Opioids: General Principles and Conversion

AJ Winer

Oral morphine equivalent (OME) conversion table

Drug

PO

IV

APAP

IR

ER

Notes
Tramadol 0.1x - - Tramadol Ultram ER™ NSAID properties
Morphine 1x 3x - Morphine IR MS-Contin™ Renally cleared
Hydrocodone 1x - Lortab Hydrocodone NA
Oxycodone 1.5x - Percocet Roxicodone™ Oxycontin™
Hydromorphone 4x 12.5* - IV, Oral - Oral is $
Fentanyl 300x 300x - IV, Buccal, Nasal Patch Dosed in ug, not mg

Abbreviations: ER, extended release; IR, immediate release; IV, intravenous; PO, oral; APAP, Acetaminophen *Note: IV Hydromorphone conversion previously was 20:1. Based on recent data, this has been changed to 12.5:1, but some providers may still use 20:1.

Opioid pharmacokinetics

Mechanism

Onset

Peak Effect

Duration
PO 30 min 1 hr 3-4 hrs
IV 5-10 min 15 min 1-2 hrs

General opioid principles

  • When first starting opioids, start short-acting as needed with availability based on half-life o When a patient is requiring 4-5 PRN doses/24h, consider starting long acting
  • Transitioning between opiates: use oral morphine equivalents (OMEs). Each drugs’ potency is compared to oral morphine (table). Ex: 1 mg IV morphine = 3 mg PO morphine
  • Up titrating the dose of the same opioid: increase dose by 25-50% for moderate pain (4-7/10) and 50-100% for severe pain (8-10/10)
  • Transitioning between opioids: reduce OME by 1/4 to 1/3 to account for cross tolerance
    • Example: if switching from oxycodone 10mg q4h PRN to morphine ER q12h: calculate 24H OME → 60 (total mg in 24h) x 1.5 (conversion) = 90 OME → reduce by 25-33% → 60-67.5 OME → morphine ER 30mg q12h)
  • IR/ER regimens: Consider switching to ER when requiring 3-4 doses of IR medications in a 24h period regularly. The ER medication should treat the chronic pain experienced by a pt. The IR preparation is for breakthrough pain. Each IR dose should be ~10-20% of the total OME dose a pt takes daily.
    • Example (using above case): total OME 90 → 10-20% = (9-18mg) is ~15mg → divide by 1.5 (converts back to oxycodone which is 1.5x as strong) → oxycodone 10mg q4h PRN breakthrough
  • Fentanyl patches: Replaced q72h. When converting from oral morphine to fentanyl patch → divide 24h OME by 2 or 3 → gives ~dose of fentanyl patch in mcg/hr q72h
  • To calculate VUMC pt’s 24-hour OME: Go to pt Summary → pain and sedation tab or morphine equivalence tab
opioid equivelency decision flowchart
opioid equivelency decision flowchart image widget. Press Enter to type after or press Shift + Enter to type before the widget

Buprenorphine Pharmacokinetics

Route

Brand Name

Onset of action
Sublingual Subutex, Suboxone 30-60 min
Buccal Belbuca 30-60 min
Transdermal Butrans 18-24 hours

Buprenorphine Conversion to OME

Oral morphine equivalent chart
Oral morphine equivalent chart image widget. Press Enter to type after or press Shift + Enter to type before the widget

Pt Controlled Analgesia (PCA)

Pumps can be programmed to deliver a continuous rate and/or a bolus dose.

  • Basal rate: a continuous infusion dosed per hour that cannot be adjusted by the pt
  • Demand dose: a pt-directed bolus that is given at a prescribed frequency whenever the pt presses the button. Both the dose and frequency can be adjusted.
  • The general rule of thumb is to calculate the total OME delivered through the demand when a pt is in steady state and convert 75% of this dose into the total continuous rate.

Calculating initial doses

  • Basal dose: Check what the pt is actually taking at home (may be different than what is prescribed, use OME). Take the total daily dose and convert to IV and then divide that by 24 hours to get an hourly rate. If moderate pain, increase dose by 25-50%; if severe, by 50-100%.
  • Demand doses: The bolus dose should be 10-20% of total daily dose. The availability is based on the half-life of the medication (2hr for IV). Adjust the availability based on how frequently you want pt to be able to have a demand dose (e.g. if q10min divide by 12 or if q15min divide by 8 for 2 hours)
  • Don’t forget to set lockouts (maximum dose that can be given over a certain period of time) that includes both basal and demand doses
  • Remember that the basal rate will not get to steady state for at least 8 hrs. When you admit pts or are transitioning to a PCA, always initiate the PCA pump with a bolus (or loading) dose

