Drug		Oral Dose (mg)	Parenteral Dose2
Morphine 3		30	10 mg
Codeine4		200	100 mg
Fentanyl5a,b		NA	100 μg
Hydrocodone (Vicodin)		30–45	NA
Hydromorphone (Dilaudid)3		8	2 mg
Levorphanol (Levo-Dromoran)		4	2 mg
Methadone6,7		The conversion ratio of methadone is variable. Please refer to the Opioid Types section and Opioid switching section.
Oxycodone (OxyContin)4		20–30	10–15 mg
Oxymorphone
	(Opana, Opana ER, and Opana IV3)	10	1 mg

IV = intravenous; NA = not available.

1. Published tables vary in the suggested doses that are equianalgesic to morphine. Many of these doses are based on clinical consensus rather than well-controlled trials. Clinical response is the criterion that must be applied for each patient; titration to clinical response is necessary. Because there is not complete cross-tolerance among these drugs, it is usually necessary to use a lower-than-equianalgesic dose when changing drugs and retitrate according to response.

2. Parenteral dosing includes IV and subcutaneous administration. Onset and duration may vary slightly between these routes; however, doses remain approximately equal. The intramuscular route is not recommended because of variability in uptake of the drug and painful injection.

3. Caution: For morphine, hydromorphone, and oxymorphone, rectal administration is an alternate route for patients unable to take oral medications. Equianalgesic doses may differ from oral to parenteral doses because of pharmacokinetic differences. Note: A short-acting opioid should normally be used for initial therapy of moderate-to-severe pain.

4. Caution: Doses of aspirin and acetaminophen in combination opioid/NSAID preparations must be adjusted to the patient’s body weight.

5a. Transdermal fentanyl is an alternative. Transdermal fentanyl dosage is not calculated as equianalgesic to a single morphine dosage but is calculated based on a 24-hour opioid dose. See package insert for dosing calculations. Transdermal fentanyl should not be used in opioid-naive patients. 5b. Transmucosal and buccal fentanyl are also available and indicated for breakthrough pain, although they are not bioequivalent. Titration of either should be conducted gradually; neither should be used in opioid-naive patients.

6. Caution: Methadone is much more potent than indicated in older published literature. On average, it is ten times more potent than morphine. However, its potency relative to morphine is not linear. When morphine at lower doses (e.g., 30–60 mg/d orally) is switched to methadone, the potency may be 3 to 5 times; when switched from high doses (e.g., >300 mg/d orally), the potency may be 12 times or even higher.

7. Caution: The oral to IV dose ratio of methadone is not well established. The IV route is very seldom used, except in cancer centers with pain service familiar with parenteral methadone. Intravenous use of methadone in combination with chlorobutanol is associated with QTc wave prolongation.[37] Subcutaneous administration may cause irritation.

References

37. Kornick CA, Kilborn MJ, Santiago-Palma J, et al.: QTc interval prolongation associated with intravenous methadone. Pain 105 (3): 499-506, 2003.  [PUBMED Abstract]