Patients perceive pain differently, depending on such factors as fatigue, insomnia, anxiety, depression, and nausea. Addressing these factors together with a supportive environment can help control pain.
Analgesic choice depends largely on pain intensity, which can be determined only by talking with and observing the patient. All pain can be relieved by an appropriately potent drug at the right dosage, which may also produce sedation or confusion.
Commonly used drugs are aspirin, acetaminophen, or NSAIDs for mild pain; codeine or oxycodone for moderate pain; and hydromorphone or morphine for severe pain. For a detailed discussion of analgesic use, see Ch. 167. Aspects of particular significance to patients with terminal illness are discussed below.
In terminal illness, oral administration of opioids is the most convenient and cost-effective route. Rectal administration provides slower absorption but with very little first-pass effect; morphine suppositories or pills may be given rectally at the same dose as used orally and titrated as needed. IV or sc administration of opioids is preferred to IM injections, which are painful and have variable absorption.
The usual effective dosage interval for opioid analgesics is 3 to 4 h, except for long-acting preparations. Always give opioids around the clock to avoid onset of pain.
When opioids are indicated, the physician should prescribe them with confidence, in adequate dosage, and on a continuous basis to prevent pain. Public and professional reticence often tragically limits their appropriate use.
Pharmacologic dependence is part of regular use but causes no problems except the need to avoid inadvertent withdrawal. Psychologic dependence is so rare as to be irrelevant in pain patients using prescribed opioids.
Morphine is the most commonly used opioid in terminal illness. Possible adverse effects include nausea, sedation, and confusion. Constipation should be treated prophylactically (see below). The patient usually develops substantial tolerance to the respiratory depressant and sedative effects of morphine but much less tolerance to the analgesic and constipating effects.
When morphine is given orally, a controlled-release form is preferred because it provides steady levels of morphine with twice-daily dosing (instead of dosing every 3 to 4 h for immediate-release morphine); however, it has a slow onset of action.
Patients are usually converted to equianalgesic dosing of controlled-release morphine based on initial attempts to control pain with short-acting opioids. Immediate-release morphine should be kept available for breakthrough pain.
Two dosing rules are useful. First, if any dose will seriously depress respiratory function, it is usually much more than twice the stable tolerated dose. Second, reestablishing pain control when a stable dose becomes inadequate ordinarily requires >= 1.5 times the previous dose.
When the oral route is not feasible, morphine may be given by suppository or parenterally (or even sublingually or in the buccal space, by tablet or 20 mg/mL solution).
In the hospital, morphine is commonly administered IV via patient-controlled analgesia (PCA) pumps.