The preceding four modules established the receptor pharmacology, drug-specific profiles, adverse effect management, and broad clinical applications of opioid analgesics. This module addresses three areas that require integrative application of all prior content: the pharmacology of neuropathic pain and the specific opioid strategies that have mechanistic rationale in this context; high-yield clinical scenarios that bridge pharmacokinetics, adverse effect management, and clinical decision-making in ways that test integration rather than recall; and a framework for individualizing opioid selection and monitoring in complex clinical cases. Together with Modules 1 through 4, this module completes the clinical pharmacology foundation required for competent, evidence-based opioid prescribing across the spectrum of pain types and patient populations.
Neuropathic pain is defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory nervous system.1 This definition distinguishes it mechanistically from nociceptive pain, which arises from activation of intact nociceptors by tissue damage, and from nociplastic pain, a recently described category in which pain arises from altered nociception without clear evidence of tissue damage or somatosensory system injury. The distinction matters pharmacologically because the mechanistic underpinnings of neuropathic pain involve pathological changes in peripheral and central neural circuits that are not reliably responsive to the same opioid doses that control nociceptive pain, and because several non-opioid analgesic classes target neuropathic pain mechanisms more specifically than opioids. The peripheral mechanisms of neuropathic pain include ectopic discharge from injured primary afferent neurons, particularly small-diameter C fibers and Adelta (A-delta) fibers, which fire spontaneously or with abnormal sensitivity to normally subthreshold stimuli.1
This ectopic activity arises from upregulation and redistribution of voltage-gated sodium (Nav) channels, particularly Nav1.7, Nav1.8, and Nav1.3, at injury sites and in the dorsal root ganglion (DRG) cell bodies. Nav channel upregulation is the target of voltage-gated sodium channel blockers including lidocaine, mexiletine, and tricyclic antidepressants (TCAs) at their sodium channel-blocking mechanism. Peripheral sensitization, defined as a reduction in the activation threshold of primary afferent nociceptors at the site of injury or inflammation, contributes to the allodynia (pain from normally non-painful stimuli) and hyperalgesia (exaggerated pain from mildly painful stimuli) that characterize neuropathic pain. Loss of inhibitory interneurons in the dorsal horn following nerve injury reduces GABAergic and glycinergic inhibition of nociceptive transmission, a phenomenon termed disinhibition, which contributes to central sensitization.1
Central sensitization is the amplification of synaptic transmission in the dorsal horn and higher pain-processing centers that maintains and amplifies pain independently of ongoing peripheral input. It is driven by glutamate-mediated activation of N-methyl-D-aspartate (NMDA) receptors in dorsal horn neurons, which removes the voltage-dependent magnesium block and allows calcium influx that initiates long-term potentiation (LTP)-like changes in synaptic strength.1 NMDA receptor activation in this context is the mechanistic basis for several key clinical features of neuropathic pain: the temporal summation phenomenon (wind-up), in which repeated low-frequency stimulation produces progressively increasing pain; the spatial spread of pain beyond the original injury territory; and the persistence of pain after peripheral healing is complete.
The pharmacological implication is that drugs targeting NMDA receptors, including ketamine, memantine, dextromethorphan, and opioids with NMDA receptor antagonist properties (methadone, levorphanol), have mechanistic rationale in neuropathic pain that extends beyond their opioid receptor activity.1 Descending pain modulation via noradrenergic and serotonergic pathways from the brainstem to the dorsal horn normally suppresses nociceptive transmission; dysfunction of these descending inhibitory systems has been documented in neuropathic pain conditions and is the mechanistic basis for the analgesic efficacy of serotonin-norepinephrine reuptake inhibitors (SNRIs) such as duloxetine and venlafaxine in neuropathic pain.
