Relative Potency And Equianalgesic Doses

Relative potency is the ratio of the doses of two analgesics required to produce the same analgesic effect. By convention the relative potency of each of the commonly used opioids is based upon a comparison with 10 mg of parenteral morphine. Data from single- and repeated-dose studies in patients with acute or chronic pain have been used to develop an equianalgesic dose table (Table II-5) that provides guidelines for dose selection when the drug or route of administration is changed. The information contained in the equianalgesic dose table does not represent standard doses, nor is it intended as an absolute guideline for dose selection. Many variables may influence the appropriate dose for an individual patient, including intensity of pain, prior opioid exposure in terms of drug, duration, and dose (and the degree of cross-tolerance that this confers), age, route of administration, level of consciousness, metabolic abnormalities (see below), and genetic polymorphism in the expression of relevant enzymes or receptors.

Table II-5. The analgesic potency of different opioids in comparison to morphine (= 1) on a mg-level

Analgesia

Opioid

Analgesic potency

Sufentanil

1000

Fentanyl

100-200

Very strong

Remifentanil

100-200

Alfentanil

40-50

Phenoperidine

10-50

Oxymorphone

12-15

Butorphanol

8-11

Hydromorphone

7-10

Diamorphine

1-5

Dextromoramide

2-4

Racemorphane

2.5

Medium

Levomethadone

2

Methadone

1.5

Isomethadone

1-1.3

Piminodine

1

Piperidine

1

Morphine

1

Nalbuphine

0.5-0.8

Hydrocodeine

0.35

Pentazocine

0.3

Weak

Meptazinol

0.15-0.2

Codeine

0.2

Pethidine

0.1

Very weak

Levallorphane

0.07-0.1

Tramadol

0.05-0.07

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