Adapted from Lynn R. McPherson’s Demystifying Opioid Conversion Calculations (2nd ed.), a widely regarded core reference for learning safe, practical opioid conversion principles in palliative care. This summary is a guide—not a substitute for supervised clinical decision‑making, case-based coaching, and hands‑on conversion workshops with faculty.

Start with PROCESS, not math

Use a 5‑step approach every time you switch opioids or routes:

1. Assess the pain (PQRSTU), goals, and non‑opioid options.
2. Add up the total daily dose (TDD) of all opioids, separating scheduled from average rescue use.
3. Convert using an equianalgesic table (ballpark, not exact).
4. Individualize—usually reduce the new opioid 25–50% for incomplete cross‑tolerance (unless switching formulation/route of the same opioid).
5. Implement and monitor with a clear safety/efficacy plan and liberal rescue access.

Key mindset: equianalgesic numbers “get you to the ballpark,” variability is large; safety trumps precision. Avoid manufacturer “conversion calculators” to convert away from their product—they’re typically conservative in one direction.

Core equivalents and incomplete cross tolerance

Opioid equivalents or equianalgesic doses are approximate dose pairs that, on average, provide similar analgesia when switching between opioids or routes. They’re derived largely from population-level studies (often single-dose or short-term, frequently in opioid-naïve or relatively controlled settings) plus clinical experience, then summarized in tables. Because real patients differ (tolerance, organ function, pain type, age/frailty, interacting meds), equianalgesic tables should be treated as a starting estimate—not a precise “exchange rate.” Clinically, use them to get into the right ballpark, then adjust for incomplete cross-tolerance (often dose-reduce when changing opioids), provide rescue dosing, and titrate to patient response and safety.

Opioid Equianalgesic Table

Incomplete Cross Tolerance

When switching between different opioids, calculate the equianalgesic TDD and reduce new opioid 25–50% for incomplete cross‑tolerance (tighter reductions if toxicity was the reason to rotate; more conservative in frailty, organ impairment, drug interactions). Note: If you choose to not reduce for incomplete cross-tolerance, you are exposing the patient to more opioid and should be treated as a dose increase.

Switching routes with the same opioid

Route changes (same opioid moiety) are about bioavailability, not cross‑tolerance. For example, bioavailability of oral morphine is ~30-40%. Therefore, when switching routes of the same opioid (morphine) you are factoring by the bioavailability between formulations.  

Example:  10 mg IV morphine = 25 mg PO morphine (factors as 40% bioavailability)

Different products may have different bioavailability. If you are unsure, always check the product information about the pharmacokinetics and bioavailability associated with each dosage formulation.

Converting between different opioids

Below are “stoichiometric” (dimensional analysis) and cross-product ways to do opioid conversions. The key is to set your conversion factors up as fractions so units cancel, just like chemistry.

Here is a common clinical anchor set for this program, please see Opioid Pocket Card for details.

• 25 mg PO morphine ≈ 20 mg PO oxycodone
• 25 mg PO morphine ≈ 5 mg PO hydromorphone
• 10 mg IV morphine ≈ 2 mg IV hydromorphone

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The method (works for any conversion)

Step 0 — Get the Total Daily Dose (TDD)

• Add scheduled + actually used PRNs over the last 24h (or best estimate).

Step 1 — Convert “current opioid” → your reference

Step 2 — Convert reference → “new opioid”

Step 3 — Reduce for incomplete cross-tolerance (usually 25–50%) when switching opioids

Step 4 — Build regimen: scheduled baseline + rescue ~10–20% of new daily dose

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The method in practice

Dimensional analysis (“stoichiometric”) examples

Example 1: PO oxycodone → PO hydromorphone (two-step with unit cancellation)

Patient used in last 24h: oxycodone total = 70 mg/day (scheduled + PRNs)

1) Oxycodone → PO morphine

70mg oxy/day * (15mg PO morph ÷ 10mg oxy) = 105mg PO morph/day

2) PO morphine → PO hydromorphone

105mg PO morph/day * (4mg PO hydro ÷ 15mg PO morph) = 28mg PO hydro/day

3) Cross-tolerance reduction (e.g., reduce 33%)

28mg * 0.67 ≈ 19mg/day hydro (start)

4) Turn that into a schedule + rescue

• Baseline option: hydromorphone 4 mg PO q6h = 16 mg/day (conservative start)
• Rescue: 10–20% of 19 mg/day ≈ 2–4 mg PO q1–2h PRN (choose lower end if frail/sedating)

Why this is “stoichiometric”: every fraction is oriented so the undesired unit cancels (mg oxy cancels, then mg morph cancels), leaving mg of the target opioid.

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Example 2: IV morphine → PO oxycodone (route + drug change)

Patient: IV morphine infusion 2 mg/hr (48 mg/day) + 2 mg IV bolus used 6 times (12 mg/day)
Total IV morphine TDD = 60 mg/day

1) IV morphine → PO morphine

Use 15 mg PO morph ≈ 6 mg IV morph:

60mg IV morph/day * (15mg PO morph ÷ 6mg IV morph) = 150mg PO morph/day

2) PO morphine → PO oxycodone

150mg PO morph/day * (10mg oxy ÷ 15mg PO morph) = 100mg PO oxy/day

3) Cross-tolerance reduction (say 50% if toxicity/fragility)

100mg * 0.5 = 50mg/day oxy (start)

4) Regimen

• Baseline: oxycodone ER 20 mg q12h (=40 mg/day) with IR rescue
• Rescue: 5–10 mg PO q1–2h PRN (10–20% of 50 mg/day = 5–10 mg)

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Example 3: PO hydromorphone → IV hydromorphone (same drug, route change)

When it’s the same opioid, you’re mostly converting bioavailability, not cross-tolerance.
Patient: hydromorphone 24 mg/day PO

Using 5 mg PO hydro ≈ 2 mg IV hydro:

24mg PO/day * (2mg IV ÷ 5mg PO) = 9.6mg IV/day

Convert to an hourly rate:

9.6mg/day ÷ 24 ≈ 0.4mg/hr IV

Then add IV rescue (institution-specific; often ~10–20% of daily IV dose per dose, with monitoring).

