What is the position of intravenous (IV) lignocaine or ketamine in the step-care approach for neuropathic pain management?

IV Lignocaine and Ketamine in the Neuropathic Pain Management Step Ladder

IV lignocaine and ketamine are considered third-line or salvage therapies for refractory neuropathic pain when first-line and second-line treatments have failed, and should be administered only in specialized settings under close monitoring. 1

Neuropathic Pain Treatment Algorithm

First-Line Treatments

1. Tricyclic antidepressants (TCAs) - such as nortriptyline or desipramine

   • Starting dose: 10-25 mg/day, titrated gradually
   • Maximum dose: 100-150 mg/day
   • Particularly effective for continuous burning pain 1

2. Serotonin-norepinephrine reuptake inhibitors (SNRIs) - duloxetine or venlafaxine

   • Duloxetine: 30-60 mg once daily
   • Venlafaxine: 75-225 mg daily in divided doses
   • More effective for platinum-based neuropathies than taxane-induced neuropathy 1

3. Anticonvulsants - gabapentin or pregabalin

   • Gabapentin: 300-1200 mg/day, target dose 1800-3600 mg/day
   • Pregabalin: 150-600 mg/day in divided doses
   • Particularly effective for shooting, lancinating pain 1

Second-Line Treatments

1. Topical agents (for localized neuropathic pain)

   • 5% lidocaine patches
   • 8% capsaicin patches (30-60 min application, effect lasting up to 90 days) 1
   • Topical baclofen-amitriptyline-ketamine combinations 1

2. Opioids - tramadol or strong opioids

   • Tramadol: 200-400 mg daily in divided doses
   • Strong opioids: smallest effective dose
   • NNT (Number Needed to Treat): 4.3-4.7 1

Third-Line/Salvage Therapies

1. IV Lignocaine (Lidocaine)

   • Typically administered at 5 mg/kg over 30-60 minutes
   • Evidence suggests efficacy in selected patients with refractory neuropathic pain 1
   • Requires cardiac monitoring during administration
   • May be considered when oral medications have failed 2

2. IV Ketamine

   • Administered at subanesthetic doses (0.1-0.5 mg/kg/hr)
   • Most evidence supports short-term use for complex regional pain syndrome, fibromyalgia, and traumatic spinal cord injury 2, 3
   • Long-term infusions (4-14 days) may provide analgesic effects lasting up to 3 months 3
   • Requires close monitoring for psychomimetic side effects, often mitigated with benzodiazepines 3, 4

Key Considerations for IV Lignocaine and Ketamine

Indications

• Refractory neuropathic pain not responding to first and second-line treatments
• Complex pain syndromes with neuropathic components
• Pain crises requiring rapid intervention

Administration Setting

• Should only be administered in specialized pain centers or under supervision of pain specialists 5
• Requires appropriate monitoring facilities for potential adverse effects

Monitoring Requirements

• Cardiac monitoring for IV lignocaine (risk of arrhythmias)
• Neurological monitoring for ketamine (psychomimetic effects)
• Vital signs monitoring during infusion
• Liver function tests for prolonged ketamine use 3

Limitations and Risks

• IV lignocaine: cardiac arrhythmias, CNS toxicity, hypotension
• Ketamine: psychedelic symptoms, nausea/vomiting, cardiovascular stimulation, potential hepatotoxicity 3
• Limited duration of effect for short-term infusions
• Lack of standardized protocols for administration 4

Optimizing IV Ketamine Protocols

Research suggests better outcomes with ketamine when:

1. Higher total doses are administered
2. Infusions are prolonged (though infusion rate is less important)
3. Adjunct medications like midazolam or clonidine are co-administered to manage side effects 4

Practical Considerations

• Oral ketamine may be considered in some cases with potentially fewer side effects than IV administration 6
• Pre-treatment with haloperidol may prevent ketamine-induced psychomimetic effects 6
• Combination therapy with first or second-line agents may enhance efficacy
• Regular reassessment of pain control and side effects is essential

Despite their position as third-line therapies, IV lignocaine and ketamine represent important options for patients with intractable neuropathic pain who have failed conventional treatments. Their use should be carefully considered within the context of a comprehensive pain management strategy, with appropriate monitoring and follow-up.