The major clinical neuropathic pain syndromes share mechanistic features but differ in etiology, temporal course, and optimal pharmacological management. Understanding the opioid role in each requires integrating the mechanistic framework above with clinical evidence from randomized controlled trials (RCTs). Postherpetic neuralgia (PHN) is the most common complication of herpes zoster reactivation, occurring in 10–20% of patients with zoster overall and in 30–50% of those over age 60.2 PHN is defined as pain persisting beyond three months after the acute zoster rash, and it can last years. Its mechanisms include peripheral sensitization from direct neuronal injury by varicella-zoster virus (VZV) and central sensitization from the barrage of nociceptive input during the acute phase. The pharmacological cornerstones of PHN treatment are gabapentinoids (gabapentin and pregabalin), TCAs (most evidence for nortriptyline and amitriptyline), the 5% lidocaine patch, and the high-concentration (8%) capsaicin patch.2
Opioids, primarily tramadol, oxycodone, and morphine, have randomized controlled trial (RCT) evidence for efficacy in PHN and are used as second- or third-line agents when first-line treatments fail. Strong full mu-opioid receptor (MOR) agonists produce meaningful PHN pain reduction but carry all the systemic adverse effects of chronic opioid therapy including tolerance and physical dependence, which are particularly problematic in the elderly population predominantly affected by PHN. Tramadol's dual mechanism (MOR agonism plus serotonin-norepinephrine reuptake inhibition) may offer some mechanistic advantage in PHN through its monoaminergic augmentation of descending inhibition, though it has not been shown to be superior to other opioids in head-to-head trials.2
Diabetic peripheral neuropathy (DPN) is the most prevalent neuropathic pain condition globally, affecting approximately 10–20% of people with diabetes mellitus.2 The mechanisms include metabolic injury to peripheral sensory neurons, including chronic hyperglycemia-induced oxidative stress, advanced glycation end-product (AGE) accumulation, and microvascular ischemia of the vasa nervorum, producing a length-dependent dying-back neuropathy that begins with small fiber loss in the distal extremities and progresses centrally. First-line pharmacological therapy for painful DPN per guidelines from the American Diabetes Association (ADA) and the American Academy of Neurology (AAN) includes duloxetine, pregabalin, gabapentin, and for some patients amitriptyline or nortriptyline.2 Opioids are not first-line agents for DPN; the evidence for their long-term efficacy in DPN specifically is less robust than for first-line agents, and the long-term metabolic consequences of opioids (including opioid-induced hypogonadism, immune suppression, and opioid-induced hyperalgesia) are particularly concerning in a chronic condition where patients may require decades of pharmacological pain management. When opioids are used in DPN, tramadol and tapentadol have both demonstrated efficacy in RCTs; tapentadol's relatively greater norepinephrine reuptake inhibition compared to serotonin reuptake inhibition may offer analgesic advantages with a more favorable drug interaction profile than tramadol.2
Central post-stroke pain (CPSP), also termed thalamic pain syndrome, occurs in approximately 8–11% of stroke patients and results from injury to spinothalamic tract pathways, thalamic nuclei, or cortical pain-processing areas. It is characterized by burning, shooting, or aching pain in the affected body area, with allodynia and dysesthesias, that can be refractory to all classes of analgesics. TCAs (amitriptyline) and lamotrigine have the most evidence for CPSP; opioids including morphine and tramadol have some efficacy in controlled studies.2 The opioid analgesic response in CPSP is often incomplete and less predictable than in peripheral neuropathic pain conditions, reflecting the location of the pathological changes above the level of opioid-sensitive spinal circuits.
Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting complication of multiple chemotherapeutic agents, including taxanes (paclitaxel, docetaxel), platinum compounds (cisplatin, oxaliplatin, carboplatin), vinca alkaloids (vincristine), and proteasome inhibitors (bortezomib).2 CIPN involves injury to peripheral sensory and autonomic nerve fibers through disruption of microtubule assembly (taxanes and vinca alkaloids), DNA adduct formation in dorsal root ganglion (DRG) neurons (platinum compounds), and mitochondrial dysfunction. Duloxetine is the only agent with RCT evidence supporting moderate efficacy for CIPN pain, and it is the preferred pharmacological treatment per American Society of Clinical Oncology (ASCO) guidelines.2 Opioids have no specific evidence of superiority over non-opioid analgesics in CIPN and are used empirically for refractory cases following failure of first-line agents. The neuropathic mechanism of CIPN, with its DRG neuronal injury pattern, may explain the limited opioid responsiveness compared to perioperative or cancer-related nociceptive pain.
