PRECAUTIONS Tolerance and Physical Dependence
Tolerance is the need for increasing doses of opioids to maintain
a defined effect such as analgesia (in the absence of disease progression or
other external factors). Physical dependence is manifested by withdrawal
symptoms after abrupt discontinuation of a drug or upon administration of an
antagonist. Physical dependence and tolerance are not unusual during chronic
opioid therapy.
The opioid abstinence or withdrawal syndrome is characterized by some or all
of the following: restlessness, lacrimation, rhinorrhea, yawning, perspiration,
chills, myalgia, and mydriasis. Other symptoms also may develop, including:
irritability, anxiety, backache, joint pain, weakness, abdominal cramps,
insomnia, nausea, anorexia, vomiting, diarrhea, or increased blood pressure,
respiratory rate, or heart rate. In general, opioids should not be abruptly
discontinued (see Dosage and Administration: Cessation of Therapy).
If Darvon-N is abruptly discontinued in a physically dependent patient, an
abstinence syndrome may occur (see Drug Abuse and Dependance). If signs and symptoms of withdrawal occur, patients
should be treated by reinstitution of opioid therapy followed by gradual tapered
dose reduction of Darvon-N combined with symptomatic support (see Dosage and Administration: Cessation of Therapy).
Use in Pancreatic/Biliary Tract Disease
Darvon-N may cause spasm of the sphincter of Oddi and should be
used with caution in patients with biliary tract disease, including acute
pancreatitis. Opioids like Darvon-N may cause increases in the serum amylase
level.
Hepatic or Renal Impairment
Insufficient information exists to make appropriate dosing
recommendations regarding the use of either propoxyphene in patients with
hepatic or renal impairment as a function of degree of impairment. Higher plasma
concentrations and/or delayed elimination may occur in case of impaired hepatic
function and/or impaired renal function (see Clinical Pharmacology). If the drug is used in these
patients, it should be used with caution because of the hepatic metabolism and
renal excretion of propoxyphene metabolites.
Information for Patients/Caregivers
- Patients should be advised to report pain and adverse experiences occurring
during therapy. Individualization of dosage is essential to make optimal use of
this medication.
- Patients should be advised not to adjust the dose of Darvon-N without
consulting the prescribing professional.
- Patients should be advised that Darvon-N may impair mental and/or physical
ability required for the performance of potentially hazardous tasks (e.g.,
driving, operating heavy machinery).
- Patients should not combine Darvon-N with central nervous system depressants
(e.g., sleep aids, tranquilizers) except by the orders of the prescribing
physician, because additive effects may occur.
- Patients should be instructed not to consume alcoholic beverages, including
prescription and over-the-counter medications that contain alcohol, while using
Darvon-N because of risk of serious adverse events including death.
- Women of childbearing potential who become, or are planning to become,
pregnant should be advised to consult their physician regarding the effects of
analgesics and other drug use during pregnancy on themselves and their unborn
child.
- Patients should be advised that Darvon-N is a potential drug of abuse. They
should protect it from theft, and it should never be given to anyone other than
the individual for whom it was prescribed.
- Patients should be advised that if they have been receiving treatment with
Darvon-N for more than a few weeks and cessation of therapy is indicated, it may
be appropriate to taper the Darvon-N dose, rather than abruptly discontinue it,
due to the risk of precipitating withdrawal symptoms. Their physician can
provide a dose schedule to accomplish a gradual discontinuation of the
medication.
Drug Interactions with Propoxyphene Propoxyphene is metabolized mainly via the human cytochrome P450
3A4 isoenzyme system (CYP3A4), therefore potential interactions may occur when
propoxyphene is administered concurrently with agents that affect CYP3A4
activity.
The metabolism of propoxyphene may be altered by strong CYP3A4 inhibitors
(such as ritonavir, ketoconazole, itraconazole, troleandomycin, clarithromycin,
nelfinavir, nefazadone, amiodarone, amprenavir, aprepitant, diltiazem,
erythromycin, fluconazole, fosamprenavir, grapefruit juice, and verapamil)
leading to enhanced propoxyphene plasma levels. Coadministration with agents
that induce CYP3A4 activity may reduce the efficacy of propoxyphene. Strong
CYP3A4 inducers such as rifampin may lead to enhanced metabolite
(norpropoxyphene) levels.
