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Buprenorphine, a derivative of thebaine, is an opiate that has been
marketed in the United States as the Schedule V parenteral analgesic
Buprenex®. In 2002, based on a re-evaluation of available evidence
regarding the potential for abuse, diversion, dependence, and side
effects, the DEA reclassified buprenorphine from a Schedule V to
a Schedule III narcotic.
In October 2002, Reckitt Benckiser received FDA approval to market
a buprenorphine monotherapy product, Subutex®, and a buprenorphine/naloxone
combination product, Suboxone®, for use in opioid addiction
treatment. The combination product is designed to decrease the potential
for abuse by injection. Subutex® and Suboxone® are currently
the only medications to have received FDA approval for this indication.
In January 2003, Reckitt Benckiser began shipments of Suboxone®
to pharmacies in the United States.
The approval of these formulations does not affect the treatment
standards of previously approved medication-assisted treatments,
such as methadone and LAAM (levo-alpha-acetyl-methadol). As indicated
in Title 42 Code of Federal Regulations Part 8 (42 CFR Part 8),
these therapies can only be dispensed, and only in the context of
an Opioid Treatment Program. Also, neither the approval of Subutex®
and Suboxone®, nor the provisions of DATA 2000, affect the use
of other Schedule III, IV, or V medications, such as morphine, that
are not approved for the treatment of addiction. Lastly, note that
other forms of buprenorphine besides Subutex® and Suboxone®,
e.g., Buprenex®, are not approved for treatment of opioid addiction. sona classified
Applied Pharmacology
Buprenorphine is an opioid partial agonist. This means that, although
buprenorphine is an opioid, and thus can produce typical opioid
agonist effects and side effects, such as euphoria and respiratory
depression, its maximal effects are less than those of full agonists
like heroin and methadone. At low doses, buprenorphine produces
sufficient agonist effect to enable opioid-addicted individuals
to discontinue the misuse of opioids without experiencing withdrawal
symptoms. The agonist effects of buprenorphine increase linearly
with increasing doses of the drug until at moderate doses they reach
a plateau and no longer continue to increase with further increases
in dose—the so-called “ceiling effect.” Thus,
buprenorphine carries a lower risk of abuse, dependence, and side
effects compared to full opioid agonists. In fact, in high doses
and under certain circumstances, buprenorphine can actually block
the effects of full opioid agonists and can precipitate withdrawal
symptoms in an acutely opioid-intoxicated individual.
Buprenorphine has poor oral bioavailability and moderate sublingual
bioavailability. Thus, formulations for opioid dependence treatment
are in the form of sublingual tablets.
Buprenorphine is highly bound to plasma proteins. It is metabolized
by the liver via the cytochrome P4503A4 enzyme system into norbuprenorphine
and other metabolites. The half-life of buprenorphine is 24–60
hours.
Safety
Because of its ceiling effect and poor bioavailability, buprenorphine
is safer in overdose than opioid full agonists. The maximal effects
of buprenorphine appear to occur in the 16–32 mg dose range
for sublingual tablets. Higher doses are unlikely to produce greater
effects.
Respiratory depression from buprenorphine (or buprenorphine/naloxone)
overdose is less likely than from other opioids. There is no evidence
of organ damage with chronic use of buprenorphine, although increases
in liver enzymes are sometimes seen. Likewise, there is no evidence
of significant disruption of cognitive or psychomotor performance
with buprenorphine maintenance dosing.
Information about the use of buprenorphine in pregnant, opioid-dependent
women is limited; the few available case reports have not demonstrated
any significant problems due to buprenorphine use during pregnancy.
Suboxone® and Subutex® are classified by the FDA as Pregnancy
Category C medications.
Side Effects
Side effects of buprenorphine are similar to those of other opioids
and include nausea, vomiting, and constipation. Buprenorphine and
buprenorphine/naloxone can precipitate the opioid withdrawal syndrome.
