OVERDOSAGE
Overdose of Darvon-N may present with the signs and symptoms of
propoxyphene overdose. Fatalities within the first hour of overdosage are not
uncommon.
In all cases of suspected overdosage, call your regional Poison Control
Center to obtain the most up-to-date information about the treatment of
overdose. This recommendation is made because, in general, information regarding
the treatment of overdosage may change more rapidly than do package inserts.
Initial consideration should be given to the management of the CNS effects of
propoxyphene overdosage. Resuscitative measures should be initiated promptly.
Symptoms of Propoxyphene Overdosage
The manifestations of acute overdosage with propoxyphene are
those of narcotic overdosage. The patient is usually somnolent but may be
stuporous or comatose and convulsing. Respiratory depression is characteristic.
The ventilatory rate and/or tidal volume is decreased, which results in cyanosis
and hypoxia. Pupils, initially pinpoint, may become dilated as hypoxia
increases. Cheyne-Stokes respiration and apnea may occur. Blood pressure and
heart rate are usually normal initially, but blood pressure falls and cardiac
performance deteriorates, which ultimately results in pulmonary edema and
circulatory collapse, unless the respiratory depression is corrected and
adequate ventilation is restored promptly. Cardiac arrhythmias and conduction
delay may be present. A combined respiratory-metabolic acidosis occurs owing to
retained CO2 (hypercapnia) and to lactic acid formed
during anaerobic glycolysis. Acidosis may be severe if large amounts of
salicylates have also been ingested. Death may occur.
Treatment of Propoxyphene Overdosage
Attention should be directed first to establishing a patent
airway and to restoring ventilation. Mechanically assisted ventilation, with or
without oxygen, may be required, and positive pressure respiration may be
desirable if pulmonary edema is present. The opioid antagonist naloxone will
markedly reduce the degree of respiratory depression, and should be administered
promptly, preferably intravenously. The duration of action of the antagonist may
be brief. If no response is observed after 10 mg of naloxone have been
administered, the diagnosis of propoxyphene toxicity should be questioned.
In addition to the use of an opioid antagonist, the patient may require
careful titration with an anticonvulsant to control convulsions. Activated
charcoal can adsorb a significant amount of ingested propoxyphene. Dialysis is
of little value in poisoning due to propoxyphene. Efforts should be made to
determine whether other agents, such as alcohol, barbiturates, tranquilizers, or
other CNS depressants, were also ingested, since these increase CNS depression
as well as cause specific toxic effects or death.
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DRUG ABUSE AND DEPENDENCE
Controlled Substance
Darvon-N is a Schedule IV narcotic under the U.S. Controlled
Substances Act. Darvon-N can produce drug dependence of the morphine type, and
therefore, has the potential for being abused. Psychic dependence, physical
dependence and tolerance may develop upon repeated administration. Darvon-N
should be prescribed and administered with the same degree of caution
appropriate to the use of other narcotic-containing medications.
Abuse
Since Darvon-N is a mu-opioid agonist, it may be subject to
misuse, abuse, and addiction. Addiction to opioids prescribed for pain
management has not been estimated. However, requests for opioids from
opioid-addicted patients occur. As such, physicians should take appropriate care
in prescribing Darvon-N.
Dependence
Opioid analgesics may cause psychological and physical
dependence. Physical dependence results in withdrawal symptoms in patients who
abruptly discontinue the drug after long term administration. Also, symptoms of
withdrawal may be precipitated through the administration of drugs with
mu-opioid antagonist activity, e.g., naloxone or mixed agonist/antagonist
analgesics (e.g., pentazocine, butorphanol, nalbuphine, dezocine) (see Overdosage). Physical dependence usually
does not occur to a clinically significant degree, until after several weeks of
continued opioid usage. Tolerance, in which increasingly larger doses are
required to produce the same degree of analgesia, is initially manifested by a
shortened duration of an analgesic effect and subsequently, by decreases in the
intensity of analgesia.
In chronic pain patients, and in opioid-tolerant cancer patients, the
administration of Darvon-N should be guided by the degree of tolerance
manifested and the doses needed to adequately relieve pain.
The severity of the Darvon-N abstinence syndrome may depend
on the degree of physical dependence. Withdrawal is characterized by rhinitis,
myalgia, abdominal cramping, and occasional diarrhea. Most observable symptoms
disappear in 5 to 14 days without treatment; however, there may be a phase of
secondary or chronic abstinence which may last for 2 to 6 months characterized
by insomnia, irritability, and muscular aches. The patient may be detoxified by
gradual reduction of the dose. Gastrointestinal disturbances or dehydration
should be treated with supportive care.
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