Updated: 6/10/2019

Opiates & Analgesic Medications

Topic
Review Topic
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Questions
6
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Evidence
9
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Videos
8
Introduction
  • Definitions
    • acute pain
      • implies presence of tissue damage
    • chronic pain (3-6 months)
      • no implication of tissue damage necessary
    • pathologic pain
      • pain from abnormal nervous system functioning (neuropathic)
  • Pathophysiology
    • afferent pain pathways
      • nociceptors
        • transduce signal through various substances
          • Substance P
            • a sensory neurotransmitter that plays an important role in pain
            • depletion of substance P increases the threshold to painful stimuli
            • Capsaicin is thought to function by decreasing Substance P
      • peripheral nerves
        • nociceptors transmit pain to type A and C peripheral nerve fibers
      • spinal cord
        • peripheral nerves transmit the pain signal via the dorsal column and spinothalamic tract
      • brainstem
        • spinal cord transmits the pain signal to the thalamus
        • site of pain modulation with endogenous opiates
  • Agents (details below)
    • Acetaminophen
    • NSAIDS
    • Opiates
    • Gaba synthesis agents
    • Adjunctive agents
Indications & Special Consideratoins
  • Pediatric patients
    • follow specific dosing guidelines for children which have been tested and recommended by the American Academy of Pediatrics
  • Geriatric patients
    • may have increased sensitivity to opioid pain medicines with higher rates of side effects
      • decreased total body mass with increased body fat percentage
      • potentially decreased hepatic and renal function
  • Obese patients
    • achieving adequate peri-operative pain control in the morbidly obese can be difficult
    • the most accurate method to control pain and avoid respiratory depression should include patient controlled analgesia (PCA), which is based on the patient's ideal weight 
    • intramuscular injections should be avoided due to the difficulty of avoiding injection into muscle and the poor vascularity of the subcutaneous adipose tissue 
  • Red-haired patients
    • often require more anaesthesia to maintain MAC levels and higher opioid dosages postoperatively compared to other hair types  
  • Chronic regional pain syndrome
    • Vitamin C has been shown to possibly prevent CRPS specifically related to distal radius fractures
Acetaminophen
  • Mechanism
    • not fully understood
    • inhibits prostaglandin synthesis 
    • minimal antinflammatory effects
  • As effective for pain control as aspirin
  • Toxicity
    • overdose leads to hepatic disfunction
    • contraindicated in the setting of pre-existing hepatic dysfunction
NSAIDs
  • Mechanism
    • decrease transduction of pain
  • See anti-inflammatory medications 
Local anesthetics
  • Mechanism
    • decrease transduction of pain
    • interfere with nerve conduction to provide a reversible loss of sensation in a specific location
      • affects the depolarization phase of action potentials (cells fail to depolarize enough to fire after excitation leading to a blocked action potential)
  • Examples
    • amide family  
      • lidocaine (Xylocaine)
      • bupivacaine (Marcaine)
    • esters of p-aminobenzoic acid
      • procaine (Novocain)
      • butethamine (Monocaine)
    • esters of meta-aminobenzoic acid
      • cyclomethycaine (Surfacaine)
      • metabutoxycaine (Primacaine)
    • esters of benzoic acid
      • cocaine
      • ethyl aminobenzoate (Benzocaine)
  • Adverse effects
    • FDA warning on the administration of continuous intra-articular infusion of local anesthetics for pain control
      • Some patients have been noted to have chondrolysis following infusion 
Opiates
  • Overview
    • useful in chronic nociceptive pain
  • Mechanism
    • perispinal method affects modulation of pain
    • systemic opiates change the perception and modulation of pain
  • Administration
    • oral, IV, intraspinal
    • oral administration preferred (more convenient and less costly)
      • bony procedures require more analgesia than soft tissue procedures 
    • patient compliance can improve with long-acting preparations that providue more uniform serum drug levels
    • implantable systems are available for intrathecal administration
  • Prescription dosing guide for upper extremity surgery
    • no narcotics
      • trigger finger release, nonop Dupuytren's release, small lumps/bumps
    • 10 narcotic tablets
      • mucous cyst, carpal tunnel, deQuervain’s, Dupuytren’s releases and small joint fusion
    • 20 narcotic tablets
      • wrist ganglion cysts, hand fracture ORIF, LRTI and tendon transfers
    • 40 narcotic tablets
      • large trauma, wrist fusion, open carpal surgery and DRUJ reconstruction
  • Chronic use
    • addiction occurs in a minority of patients
    • chronic opiates should be prescribed by pain management specialists
    • written contracts should be obtained
    • prescriptions should always be refilled in person
Methadone
  • Synthetic diphenylheptaine-derivative opioid receptor agonist
  • High bioavailability (three times as much as morphine), effective, and inexpensive
  • Metabolism
    • cytochrome P450 system
  • Rapid distribution phase (2-3 hours) and prolonged elimination phase (15-60 hours)
  • Caution
    • can accumulate to high levels with repeated dosing
    • rates of elimination vary considerably
    • risk of respiratory depression, cardiac toxicity (torsades de pointes)
    • consult with a qualified pain specialist when prescribing for the first-time
GABA agents
  • Agents
    • Pregabalin (Lyrica)
    • Gabapentin (Neurontin)
  • Mechanism
    • decrease transduction of pain
      • reduce hyper-excitability of voltage dependent Ca2+ channels in activated neurons.
  • Gabapentin is an anticonvulsant also used to treat neuropathic pain 
    •  binds presynaptic calcium channels to inhibit release of neurotransmitters
  • Efficacy
    • evidence of effectiveness primarily for postherpetic neuralgia, diabetic nueropathy, and fibromyalgia
    • little evidence for other uses, though often prescribed for other forms of chronic neuropathic pain (such as complex regional pain syndrome, CRPS)
    • gabapentin has been shown to be as effective and less expensive than pregabalin
  • Discontinuation requires a tapering dose
Muscle relaxants