Additionally, the withdrawal syndrome can be precipitated in individuals
maintained on buprenorphine. Signs and symptoms of opioid withdrawal
include:
Dysphoric mood
Nausea or vomiting
Muscle aches/cramps
Lacrimation
Rhinorrhea
Pupillary dilation
Sweating
Piloerection
Diarrhea
Yawning
Mild fever
Insomnia
Craving
Distress/irritability
Abuse Potential
Because of its opioid agonist effects, buprenorphine is abusable,
particularly by individuals who are not physically dependent on
opioids. Naloxone is added to buprenorphine to decrease the likelihood
of diversion and abuse of the combination product. Sublingual buprenorphine
has moderate bioavailability, while sublingual naloxone has poor
bioavailability. Thus, when the buprenorphine/naloxone tablet is
taken in sublingual form, the buprenorphine opioid agonist effect
predominates, and the naloxone does not precipitate opioid withdrawal
in the opioid-dependent user.
Naloxone via the parenteral route, however, has good bioavailability.
If the sublingual buprenorphine/naloxone tablets are crushed and
injected by an opioid-dependent individual, the naloxone effect
predominates and can acutely precipitate the opioid withdrawal syndrome.
Under certain circumstances buprenorphine by itself can also precipitate
withdrawal in opioid-dependent individuals. This is more likely
to occur with higher levels of physical dependence, with short time
intervals (e.g., less than 2 hours) between a dose of opioid agonist
(e.g., methadone) and a dose of buprenorphine, and with higher doses
of buprenorphine.
Evidence of Effectiveness
Studies have shown that buprenorphine is more effective than placebo
and is equally as effective as moderate doses of methadone and LAAM
in opioid maintenance therapy. Buprenorphine is unlikely to be as
effective as more optimal-dose methadone, and therefore may not
be the treatment of choice for patients with higher levels of physical
dependence.
Few studies have been reported on the efficacy of buprenorphine
for completely withdrawing patients from opioids. In general, the
results of studies of medically assisted withdrawal using opioids
(e.g., methadone) have shown poor outcomes. Buprenorphine, however,
is known to cause a milder withdrawal syndrome compared to methadone
and for this reason may be the better choice if opioid withdrawal
therapy is elected.
Non-pharmacological Therapies
Effective treatment of drug addiction requires comprehensive attention
to all of an individual’s medical and psychosocial co-morbidities.
Pharmacological therapy alone rarely achieves long-term success.
Thus Suboxone® and Subutex® treatment should be combined
with concurrent behavioral therapies and with the provision of needed
social services.
The choice of treatment setting in which to provide non-pharmacological
therapies should be determined based on the intensity of intervention
required for a patient. The continuum of treatment setting intensities
ranges from episodic office-based therapy to intensive inpatient
therapy.
Ideal candidates for opioid addiction treatment with buprenorphine
are individuals who have been objectively diagnosed with opioid
addiction, are willing to follow safety precautions for treatment,
can be expected to comply with the treatment, have no contraindications
to buprenorphine therapy, and who agree to buprenorphine treatment
after a review of treatment options. There are three phases of buprenorphine
maintenance therapy: induction, stabilization, and maintenance.
The induction phase is the medically monitored startup of buprenorphine
therapy. Buprenorphine for induction therapy is administered when
an opioid-dependent individual has abstained from using opioids
for 12–24 hours and is in the early stages of opioid withdrawal.
If the patient is not in the early stages of withdrawal, i.e., if
he or she has other opioids in the bloodstream, then the buprenorphine
dose could precipitate acute withdrawal.
Induction is typically initiated as observed therapy in the physician’s
office and may be carried out using either Suboxone® or Subutex®,
dependent upon the physician’s judgment. As noted above, Buprenex®,
the parenteral analgesic form of buprenorphine, is not FDA-approved
for use in opioid addiction treatment.
The stabilization phase has begun when the patients have discontinued
or greatly reduced the use of their drug of abuse, no longer has
cravings, and is experiencing few or no side effects. The buprenorphine
dose may need to be adjusted during the stabilization phase. Because
of the long half-life of buprenorphine it is sometimes possible
to switch patients to alternate-day dosing once stabilization has
been achieved.
The maintenance phase is reached when the patient is doing well
on a steady dose of buprenorphine (or buprenorphine/naloxone). The
length of time of the maintenance phase is individualized for each
patient and may be indefinite. The alternative to going into (or
continuing) a maintenance phase, once stabilization has been achieved,
is medically supervised withdrawal. This takes the place of what
was formerly called “detoxification.”
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