Antidepressants and antiepileptic drugs, as discussed further on, may have a beneficial effect on pain even in the absence of overt depression. This is considered to be true particularly in cases of neuropathic pain (painful polyneuropathy and some types of radicular pain). Sometimes these nonnarcotic agents may, in themselves or in combination with these treatment modalities, be sufficient to control the patient’s pain and the use of narcotics can then be kept in reserve.
Should the foregoing measures prove to be ineffective, one may turn to narcotic agents. In chronic disease, methadone and related drugs are sometimes useful with which to begin because of their effectiveness by mouth and the relatively slow development of tolerance. Some pain specialists prefer the use of shorter-acting drugs such as oxycodone, hydrocodone, given more frequently through the day. Longer acting, orally administered drugs are used but may also be problematic because the doses may be more difficult to manage. The oral route should be used whenever possible, as it is more comfortable for the patient than the parenteral route. Also, the oral route is associated with fewer side effects except for nausea and vomiting. Nevertheless, should parenteral administration be necessary, one must be aware of the ratios of oral-to-parenteral dosages required to produce equivalent analgesia. The main medications used in the treatment of pain are summarized in Table 7-3.
A useful way in which to undertake the management of chronic pain that affects several parts of the body, as in the patient with metastases, is with narcotics taken together with aspirin, acetaminophen, or another analgesic drug. The analgesic effects of these types of drugs are additive, which is not the case when narcotics are combined with benzodiazepines.
If oral medication fails to control the pain, the parenteral administration of opioids may become necessary. One may begin with morphine, dihydromorphine, or levorphanol, given at intervals of 4 to 6 h because of their relatively long duration of action (particularly in comparison to meperidine). Alternatively, one may first resort to the use of transdermal patches of drugs such as fentanyl, which provide relief for 24 to 72 h and which we have found particularly useful in the treatment of pain from brachial or lumbosacral plexus invasion by tumor and of painful neuropathies such as those caused by diabetes and systemic amyloidosis. Long-acting morphine preparations are useful alternatives.
Should long-continued injections of opiates become necessary, the optimal dose for the relief of pain should be established and the drug then ideally given at regular intervals, rather than “as needed” in order to avoid breakthrough pain that requires higher cumulative doses of drugs. The administration of morphine (and other narcotics) in this way represents a laudable shift in attitude among physicians because for many years it was widely believed that the drug should be given in the smallest possible doses, spaced as far apart as possible, and repeated only when severe pain reasserted itself. It has become clear that this approach results in unnecessary discomfort and, in the end, the need to use larger doses. Most physicians now realize that the fear of creating narcotic dependence and the expected phenomenon of increasing tolerance must be balanced against the overriding need to relieve pain. The most pernicious aspect of addiction, that of compulsive drug-seeking behavior with its attendant sociopathic behaviors, occurs only infrequently in this setting and usually in patients with a previous history of addiction or alcoholism, with depression as the primary problem, or with certain traits that have been loosely referred to as “addiction proneness,” which may have genetic components. Even in patients with severe acute or postoperative pain, the best results are obtained by allowing the patient to determine the dose and frequency of intravenous medication, a method known as patient-controlled analgesia (PCA). Again, the danger of producing addiction is minimal.