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Opioid-Related Disorders

Chapter 467 | Part 13: Neurologic Disorders · Part 13 – Neurologic Disorders · Chapter 467

Key Clinical Points

  1. Opioid Use Disorder (OUD) is defined in DSM-5 (2022) as repeated use of the opiate during a 12-month period while producing problems in two or more areas including tolerance, withdrawal, use of greater amounts than intended, craving, and use despite adverse consequences.
  2. In 2022, 8.9 million U.S. residents misused pain relievers; >76,000 overdose deaths involved opioids (nearly half combined with stimulants).
  3. Naloxone dosing for fentanyl overdoses may require twice the amount needed for other opioids; recent rescue preparations contain double the traditional dose.
  4. Methadone can prolong the QT interval by up to 16% compared to non-methadone-maintained, drug-injecting patients.
  5. Buprenorphine is a partial opioid agonist; at high doses, it exhibits more antagonist than agonist activity, making overdose nearly impossible.
  6. Withdrawal symptoms begin 8–10 h after the last dose; acute course lasts 7–10 days; protracted abstinence lasts 26–30 weeks.
  7. Clonidine and lofexidine are alpha-adrenergic agonists used to suppress noradrenergic (NE) neuronal activation during detoxification.
  8. Naltrexone must be administered only after successful detoxification from opioids to avoid precipitating withdrawal.
  9. Intravenous opioid use carries risks of hepatitis B, HIV/AIDS, septic complications (meningitis, osteomyelitis, abscesses), and tissue necrosis with xylazine addition.
  10. Slow administration routes (oral, transdermal) provide analgesia and sedation but do not produce an opioid 'high' because they do not cause the rapid dopamine changes associated with smoking or intravenous use.

1. DEFINITION & OVERVIEW

• Historical Context: Opioid analgesics have been used since at least 300 B.C. (e.g., Nepenthe). • Modern Era: Since the first chemical isolation of opium and codeine 200 years ago, a wide range of synthetic opioids have been developed. • Clinical Impact: Two primary adverse effects are opioid use disorder (OUD) and overdose. • Epidemiological Data: In 2022, 8.9 million U.S. residents misused pain relievers; >76,000 deaths involved opioids (nearly half combined with stimulants). • Fentanyl Crisis: Death rates are accelerating due to high-potency fentanyl derivatives and the fact that reversing fentanyl overdoses may require severalfold larger doses of naloxone than standard intranasal devices.

1.1 Diagnostic Criteria • DSM-5 (2022) Definition: Opioid use disorder is defined as repeated use of the opiate during a 12-month period while producing problems in two or more areas including: ◦ Tolerance ◦ Withdrawal ◦ Use of greater amounts than intended ◦ Craving ◦ Use despite adverse consequences • Note: This reduction from three to two primary problem areas has not changed clinical rates as most users meet more than three criteria.

2. EPIDEMIOLOGY

• Gateway Drug Status: Since 2007, prescription opiates have been the most common illicit drug for initial use among adolescents in the U.S. • Shift in Usage: ◦ Pre-2015: Most used were diverted prescriptions (oxycodone, hydrocodone). ◦ Post-2015: Fentanyl misuse and lethal overdoses rose exponentially. • Maintenance Agents: Methadone and buprenorphine are misused at substantially lower rates. • Other Opioids: Butorphanol, tramadol, and pentazocine are used even less frequently.

