Oral Ketamine Administration in Patients With Peripheral Neuropathic Pain

Nowadays, available drugs cannot always produce pain relief in patients with neuropathic pain disease.

It is believed that drugs acting as antagonists of the N-methyl-D-aspartic acid (NMDA) receptor may have been efficient in the treatment of neuropathic pain disorders.

Ketamine is the only NMDA receptor antagonist commercially available in France. Ketamine is usually administered intravenously for surgical anesthesia.

The intravenous administration of ketamine will be difficult to manage in the treatment of chronic neuropathic pain.

Some trials using oral ketamine for the treatment of neuropathic pain were conducted but results were heterogeneous. This may be explained by the different range of ketamine doses tested.

The aim of this clinical trial is to identify a safe and an efficient dose of orally administrated ketamine for the treatment of peripheral neuropathic pain.

The clinical trial will be conducted in Toulouse Hospital, France. This study is a randomized, double-blind, placebo-controlled trial. The study will be conducted using 4 parallel groups (three doses of ketamine versus placebo).

In previous studies, it was shown that when ketamine was administrated by the intravenous route, its analgesic action was rapid. In one study, when oral ketamine was administrated to patients suffering from neuropathic pain, in six out of nine patients, pain was relieved after 24 hours post-administration.

In this study, ketamine will be administrated during seven days, which will allow us to evaluate ketamine efficiency and safety.

The effect of ketamine on pain intensity will be mainly studied using a visual analogue scale (VAS) but also taking into account the score assigned by the patient to his pain. This score will be noted down by patients before, during and after ketamine treatment.

Evaluation of benefit/risk for ketamine administration during this trial, shows that even if adverse events are not excluded, the benefit for the patients may be neuropathic pain relief.

Because clinical current knowledge regarding oral administration of ketamine is limited, this trial intends to enlarge information about ketamine efficiency and safety, more particularly in neuropathic pain disorders.

Eligibility Criteria:
Inclusion Criteria:

* Patients must suffer from peripheral neuropathic chronic pain.
* Pain score must be at least 40 mm in a VAS (reflecting pain intensity during the 7 days and the day before visit 1).
* Patients in which pain is not satisfactory relieved by level 1, 2 or 3 analgesic drugs (associated or not with antidepressants or antiepileptic drugs). Patients treated with level 2 or 3 analgesic drugs must stop these treatments one week before and during ketamine treatment.
* Patients must benefit from the French Social security system.
* Patients must be able to complete the tests.
* Patients must give a written informed consent.
* Patients must be aged from 30 to 90 years.
* Female fertile patients must use an efficient method of contraception.

Exclusion Criteria:

* Patients not suffering from peripheral neuropathic chronic pain.
* Pain score is less than 40 mm in a VAS (reflecting pain intensity during the 7 days and the day before visit 1).
* Patients not able to complete the tests.
* Patients not able to stop level 2 or 3 analgesic drugs.
* Patients in which ketamine is contraindicated:

  * Hypersensibility to one of the compounds of the ketamine syrup
  * Uncontrolled arterial hypertension
  * Recent cardio vascular accident
  * Severe cardiac problems
  * Drug abuse
  * Psychosis