The present investigation aimed to elucidate the
analgesic efficacy of 30 mg of intravenous
orphenadrine citrate (CAS 4682-36-4) in a human
pain model. Eighteen healthy female and male subjects were enrolled and received single infusions of 30 mg
orphenadrine citrate and matching placebo in two periods which were separated by a 1 week washout period. The study was designed as a randomised, double-blind, placebo-controlled, two-period, cross-over trial. The intended
neurogenic inflammation and
hyperalgesia were induced by topical, occlusive application of 1%
capsaicin solution (INCI: Capsicum frutescens, containing capsaicinoides from Capsicum annuum annuum, CAS 84603-55-4) for 30 min on defined skin areas of the back. The
pain response to
CO2 laser pulses applied to the
capsaicin pre-treated skin was measured by event related Vertex-EEG recordings. This technique allowed studying the influence of
orphenadrine citrate on the (central) P2-component and the (peripheral) Ni-component of the
pain response (LSEP). Both,
orphenadrine citrate and placebo were given as
intravenous infusions over 60 min.
Orphenadrine citrate exerted a significant reduction in central and peripheral components of the
pain response when compared to placebo. The effect on the central component was highly significant and more pronounced than the peripheral effect of the
drug. The
analgesic effect developed fast, was already present during infusion, was ongoing, and exceeded the observational period of 4 h after start of infusion. In summary,
orphenadrine citrate was able to exert an
analgesic/anti-hyperalgesic effect in a low-dose paradigm (30 mg dose) which was predominantly due to central/spinal mechanisms in this
capsaicin model with
laser somatosensory evoked potentials.