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Opioids: General Principles & Conversion

Eli Cohen

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  NA  Lortab  Hydrocodone  NA   
Oxycodone  1.5x  -  Percocet  Roxicodone™  Oxycontin™   
Hydromorphone  4x  20x  -  IV, Oral  -  Oral is $ 
Fentanyl  300x  300x  -  IV’ Buccal, Nasal  Patch  Dosed in ug, not mg 
Abbreviations: ER = extended release; IR = immediate release; APAP = acetaminophen

Conversion:

  • Transition between opiates is done using OME. Each drugs’ potency is compared to oral morphine (see table). Ex: 1 mg IV morphine = 3 mg PO morphine
  • When transitioning, doses are traditionally reduced by ¼ to ⅓ due to cross tolerance
  • IR/ER regimens: Consider switching to extended release when requiring 3-4 doses of intermediate release (IR) medications in a 24-hour period regularly. The ER medication should treat the chronic pain experienced by a patient. The IR preparation is indicated for breakthrough pain. The IR dose should be calculated as 10-20% of the total OME dose a patient takes daily. Fentanyl patches should last 72 hours

opiate conversions

Opiate conversions

Patient Controlled Analgesia (PCAs)

  • 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 patient

    • Demand dose = a patient-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 patient 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 half-life of the medication (2hr for IV). Adjust the availability based on how frequently you want patient to be able to have a demand dose (ex: if q10min divide by 12 or if q15min divide by 8 for 2 hours)

  • Don’t forget to set lock-outs (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 pts 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 inpatient PCA): Order “Fentanyl PCA”

    • *Morphine: Order “Morphine PCA”

  • Select “[Analgesic] PCA syringe” and adjust the following to pt needs:

    • PCA Dose (“Demand”): amount the patient 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 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 “Patient 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 has 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 patient pushed the button without receiving a dose

Opioid Side effects

  • Constipation: dose-dependent and will not develop tolerance. If pt has opioids, they 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 patients with chronic opioid-induced constipation as an outpatient can trial oral agents like MovantikTM (naloxgeol). Can also consider PO naloxone but it does have small amount of bioavailability so watch for systemic reversal

  • Nausea: occurs with opiate naïve pts. 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 outpatient, need naloxone 4 mg intranasal

    • If a patient 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 patients 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 to this symptom

  • 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

Last update: 2022-07-05 14:41:01