Common Antibiotic May Treat, Prevent PTSD

Megan Brooks

April 11, 2017

The antibiotic doxycycline (multiple brands) appears to block the formation of negative thoughts and fear memories, which may be help in the prevention and/or treatment of posttraumatic stress disorder (PTSD), new research suggests.

In experiments with healthy adults, those who received doxycycline had significantly lower fear response to fearful stimuli than those given placebo.

"We have demonstrated a proof-of-principle for an entirely new treatment strategy for PTSD," Dominik Bach, MD, PhD, of the Division of Clinical Psychiatry Research, University of Zurich, Switzerland, said in a news release.

The theory is based on accumulating evidence indicating that extracellular matrix enzymes play a role in memory formation. Doxycycline is a potent inhibitor of metalloproteinase-9 and other metalloproteinases.

"Our results support this theory, opening up an exciting avenue of research that might help us to find treatments for PTSD," Dr Bach told Medscape Medical News.

The study was published online April 4 in Molecular Psychiatry.

Lower Fear Response

The placebo-controlled, double-blind, randomized controlled trial included 76 healthy volunteers. In the first session, they were given either doxycycline or placebo and were taught to associate a certain color with an electric shock. A week later, they were shown the same colors accompanied by a loud sound, but without an electric shock.

Fear responses were measured by tracking the participants' eye blinks, because this is an instinctive response to sudden threats. The response was calculated by subtracting the baseline startle response from the response to the sound when the "threatening" color was shown.

According to the researchers, the fear response was 60% lower in those who received doxycycline in the first session compared to those who received placebo, suggesting that the fear memory was significantly suppressed by the antibiotic. Other cognitive measures, including sensory memory and attention, were not affected.

"In our study, healthy volunteers were given doxycycline before forming negative memories. Of course, it would be challenging to take a drug before a traumatic event to prevent PTSD, because we rarely know when it will occur," said Dr Bach.

"However, there is growing evidence that people's memories and associations may be changed after the event. The idea is that when people actively imagine previous negative events, this makes memory labile, and that to persist, it needs to be stabilized by a process called 'reconsolidation.' In a next step, we will test in healthy volunteers whether doxycycline impacts on reconsolidation of negative memories as well.

"If our next study on reconsolidation is successful, we hope to be running clinical trials within the next couple of years," he added.

Promising Research

Reached for comment, Steven Thorp, PhD, California School of Professional Psychology, San Francisco, told Medscape Medical News there has been a "surge of interest in different agents to disrupt memory consolidation in recent years, and I think it is a promising line of research.

"Most of the work I have seen has been related to how pain medications can make memories less salient, because extreme pain makes consolidation stronger," Dr Thorp noted.

The current study, he said, "seems very reasonable, the methodology has been used in many other trials, the subjects were randomized, and the sample size looks adequate. As the authors note, these are healthy volunteers and not a clinical sample, but these results merit additional research."

Dr Thorp agrees with the authors that using drugs to prevent PTSD will be challenging, but says there are instances when such a drug, if truly effective in clinical trials, could be used proactively.

"Many occupations entail tasks that have a high risk of leading to traumatic events. These include jobs for emergency personnel such as police, firefighters, paramedics, morgue workers, and military combat personnel," he explained.

"Depending on the window of clinical effectiveness – that is, for how many hours before and after an event memory consolidation could be disrupted, a chemical agent could be administered to prevent PTSD either before a planned operation, rescue, battle, etc, or immediately after such an event," Dr Thorp said.

The research was supported by the Swiss National Science Foundation, the University of Zurich, and the Wellcome Trust Center for Neuroimaging. The authors have disclosed no relevant financial relationships.

Mol Psychiatry. Published online April 4, 2017. Full text

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