Severe, constant pain is usually relieved with opioid analgesics having high intrinsic activity (see Table 31–2), whereas sharp, intermittent pain does not appear to be as effectively controlled.
The pain associated with cancer and other terminal illnesses must be treated aggressively and often requires a multidisciplinary approach for effective management. Such conditions may require continuous use of potent opioid analgesics and are associated with some degree of tolerance and dependence. However, this should not be used as a barrier to providing patients with the best possible care and quality of life. The World Health Organization Ladder (see http:// www.who.int/cancer/palliative/painladder/en/) was created in 1986 to promote awareness of the optimal treatment of pain for individuals with cancer and has helped improve pain care for cancer patients worldwide. Research in the hospice setting has also demonstrated that fixed-interval administration of opioid medication (ie, a regular dose at a scheduled time) is more effective in achieving pain relief than dosing on demand. New dosage forms of opioids that allow slower release of the drug are now available, eg, sustained-release forms of morphine (MS Contin) and oxycodone (OxyContin). Their purported advantage is a longer and more stable level of analgesia. However, there is little evidence to support long-term (greater than 6 months) use of sustained-release opioids to manage chronic pain in the noncancer patient. Furthermore, attempts to control chronic pain with opioids alone may lead to excessive use and dependence (see Box: Educating Opioid Prescribers).
If disturbances of gastrointestinal function prevent the use of oral sustained-release morphine, then a fentanyl transdermal system (fentanyl patch) can be used over long periods. Furthermore, buccal transmucosal fentanyl can be used for short episodes of breakthrough pain (see Alternative Routes of Administration). Administration of strong opioids by nasal insufflation is also efficacious, and nasal preparations are now available in some countries. Approval of such formulations in the USA is growing. In addition, stimulant drugs such as the amphetamines can enhance the analgesic actions of opioids and thus may be very useful adjuncts in the patient with chronic pain.
Opioid analgesics are often used during obstetric labor. Because opioids cross the placental barrier and reach the fetus, care must be taken to minimize neonatal depression. If it occurs, immediate injection of the antagonist naloxone will reverse the depression. The phenylpiperidine drugs (eg, meperidine) appear to produce less depression, particularly respiratory depression, in newborn infants than does morphine; this may justify their use in obstetric practice.
The acute, severe pain of renal and biliary colic often requires a strong agonist opioid for adequate relief. However, the drug-induced increase in smooth muscle tone may cause a paradoxical increase in pain secondary to increased spasm. An increase in the dose of opioid is usually successful in providing adequate analgesia.
B. Acute Pulmonary Edema
The relief produced by intravenous morphine in patients with dyspnea from pulmonary edema associated with left ventricular heart failure is remarkable. Proposed mechanisms include reduced anxiety (perception of shortness of breath) and reduced cardiac preload (reduced venous tone) and afterload (decreased peripheral resistance). However, if respiratory depression is a problem, furosemide may be preferred for the treatment of pulmonary edema. On the other hand, morphine can be particularly useful when treating painful myocardial ischemia with pulmonary edema.
C. Cough
Suppression of cough can be obtained at doses lower than those needed for analgesia. However, in recent years, the use of opioid analgesics to allay cough has diminished largely because of the availability of a number of effective synthetic compounds that are neither analgesic nor addictive. These agents are discussed below.
D. Diarrhea