as reduced CNS side effects as measured by the modified Irwin test. The in vitro and in vivo studies presented here demonstrate that NKTR-181 is the first selective mu-opioid agonist to combine analgesic efficacy and reduced abuse liability through the alteration of brain-entry kinetics.

Evaluation of drug precipitation of solubility-enhancing liquid formulations using milligram quantities of a new molecular entity (NME).

A precipitation screening method using a 96-well microtiter plate was developed to evaluate in vitro drug precipitation kinetics of liquid formulations for poorly water-soluble compounds, using milligram quantities of compounds and milliliter volumes of biorelevant media. By using this method we identified three formulations showing distinct in vitro precipitation kinetics (fast, slow, and no precipitation) for a model new molecular entity (JNJ-25894934). The in vitro precipitation profiles in simulated intestinal fluid (SIF), fasted state simulated intestinal fluid (FaSSIF), and fed state simulated intestinal fluid (FeSSIF) were compared with those measured by a USP dissolution method, and with in vivo absorption at the fasted and fed states in canine pharmacokinetic (PK) studies. The precipitation kinetics of all three formulations in the initial hours measured by the screening method correlated to those determined by the USP method (R(2) = 0.96). The PK results showed that the fast-precipitation formulation had the lowest bioavailability. However, a similar bioavailability was observed for the slow- and no-precipitation formulations. The oral bioavailability of JNJ-25894934 at the fed state was also significantly higher than that at the fasted state for all three formulations (p < 0.05). In addition, the in vitro precipitation profiles in FeSSIF correlated better with in vivo absorption than those in SIF and FaSSIF.