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Cross-product (“ratio”) examples

Cross-product is the same math, just framed as proportions.

Example 4: Oxycodone → Morphine using a proportion

From the table: 10 mg oxy ≈ 15 mg morph PO
Set up:

10mg oxy / 15mg morph = 70mg oxy / x mg morph

Cross-multiply:

10x = 70 * 15
x = 1050 / 10 = 105 mg morph/day

Then PO morphine → PO hydromorphone:

15mg morph / 4mg hydro = 105mg morph / x mg hydro
15x = 105 * 4 → x = 28 mg hydro/day

Then apply cross-tolerance reduction as above.

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Practical checks (to prevent “conversion math” mistakes)

• Sanity check direction: if you’re switching to a more potent opioid (hydromorphone), the mg/day number should drop vs morphine.
• Keep units visible in every line (mg oxy/day → mg morph/day → mg hydro/day).
• Round safely to available strengths and your patient risk profile.
• Always pair the new baseline with rescue and reassessment criteria.
• If you’re rotating because of toxicity, reduce more (closer to 50%) and titrate slowly.

If you want, paste a real regimen (current opioid, route, scheduled doses, and typical PRN use), and I’ll lay it out in both formats exactly like above (including a suggested starting schedule + rescue)

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Around‑the‑clock (ATC) & rescue titration

Know the formulations. IR = short‑onset, ~4‑hour duration; ER/CR = designed for 12–24‑hour dosing. Never use ER products for breakthrough pain.

Rescue (“breakthrough”) dosing while on a long‑acting baseline:

• Dose: 10–20% of the ATC TDD (same opioid if possible).
• Interval: allow every 1–2 hours PO (not “q4–6h”), reassessing 1 hour after a dose.
• Incident pain: pre‑medicate 45–60 minutes prior; doses may be higher than for spontaneous pain.

When to adjust the baseline: if the patient routinely needs ~2–4 rescue doses/day, recalc the new TDD = current ATC + average rescue, adjust the long‑acting dose accordingly, and reset rescue to 10–20% of the new ATC TDD. (Also reassess for co‑analgesics and disease progression.)

Crucial nuance: Do not include incident‑pain rescue doses when you’re computing a baseline conversion; handle incident pain separately.

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Transdermal & parenteral fentanyl essentials

Transdermal fentanyl (TDF) = for opioid‑tolerant patients only. Opioid‑tolerance typically means ≥ 60 mg oral morphine/day (or an equianalgesic) for ≥1 week. Do not use for acute, intermittent, or opioid‑naïve pain.

Onset & kinetics: after applying TDF, expect ≥12 hours to meaningful effect, ~36 hours to Cmax, and up to 3–6 days to steady state. Heat, fever, and cachexia can increase variability (heat ↑ absorption; cachexia/hypoalbuminemia ↓ effective exposure). Monitor—don’t “set and forget.”

Converting to TDF from oral morphine equivalents:

• Practical rule: 1 mcg/hr TDF ≈ 2 mg/day oral morphine (i.e., 50 mcg/hr ≈ ~100 mg/day OM).
• Alternative “Reddy” estimate: 100 mg/day OM ≈ ~40 mcg/hr TDF (≈2.5:1 OM:mcg/hr).
• After the first patch, don’t up‑titrate sooner than day 3, and then no more often than every 6 days, using days 2–3 rescue use to guide titration.

Bridging at initiation (oral long‑acting → TDF): give the last dose of the long‑acting oral opioid when the first patch is applied (or a couple of short‑acting scheduled doses over the first 8 hours), and ensure rescue availability while TDF ramps.

Rescue while on TDF: base doses on the oral morphine equivalent of the patch (e.g., TDF 100 mcg/hr ≈ 200 mg/day OM → 20–30 mg morphine PR q2h), or convert to an appropriate parenteral breakthrough dose if needed.

Do not apply the routine 25–50% cross‑tolerance reduction to TDF conversions—the standard methods for TDF already account for it (same caution applies in methadone, which you’ll cover in its own page).

Safety pearls & common pitfalls

• Equianalgesic tables are approximations; patient factors (age, renal/hepatic function, drug interactions) can substantially shift potency. Err on safety, then titrate.
• Renal impairment: be extra careful with morphine/hydromorphone (neurotoxic metabolites); fentanyl is generally safer renally (methadone as well, covered elsewhere).
• Order clarity: avoid vague “range” PRN orders; if you must, tie ranges to objective anchors (e.g., moderate vs. severe) and keep a q1–2h option.

Bottom line for fellows/clinicians

1. Follow the 5 steps; do the math carefully; then individualize with a 25–50% reduction when switching opioids (except TDF methods).
2. Use rescue well (10–20% TDD q1–2h) and let rescue use guide ATC titration.
3. With fentanyl patches, know the lag, titration intervals, who qualifies, and the conversion rules above; monitor closely.