Several opioids have pharmacological properties that extend beyond mu-opioid receptor (MOR) agonism and provide theoretical or demonstrated advantages in neuropathic pain syndromes. Understanding these properties guides rational agent selection when opioids are indicated for neuropathic pain. Methadone's status as both a full MOR agonist and an N-methyl-D-aspartate (NMDA) receptor antagonist gives it a dual mechanism that addresses both the opioid-responsive component of neuropathic pain and the central sensitization component mediated by NMDA receptor activation.3
The R-enantiomer of racemic methadone (d-methadone) carries the preponderance of NMDA receptor antagonist activity; d-methadone (REX-001 or dextromethorphan-related compounds) has been studied as a potential analgesic targeting the NMDA mechanism specifically. Clinically, methadone is used as a second-line agent in neuropathic pain that has failed first-line non-opioid and standard opioid therapy; several retrospective case series and small controlled studies support its efficacy in conditions including postherpetic neuralgia (PHN), chemotherapy-induced peripheral neuropathy (CIPN), and cancer-related neuropathic pain. Methadone's NMDA receptor antagonism may also attenuate opioid-induced hyperalgesia (OIH) and slow the development of tolerance, which are advantages in patients requiring long-term opioid therapy for neuropathic pain. These potential benefits must be weighed against methadone's well-characterized risks: prolonged and variable half-life, QTc prolongation, complex drug interactions through CYP3A4 (cytochrome P450 3A4), and the need for specialized prescriber familiarity.3
Levorphanol shares methadone's NMDA receptor antagonist property along with MOR agonism, and additionally has delta-opioid receptor (DOR) and kappa-opioid receptor (KOR) activity at clinical doses, providing a broader receptor engagement profile than most opioids.3 Its prolonged half-life (11–16 hours) allows twice-daily dosing but requires careful titration to avoid accumulation. Small clinical series support its use in neuropathic pain conditions refractory to other opioids. Levorphanol is available in the United States but is infrequently prescribed due to limited prescriber familiarity; its utility in neuropathic pain is primarily as an option when methadone is not appropriate due to QTc concerns or drug interaction burden.
Buprenorphine has a distinct pharmacological rationale in neuropathic pain through its KOR antagonism and partial MOR agonism.3 KOR activation in the spinal cord and supraspinal circuits contributes to the dysphoric and aversive quality of chronic pain, and KOR antagonism, an intrinsic property of buprenorphine at therapeutic doses, may reduce the affective burden of neuropathic pain independently of MOR-mediated analgesia. Buprenorphine's ceiling effect for respiratory depression and its favorable pharmacokinetic profile in renal impairment make it an attractive opioid choice in elderly patients with neuropathic pain and comorbid kidney disease, a combination that is common in the diabetic and post-herpetic neuropathy populations. The transdermal buprenorphine patch (Butrans) and buccal film (Belbuca) provide continuous low-dose exposure appropriate for stable neuropathic pain, while sublingual formulations allow dose titration for variable pain intensity.3
Tramadol and tapentadol target both MOR and monoaminergic mechanisms, making them theoretically well-suited for neuropathic pain conditions where descending inhibitory system dysfunction contributes to pain amplification.3 Tramadol's serotonin and norepinephrine reuptake inhibition augments descending noradrenergic inhibition in the dorsal horn, using the same mechanism by which duloxetine and amitriptyline produce analgesia in neuropathic pain. Tapentadol's relatively selective norepinephrine reuptake inhibition (greater than its serotonin effect) may offer analgesic advantages through the noradrenergic pathway with less serotonin-mediated adverse effect and drug interaction risk. In RCTs for diabetic peripheral neuropathy (DPN) and low back pain with neuropathic features, tapentadol extended-release produced comparable pain relief to oxycodone extended-release with significantly lower rates of nausea, constipation, and vomiting, an important practical advantage for long-term neuropathic pain management.3