3. ETIOLOGY & PATHOPHYSIOLOGY

• Mechanism of Action: ◦ Binding to μ receptors → activation of G_{i/o} proteins → inhibition of Adenylyl Cyclase (AC) and activation of G protein-coupled inwardly rectifying potassium channels (GIRKs). ◦ GIRK Activation: Increases permeability to potassium ions → hyperpolarization → inhibition of action potential. • Neurobiology of 'High': ◦ Reward pathway: Mesolimbic dopaminergic pathway (VTA to NAc) where opioids inhibit GABAergic neurons that normally inhibit the VTA and NAc. ◦ Requirement for 'High': Only occurs when the rate of change in dopamine is rapid. ◦ Route Impact: Rapid routes (IV, smoking) produce a 'high'; slow routes (oral, transdermal) provide analgesia/sedation but no 'high'. • Tolerance & Withdrawal: ◦ Related to genetic polymorphisms and the cAMP-PKA-CREB cascade in the locus coeruleus (LC). ◦ Chronic Exposure: Sustained inhibition of cAMP → upregulation of cAMP enzyme activity to compensate. ◦ Withdrawal Mechanism: Removal of opioid → unoppressed noradrenergic (NE) neurotransmission in LC neurons. • Neuroplasticity: Upregulated PKA phosphorylates CREB → expression of genes such as tyrosine hydroxylase (TH) and brain-derived neurotrophic factor (BDNF).

3.1 Receptor Actions

Table 467-1 summarizes the actions of opioid receptors:

RECEPTOR TYPE ACTIONS
Mu (μ) (e.g., morphine, buprenorphine) Analgesia, reinforcement euphoria, cough and appetite suppression, decreased respirations, decreased GI motility, sedation, hormone changes, dopamine and acetylcholine release
Kappa (\kappa) (e.g., butorphanol) Dysphoria, decreased GI motility, decreased appetite, decreased respiration, psychotic symptoms, sedation, diuresis, analgesia
Delta (δ) (e.g., etorphine) Analgesia, euphoria, physical dependence, hormone changes, appetite suppression, dopamine release
Nociceptin/orphanin FQ Analgesia, appetite, anxiety, tolerance to opioids, hypotension, decreased GI motility, 5-HT and NE release

4. CLINICAL FEATURES

• Route of Administration: ◦ IV/Smoked: Rapid concentration → 'rush', euphoria, tranquility, sleepiness ('the nod'). ◦ Oral/Transdermal: Slower increase → analgesia and sedation; no 'high'. • Systemic Effects: ◦ Hormonal: Inhibition of CRF and LH (reduced cortisol/sex hormones); increased prolactin (reduced libido); reduced thyrotropin; increased growth hormone. ◦ Gastrointestinal: Reduced motility → nausea, constipation, anorexia. Risk of toxic megacolon with methadone. ◦ Cardiovascular: Potential for orthostatic hypotension (histamine release) and QT prolongation (methadone). ◦ Respiratory: Insensitivity of brainstem neurons to increased CO_2 → respiratory depression. • Complications of IV Use: ◦ Infections: Hepatitis B, HIV/AIDS, sepsis (meningitis, osteomyelitis, abscesses). ◦ Toxins: MPTP (parkinsonism) or Xylazine (increased respiratory suppression and tissue necrosis/amputation risk).

4.1 Overdose Signs • Clinical Presentation: ◦ Shallow and slow respirations. ◦ Pupillary miosis (mydriasis only occurs with significant brain anoxia). ◦ Bradycardia. ◦ Hypothermia. ◦ Stupor or coma.

4.2 Withdrawal Timeline • Onset: 8–10 h after last dose. • Early Symptoms: Lacrimation, rhinorrhea, yawning, sweating. • Later Symptoms: Restless sleep, weakness, chills, gooseflesh, nausea/vomiting, muscle aches, involuntary movements, hyperpnea, hyperthermia, hypertension. • Acute Course: 7–10 days. • Protracted Abstinence (26–30 weeks): Hypotension, bradycardia, hypothermia, mydriasis, decreased responsiveness to CO_2.

5. DIFFERENTIAL DIAGNOSIS

• Polydrug Use: Alcohol, sedatives, cannabinoids, stimulants can mimic or complicate opioid withdrawal. • Xylazine Addition: Mimics opioid overdose but with increased respiratory suppression and necrosis. • MPTP Neurotoxin: Can cause parkinsonism. • Precipitated Withdrawal: Occurs in patients dependent on fentanyl or on maintenance doses of methadone (>80 mg daily) when starting buprenorphine.

