SAN DIEGO--With the explosion of the hospice movement, the creation
of pain management teams, and the use of pain ladders to guide
treatment, "pain management is becoming a trendy area of
medicine," said Daniel B. Carr, MD, Saltonstall Professor of
Pain Research, New England Medical Center. "We didnt hear
much about treating cancer pain 20 years ago; it was on the fringes."
But, Dr. Carr said, the medical community still has a long way to go
to ensure that all cancer patients with pain are kept comfortable.
And the challenge will be even more daunting as the baby boomers age
and begin to succumb to terminal diseases.
Speaking at an educational course sponsored by the American Academy
of Pain Medicine, Dr. Carr reviewed some of the methods clinicians
can use to keep their oncology patients pain free.
One common mistake physicians make when assessing pain is assuming
that the pain is being caused by the cancer itself. "Keep an
open mind; dont jump to the conclusion that if its
cancer, the pain is due to cancer," he said.
Use of the World Health Organizations pain ladder can relieve
pain in 90% of terminal cancer patients, he said. Some physicians,
however, mistakenly believe that they should start at the bottom of
the ladder when tackling moderate-to-severe pain. Instead, clinicians
may need to begin on the second or third rung of the ladder when pain
is advanced beyond the mild-to-moderate stage.
Morphine is the most commonly used opioid for moderate-to-severe
pain, he said, due to its availability in a wide variety of dosage
forms, well-characterized pharmacokinetics and pharmacody-namics, and
relatively low cost. For use in meeting baseline analgesic needs that
are stable, Dr. Carr said, controlled-release morphine tablets are
useful, as are transdermal fentanyl patches (Duragesic).
He also noted that meperidine may help for a few days to treat acute
pain, but generally should be avoided in cancer patients for two
reasons: First, it has a toxic metabolite--normeperidine--that
accumulates with continued use, particularly when renal function is
impaired, causing dysphoria, agitation, or seizures. Second,
meperidines duration of action is short--2.5 to 3.5 hours.
Of course, opioids are not always going to work, Dr. Carr said, but
it makes sense to try, sequentially, more than one opioid before
opting for an anesthetic, neurosurgical, or other invasive approach
to relieving stubborn pain. For example, a patient who experiences
nausea or mental clouding while on oral morphine, may do just fine
with hydromorphone or fentanyl, he said.
Dr. Carr also talked about the more involved approaches to pain
control, including spinal opioid therapy. The site, nature, and stage
of the underlying condition; the type of pain; and the life
expectancy of the patient need to be considered before deciding
whether to start this kind of treatment.
Neuropathic pain is, in general, resistant to opioids no matter how
they are delivered, as is movement-related pain. However, deep
constant somatic pain is usually more responsive.
Because responses to spinal opioids vary greatly, it is always better
to carry out a trial through a standard percutaneous catheter before
embarking on more invasive implantation of an epidural or intrathecal
system for long-term therapy. For patients who are near death, a
percutaneous temporary spinal catheter may be all that is needed, he noted.
Dr. Carr also referred to clinical trials that have explored whether
opioid epidurals offer advantages over systemic infusion.
Unfortunately, he noted, many of the long-term studies of treatment
with spinal opioids are not as informative as they might have been.
For instance, in 13 of 18 long-term studies of spinal opioid use
reviewed by one researcher, physicians had used morphine alone. And
yet typically today, clinicians choose morphine plus a local
anesthetic or clonidine.
Another effort to combine data from multiple trials of neuraxial
opioid delivery--published by Dr. Carr and his colleagues in
1996--was frustrated by the many different drug regimens used in the
studies and the paucity of detailed information about patient
characteristics and analgesic responses. But Dr. Carr was able to
reach some conclusions after pooling data into "crude"
categories of analgesic efficacy and complication rates.
The results showed that the analgesic success rate was about the same
(70%) whether the drugs were delivered by the epidural, intrathecal,
or intracerebroven-tricular route. Catheter and system problems, such
as pump failure, leakage, or infection, were greatest in the epidural
group and significantly lower during intracerebroventricular therapy.
Although this last technique is promising, he noted, it requires
surgery and is not suited to preimplantation therapeutic trials. And
it cannot be recommended at this point for drug mixtures such as
opioid plus local anesthetic or clonidine.
Finally, Dr. Carr offered a simple mnemonic--ABCDE--to keep in mind
when treating cancer pain (see Table).