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VOLUME 18 NO.6 JUNE 2003
PAIN MANAGEMENT: PHARMACOLOGICAL APPROACHES TO TREATING PAIN
There are three broad categories of pain: acute, chronic and malignant or cancer pain. Acute pain is the kind of pain that follows trauma, surgery, or self-limiting diseases. In most cases, acute pain persists for a limited duration of time. Chronic pain may be described as pain persisting for 3-6 months. It may be episodic or persistent, and it may be associated with disabling physical and emotional symptoms. Cancer pain may include acute, chronic, or intermittent pain related to the malignancy and its treatment.
The management of chronic and/or cancer pain is more challenging due to the duration of pain, its etiology, and the complexity of emotional and psychological components. All pain experienced by patients should be routinely monitored, and a clinical approach to pain assessment and management should be followed. This review will focus on the pharmacologic approach to pain management and available therapy options.
In the pharmacologic management of pain, non-narcotic analgesics, narcotic analgesics, and adjuvant drugs may have a role in patient therapy.
NONSTEROIDAL ANTI-FLAMMATORY DRUGS (NSAIDS) AND ACETAMINOPHEN:
Non-narcotic analgesics such as the NSAIDS and acetaminophen are the most helpful for mild to moderate acute pain and acute exacerbations of chronic pain, or "flares." NSAIDS are also helpful in painful conditions related to chronic inflammatory conditions (eg arthritis). It is generally accepted that some patients respond better to one NSAID than others, and different agents may need to be given if results are unsatisfactory. The most common adverse effects of NSAIDS are gastrointestinal irritation and ulceration. The newer cyclooxygenase-2 (COX-2) selective NSAIDS (eg Rofecoxib [VIOXX]) may have less GI effects, and may be preferred if chronic therapy is anticipated. Renal effects may also occur with high dose or long term use of NSAIDS.
Acetaminophen is a very useful agent for acute pain, and it is used quite frequently. It must be remembered that acetaminophen is also contained in many combination analgesic drugs. If used alone or in conjunction with other drugs, total daily dose of acetaminophen should not generally exceed 4000mg. The risk of hepatic damage due to high-dose or chronic use of acetaminophen is well established. Greater risk is evident in patients with pre-existing liver disease or alcoholics.
NARCOTIC ANALGESICS:
Narcotic analgesics or "opioid" drugs are used for moderate to severe pain and have become more accepted as management of many acute and chronic pain conditions. Some of the concerns regarding narcotic analgesics use have stemmed from misconceptions or confusion regarding the risks of addiction, tolerance and physical dependence. Addiction or psychological dependence is rare in patients receiving opioids for pain management. Some degree of physical dependency will occur in patients who receive long-term therapy with opioids. This should not be confused with addiction. Gradual tapering of opioid therapy will ease withdrawal symptoms. Tolerance occurs when a specific opioid dose not produce as much analgesia as it previously did. There are various reasons for this, although it does not occur in all patients. Many patients remain on stable doses of opioids for long periods without evidence of tolerance.
Due to the inherent CNS depressant effects of opioids, clinicians and patients have feared that chronic opioid therapy may impair cognitive and psychomotor function. Studies have shown, however, that opioids can be safely administered without impairment of daily activities, and in fact, tolerance to the CNS depressant effects of opioids develop rather quickly.
In order to minimize sedation and cognitive impairment, doses of opioids should be started low and gradually escalated to establish pain relief with minimal adverse effects. The most persistent adverse effect of opioid therapy is constipation. It is best managed with a regular regimen of laxatives, hydration, and a high-fiber diet. Nausea and vomiting, lightheadedness and dizziness also commonly occur with opioid use.
Narcotic analgesics vary in their dosage and potency, and an effective analgesic dose varies considerably between patients. Therefore, dosage titration is essential for each patient, with careful review of pain assessments by clinicians in the determination of the most appropriate dose and frequency. In most cases, patients should receive regularly scheduled doses for persistent pain. Exacerbations of pain (i.e. breakthrough pain) may receive additional intermittent doses of analgesics.
ADJUVANT ANALGESICS:
Adjuvant analgesics represent a diverse group of drugs that are analgesic in specific circumstances. Tricyclic antidepressants (eg amitriptyline, imipramine) and anti-convulsants (eg gabapentin) are used for neuropathic pain. Other agents used to treat specific pain conditions include corticosteroids, mexiletine, and clonidine.
The following table describes medications used for pain management in JHMC, including dosage forms, usual effective dose and duration of action. Narcotic analgesics are described in potency in relation to morphine, considered the standard for comparison, including approximate equi-analgesic doses to morphine 10mg.
PAIN MANAGEMENT
JAMAICA HOSPITAL MEDICAL CENTER
HOSPITAL FORMULARY