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Acute and Chronic Pain

Thomas Horton, Soibhan Kelley

  • There are physiological AND emotional components to pain. Biopsychosocial factors must be addressed. Ex: anxiety/depression, physical debility, and poor social support. Many pts will never be completely free of pain, so it is important to set realistic expectations.
  • Central sensitization is a phenomenon where the nervous system persists in a state of high reactivity which lowers the threshold for pain stimuli. Two characteristics of centralized pain are allodynia (pain from non-painful stimuli) and hyperalgesia (painful stimuli perceived as more painful).

Pharmacologic Therapy


  • 650mg q6hr or 1g q8h. <3g/day. (<2g in liver pts)
  • Avoid if you are worried about masking fevers


  • a great option for acute pain, especially musculoskeletal, headache, and nephrolithiasis in eligible pts (IV/PO ketorolac, ibuprofen, naproxen, etc.)
  • Avoid in acute or chronic kidney disease and ↑ risk of bleeding. Caution in CAD/PVD

Topical analgesics:

  • best for localized pain but utilized frequently as part of a multimodal regimen
  • Lidocaine ointment, patches
  • Menthol salicylate gel
  • Diclofenac gel
  • Capsaicin gel
  • Morphine gel (typically limited to oncology pts with tumor breakdown through skin)

Neuropathic agents:

  • Best for neuropathic pain but can be tried for other chronic pain or as part of acute pain regimen. SNRIs and TCAs can provide additional benefit if a pt has comorbid depression, anxiety, or insomnia (TCA). Most agents take 6-8 weeks for peak effect.
  • Gabapentin (Initial: 100 to 300 mg 1 to 3 times daily). Can be used for acute pain
  • Pregabalin (Initial: 25 to 150 mg/day in 2 to 3 divided doses). Has better bioavailability. May work in pts who did not tolerate or did not have success with gabapentin
  • Duloxetine (Initial: 30 mg daily for 1 to 2 weeks, then increase to 60 mg daily as tolerated)
  • Amitriptyline (Initial: 10 to 25 mg once daily at bedtime)

Muscle relaxants:

  • Should be used temporarily and intermittently but some benefit from longer term use. Great for paraplegia, spinal injury, and spasticity
  • Methocarbamol (Initial: 1.5 g 3 to 4 times daily for 2 to 3 days then decrease dose to ≤4.5 g/day in 3 to 4 divided doses). Preferred initial agent as has least SE.
  • Tizanidine (Initial: 2 to 4 mg every 6 to 12 hours as needed and/or at bedtime) – important to watch out for withdrawal in pts that take frequently at home.
  • Cyclobenzaprine (Initial: 5 to 10 mg once daily before bedtime)
  • Metaxalone (Oral: 800 mg 3 to 4 times daily)


  • Frequently used in hospital for acute pain. Limit use as much as possible in chronic pain as it contributes to long-term central sensitization. May benefit some pt populations but should always be used as a component of a comprehensive, multimodal, pt-specific treatment plan.
  • Refer to section under “Opioids: General Principles and Conversions” for OME equivalents
    • If >80 OME per day, ensure pt is prescribed naloxone
    • If >120 OME per day, refer to pain clinic
  • Common choices for acute pain in hospital (always start at low end for opioid naïve):
    • Oxycodone (PO) 5-10mg q4 to 6 hours prn
    • Hydromorphone (IV) 0.25 to 1mg q2 to 3 hours prn
  • For pts on opioids at home, should always continue in hospital to avoid withdrawal unless clinically contraindicated. Can always titrate dose as needed.
  • Tramadol: Has opioid and NSAID properties. Of note, tramadol also inhibits serotonin and norepinephrine reuptake. Metabolized by CYP3A4 and CYP2D6 so there is variability between pts. Typical dose: 25 to 50mg q4 to 6 hours PRN

NMDA antagonists:

  • usually prescribed by our pain management colleagues but worthwhile to think about as a potential option if a pt’s pain continues to be difficult to control
  • Ketamine (IV infusion): SE includes AMS/delirium, hallucinations, and dissociation.
  • Memantine (PO)

Alpha 2 agonists (central pain):

  • not commonly utilized in everyday practice, but helpful in certain pts with chronic pain (off-label), guanfacine vs. clonidine

Medications for Imminently Dying Pts

General recommendations

  • At VUMC, there is a very helpful order set titled “Comfort Care Orders (Trauma, MICU, SICU, NEURO ICU, Palliative Care)”
  • Make sure to remove unnecessary medications, labs, telemetry, nursing text orders, etc.


