Table of
Contents
Definition
Analgesics are medicines that relieve pain.
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Purpose
Analgesics are those drugs whose primary purpose is
pain relief. The primary classes of analgesics are the
narcotics, including additional agents that are
chemically based on the morphine molecule but have
minimal abuse potential; nonsteroidal
anti-inflammatory drugs (NSAIDs) including the
salicylates; and acetaminophen. Other drugs,
notably the tricyclic antidepressants and anti-epileptic
agents such as gabapentin, have been used to relieve
pain, particularly neurologic pain, but are not
routinely classified as analgesics. Analgesics provide
symptomatic relief, but have no effect on causation,
although clearly the NSAIDs, by virtue of their dual
activity, may be beneficial in both regards.
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Description
Pain has been classified as "productive" pain and
"non-productive" pain. While this distinction has no
physiologic meaning, it may serve as a guide to
treatment. "Productive" pain has been described as a
warning of injury, and so may be both an indication of
need for treatment and a guide to diagnosis.
"Non-productive" pain by definition serves no purpose
either as a warning or diagnostic tool.
Although pain syndromes may be dissimilar, the common
factor is a sensory pathway from the affected organ to
the brain. Analgesics work at the level of the nerves,
either by blocking the signal from the peripheral
nervous system, or by distorting the interpretation by
the central nervous system. Selection of an appropriate
analgesic is based on consideration of the risk-benefit
factors of each class of drugs, based on type of pain,
severity of pain, and risk of adverse effects.
Traditionally, pain has been divided into two classes,
acute and chronic, although severity and projected
patient survival are other factors that must be
considered in drug selection.
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Acute pain
Acute pain is self limiting in duration, and includes
post-operative pain, pain of injury, and childbirth.
Because pain of these types is expected to be short
term, the long-term side effects of analgesic therapy
may routinely be ignored. Thus, these patients may
safely be treated with narcotic analgesics without
concern for their addictive potential, or NSAIDs with
only limited concern for their ulcerogenic risks. Drugs
and doses should be adjusted based on observation of
healing rate, switching patients from high to low doses,
and from narcotic analgesics to non-narcotics when
circumstances permit.
An important consideration of pain management
in severe pain is that patients should not be subject to
the return of pain. Analgesics should be dosed
adequately to assure that the pain is at least
tolerable, and frequently enough to avoid the anxiety
that accompanies the anticipated return of pain.
Analgesics should never be dosed on a "prn" (as needed)
basis, but should be administered often enough to assure
constant blood levels of analgesic. This applies to both
the narcotic and non-narcotic analgesics.
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Chronic pain
Chronic pain, pain lasting over three months and
severe enough to impair function, is more difficult to
treat, since the anticipated side effects of the
analgesics are more difficult to manage. In the case of
narcotic analgesics this means the addiction
potential, as well as respiratory depression and
constipation. For the NSAIDs, the risk of gastric
ulcers may be dose limiting. While some classes of
drugs, such as the narcotic agonist/antagonist drugs
bupronophine, nalbuphine and pentazocine, and the
selective COX-2 inhibitors celecoxib and rofecoxib
represent advances in reduction of adverse effects, they
are still not fully suitable for long-term management of
severe pain. Generally, chronic pain management requires
a combination of drug therapy, life-style modification,
and other treatment modalities.
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Narcotic
analgesics
The narcotic analgesics, also termed "opioids", are all
derived from opium. The class includes morphine,
codeine, and a number of semi-synthetics including
meperidine (Demerol), propoxyphen (Darvon) and others.
The narcotic analgesics vary in potency, but all are
effective in treatment of visceral pain when used in
adequate doses. Adverse effects are dose related.
Because these drugs are all addictive, they are
controlled under federal and state laws. A variety of
dosage forms are available, including oral solids,
liquids, intravenous and intrathecal injections, and
transcutaneous patches.
NSAIDs, non-steroidal anti-inflammatory drugs, are
effective analgesics even at doses too low to have any
anti-inflammatory effects. There are a number of
chemical classes, but all have similar therapeutic
effects and side effects. Most are appropriate only for
oral administration; however ketorolac (Toradol) is
appropriate for injection and may be used in moderate to
severe pain for short periods.
Acetaminophen is a non-narcotic analgesic with no
anti-inflammatory properties. It is appropriate for mild
to moderate pain. Although the drug is well tolerated in
normal doses, it may have significant toxicity at high
doses. Because acetaminophen is largely free of side
effects at therapeutic doses, it has been considered the
first choice for mild pain, including that of
osteoarthritis.
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Recommended
dosage
Appropriate dosage varies by drug, and should
consider the type of pain, as well as other risks
associated with patient age and condition. For example,
narcotic analgesics should usually be avoided in
patients with a history of substance abuse, but may be
fully appropriate in patients with cancer pain.
Similarly, because narcotics are more rapidly
metabolized in patients who have used these drugs for a
long period, higher than normal doses may be needed to
provide adequate pain management. NSAIDs, although
comparatively safe in adults, represent an increased
risk of gastrointestinal bleeding in patients over the
age of 60.
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Precautions
Narcotic analgesics may be contraindicated in
patients with respiratory depression. NSAIDS may be
hazardous to patients with ulcers or an ulcer history.
They should be used with care in patients with renal
insufficiency or coagulation disorders. NSAIDs
are contraindicated in patients allergic to aspirin.
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Side effects
Review adverse effects of each drug individually.
Drugs within a class may vary in their frequency and
severity of adverse effects.
The primary adverse effects of the narcotic
analgesics are addiction, constipation, and respiratory
depression. Because narcotic analgesics stimulate the
production of enzymes that cause the metabolism of these
drugs, patients on narcotics for a prolonged period may
require increasing doses. This is not the same thing as
addiction, and is not a reason for withholding
medication from patients in severe pain.
NSAIDs are ulcerogenic and may cause kidney problems.
Gastrointestinal discomfort is common, although in some
cases, these drugs may cause ulcers without the prior
warning of gastrointestinal distress. Platelet
aggregation problems may occur, although not to the same
extent as if seen with aspirin.
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Key Terms
- Acute pain
- Pain that is usually temporary and
results from something specific, such as a
surgery, an injury, or an infection.
- Analgesic
- Medicine used to relieve pain.
- Chronic pain
- Pain that lasts more than three months
and threatens to disrupt daily life.
- Inflammation
- Pain, redness, swelling, and heat that
usually develop in response to injury or
illness.
- Osteoarthritis
- Joint pain resulting from damage to the
cartilage.
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