The primary outcome is to compare the analgesic efficacy of intravenous ketamine treatment to
that of a placebo in patients with refractory neuropathic pain.
The secondary outcomes are:
1. - To compare the additive analgesic efficacy of prior administration of magnesium
sulfate to that of placebo and ketamine only, on the effectiveness of intravenous
ketamine treatment,
2. - To study the evolution time of pain and analgesia after the intravenous administration
of ketamine and placebo,
3. - To study the correlation of the analgesic response to administered products
respectively ketamine, ketamine and magnesium sulfate, placebo.