 |
Patient Care - Pain Relief
PAIN RELIEF
A. General
comments. Numerous drugs are available to control pain.
The drug or combination of drugs employed depend
on many
factors, especially the cause, severity, and chronicity of the pain
and the
personality of the patient.
B.
Nonnarcotic preparations should be used whenever possible.
Salicylates.
Acetylsalicylic acid is the most commonly used analgesic
antipyretic drug. Its
mechanism of action as an analgesic drug is not yet defined, but probably
involves blockade of impulse generation in peripheral pain-mediating
chemoreceptors. It is the mainstay of treatment in acute
rheumatic fever, rheumatoid arthritis, and degenerative joint disease. Its
uricosuric effects may be marked in dosages of 5-6 gm daily, but urate
retention and hyperuricemia occur with smaller doses. Aspirin should
not be given concurrently with warfarin because it prolongs the prothrombin
time; and contraindicated in patients with liver disease,
a history of peptic ulcer, and coagulation disorders (e.g., hemophilia,
von Willebrand's disease).
a. Preparation and dosage. Acetylsalicylic acid (aspirin) is the
preparation of
choice. Sodium salicylate, choline salicylate, buffered preparations, and
enteric-coated tablets (which are often poorly absorbed)
may also be given. The dosage of aspirin for. treatment of
rheumatic fever
and arthritis is discussed in Chaps. 10 and 20. Very low albumin levels
'will decrease the dosage requirement of aspirin. The usual dosages of
aspirin for relieving pain or reducing fever are as follows:
(1) Oral. 0.3-1.0 gm (5-15 grains) q3-4h.
(2)
Rectal.
0.3 gm suppositories, 1 or 2 q3-4h.
(3) Intravenous. Sodium salicylate, 0.5 gm, may
be added to fluids and
infused IV over 4-8 hours; generally, the dosage should not exceed
1 gm/24 hr. Rapid
infusion may cause thrombophlebitis, and
extravasation may lead to soft-tissue necrosis.
b. Toxic effects.
Significant toxicity will occur when high doses of aspirin are
given. Major problems are upper GI tract distress, tinnitus, and
diminished auditory acuity. Idiosyncratic
reactions are very rare and usually mild, but severe and fatal reactions
have occurred.
Because asthma is the major allergic manifestation of aspirin
sensitivity, caution
should be exercised when aspirin is prescribed for patients
with
asthma.
Not to be confused with asthmatiform reaction.
(1) Salicylic is characterized by dizziness, tinnitus, decreased
auditory and
visual acuity; sweating, thirst, nausea and vomiting
(Due to CNS effects as well as local gastric irritation)" confusion,
and,
rarely, by an erythematous skin rash. Symptoms subside
when the dosage is reduced.
(2) Gastrointestinal toxicity is common, primarily due to irritation
of
the gastric mucosa. In the majority of patients, small amounts of
blood are
regularly lost into the GI tract. Mucosal ulceration,
blood loss sufficient to cause iron-deficiency anemia, and even
massive
bleeding may occur.
Use of antacids apparently will prevent these complications. (3)
Severe toxic symptoms include CNS manifestations (restlessness, incoherent
speech, anorexia, diplopia, hallucinations, stupor, convulsions, and
coma) and bleeding due to hypoprothrombinemia, which
can be corrected by administration of vitamin K,. Manifestations
are seldom at serum salicylate levels below 20 mg/lOO ml.
Protein and
formed elements (white cells, red cells, casts) may
appear in the urine and then disappear when salicylates are
discontinued.
Since approximately half of salicylate excretion is by
the renal
route, severe toxic symptoms may develop when renal
function is impaired. Rarely, aspirin administration may induce
bone
marrow failure.
2.
Para-aminophenol derivatives
a. Preparations
(1) Phenacetin is a common constituent of a number of proprietary analgesic
mixtures. Although the drug does not have anti-Inflammatory
properties, its antipyretic and analgesic actions are essentially
the same as those of aspirin. Prothrombin time is not affected.
(2) Acetaminophen is the major metabolite of phenacetin, and its pharmacologic
actions are essentially identical. The usual dosage for
adults is 300-600 mg q4-6h; preparations include Tylenol or Tempra
tablets (325 mg) (5 grains) and Tylenol elixir or Tempra Syrup
(125 mg/5 mI).
b. Side effects and toxic reactions. Side effects are rare and occur
usually only
with high doses. Methemoglobinemia,
hemolytic anemias (particularly in patients with glucose
6-phosphate dehydrogenase deficiency), skin rash, hepatic injury, vascular
collapse, and drug fever may occur. A
number of reports have suggested an association between "analgesic abuse"
and renal disease, and most implicate phenacetin as the offending
agent. Whether
nephrotoxicity is due to phenacetin per se, to its metabolites, or to
certain impurities occasionally present is not known. Clinically,
analgesic nephropathy has been reported to occur in
patients ingesting large amounts of the drug over a number of years-at
least 1-3 gm daily for a total intake of 5 kg or more. Azotemia
and polyuria (due to decreased concentrating ability) are the
major manifestations; pyuria, bacteriuria, renal papillary necrosis, and
acidosis associated with progressive renal insufficiency may occur. Acetaminophen
overdose is associated with hepatic insufficiency
when more than 15 gm has been ingested.
3. Propoxyphene hydrochloride (Darvon) is a nonnarcotic analgesic
structurally related
to methadone. Its potency is probably less than that of aspirin
and codeine, but it is better tolerated than codeine. Side effects,
which include nausea, vomiting, epigastric distress, dizziness,
drowsiness,
pruritus, and skin rashes, are minimal. Its use has been
associated with
hypoglycemia and pulmonary edema. The
dosage is 65 mg q4- 6h
PO. Combinations
of propoxyphene and salicylates are more effective than
either agent alone.
4. Pentazocine (Talwin) is a nonnarcotic analgesic that produces
significant analgesia
15-20 minutes after 1M injection;
30 mg is usually as effective as 10 mg of morphine. Drug addiction has
not been
reported with oral administration, although withdrawal symptoms may
occur after longterm use. Because it is a mild narcotic antagonist, it must
be given with caution to patients receiving narcotics. Adverse effects
include oversedation, nausea, vomiting, CNS
disturbances (dizziness, euphoria, hallucinations), and
respiratory depression. The dosage is 30 mg 1M, or 50 mg
PO
q3-4h (one-third as effective). Its primary clinical usefulness is in patients
who require long-term administration of analgesics.
|
|
|