Opiate Principles

Opioids: General Principles & Conversion – Brian Grieb

Oral Morphine Equivalent (OME) Conversion Table:













Ultram ER™

NSAID properties





Morphine IR


Renally cleared



















IV, Oral


Oral is $





IV’ Buccal, Nasal


Dosed in ug, not mg

Abbreviations: ER, extended release; IR, immediate release; IV, intravenous; PO, oral; APAP, Acetaminophen



  • Transition between opiates is done using oral morphine equivalents (OMEs), in which each drugs’ potency is compared to oral morphine (see table).  For example, 1 mg of IV morphine is equal to 3 mg of oral morphine. 
  • When transitioning, doses are traditionally reduced by 1/4 to 1/3 due to cross tolerance. (Oxycodone 5 is a pretty standard dose, which converts to 7.5 mg of oral morphine, 2.5 mg of iv morphine, and 0.375 of iv hydromorphone.)


Opiate Conversions




Patient Controlled Analgesia (PCAs) aka Pain Pumps:

  • Pumps can be programmed to deliver a continuous rate and/or a bolus dose. The basal rate is a continuous infusion dosed per hour that cannot be adjusted by the patient. The demand dose is a patient-directed bolus that is given at a prescribed frequency (whenever the pt presses the button).  Both the actual dose and frequency of bolus dose 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 or basal infusion. Alternatively, if a pt is chronically on a long-acting opioid, this total amount of OME (sustained release) can be converted into a basal rate of opioid.  The demand dose is 25% of the hourly rate given every 15 minutes.
  • Remember that the basal rate will not get to steady state for at least 8 hrs; therefore, 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 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”)
    1. Optional: many palliative care providers may not include this to allow patients more liberty to control their pain, depending on the situation
    • 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. If it does not display info about PCA, 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 (due to pushing the button during the lockout interval).
  • If you have questions about interrogating the PCA, ask the nurses! They are a great resource!



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 Relistor (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 Movantik (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. With respiratory depression in chronic opioid pts start with IV 0.02 mg q2-3min to avoid profound withdrawal. This helps prevent acute pain crisis. In pts taking long-acting opioids, may need to redose q30min and consider IV infusion for them. For pts prescribed opioids as outpatient, need naloxone 4 mg intransasal.
  • 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 or renal failure.