May 1st 2000
To assist in converting patients from one opioid agent to another in their daily practice, many oncologists carry pocket dosage conversion guides based on package inserts approved by the US Food and Drug Administration (FDA). One such guide issued by the manufacturer of transdermal fentanyl (Duragesic), reproduced in Table 3 of the expert consensus article written by Breitbart et al, presents the equivalent of 25 µg/h of transdermal fentanyl as 45 to 134 mg/d of oral morphine. In another guide, distributed by one of the manufacturers of controlled-release morphine, the 25 µg/h strength of transdermal fentanyl is said to be equianalgesic to 15 mg of controlled-release morphine administered every 12 hours (and both are deemed equivalent to 10 mg of controlled-release oxycodone every 12 hours). Faced with such a wide range of conversion factors, it is of little surprise-as Breitbart et al point out-that clinicians often fail to achieve equianalgesia when converting patients from one opioid to another.