The preclinical discovery of lofexidine for the treatment of opiate addiction

Improving Translational Research Outcomes for Opioid Use Disorder Treatments

Purpose of Review

Pharmacotherapies are the most effective means of reducing the harms associated with opioid use disorder (OUD). Translational research seeking to develop novel medications to treat OUD has been challenging due to the complex etiology of addiction. Preclinical outcome measures are often behavioral, and it is difficult, if not impossible, to fully mirror the various emotional and cognitive processes that motivate opioid use in humans. The goal of the current narrative review was to summarize the translational progression of three potential medications for OUD, which had varying levels of success.

Recent Findings

Memantine, lorcaserin, and lofexidine all showed promise in preclinical studies; however, only lofexidine was able to consistently replicate these findings in human subjects, and receive FDA approval. It was the authors' objective to use this review to identify areas of needed improvement in translational research for OUD.

Summary

Preclinical studies vary significantly in their ability to forecast effectiveness in clinical trials. Among the various preclinical models, suppression of opioid self-administration appears to have the best predictive validity. As they model a mostly physiological phenomenon, preclinical assessments of opioid withdrawal also appear to have high predictive validity. In our review of the literature, the authors noted numerous examples of clinical trials that were underpowered, lack precision, and proper outcomes. Better-validated preclinical targets and improved design of proof-of-concept human studies should allow investigators to more efficiently develop and test medications for OUD.

The Role of Lofexidine in Management of Opioid Withdrawal

Fear of withdrawal symptoms has been cited by survey respondents as the main reason that they continued to use opioids. Lofexidine is an α2-adrenergic agonist that decreases the sympathetic outflow that results in the characteristic symptoms of opioid withdrawal. A structural analog of clonidine, lofexidine has a higher affinity and specificity for the α2a receptors and does not reinforce opioid dependence. Withdrawal symptoms correlate approximately to the half-life of the opioid; patient factors such as age, duration of opioid exposure, physical status, and other considerations may influence the nature and duration of withdrawal symptoms. For patients with opioid use disorder and psychiatric comorbidities, withdrawal may be destabilizing and may exacerbate mental health status. Lofexidine has been shown in clinical trials to be safe and effective in helping to manage the symptoms of withdrawal and has been recommended in guidelines for this purpose. Adverse events associated with lofexidine include QT prolongation, hypotension, orthostasis, and bradycardia. The maximum course of treatment is 14 days, and doses should be titrated, with the recommended maximum dose to coincide with the most severe withdrawal symptoms (about 5-7 days after opioid discontinuation).