The clinical evidence for opioid efficacy in neuropathic pain is more nuanced and less robust than the evidence for opioid efficacy in acute nociceptive pain, and prescribers must approach this literature with appropriate attention to study design limitations.4 Multiple RCTs demonstrate that opioids produce statistically significant reductions in pain scores in neuropathic pain conditions including postherpetic neuralgia (PHN), diabetic peripheral neuropathy (DPN), and central neuropathic pain compared to placebo. However, the clinical significance of these reductions, typically 1–2 points on a 10-point numeric rating scale, and the proportion of patients achieving clinically meaningful relief (commonly defined as a 30–50% pain reduction) are both modest. Approximately 30–40% of patients in neuropathic pain opioid RCTs achieve clinically meaningful relief versus 15–20% on placebo, indicating number-needed-to-treat (NNT) values that are generally comparable to or only modestly better than first-line non-opioid agents such as gabapentinoids and duloxetine.4
The comparative effectiveness literature, comparing opioids directly to non-opioid analgesics in neuropathic pain, is limited by relatively short trial durations (most RCTs are 4–12 weeks) and attrition rates that may bias results in favor of active treatment. Long-term data on opioid efficacy in neuropathic pain beyond 12 weeks are sparse, and tolerance development over extended periods substantially reduces initial gains.4
The adverse effect burden of opioids in neuropathic pain RCTs, particularly sedation, constipation, nausea, and dizziness, produces high discontinuation rates that further complicate long-term efficacy assessment. Current guidelines from the International Association for the Study of Pain (IASP) Special Interest Group on Neuropathic Pain (NeuPSIG) and the Canadian Pain Society recommend opioids as third-line agents for neuropathic pain conditions where first-line (gabapentinoids, SNRIs, TCAs) and second-line (lidocaine patch, capsaicin) therapies have failed or are not tolerated.4 Tramadol occupies a lower risk tier than strong opioids in these guidelines and may be considered earlier in the treatment sequence for neuropathic pain; strong opioids (morphine, oxycodone, and others) are reserved for refractory cases. The practical clinical implication is that the decision to prescribe a strong opioid for neuropathic pain requires documented failure of at least two first-line agents, a realistic expectation of modest rather than complete pain relief, explicit discussion with the patient of the chronic adverse effect risks, and a plan for ongoing reassessment of the benefit-risk ratio.4
Individualized opioid selection for a specific patient requires simultaneous consideration of the pain type and mechanism, the patient's pharmacokinetic profile (renal and hepatic function, CYP genetic variants), the adverse effect vulnerability (age, comorbid respiratory disease, cardiovascular disease, CNS disease), the drug interaction landscape of concurrent medications, and the patient's goals and values. The following framework integrates the pharmacological principles from Modules 1 through 4 into a systematic approach to these decisions.5 The first consideration is renal function, because several opioid-specific toxic metabolites are renally cleared and accumulate dangerously in renal impairment. The critical principle established in Module 2 is that morphine, hydromorphone, and to a lesser extent codeine and oxycodone produce renally cleared metabolites (morphine-3-glucuronide, morphine-6-glucuronide, and hydromorphone-3-glucuronide) with neuroexcitatory or potent analgesic properties that can accumulate to toxic concentrations as estimated glomerular filtration rate (eGFR) declines below 30 mL/min/1.73m2.