Propoxyphene is also thought to possess CYP3A4 and CYP2D6 enzyme inhibiting
properties and coadministration with drugs that rely on either of these enzymes
for metabolism may result in increased pharmacologic or adverse effects of that
drug. Severe neurologic signs, including coma, have occurred with concurrent use
of carbamazepine (metabolized by CYP3A4).
Increased risk of bleeding has been observed with warfarin-like agents when
given along with propoxyphene; however, the mechanistic basis of this
interaction is unknown.
CNS Depressants Patients receiving narcotic analgesics, general anesthetics,
phenothiazines, other tranquilizers, sedative-hypnotics or other CNS depressants
(including alcohol) concomitantly with propoxyphene may exhibit an additive CNS
depression. Interactive effects resulting in respiratory depression,
hypotension, profound sedation, or coma may result if these drugs are taken in
combination with the usual dosage of Darvon-N. When such combined therapy is
contemplated, the dose of one or both agents should be reduced.
Mixed Agonist/Antagonist Opioid Analgesics Agonist/antagonist analgesics (i.e., pentazocine, nalbuphine,
butorphanol and buprenorphine) should be administered with caution to patients
who have received or are receiving a course of therapy with a pure opioid
agonist analgesic such as Darvon-N. In this situation, mixed agonist/antagonist
analgesics may reduce the analgesic effect of Darvon-N and/or may precipitate
withdrawal symptoms in these patients.
Monoamine Oxidase Inhibitors (MAOIs) MAOIs have been reported to intensify the effects of at least one
opioid drug causing anxiety, confusion and significant depression of respiration
or coma. The use of Darvon-N is not recommended for patients taking MAOIs or
within 14 days of stopping such treatment.
Carcinogenesis, Mutagenesis, Impairment of Fertility
The mutagenic and carcinogenic potential of propoxyphene has not
been evaluated.
In animal studies there was no effect of propoxyphene on mating behavior,
fertility, duration of gestation, or parturition when rats were fed propoxyphene
as a component of their daily diet at estimated daily propoxyphene intake up to
8-fold greater than the maximum human equivalent dose (HED) based on body
surface area comparison. At this highest dose, fetal weight and survival on
postnatal day 4 was reduced.
Pregnancy Risk summary Pregnancy category C. There are no adequate and well-controlled studies of propoxyphene
in pregnant women. While there are limited data in the published literature,
adequate animal reproduction studies have not been conducted with propoxyphene.
Therefore, it is not known whether propoxyphene can affect reproduction or cause
fetal harm when administered to a pregnant woman. Propoxyphene should be given
to a pregnant woman only if clearly needed.
Clinical considerations Propoxyphene and its major metabolite, norpropoxyphene, cross the
human placenta. Neonates whose mothers have taken opiates chronically may
exhibit respiratory depression or withdrawal symptoms.
Data In published animal reproduction studies, no teratogenic effects
occurred in offspring born to pregnant rats or rabbits that received
propoxyphene during organogenesis. Pregnant animals received propoxyphene doses
approximately 10-fold (rats) and 4-fold (rabbits) the maximum recommended human
dose (based on mg/m2 body surface area comparison).
Nursing Mothers Propoxyphene, norpropoxyphene (major metabolite), are excreted in
human milk. Published studies of nursing mothers using propoxyphene detected no
adverse effects in nursing infants. Based on a study of six mother-infant pairs,
an exclusively breastfed infant receives approximately 2% of the maternal
weight-adjusted dose. Norpropoxyphene is renally excreted and renal clearance is
lower in neonates than in adults. Therefore, it is possible that prolonged
maternal propoxyphene use could result in norpropoxyphene accumulation in a
breastfed infant. Watch breastfeeding infants for signs of sedation including
poor feeding, somnolence, or respiratory depression. Caution should be exercised
when Darvon-N is administered to a nursing woman.
Pediatric Patients Safety and effectiveness in pediatric patients have not been
established.
Elderly Patients Clinical studies of Darvon-N did not include sufficient numbers
of subjects aged 65 and over to determine whether they respond differently from
younger subjects. However, postmarketing reports suggest that patients over the
age of 65 may be more susceptible to CNS-related side effects. Therefore, dose
selection for an elderly patient should be cautious, usually starting at the low
end of the dosing range, reflecting the greater frequency of decreased hepatic,
renal, or cardiac function, and of concomitant disease or other drug therapy.
Decreased total daily dosage should be considered (see Dosage and Administration).