How to order PCA at VUMC

  • Select Analgesic:
    • *Hydromorphone (most common): Order “Hydromorphone (DILAUDID) PCA”
    • Fentanyl (if on at home; not a good inpt PCA): Order “Fentanyl PCA”
    • *Morphine: Order “Morphine PCA”→ pick from 3 different concentrations (mg/mL = 1:1, 5:1, 10:1). 1:1 is often suggested for start. 5mg/mL for pts requiring more than 60mg/24h. 10mg/mL for pts requiring more than 300mg/24h. Avoid basal rate if renal impairment)
  • Select “[Analgesic] PCA syringe” and adjust the following to pt’s needs:
    • PCA Dose (“Demand”): amount the pt gets when s/he presses the button
    • Lockout Interval: time between which “demand” doses will not be administered if s/he presses the button (i.e., the PCA “locks out”)
    • Continuous Dose (“Basal”): amount the pt gets per hr. in continuous infusion
    • Max Dose: maximum amount of analgesic (Basal + Demand) pt can get in 24 hours
  • Select “IV Carrier Fluid Options”> Choose Fluid option - Select all “PCA Nursing Orders”
  • How to Order PCA at VA:
    • Under Orders, select “Pain/Sedation Infusions”
    • Under “PCAs,” select Analgesic of choice (Hydromorphone or Morphine)
    • Adjust the following:
      • Load: amount the pt will receive on initial set up of PCA
      • Basal: amount the pt gets per hour in continuous infusion
      • Demand: amount the pt gets when s/he presses the button

Interrogating PCA (to determine amount of analgesia pt received)

  • Look at IV pump display and hit “Channel Select” on PCA
  • Select “Options” in bottom left of IV pump - Select “Pt History” on the left of the screen. This shows the administration history for a certain time period (e.g., 24h, 12h, 4h, etc.)
  • Hit “Zoom” on bottom of screen to change time period to 24 hours. Should show:
    • Total Drug: total amount of drug received in last 24 hours
    • Total Demands: amount of times the pt had pushed the button for demand dose
    • Delivered: amount of times the pt actually received a demand dose
    • The difference between “Total Demands” and “Delivered” is the number of times the pt pushed the button without receiving a dose 

If you have questions about interrogating the PCA, ask your patient’s bedside RN.

Opioid side effects

  • Constipation: Dose-dependent and will not develop tolerance. If pt is taking opioids, s/he need robust bowel regimen (MiraLAX, senna) with goal of BM ≥every 3 days
    • For opioid-specific constipation can do SQ RelistorTM (methylnaltrexone), but this is expensive and can only be given in the PCU or oncology floors at VUMC. For pts with chronic opioid-induced constipation as an outpt, can trial oral agents like MovantikTM (NaloxgeolTM). Can also consider PO naloxone but it does have small amount of bioavailability so watch for systemic reversal.
  • Nausea: Occurs with opiate naïve p. Consider starting an anti-emetic concurrently. Most pts will develop tachyphylaxis with this over a day, so the antiemetic can be discontinued
  • Urinary retention: Consider role of opioids in pts with new-onset or worsening urinary retention. Try to de-escalate opioid dosing if possible.
  • Overdose: In pts with apneic emergency, IV 0.4 mg Naloxone; however, low threshold for multiple doses until response. For pts prescribed opioids as outpt, need naloxone 4 mg intranasal.
    • If a pt with chronic opiate dependence is over sedated but not in immediate danger of respiratory failure, one can 1) hold the dose of opioid and let them wake up on their own or 2) give a dose of naloxone 0.02-0.04mg (1/10 of the usual dose). This latter strategy prevents opioid withdrawal and precipitation of pain crisis in pts on chronic opioids
  • Pruritis: Due to histamine release from mast cells; can be treated with antihistamines. The opioid can also be rotated. Some but not all pts will develop tachyphylaxis.
  • Toxicity: Hyperalgesia and neuroexcitatory effects (AMS, myoclonic jerking, seizures). Risk factors for neuroexcitatory effects are rapid titration, dehydration, and/or renal failure. Treatment is to rotate to a higher potency opioid and hydrate when possible.

Non-pharmacologic therapies

  • Procedural Intervention: best utilized when there is a specific, targetable
    • Referral to chronic/interventional pain management (Nerve blocks or Radio-ablative therapy) and neurosurgery (chordotomy, cingulotomy, myelotomy)
  • Adjunct therapies: Pt’s will have varying opinions and responses on adjunctive therapies, but these can be as important as any pharmacologic therapy. CBT, personalized exercise regimen, PT/OT, chiropractor, acupuncture
  • Additional Resources for Residents
  • Pain Management Center at VUMC
  • Pain Clinic at the VA. Would specify whether or not you are OK with them initiating opioids.
  • Complementary and Integrative Health consult at VA, or Osher Center at VUMC Consult cardiology for assistance
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