In patients with significant renal impairment (eGFR below 30) or end-stage renal disease (ESRD) requiring dialysis, fentanyl is the preferred opioid for ongoing analgesia because its hepatic CYP3A4 (cytochrome P450 3A4)-mediated metabolism to inactive norfentanyl produces no renally toxic metabolites. Buprenorphine is also renally safe through the same mechanism: its metabolic products do not accumulate in renal failure, and its pharmacokinetic profile in patients on dialysis is well characterized. Methadone is theoretically renally safe (primarily fecal excretion) but its complex pharmacokinetics limit its utility in non-specialist settings.5
The second consideration is hepatic function. Because virtually all opioids are primarily hepatically metabolized, significant hepatic impairment alters opioid pharmacokinetics through multiple mechanisms: reduced first-pass extraction increases the oral bioavailability of high-hepatic-extraction opioids (morphine, fentanyl), producing higher than expected plasma concentrations after standard oral doses; decreased hepatic enzyme activity prolongs the half-lives of CYP-metabolized opioids (fentanyl, methadone, alfentanil); and reduced albumin and alpha-1-acid glycoprotein synthesis increases the free fraction of highly protein-bound opioids. In Child-Pugh Class C hepatic impairment, all opioids require dose reductions with extended dosing intervals and careful monitoring; in Child-Pugh Class B, the same caution applies with somewhat more flexibility. Buprenorphine at reduced doses and morphine at reduced doses are generally the best-tolerated opioids in hepatic impairment among the commonly used agents; methadone requires particular caution.5
The third consideration is cardiac disease, primarily for its implications regarding QTc-prolonging medications. Methadone is the only commonly used opioid that produces clinically meaningful QTc prolongation at therapeutic doses through hERG (IKr) channel blockade. Patients with baseline QTc prolongation (greater than 450 ms in men, greater than 470 ms in women), underlying cardiac structural disease, electrolyte disturbances (hypokalemia, hypomagnesemia), or concurrent use of other QTc-prolonging agents (antiarrhythmics, macrolide antibiotics, antipsychotics, azole antifungals) face substantially higher risk of torsades de pointes from methadone. In these patients, methadone should either be avoided or used with baseline ECG and serial monitoring.5 No other first-line or second-line opioid analgesic requires QTc monitoring.
The fourth consideration is the concurrent medication burden, specifically the drug interaction profile discussed in detail in Module 2, Section 9. Patients on CYP3A4 inhibitors require careful attention if prescribed fentanyl, methadone, or oxycodone, as plasma concentrations of these agents will rise. Patients on CYP3A4 inducers (rifampin, carbamazepine, phenytoin) on a stable methadone or buprenorphine regimen will experience reduction in plasma concentrations and may require dose increases. Patients on serotonergic medications (SSRIs, SNRIs, MAOIs, linezolid) should not receive tramadol without careful evaluation of serotonin syndrome risk, and meperidine is absolutely contraindicated in this context.5
Patients on benzodiazepines require specific counseling and risk stratification for the combined respiratory depression risk; when both are prescribed, both should be at the lowest effective doses, and naloxone should be co-prescribed.
The fifth consideration is functional goals and patient values. The decision to use opioids, particularly for chronic non-cancer pain (CNCP), should be explicitly framed in terms of functional outcomes, not merely pain scores. A patient whose pain is 7/10 but who is working, socially engaged, and sleeping adequately may be managing well without opioids; a patient whose pain is 6/10 but who is bedbound, unable to work, and socially isolated may have a compelling argument for opioid therapy if non-opioid agents have failed. The 2022 CDC guideline emphasizes that individualized benefit-risk assessment, not population-level dose thresholds applied without clinical judgment, should guide prescribing decisions for CNCP. Patient preferences regarding the adverse effect profile of different opioids (some patients prioritize avoiding constipation; others prioritize cognitive clarity; others prioritize convenient dosing) are legitimate inputs into agent selection when multiple pharmacologically appropriate options exist.5
Palliative sedation, defined as the deliberate reduction of consciousness to relieve refractory suffering in patients near the end of life, represents a specific and ethically significant clinical application of opioids and sedative agents that requires pharmacological and ethical literacy from the prescribing clinician.6 Refractory symptoms at end of life that may warrant palliative sedation include pain, dyspnea, existential suffering, agitated delirium, and intractable nausea or vomiting. The ethical distinction between palliative sedation and euthanasia or physician-assisted death is grounded in the principle of double effect and in the clinical evidence that appropriately titrated opioids and sedatives for symptom control in dying patients do not hasten death when used at doses calibrated to symptom relief rather than to respiratory suppression.6
Observational studies in hospice and palliative care consistently show that patients receiving opioid infusions for dyspnea or pain at end of life do not have shorter survival than matched controls, and that the primary determinants of survival are the underlying disease trajectory rather than the analgesic regimen. Opioids for dyspnea at end of life act through mu-opioid receptor (MOR) activation in brainstem respiratory centers to reduce the respiratory effort drive and the subjective perception of breathlessness, providing comfort even when objective respiratory parameters (rate, saturation) remain abnormal.6 The doses required for dyspnea relief in opioid-naive patients are typically lower than analgesic doses; morphine 2.5–5 mg orally every 4 hours or 1–2 mg IV every 4 hours is a common starting point. In opioid-tolerant patients, additional opioid above the analgesic baseline may be required to achieve dyspnea relief.