 

  •  Overview
    • Useful to treat pain secondary to muscle spasms
  • Agents
    • Cyclobenzaprine (Flexeril)
      • mechnism of action not fully understood
      • centrally acting
      • potentiates norepinephrine and binds serotonin receptors
  • Use
    • may decrease pain during first two weeks after an injury
    • no proven benefit after first two weeks
    • may be effective for fibromyalgia
    • not effective to reduce spasticity secondary to neuromuscular disorders
  • Toxicity
    • overdose rare
    • may interact with other substances
      • MAOIs
      • alcohol

 

Adjuvant agents
  • Heterogeneous class of medications the provide additive analgesic effect to traditional NSAIDs and opioids
    • anticonvulsants
    • antidepressants
    • antihistamines
    • psychostimulants
    • anti-spasmodics
 

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Questions (6)

(OBQ13.150) Figures A and B show radiographs of a 24-year-old female with a soccer injury. A physical examination reveals an isolated, closed injury with no clinical features of neurovascular injury or compartment syndrome. She has been consented to be treated with intramedullary nail fixation. A pre-operative note by the anaesthesiology team makes reference to the patients fair skin and natural red-hair color. How will this information affect the post-operative management of this patient? Review Topic

QID: 4785
FIGURES:
1

Longer duration of anticoagulation due to increased risk of DVT

7%

(184/2597)

2

Avoiding anticoagulation medications due to increased risk of bleeding

7%

(188/2597)

3

Require higher dosages of post-operative analgesia

74%

(1916/2597)

4

Longer period of non-weight bearing on surgical limb

4%

(100/2597)

5

Avoiding opioids due to higher risk of unrecognized allergies

7%

(191/2597)

ML 3

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PREFERRED RESPONSE 3
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(OBQ08.249) What is the most appropriate delivery route for pain medication to a morbidly obese post-operative patient to ensure a therapeutic plasma concentration? Review Topic

QID: 635
1

Oral tablets

4%

(50/1387)

2

Oral liquid solution

1%

(7/1387)

3

Subcutaneous injections

1%

(16/1387)

4

Intravenous patient controlled analgesia based on actual body weight

40%

(555/1387)

5

Intravenous patient controlled analgesia based on ideal body weight

54%

(755/1387)

ML 3

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ11.226) A 35-year-old male presents with pain and limited range of motion 3 months after arthroscopic Bankart repair of his right shoulder. His postoperative course included a continuous intra-articular infusion pump for 3 days, use of a sling for 4 weeks, and initiation of passive range of motion below the level of the shoulder. At 4 weeks postoperatively he started active range of motion exercises, and started an isotonic strengthening program at the 9 week interval. Which of the following options is the MOST appropriate step in his management? Review Topic

QID: 3649
1

Reassurance and appropriate followup

10%

(164/1713)

2

Focused physical therapy on aggressive ROM exercises and modalities

26%

(438/1713)

3

Intra-articular injection of corticosteroids to decrease post-operative inflammation

3%

(47/1713)

4

Shoulder radiograph series to assess for chondrolysis

60%

(1030/1713)

5

Arthroscopic vs open Bankart revision surgery for failed repair

1%

(23/1713)

ML 3

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PREFERRED RESPONSE 4
ARTICLES (18)
VIDEOS (8)
Topic COMMENTS (1)
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