Opioids
GENERAL PRINCIPLES
Pathophysiology
• Opioids are naturally occurring or synthetic xenobiotics that act at the opioid receptors in the brain, spinal cord, and periphery.
• Most of the clinically relevant effects of opioids are related to mu-opioid agonism.
DIAGNOSIS
Clinical Presentation
• Patients with opioid poisoning present with a depressed level of consciousness (ranging from drowsiness to coma), respiratory depression, and miosis.
î Miosis may be absent in patients who have seized, patients who are profoundly hypoxemic or acidotic, or patients poisoned by certain opioids (e.g., meperidine).
• Blood pressure and heart rate may be mildly decreased in opioid poisoning, but profound hemodynamic instability suggests an alternative etiology.
Diagnostic Testing
LABORATORIES
• Obtain a point-of-care blood glucose to rule out hypoglycemia, which may mimic opioid poisoning.
• Other laboratory tests (such as blood gases, electrolytes, UDS) are not generally helpful in acute medical management.
ELECTROCARDIOGRAPHY
Obtain an ECG in cases of known or suspected methadone poisoning, as methadone may substantially prolong the QT interval.
TREATMENT
• The goal of treatment is to maintain adequate respiration, not to produce complete wakefulness.
• In many cases of mild opioid poisoning, close monitoring is sufficient, and no active treatment is required.
î Continuous monitoring of end-tidal carbon dioxide (ETCO2) is more sensitive for hypopnea, bradypnea, and apnea than pulse oximetry.
Medications
• Naloxone, a mu-opioid antagonist, is the antidote for opioid poisoning.
î The lowest effective dose that restores normal respiration should be used. Excess naloxone will provoke opioid withdrawal in opioid-dependent patients.
î The typical starting dose is 0.04 mg IV. This dose may be repeated or increased as necessary to achieve sustained normal respiration.
A patient who has not improved with 10 mg naloxone should prompt an alternative diagnosis.î Poisoning by long-acting may require a naloxone infusion typically started at two-thirds the effective reversal dose per hour titrated to adequate respiratory rate. 9
î If IV access is not available, naloxone may be administered by the intranasal, intramuscular, endotracheal, or intraosseous routes. Higher doses are required when using these alternate routes.
Nonpharmacologic Therapies
• Support of respiration by bag-valve mask may be required prior to naloxone administration.
• Endotracheal intubation is rarely indicated in isolated opioid poisoning (as respiratory depression should be reversed by naloxone) but may be necessary in cases of polysubstance intoxication or cooccurring major trauma or medical illness.
SPECIAL CONSIDERATIONS: OPIOID USE DISORDER
• Opioid use disorder (OUD) is a problematic pattern of opioid use leading to clinically significant impairment or distress. Patients appropriately taking prescribed opioids may develop tolerance or dependence, but this does not indicate the presence of OUD.
• There are two primary options for medication for opioid use disorder (mOUD): methadone and buprenorphine (Table 28-4). mOUD produces sustained remission, prevents relapse and overdose, improves quality of life, and prevents premature death.
TABLE 28-4
| MEDICATIONS FOR OPIOID USE DISORDER | |||
| Buprenorphine (Sublingual or IM) | Methadone | IM Naltrexone (Vivitrol) | |
| Pharmacology on #956;-opioid receptors | Partial agonist, very high receptor affinity | Full agonist, high receptor affinity | Antagonist |
| Estimated elimination half-life | 24-42 h | 13-47 h | 5-10 d |
| Typical dosing | 4-32 mg total daily dose, divided twice or three times daily | 30-150 mg daily | 380 mg monthly |
| Considerations | Can be prescribed in an acute care hospital without DEA waiver, outpatient Rx requires “X-waiver” | Outpatient administration only at a methadone clinic. Requires daily transport to clinic | Requires period of opioid abstinence and 7 d oral naltrexone prior to administration. Does not treat cravings or withdrawal symptoms |
• Symptomatic treatment of opioid withdrawal may be helpful in patients who decline mOUD or during the initiation of mOUD.
° Clonidine (starting dose 0.1 mg PO q8 hours as needed) may help treat anxiety, psychomotor agitation, and malaise.
î Symptomatic treatment of GI symptoms (e.g., antiemetics for nausea and vomiting, loperamide for diarrhea) may be helpful.
î Hydroxyzine may be helpful for pruritus, anxiety, and insomnia.
• Patients taking mOUD may sometimes require opioids for the treatment of acutely painful medical conditions. Consultation with Pain Management and Addiction Medicine may be helpful in these circumstances.
• Patients with known or suspected OUD should be referred for outpatient evaluation and treatment and prescribed naloxone for use in case of accidental overdose.