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Adjuvants/ Non-opioids

Non-Opioid and Adjuvant Analgesics

This didactic provides an overview of non-opioid and adjuvant analgesics used in palliative care, emphasizing practical strategies for selecting and titrating these medications to manage complex pain syndromes. These agents are crucial tools for addressing pain through mechanisms distinct from opioids, often providing better relief for neuropathic or mixed pain while also helping reduce opioid burden and side effects.

Key Definitions

  • Non-Opioid Analgesics: Medications primarily indicated for pain, such as acetaminophen, aspirin, and NSAIDs.
  • Adjuvant Analgesics: Drugs primarily developed for other conditions (e.g., depression, epilepsy) that have analgesic properties in certain pain contexts. Examples include tricyclic antidepressants (TCAs), serotonin-norepinephrine reuptake inhibitors (SNRIs), antiepileptics (AEDs), corticosteroids, and muscle relaxants.

These medications may also address coexisting symptoms like depression, insomnia, or seizures—common in palliative care populations.

Rationale for Use

Non-opioid and adjuvant agents:

  • Provide analgesia via non-opioid pathways (e.g., serotonin-norepinephrine modulation, sodium or calcium channel inhibition).
  • Can be opioid-sparing, reducing the required opioid dose.
  • May be better suited for specific pain types, particularly neuropathic and inflammatory pain.

An understanding of each agent’s mechanism, typical indications, and adverse effect profile allows clinicians to individualize treatment and anticipate complications.

NSAIDs: Efficacy and Safety Considerations

Nonsteroidal anti-inflammatory drugs (NSAIDs) are a cornerstone of nociceptive pain management, especially in musculoskeletal and inflammatory conditions. Their mechanism involves reversible inhibition of cyclooxygenase (COX) enzymes, which mediate prostaglandin production and inflammation. NSAIDs can be classified into:

  • Non-selective COX inhibitors (e.g., ibuprofen, naproxen, ketorolac)
  • Selective COX-2 inhibitors (e.g., celecoxib, meloxicam, diclofenac)

Efficacy:
NSAIDs are highly effective in reducing inflammation-driven pain. NNTs range from 2.5 to 5 in musculoskeletal pain syndromes, indicating strong analgesic efficacy.

Adverse Effects and Clinical Considerations

While effective, NSAIDs carry significant risks that must be carefully weighed—particularly in older adults and patients with complex comorbidities.

  1. Gastrointestinal (GI) Toxicity:
    • Risk includes dyspepsia, gastric ulcers, and gastrointestinal bleeding (GIB).
    • At-risk populations:
      • Age >65
      • H. pylori infection
      • History of peptic ulcer or prior GIB
      • Concomitant use of corticosteroids, aspirin, or anticoagulants
      • Cancer, smoking, alcohol use
    • Mitigation Strategies:
      • Co-prescription of a proton pump inhibitor (PPI) or misoprostol significantly reduces GI risk.
      • Use the lowest effective dose for the shortest necessary duration.
  2. Renal Toxicity:
    • NSAIDs reduce prostaglandin-mediated renal perfusion, leading to increased risk of:
      • Acute kidney injury (especially in volume-depleted states)
      • Sodium and water retention → hypertension, edema
    • At-risk populations:
      • Chronic kidney disease (CKD)
      • Cirrhosis
      • Congestive heart failure (CHF)
      • Elderly or frail patients
      • Patients on diuretics or nephrotoxic agents
  3. Cardiovascular Risk:
    • NSAIDs (especially COX-2 inhibitors) are associated with increased thrombotic risk, including:
      • Myocardial infarction
      • Stroke
      • Peripheral artery thrombosis
    • All NSAIDs carry an FDA black box warning for potential CV events.
    • Celecoxib should be avoided in patients with prior stroke or CAD.
  4. Other Contraindications:
    • Active GI bleed within the past year
    • NSAID-induced asthma or allergy
    • Severe renal failure
  5. Relative Contraindications:
    • Poorly controlled hypertension
    • Diabetes mellitus
    • Hepatic impairment
    • Concurrent use of other ulcerogenic or anticoagulant medications

Other Adjuvant Classes:

Tricyclic Antidepressants (TCAs):

  • First-line for neuropathic pain conditions (e.g., PDN, PHN, central post-stroke pain).
  • Nortriptyline and desipramine (secondary amines) preferred due to fewer anticholinergic effects.
  • NNT ~3.6. Adequate trial: 6–8 weeks.

Adverse effects:

  • Anticholinergic (dry mouth, constipation, urinary retention)
  • QT prolongation, orthostatic hypotension
  • Cognitive effects, especially in older adults

SNRIs (Duloxetine, Venlafaxine):

  • Effective in neuropathic pain and fibromyalgia.
  • NNT ~6.4.
  • Side effects: nausea, increased BP, withdrawal symptoms if stopped abruptly.

Calcium Channel α2-δ Ligands (Gabapentin, Pregabalin):

  • Useful for diabetic neuropathy, PHN, and neuropathic cancer pain.
  • NNT ~7.2–7.7.
  • Adverse effects: sedation, dizziness, ataxia, edema.

Muscle Relaxants:

  • Indicated for spasm or post-op pain; mechanisms vary.
  • Risks include sedation, falls, and dependence (especially with agents like carisoprodol or benzodiazepines).

Topicals (Lidocaine, Capsaicin):

  • Localized pain relief with minimal systemic effects.
  • Particularly helpful for focal neuropathic syndromes like PHN.

Clinical Pearls

  • Tailor selection to pain type (nociceptive vs neuropathic vs mixed), patient comorbidities, and concurrent symptoms.
  • Start low and titrate slowly, especially in elderly or frail patients.
  • Consider drug-drug interactions and cumulative sedative burden when layering agents.
  • Document the goal of therapy and reassess efficacy regularly.

Resources

2018 – Schuchen – Systematic review and meta-analysis on non-opioid analgesics in palliative medicine

2016 – Beuken‐van Everdingen – Pharmacological Treatment of Pain in Cancer Patients The Role of Adjuvant Analgesics