Ketamine Suppresses Morphine Tolerance – Old Dog Learns New Tricks

Overview

Low-dose ketamine prevents opioid tolerance during long-term pain therapy or abuse of opioids by NMDA receptor blockand improves morphine analgesia. Two cases are presented, where this effect was used. The first case was a young woman(24 years) dependent on heroin (daily dose approx. 1 g intranasally). She was admitted for surgery and operated for bilateralgluteal abscesses. After surgery she suffered a severe pain at rest, pain at visual analogue scale (VAS 0–10) was 8 in spiteof three days therapy with slow release morphine (MST Continus) 2x60 mg p.o. per day and intramuscular morphine 10 mgevery 4 hours. Ketamine 40 mg p.o. every 4 hours was started and pain at rest decreased to VAS 0, pain during movementto VAS 2–3 45 min after ketamine. On the second day ketamine was further administered 4 times daily and completelyremoved during the next 2 days. Morphine could be also reduced and when eventually abandoned, the patient remainedpain free. The second case was a male (39 years) with an inoperable rectal carcinoma initially treated with a daily dose ofepidural morphine 120 mg and bupivacaine 500 mg. The epidural catheter had to be removed because of meningitis and thepatient was administered 2x300 mg MST orally which was gradually increased to 2x700 mg. In spite of this the pain at restremained VAS 4 and breakthrough pain was VAS 7. Therapy with ketamine was started during the patient’s admission witha total daily dose of 50 mg ketamine in 100 ml of water, which the patient used irregularly during a day. The patient wassatisfied with ketamine-induced analgesia after ketamine (VAS max. 4), but dizziness limited its further use. Otherpossibilities of low-dose ketamine therapy are discussed.

Key words:
pain therapy – dependence – tolerance – morphine – ketamine