Am Fam Physician. 2000;61(6):1860
Many cancer patients develop significant pain during the course of their illness. Most of this pain can be controlled with the use of opioids. It is important to remember that better pain control can be achieved with around-the-clock dosing, with the addition of rescue doses for breakthrough pain. Some patients develop uncontrolled adverse effects to opioid therapy, such as generalized myoclonus, delirium, nausea and vomiting, or severe sedation, before adequate pain control can be obtained. Some of these effects can be controlled or prevented, but in some cases, this cannot be accomplished. Mercadante states that in these patients, opioid rotation should be considered. This rotation can be achieved by providing the same opioid but using a different route or by using a different opioid by the same route.
The optimal route for morphine in pain management is oral. However, this route is associated with a higher incidence of adverse effects when compared with the parenteral route. The parenteral route also allows for a more rapid titration to the therapeutic dosage. Parenteral routes include subcutaneous, rectal and transdermal.
One option for transdermal administration when patients cannot tolerate morphine is the fentanyl patch. The recommended conversion rate for morphine to fentanyl is 100 mg:1 mg. The advantage of the patch is that it can be changed every 72 hours. The disadvantages are that it is difficult to titrate and patients still need to have breakthrough medications available.
Another option when it is necessary to switch opioids is methadone. One advantage to the latter is that it is inexpensive. However, it has a long half-life and an unknown equianalgesic dose, so it is difficult to manage.
The author concludes that guidelines are useful in the treatment of cancer pain. However, because patients have varying responses to opioids, pain management must be individualized. When patients are unable to tolerate opioid therapy because of adverse effects, it is appropriate to change the route of administration or switch to another opioid.