According to research conducted at University College London and the University of Zurich, an antibiotic used to treat bacterial infections may be helpful in treating or preventing the negative thoughts associated with post-traumatic stress disorder (PTSD). The antibiotic, known as doxycycline, has been in use since the 1960s.
The researchers tested doxycycline in a clinical trial involving 76 heathy individuals. The volunteers were randomly assigned to receive the antibiotic drug, or a placebo.
Patients given doxycycline showed a 60 percent lower fear response, compared to study participants on the placebo. The researchers believe that doxycycline blocks the creation of fear memories by inhibiting an extracellular enzyme, known as matrix metalloproteinase (MMP) 9.
“We have demonstrated a proof-of-principle for an entirely new treatment strategy for PTSD,” said lead study author Dr. Dominik Bach, a professor at University College London and the University of Zurich. The researchers published their findings in the Nature journal, Molecular Psychiatry.
After being dosed with doxycycline or a placebo, the trial participants were asked to sit in front of a computer screen which would randomly flash blue or red. One of the colours was associated with a painful electric stimulation, which would be administered 50 percent of the time that colour was displayed.
Using human Pavlovian fear conditioning, the study volunteers learned to associate the one colour with the electric shock after viewing 160 flashes of blue and red. This same experiment was repeated one week later, however the participants were not dosed prior to the test. Instead of having an electric shock associated with one colour, startling sounds were played after either colour.
By tracking eye blinks, which are instinctively sped up in response to threats, the researchers were able to measure participants’ fear response. They then calculated fear memory by comparing the baseline startle response when the innocuous colour was shown, to the response associated with the shock and the loud sound.
The observed 60 percent reduction in fear response in participants who were treated with doxycycline during the first session, was not associated with any cognitive deficits in sensory memory or attention. Because of this important finding, the researchers suggest that the antibiotic could potentially be used to prevent PTSD in individuals – such as those in the military – who are likely to experience trauma.
“When we talk about reducing fear memory, we’re not talking about deleting the memory of what actually happened,” said Bach. “The participants may not forget that they received a shock when the screen was red, but they ‘forget’ to be instinctively scared when they next see a red screen.
“Learning to fear threats is an important ability … helping us to avoid dangers. [But] over-prediction of threat can cause tremendous suffering and distress in anxiety disorders such as PTSD.”