Opioid use disorder Study Guide

📖 Core Concepts Opioid Use Disorder (OUD): A substance‑use disorder marked by cravings, continued use despite harm, tolerance, and withdrawal. Addiction vs. Dependence: Addiction = compulsive use; dependence = physiological adaptation causing withdrawal when stopped. Mesocorticolimbic Reward Circuit: Opioids overstimulate this dopamine pathway (ventral tegmental area → nucleus accumbens), driving “wanting” (compulsive seeking) even when “liking” wanes. Morphine Milligram Equivalents (MME): Standardized metric to compare opioid potency; daily MME guides safe prescribing. Diagnostic Criteria (DSM‑5): ≥2 of 11 criteria in 12 months → mild (2‑3), moderate (4‑5), severe (≥6). Tolerance/withdrawal excluded when opioids are used only as prescribed. Medication‑Assisted Treatment (MAT): Methadone (full agonist), buprenorphine/naloxone (partial agonist + antagonist), extended‑release naltrexone (antagonist). Naloxone: Competitive opioid antagonist; reverses respiratory depression within minutes via IM, IV, sub‑Q, IN, or inhalation routes. 📌 Must Remember MME Thresholds: >90 mg/day = high risk for overdose; consider taper or alternative therapy. Withdrawal Timing: Short‑acting opioids → symptoms start within hours; long‑acting (e.g., methadone) → up to 2 days. Buprenorphine Induction: Start at Clinical Opiate Withdrawal Scale (COWS) ≈ 12 (moderate withdrawal) for standard induction; micro‑dosing can begin without waiting for withdrawal. Naloxone Access: Standing orders & pharmacy‑dispensed kits are legal in most states; Good Samaritan laws protect by‑standers. Genetic Influence: 50 % of OUD liability is heritable; CYP2D6 variants affect metabolism of many opioids. Four Waves of the U.S. Epidemic: 1) Prescription opioids → 2) Heroin → 3) Illicit fentanyl → 4) Polysubstance (synthetic opioids + stimulants). 🔄 Key Processes Diagnosing OUD (DSM‑5) Screen for 11 criteria → count positive items → assign severity. MME Calculation Convert each opioid dose to morphine equivalents using published conversion factors → sum for 24‑hour total. Buprenorphine Induction (Standard) Confirm moderate withdrawal (COWS ≥12) → give 2‑4 mg buprenorphine → reassess after 1–2 h → titrate to 8–16 mg/day. Methadone Initiation Assess opioid tolerance, time since last dose, and prior opioid type → start 20‑30 mg; increase cautiously (max 10 mg/dose) with ECG monitoring for QT prolongation. Naloxone Administration Recognize overdose (pin‑point pupils, respiratory depression) → give 0.4‑2 mg IM/IN → repeat every 2–3 min if no response. 🔍 Key Comparisons Methadone vs. Buprenorphine/Naloxone Methadone: Full agonist, longer half‑life (up to 56 h), higher overdose risk, requires daily clinic dosing. Buprenorphine/Naloxone: Partial agonist, ceiling effect on respiratory depression, can be prescribed in office‑based settings, lower cardiac risk. Naloxone (IM) vs. Intranasal IM: Faster onset, higher bioavailability, requires needle. IN: Needle‑free, slightly slower onset, easier for laypersons. Standard Induction vs. Micro‑dosing Standard: Wait for moderate withdrawal before first dose. Micro‑dosing: Begin with sub‑therapeutic buprenorphine (0.5‑1 mg) while still using full agonist, avoiding withdrawal. ⚠️ Common Misunderstandings “Tolerance = Addiction” – Tolerance is a physiological adaptation; addiction requires compulsive use despite harm. “Naloxone causes withdrawal in chronic users” – It can precipitate withdrawal but the life‑saving reversal of respiratory depression outweighs discomfort. “Prescription opioids are safe if taken as directed” – Even appropriate use can lead to dependence; daily MME >90 mg markedly raises overdose risk. “Buprenorphine can’t be used in pregnancy” – Buprenorphine is actually preferred (lower preterm birth risk) over methadone; naltrexone is avoided. 🧠 Mental Models / Intuition “Reward Circuit = Battery”: Opioids over‑charge the dopamine battery (mesocorticolimbic pathway). When the battery is full, “wanting” (search for more charge) persists even after “liking” (enjoyment) fades. “MME = Alcohol‑Standard‑Drink Analogy”: Just as drinks are converted to standard units to gauge intoxication, opioids are converted to MMEs to gauge overdose risk. 🚩 Exceptions & Edge Cases Tolerance/Withdrawal Not Counted: When opioids are taken only under proper medical supervision, these criteria are excluded from DSM‑5 diagnosis. Methadone QT Prolongation: Requires ECG monitoring in patients with cardiac risk factors; dose may need reduction. CYP2D6 Ultra‑rapid Metabolizers: May experience higher active metabolite levels → increased overdose risk, especially with codeine or tramadol. 📍 When to Use Which Mild‑Moderate OUD, outpatient stable → Buprenorphine/naloxone (office‑based). Severe OUD, high relapse risk, need daily supervision → Methadone (licensed opioid treatment program). Post‑detox, patient abstinent & motivated → Extended‑release naltrexone (monthly injection). Acute overdose in community → Intranasal naloxone (layperson) or IM/IV naloxone (EMS). Pregnant patient → Buprenorphine (preferred) or methadone if already stable on methadone. 👀 Patterns to Recognize Pin‑point pupils + respiratory depression → Classic opioid overdose (but remember dilated pupils do NOT rule it out). Rapid escalation of opioid dose + high daily MME → Red flag for impending misuse/overdose. Polysubstance involvement (opioid + stimulant) → Higher mortality; look for mixed‑toxin overdose signs (tachycardia + brady‑respiration). Withdrawal timeline: Short‑acting → symptoms within hours; long‑acting → delayed onset (up to 48 h). 🗂️ Exam Traps “Naloxone precipitates fatal withdrawal” – Wrong; it may cause uncomfortable withdrawal but saves life. “Tolerance alone meets DSM‑5 criteria” – Incorrect; need ≥2 other criteria unless use is unsupervised. “Methadone can be prescribed in any office” – False; requires enrollment in a federally‑certified opioid treatment program. “All opioids have the same MME conversion” – Misleading; each opioid has a specific factor (e.g., fentanyl ≈ 100× morphine). “Withdrawal symptoms start immediately after last dose” – Not for long‑acting agents (e.g., methadone may take 24‑48 h). --- Use this guide for a rapid, confidence‑boosting review before your exam. Good luck!