Adjuvant Analgesics

Adjuvant Basics - Pain's Sidekicks

• Definition: Drugs with primary indications other than pain, but enhance analgesia or manage analgesic side effects.
• Purpose:
  • Improve efficacy of primary analgesics (opioids, NSAIDs).
  • Provide analgesia in specific pain types (e.g., neuropathic).
  • Reduce side effects of primary analgesics, allowing dose reduction.
• Key Categories:
  • Antidepressants (TCAs, SNRIs)
  • Anticonvulsants (Gabapentinoids)
  • Corticosteroids
  • NMDA Antagonists (Ketamine)
  • Alpha-2 Agonists (Clonidine)

⭐ Adjuvant analgesics are primarily indicated for conditions other than pain but provide analgesia in specific pain states, especially neuropathic pain.

Antidepressants & Anticonvulsants - Nerve Calm Crew

• Antidepressants (Neuropathic Pain)
  • TCAs (Amitriptyline, Nortriptyline)
    • Mech: ↑NE/5-HT, Na+ block.
    • Amitriptyline: 10-25mg HS to 75-150mg.
    • SEs: Anticholinergic, sedation. 📌 "Tri-CyclicS": Sedation, Cardiac, antiSlud.
    • Nortriptyline: Often better tolerated.
  • SNRIs (Duloxetine, Venlafaxine)
    • Mech: ↑NE/5-HT.
    • Duloxetine: 30-60mg/d (diabetic neuropathy).
    • Venlafaxine: 75-225mg/d.
    • SEs: Nausea, dizziness.
• Anticonvulsants (Neuropathic Pain)
  • Gabapentinoids (Gabapentin, Pregabalin)
    • Mech: α2δ Ca2+ channel ligand.
    • Gabapentin: 100-300mg TDS to 3600mg/d.
    • Pregabalin: 25-75mg BD/TDS to 300-600mg/d.
    • SEs: Dizziness, somnolence, edema.
  • Carbamazepine
    • Trigeminal Neuralgia DOC. Dose: 200-1200mg/d.
    • ⚠️ Monitor: Agranulocytosis.

⭐ Amitriptyline (TCA) is often a first-line adjuvant for neuropathic pain, but its anticholinergic side effects limit use; Pregabalin often preferred for better tolerability.

Steroids & NMDA Blockers - Pathway Modulators

• Corticosteroids (e.g., Dexamethasone, Prednisolone)

  • Mechanism: Potent anti-inflammatory; ↓ edema, ↓ ectopic neuronal firing. Inhibit phospholipase A2.
  • Uses: Neuropathic pain (nerve compression, tumor infiltration), inflammatory pain, cancer pain.
  • Dexamethasone: 4-8 mg BD/TDS for nerve compression pain, then taper.
  • Side Effects (long-term): Hyperglycemia, immunosuppression.

  ⭐ Dexamethasone is particularly useful for pain from nerve compression by tumors due to its potent anti-inflammatory and edema-reducing effects.

• NMDA Receptor Antagonists (e.g., Ketamine, Memantine)

  • Mechanism: Block NMDA receptors in dorsal horn; ↓ central sensitization, wind-up, opioid tolerance.
  • Uses: Neuropathic pain, opioid-resistant pain, CRPS, phantom limb pain.
  • Ketamine: Sub-anesthetic dose (e.g., 0.1-0.5 mg/kg IV). Risk: psychomimetic effects.
  • Memantine: Oral, 5-20 mg/day. Better tolerated, less potent.

α2-Agonists & Topicals - Targeted Relief

• α2-Adrenergic Agonists
  • Clonidine: Oral, transdermal, epidural. Reduces sympathetic tone, opioid-sparing.
  • Dexmedetomidine: IV. Highly selective. Sedation, analgesia.
  • Common Side Effects: Hypotension, bradycardia, sedation.

  ⭐ Clonidine, an alpha-2 agonist, can potentiate opioid analgesia and reduce opioid requirements, useful in managing chronic pain and opioid tolerance.

• Topical Agents (Local Action, ↓ Systemic AEs)
  • NSAIDs (e.g., Diclofenac gel): Osteoarthritis, sprains.
  • Capsaicin cream/patch: Neuropathic pain (postherpetic neuralgia). Depletes substance P. 📌 "Capsaicin burns P(ain) away."
  • Lidocaine 5% patch: Postherpetic neuralgia, localized neuropathic pain.

High‑Yield Points - ⚡ Biggest Takeaways

• TCAs (amitriptyline) & SNRIs (duloxetine) are first-line for neuropathic pain.
• Gabapentinoids (gabapentin, pregabalin) are crucial for neuropathic pain and fibromyalgia.
• Corticosteroids (dexamethasone) reduce inflammatory and nerve compression pain.
• Ketamine (NMDA antagonist) targets central sensitization and opioid-refractory pain.
• Alpha-2 agonists (clonidine) aid in neuropathic pain and opioid sparing.
• Bisphosphonates (zoledronate) manage cancer-related bone pain.
• Topical lidocaine provides relief for localized neuropathic pain like Postherpetic Neuralgia (PHN).