Naltrexone is an opioid receptor antagonist used primarily in the management of alcohol and opioid dependence. After the publication of two randomised controlled trials in 1992 a number of study confirmed the efficacy of Naltrexone in reducing the frequency and severity of relapse to drinking. The multicentre COMBINE study recently proved the usefulness of naltrexone in an ordinary primary care setting with adjunct psychotherapy.
The standard regimen is one 50mg tablet per day. However a major issue with oral naltrexone is its poor and very variable bio-availability. At best the body will make 40% of the oral dose available and at worst 5%. Prescribers therefore have no way to establish how well an individual is likely to respond to treatment. This variable bioavailability is due to liver metabolism (first pass metabolism) which if avoided can dramatically improve the drugs performance.
In order to address the issue of poor bioavailability and to ensure patient compliance, a depot injectable naltrexone was developed and approved by FDA in 2006 for the treatment of alcoholism. The medication is administered by intra-muscular injection (thereby avoiding first pass metabolism) and last for up to 30 days.
Market research suggests that many patients are unhappy with the discomfort associated with depot injections and in addition the need for healthcare staff to administer the drug places pressure on health care systems.
There remains a need for more effective ways of delivering naltrexone which are less invasive.
Syntropharma have completed preliminary formulation work. Patents have since been filed on two naltrexone inventions.