Continuous subcutaneous or IV infusion is the preferred delivery method in patients who cannot take oral medications in the final hours to days of life; morphine, hydromorphone, oxymorphone, and fentanyl are all compatible with continuous infusion in palliative care settings.6 Midazolam is commonly combined with opioids in continuous infusion for refractory agitation and dyspnea near death; the combination provides complementary sedation and anxiolysis through gamma-aminobutyric acid type A (GABA-A) receptor potentiation while the opioid addresses the dyspnea and pain components. Dexamethasone may reduce tumor-related pain and airway inflammation, and octreotide manages secretions and bowel obstruction-related symptoms. The palliative care prescriber must be comfortable calculating and adjusting infusion rates in response to symptom assessment at the bedside and with communicating the goals of medication titration clearly to nursing staff, patients (when conscious), and families.6
No pharmacology curriculum for clinicians is complete without situating opioid prescribing within the context of the opioid crisis that has claimed hundreds of thousands of lives in the United States since the late 1990s and that continues to evolve in its character and geography.7 Understanding the epidemiology of opioid-related harm is not tangential to clinical pharmacology; it directly informs risk assessment, prescribing practice, and the prescriber's responsibilities to individual patients and to public health. The US opioid crisis has unfolded in three overlapping waves. The first wave, beginning in the late 1990s, was driven by dramatic increases in prescription opioid prescribing, particularly extended-release oxycodone, following aggressive promotion by pharmaceutical manufacturers (most notably Purdue Pharma) that overstated safety and minimized addiction risk for non-cancer pain indications.7 Prescription opioid overdose deaths increased steadily through the 2000s, peaking around 2010–2012.
The second wave was characterized by a rise in heroin use and overdose deaths beginning around 2010–2012, driven in part by prescription opioid users transitioning to cheaper, more accessible heroin. The third and most deadly wave began approximately 2013–2014 with the widespread introduction of illicitly manufactured fentanyl (IMF) and fentanyl analogs into the heroin and then the broader illicit drug supply; this wave has been characterized by exponentially increasing overdose death rates driven by IMF's extreme potency and the unpredictability of dose in illicit supply chains.7
By 2021, synthetic opioids (primarily IMF) accounted for over 70,000 of approximately 107,000 drug overdose deaths in the United States, a figure that exceeds the death toll of any prior year and that represents a public health crisis of unprecedented scale. The prescriber's role in the third wave of the opioid crisis is not primarily about restricting access to pharmaceutical opioids, though responsible prescribing remains foundational, but about recognizing the landscape of risk that patients face, providing naloxone to patients at risk regardless of opioid source, engaging in non-judgmental substance use assessment and treatment referral, and maintaining the analgesic access that patients with legitimate pain require.7
The 2022 CDC guideline explicitly acknowledges that prior overly restrictive interpretations of the 2016 guideline contributed to undertreated pain and harmful forced tapers, and that the goal of opioid stewardship is balance, reducing unnecessary and high-risk opioid exposure while ensuring that patients who need opioids can access them without excessive burden. Harm reduction strategies, including naloxone distribution, fentanyl test strips, safe supply programs, and medication-assisted treatment for opioid use disorder (OUD), are evidence-based public health interventions that reduce opioid overdose mortality and that clinicians in all specialties can support, refer to, or directly provide within their scope of practice.7
The clinical scenarios presented in Tiers 3 and 4 of this chapter's question bank require integration of pharmacological principles across multiple domains simultaneously. This section provides the reasoning framework that connects those domains and that should guide complex opioid prescribing decisions in clinical practice. When approaching a complex opioid prescribing problem, the following sequence of questions structures the decision: What is the pain type and mechanism, whether nociceptive, neuropathic, nociplastic, or mixed, and what does this imply about opioid responsiveness and the role of non-opioid adjuvants? What is the patient's current opioid tolerance state, and how does this affect dose selection and titration strategy?
