Intravenous infusion of lignocaine or ketamine at subanaesthetic doses can be used for the treatment of chronic neuropathic pain disorders, for example phantom limb pain, post-herpetic neuralgia, complex regional pain syndromes, diabetic neuropathy and pain related to stroke or spinal cord injuries.

Case 1

A middle-aged man was injured in a landmine explosion. He suffered from spinal injuries that left him paraplegic, accompanied by chronic back and leg pain. He had a spinal fusion surgery in 1996 and is confined to a wheel chair. From 1995 to 2006 his pain was treated with high doses of different opioids in combination, including fentanyl up to 2,000mcg/day, Oramorph 20mg tds, OxyContin 5mg nocte, Cyclimorph 10mg tds, and paracetamol 1g qds.

In 2006 he was taking fentanyl (Actiq lozenges) 800mcg/day for pain relief with a pain score of five out of 10. The fentanyl was gradually reduced and replaced with oral ketamine and oral morphine. Lumbar region interventions were performed in 2006-2007 but were not useful. In 2012 the fentanyl was totally stopped for oral morphine alone.

In early 2013 he was administered intravenous lignocaine and ketamine at the hospital, which provided him with immense pain relief for 10 to 12 weeks decreasing his pain score to two out of 10. Currently he takes no fentanyl and is on a lower total daily dose of oral morphine.

Case 2

A 46-year-old man had a longstanding history of lower back pain. On examination in 1995 and investigation (CT, MRI) he was diagnosed as having degenerative lumbar spine disease, mainly at L5-S1 and also prolapse disc at L5-S1. He was treated by chemolysis in 1995. Over the years he underwent multiple facet joint rhizotomies, injection interventions in the lower lumbar spines and a discectomy in 1998, all of which had limited success. For pain relief he took Brufen 400mg tds, paracetamol 1g tds and Ponstan 500mg tds.

He attended the pain service at the hospital in 2012 and was diagnosed as having mechanical back pain. He was administered intravenous lignocaine and ketamine infusion and was also commenced on 5% lignocaine patches, pregabalin 25mg bd; and paracetamol/ibuprofen as required. 

The patient has had three infusions at intervals with beneficial results and has decreased his dependency on other analgesics.

Conclusion

Ketamine primarily acts on N-methyl-D-aspartate (NMDA) receptors but is also active at opioid, norepinephrine, serotonin and muscarinic cholinergic receptors. Lignocaine acts on sodium channel receptors and suppresses the ectopic and abnormal discharges of injured nerves in many neuropathic pain conditions.

In each of these two cases, a combination of intravenous lignocaine and ketamine greatly relieved the pain of the patient and reduced their requirement for other analgesic drugs, including opioids.

References

1. Kvarnstrom A. The analgesic effect of intravenous ketamine and lignocaine on pain after spinal cord injury. Acta Anaesthesiol Scand 2004 (Apr); 48(4): 498-506
2. Finnerup NB. Intravenous lidocaine relieves spinal cord injury pain; a randomized controlled trial. Anaesthesiology. 2005 (May); 102(5): 1023-30