Pharmacology · Opioid Pharmacology

Clinical Applications and Management of Opioid Use Disorder

WHO analgesic ladder, medications for opioid use disorder, and special populations

The WHO analgesic ladder structures pain management as three steps — non-opioids alone, then weak or low-dose opioids added, then strong opioids titrated to effect — with the guiding principle of dosing by mouth, by the clock, and by the ladder.
Methadone for MOUD requires licensed opioid treatment programs and carries QTc monitoring obligations and CYP3A4 drug interaction risks; buprenorphine/naloxone can be prescribed in any office setting but demands that the patient be in spontaneous withdrawal at induction to avoid precipitated withdrawal.
Extended-release naltrexone requires full detoxification (7–10 days minimum off short-acting opioids) before initiation — giving it to a dependent patient precipitates severe withdrawal; once established, it blocks opioid reward completely.
In renal impairment, avoid meperidine entirely (normeperidine → seizures) and use morphine cautiously (M6G accumulation → respiratory depression); fentanyl and hydromorphone are preferred for less active metabolite accumulation.
In pregnancy, MOUD maintenance with methadone or buprenorphine is preferred over abstinence — abrupt withdrawal risks fetal distress and preterm labor; NOWS in exposed neonates is managed with supportive care and weaning opioids when needed, and is not a contraindication to maternal treatment.

Abbreviations: WHO = World Health Organization · MOUD = medications for opioid use disorder · OUD = opioid use disorder · QTc = corrected QT interval · CYP3A4 = cytochrome P450 3A4 · M6G = morphine-6-glucuronide · NOWS = neonatal opioid withdrawal syndrome · NSAID = nonsteroidal anti-inflammatory drug

World Health Organization Analgesic Ladder

Step 1

Mild Pain

Acetaminophen
NSAIDs
Adjuvant agents
No opioids at this step

Step 2

Mild to Moderate Pain

Add weak opioid or low-dose strong opioid
Codeine, tramadol, low-dose oxycodone
Continue Step 1 non-opioids
Continue adjuvants

Step 3

Moderate to Severe Pain

Strong opioids titrated to effect
Morphine, oxycodone, fentanyl, hydromorphone
No fixed ceiling dose for cancer pain
Guiding principles: by mouth, by the clock, by the ladder

Medications for Opioid Use Disorder Compared

Agent	Mechanism	Setting	Key Requirement	Key Monitoring
Methadone	Full mu agonist	Licensed opioid treatment programs only	Daily observed dosing initially; take-home earned with stability	QTc interval monitoring; CYP3A4 drug interactions
Buprenorphine/ naloxone	Partial mu agonist plus naloxone deterrent	Office-based — any prescriber with standard registration	Patient must be in spontaneous withdrawal before induction	Hepatic function; signs of precipitated withdrawal at induction
Extended-release naltrexone	Pure mu antagonist	Office-based or outpatient	Full detoxification first: 7–10 days minimum off short-acting opioids	Adherence; relapse risk during detoxification period

Special Populations: High-Yield Rules

Avoid or Reduce

Renal Impairment

Morphine: M6G accumulates → prolonged respiratory depression
Meperidine: normeperidine accumulates → seizures — avoid entirely
Preferred: fentanyl or hydromorphone (less active metabolite accumulation)
Oxycodone: dose reduction required

Adjust Doses

Elderly and Hepatic Disease

Elderly: start lower, titrate slower; avoid meperidine (Beers Criteria)
Hepatic disease: reduced first-pass metabolism increases bioavailability
Buprenorphine: use cautiously in severe hepatic impairment
All opioids: extended dosing intervals in hepatic disease

Pregnancy and Neonatal Opioid Withdrawal Syndrome

Preferred treatment for OUD in pregnancy: methadone or buprenorphine maintenance — not abstinence. Abrupt withdrawal in pregnancy risks fetal distress and preterm labor.

NOWS: onset 24–72 hours after birth in exposed neonates. Symptoms: irritability, high-pitched crying, tremors, poor feeding, vomiting, diarrhea, seizures in severe cases. Treatment: supportive care; oral morphine or methadone weaning if needed. Not a contraindication to maternal OUD treatment.

Suggested References

Author / Organization	Title	Source
Katzung BG (ed)	Basic and Clinical Pharmacology, 15th ed. Chapter 31: Opioid Analgesics and Antagonists	McGraw-Hill, 2021
Brunton LL, Knollmann BC (eds)	Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed. Chapter 20: Opioids, Analgesia, and Pain Management	McGraw-Hill, 2023
World Health Organization	WHO guidelines for the pharmacological and radiotherapeutic management of cancer pain in adults and adolescents	WHO. 2018
Dowell D, Haegerich TM, Chou R	CDC guideline for prescribing opioids for chronic pain — United States, 2016	JAMA. 2016;315(15):1624–1645
Substance Abuse and Mental Health Services Administration	Medications for Opioid Use Disorder: Treatment Improvement Protocol 63	SAMHSA. 2021
Mattick RP, Breen C, Kimber J, Davoli M	Methadone maintenance therapy versus no opioid replacement therapy for opioid dependence	Cochrane Database Syst Rev. 2009;(3):CD002209
Lee JD, Nunes EV, Novo P, et al	Comparative effectiveness of extended-release naltrexone versus buprenorphine-naloxone for opioid relapse prevention	Lancet. 2018;391(10118):309–318
Patrick SW, Barfield WD, Poindexter BB	Neonatal opioid withdrawal syndrome	Pediatrics. 2020;146(5):e2020029074
Volkow ND, Frieden TR, Hyde PS, Cha SS	Medication-assisted therapies — tackling the opioid-overdose epidemic	N Engl J Med. 2014;370(22):2063–2066
American Geriatrics Society Beers Criteria Update Expert Panel	American Geriatrics Society 2023 updated AGS Beers Criteria for potentially inappropriate medication use in older adults	J Am Geriatr Soc. 2023;71(7):2052–2081