Background Ketamine has been shown to be effective not only for its anaesthetic properties but also for the analgesic and opiate-sparing effects.

Purpose To describe the use of ketamine as an adjuvant in the treatment of malignant neuropathic pain. To analyse its effectiveness and safety, and to determine whether its use reduces the required doses of opioids.

Materials and methods A retrospective study based on the review of clinical records, computerised nursing care records (GACELA) and pharmacotherapeutic records (SILICON) for patients hospitalised in a Palliative Care Unit who were treated with ketamine for malignant neuropathic pain that could not be controlled with opioids and adjuvants. A 5 mg/ml oral solution of ketamine is prepared in the clinical unit using a vial of Ketolar. The pharmacy service prepares 10 mg/ml syringes of ketamine for parenteral administration. Data were gathered on demographic factors, pain location, previous analgesia, ketamine dose, effectiveness and side effects. A numerical scale 0–3 points was used to evaluate the effectiveness: 0 = no pain relief, 1 = partial effectiveness (depending on the need for analgesics/adjuvants and rescue treatment ≥2 per day), 2 = moderate efficiency (depending on the need for analgesics/adjuvants and rescue treatment ≥1 per day), 3 = full effectiveness (no pain).

Results Twelve patients (6 male), age 60 ± 15 years (32–81). Pain location: lumbar (5 patients), bones (2), lower limb (2), inguinoscrotal (1), mouth (1) and facial (1). The opioids previously used as analgesics were morphine (5), fentanyl (5) and oxycodone (2). 50% of patients used at least 3 adjuvants (benzodiazepines, antidepressants and antiepileptic drugs). 100% of patients needed to continue using strong opioids until death: fentanyl IV (4), morphine IV (4), methadone IV/SC (2), oxycodone IV (1) and intrathecal morphine (1). From the time at which ketamine was introduced, 33% of the patients required an increase in the doses of opioids, while 67% did not require changes in the basal analgesia. The previous opioid dose was reduced in three patients on using ketamine, with a 50, 12 and 8% reduction in the morphine dose respectively. The daily oral doses of ketamine were 131 ± 148 mg (15–390) and intravenously 239 ± 183 mg (60–600). The overall mean effectiveness of ketamine in addition to IV opioids was evaluated as 1.6 ± 0.7 points, which means that 50% of patients experienced a partial improvement in the control of their pain, 42% moderate improvement, and 8% became pain-free while receiving ketamine. 58% of patients experienced at least one adverse effect (drowsiness 71%, delirium 43%, restlessness/nervousness 29%).

Conclusions

• As an adjuvant, ketamine can be a useful alternative to normal analgesic treatment in controlling refractory neuropathic pain.

• While using ketamine, 25% of the patients required less opioids.

• There was a high incidence of adverse effects, although none of them were serious.

• It is important to use pain assessment scales that make it possible to precisely determine the effectiveness of the pain treatment.

No conflict of interest.