  • Morphine 2mg IV or SQ q1h PRN (avoid if renal failure)
  • Hydromorphone 0.25 – 0.5mg IV or SQ q1h PRN
  • Write as PRN, as needed for pain > 2/10 or for air hunger
  • If ineffective after 1 hour, increase by 50-100%
  • If given every hour for 3-4 hours, consider an infusion (given PRN dose as hourly rate)
  • Fentanyl is not a great option in ICU unless it is a continuous drip. Bolus lasts only 15 mins.


  • Assess for volume overload, considering decrease or stopping IVFs or tube feeds
  • Opioids are the treatment of choice for dyspnea
  • Consider benzodiazepines for air hunger not controlled by opiates
  • Supplemental oxygen for comfort (do not base on O2 sat). Consider use of cool air or fan


  • Assess for urinary retention, constipation, pain, and other modifiable factors
  • Lorazepam (Ativan) 0.5 – 1 mg PO or IV q4h PRN (tablet can be made into slurry if pt is experiencing dysphagia)


  • Ondansetron (Zofran) 4mg IV q4h or 8mg q8h PRN
  • Promethazine (Phenergan) 25mg PO or PR q6h PRN; caution can be very sedating
  • Prochlorperazine (Compazine) 10mg PO or IV q4h PRN
  • Haloperidol (Haldol)
  • If felt to be obstructive in etiology, try dexamethasone 4mg IV or SQ q8-12h with octreotide 100-400mcg IV or SQ q8h
  • If felt to be related to anxiety, try lorazepam; see dosing above
  • Scopolamine is highly anti-cholinergic and takes time to be effective, so would NOT use in imminently dying pts


  • Position for comfort; side lying if possible to move sections
  • Remember: The pt is NOT bothered by their own secretions, and it is often the family and caregivers who are likely disturbed, so avoid deep suctioning.
  • Glycopyrrolate (Robinul) 0.2 – 0.4 mg SQ or IV q6h PRN
  • Atropine 1% ophthalmic solution 2 drops sublingual 2-4h PRN

Acute Pain for Special Populations

Renal dysfunction:

  • Check that meds are renally dosed and start with non-sedating options. Avoid NSAIDs, morphine, and codeine.
  • Acetaminophen and topicals
  • Opioids: oxycodone 2.5 to 5 mg, IV hydromorphone 0.25-0.5mg, fentanyl IV 25 to 50mcg
  • Gabapentin: Start with spot 100mg. Be extremely careful with quick up titration in CKD due to sedation risk.
  • Methocarbamol: no specific renal dosing, try 500-750mg initially


  • Always avoid NSAIDs, morphine, codeine, hydromorphone (may be OK in mild to moderate cirrhosis).
  • Acetaminophen (2g max/d) and topicals are safe
  • Gabapentin: start with spot 100mg
  • Methocarbamol: no specific hepatic dosing, try 500 mg initially
  • Opioids
    • At risk for increased accumulation of toxic metabolites or increased bioavailability due to decreased first pass metabolism, liver synthetic dysfunction, and protein binding (hypoalbuminemia) i.e. opioids are stronger and last longer than expected
    • May precipitate hepatic encephalopathy
    • Degree of hepatic dysfunction determines risk of toxicity
    • Compensated cirrhosis without synthetic dysfunction is no different than general population
    • Avoid opioids if decompensated especially with hepatic encephalopathy
    • Generally should decrease typical starting doses by 50% and increase dosing intervals (start low and go slow)
    • Tramadol has reputation of being safer and is commonly used by our hepatologists here, but evidence is weak

History of substance use disorder:

  • Overnight, always review handoff as day team likely has specific plan in place.
  • With substance use history, typically rely on multimodal agents as above. Pts who are in recovery may prefer to avoid opioids themselves.
  • However, pts with OUD can and do have acute, severe pain due to injury, infections, procedures, etc. NEVER withhold opiates if clinically appropriate, regardless of substance use history.