Low-dose ketamine prevents opioid tolerance during long-term pain therapy or abuse of opioids by NMDA receptor block and 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 bilateral gluteal abscesses. After surgery she suffered a severe pain at rest, pain at visual analogue scale (VAS 0–10) was 8 in spite of three days therapy with slow release morphine (MST Continus) 2x60 mg p.o. per day and intramuscular morphine 10 mg every 4 hours. Ketamine 40 mg p.o. every 4 hours was started and pain at rest decreased to VAS 0, pain during movement to VAS 2–3 45 min after ketamine. On the second day ketamine was further administered 4 times daily and completely removed during the next 2 days. Morphine could be also reduced and when eventually abandoned, the patient remained pain free. The second case was a male (39 years) with an inoperable rectal carcinoma initially treated with a daily dose of epidural morphine 120 mg and bupivacaine 500 mg. The epidural catheter had to be removed because of meningitis and the patient was administered 2x300 mg MST orally which was gradually increased to 2x700 mg. In spite of this the pain at rest remained VAS 4 and breakthrough pain was VAS 7. Therapy with ketamine was started during the patient’s admission with a total daily dose of 50 mg ketamine in 100 ml of water, which the patient used irregularly during a day. The patient was satisfied with ketamine-induced analgesia after ketamine (VAS max. 4), but dizziness limited its further use. Other possibilities of low-dose ketamine therapy are discussed.

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