GABAergic Effects of Etifoxine and Alprazolam Assessed by Double Pulse TMS.

Introduction: There is a need for novel anxiolytics with improved side effect profiles compared to benzodiazepines. A promising candidate with alternative pharmacodynamics is the translocator protein ligand, etifoxine.

Methods: To get further insight into its mechanisms of action and side effects compared to the benzodiazepine alprazolam, we performed a double-blind, placebo-controlled, repeated-measures study in 36 healthy male subjects. Participants were examined for trait anxiety and side effects and underwent repeated transcranial magnetic stimulation (TMS) assessments, including motor evoked potentials (MEP), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP).

Results: We observed attenuation of MEPs by alprazolam but not by etifoxine. SICI was not significantly affected by alprazolam or etifoxine. However, the response pattern indicated a lowered SICI threshold after the administration of etifoxine and alprazolam compared to the placebo. ICF and CSP were influenced by neither medication. Alprazolam led to higher sedation and subjective impairment of concentration compared to etifoxine. Individual anxiety trait scores did not affect TMS parameters.

Discussion: This study indicated a favorable side effect profile of etifoxine in healthy volunteers. Moreover, it revealed differential GABA-related effects on neuromuscular function by means of TMS. The side effects and TMS profile of etifoxine are compatible with the involvement of neurosteroidogenesis and a predominant α3 subunit modulation compared to alprazolam.