What are the pharmacokinetic constraints imposed by renal function, hepatic function, and the route of administration required? What drug interactions exist with the patient's current medication regimen, and which opioids are safest in that interaction landscape? What are the patient's specific vulnerabilities for adverse effects (respiratory disease, obstructive sleep apnea (OSA), age, cognitive impairment, history of falls), and how do these influence agent selection and monitoring intensity? Is the goal acute pain control, chronic pain management, opioid use disorder treatment, or end-of-life symptom palliation, and how does the goal change the appropriate opioid, dose, and monitoring framework?5
Opioid rotation decisions require applying equianalgesic principles from Module 2, incorporating the incomplete cross-tolerance dose reduction, selecting an agent appropriate to the patient's pharmacokinetic constraints, and establishing breakthrough dosing for the new regimen. Overdose recognition and reversal require applying the toxidrome recognition principles from Module 3 alongside knowledge of naloxone dosing, duration, and the resedation risk specific to the offending opioid's half-life. Neuropathic pain management decisions require applying the receptor pharmacology from Module 1, particularly the N-methyl-D-aspartate (NMDA) receptor contribution to central sensitization, to guide the selection of opioids with NMDA antagonist properties when central sensitization appears prominent. Opioid use disorder (OUD) treatment decisions require applying the buprenorphine partial agonism and induction principles from Modules 1 and 4, the medications for opioid use disorder (MOUD) evidence base, and the regulatory context for prescribing. In each case, the pharmacology is the foundation, and clinical reasoning is the superstructure built on it.5
Jensen TS, Baron R, Haanpaa M, et al. A new definition of neuropathic pain. Pain. 2011;152(10):2204–2205
doi:10.1016/j.pain.2011.06.017Finnerup NB, Attal N, Haroutounian S, et al. Pharmacotherapy for neuropathic pain in adults: a systematic review and meta-analysis. Lancet Neurol. 2015;14(2):162–173
doi:10.1016/S1474-4422(14)70251-0McNicol ED, Midbari A, Eisenberg E. Opioids for neuropathic pain. Cochrane Database Syst Rev. 2013;(8):CD006146
doi:10.1002/14651858.CD006146.pub2Dworkin RH, O'Connor AB, Audette J, et al. Recommendations for the pharmacological management of neuropathic pain: an overview and literature update. Mayo Clin Proc. 2010;85(3 Suppl):S3–S14
doi:10.4065/mcp.2009.0649Dowell D, Ragan KR, Jones CM, Baldwin GT, Chou R. CDC clinical practice guideline for prescribing opioids for pain — United States, 2022. MMWR Recomm Rep. 2022;71(3):1–95
doi:10.15585/mmwr.rr7103a1Cherny NI, Radbruch L; Board of the European Association for Palliative Care. European Association for Palliative Care (EAPC) recommended framework for the use of sedation in palliative care. Palliat Med. 2009;23(7):581–593
doi:10.1177/0269216309107024Ciccarone D. The triple wave epidemic: supply and demand drivers of the US opioid overdose crisis. Int J Drug Policy. 2019;71:183–188
doi:10.1016/j.drugpo.2019.01.010