Long-term opioid therapy is commonly administered for the management of severe cancer pain. Increasing doses of opioids are titrated against effects until analgesia is achieved or intolerable adverse effects occur. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, has been reported to improve analgesia in patients with uncontrolled pain receiving high doses of opioids. This study aims at determining the effectiveness of ketamine as an adjuvant to opioids in relieving cancer pain.

Main objective :

To show that low analgesic doses of ketamine associated with opioids better relieve refractory cancer pain than opioids without ketamine.

Secondary objectives :

• Determine whether ketamine use allows to reduce opioid consumption

• Evaluate the adverse effects of opioids-ketamine association versus opioids-placebo.

  100 patients are expected : 50 will be treated with opioids and ketamine ; 50 will be treated with opioids and a placebo.

Treatment will be administered for 4 days. Patients will be followed-up for 5 days.

Success is defined by a decrease of the daily pain score of 50 % after 4 days. The expected rate of success in the placebo group is 10 % whereas the expected rate of success in the ketamine group is 35 %.

Primary outcome (pain score on a 11-point numerical scale) will be evaluated everyday as well as secondary outcomes (patient and clinician global impression of change, opioid consumption, adverse reactions, patient satisfaction on pain relief, sleep interference score).

Vital parameters (cardiac frequency, respiratory frequency and arterial blood pressure) will be checked everyday, many times a day : every hour for the four hours after the beginning of the treatment and then, every four hours ; every hour for the two hours following a dose shift).

Inclusion Criteria:

• Hospitalised cancer patients (informed and conscious of the cancer diagnostic)
• Undergoing opioid treatment for one month at least
• Refractory pain (score higher than 5 on an 11-point numerical pain rating scale)
• Ability to score pain on a numerical pain rating scale
• Patient written agreement

Exclusion Criteria:

• Ketamine contraindications
• Methadone or other NMDA-antagonist treatment
• Karnofsky index under 10
• Pregnancy