6. INVESTIGATIONS & DIAGNOSIS

  1. Clinical Assessment: Diagnosis based on recognition of characteristic signs (respiratory depression, miosis, bradycardia, hypothermia, stupor/coma).
  2. Toxicology Confirmation: Blood or urine studies can confirm suspected diagnosis.
  3. Immediate Management: Must be based on clinical criteria; do not delay treatment for results if life-threatening symptoms are present.
  4. Fentanyl Specifics: If fentanyl is suspected, assume a requirement for naloxone potentially double that needed for other opioids.

7. MANAGEMENT & TREATMENT

• Overdose Management (Table 467-2): 1. Establish airway; intubation and mechanical ventilation may be necessary. 2. Naloxone: 0.4–2.0 mg (IV, IM, or endotracheal tube). 3. Timing: Onset of action with IV is ≈1–2 min. 4. Repeat Dosing: Repeat doses if needed to restore respiration; or a continuous infusion can be used. 5. Maintenance Infusion: One-half to two-thirds of the initial naloxone dose that reversed respiratory depression is administered on an hourly basis (not necessary if intubated).

• Detoxification Strategy: 1. Alpha-Adrenergic Agonists: Use clonidine or lofexidine to suppress NE neuronal activation. 2. Naltrexone Timing: Must be administered only after detoxification from opioids to avoid precipitating withdrawal.

• Maintenance Therapy: 1. Methadone: ◦ Risk: Can prolong QT interval (up to 16% higher than non-methadone users). ◦ Interaction: Be aware of CYP3A4 inhibitors/inducers (e.g., rifampin, carbamazepine). 2. Buprenorphine: ◦ Mechanism: Partial opioid agonist; at high doses, it has more antagonist than agonist activity. ◦ Advantage: Can be administered in primary care; superior to clonidine for withdrawal symptoms. 3. Safety Check: Ensure patient is not on high-dose methadone (>80 mg daily) before starting buprenorphine to avoid precipitated withdrawal.

8. PROGNOSIS & COMPLICATIONS

• Clinical Outcomes: Success measured by retention in treatment, reduced drug use, lower HIV risk, and fewer overdoses. • Treatment Setting: Most successful when lasting 6–18 months; medication-free programs generally have poorer outcomes than pharmacotherapy.

9. SPECIAL CONSIDERATIONS

• Pediatric/Adolescent: Buprenorphine provided in mucosal films to prevent diversion. • Polydrug Users: Must be screened for alcohol or sedative withdrawal, which may be more dangerous than opioid withdrawal.

10. KEY PEARLS & CLINICAL TRAPS

• Naloxone for Fentanyl: Expect to use double the standard dose of naloxone. • Buprenorphine Ceiling: As a partial agonist, it has an 'antagonist' effect at high doses, making overdose nearly impossible. • Xylazine Warning: Leads to increased respiratory suppression and tissue necrosis/amputation risk. • Detox Sequence: Always ensure detoxification is complete before starting naltrexone.

Reference Tables

TABLE 467-1 Actions of Opioid Receptors

Harrison's 22e, p.3689

RECEPTOR TYPE ACTIONS
Mu (μ) (e.g., morphine,
buprenorphine)		 Analgesia, reinforcement euphoria, cough and appetite
suppression, decreased respirations, decreased GI
motility, sedation, hormone changes, dopamine and
acetylcholine release
Delta (δ) (e.g.,
etorphine)		 Analgesia, euphoria, physical dependence, hormone
changes, appetite suppression, dopamine release

TABLE 467-2 Management of Opioid Overdose Establish airway. Intubation and mechanical ventilation may be necessary.…

Harrison's 22e, p.3690

  • Establish airway. Intubation and mechanical ventilation may be necessary.
  • Naloxone 0.4–2.0 mg (IV, IM, or endotracheal tube). Onset of action with IV is
    ~1–2 min.
  • Repeat doses of naloxone if needed to restore adequate respiration or a
    continuous infusion of naloxone can be used.
  • One-half to two-thirds of the initial naloxone dose that reversed the respiratory
    depression is administered on an hourly basis (note: naloxone dosing is not
    necessary if the patient has been intubated).