Subutex
In October 2002, the FDA approved 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 Schedule III, IV, or V medications to have received FDA approval for this indication. Note that aside from Subutex® and Suboxone®, other forms of buprenorphine, e.g., Buprenex®, are not approved for treatment of opioid addiction.

The FDA approval of these buprenorphine formulations does not affect the status of other medication-assisted opioid addiction 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 treatments 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 codeine, that are not approved for the treatment of addiction. Lastly, note that aside from Subutex® and Suboxone®, other forms of buprenorphine, e.g., Buprenex®, are not approved for treatment of opioid addiction.

Formulations
Suboxone®, a sublingual tablet, comes in two dosage forms: 2 mg buprenorphine/0.5 mg naloxone and 8 mg buprenorphine/2 mg naloxone. Subutex®, also a sublingual tablet, is available in 2 mg and 8 mg strengths. The Subutex® and Suboxone® drug labels are available on the FDA Web site at:

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 "ceiling effect." Thus, buprenorphine carries a lower risk of abuse, addiction, 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 if administered to an opioid-addicted individual while a full agonist is in the bloodstream.

Buprenorphine has poor oral bioavailability and moderate sublingual bioavailability. Formulations for opioid addiction 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-addicted 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.

See the Buprenorphine Clinical Practice Guidelines (available soon on this Web site) for more information about the use of buprenorphine in pregnancy. Currently, methadone remains the standard of care for the medication-assisted treatment of opioid-addicted women in the United States.

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
  

Drug Interactions, Cautions and Contraindications
Refer to the Subutex® and Suboxone® package inserts (http://www.fda.gov/cder/drug/infopage/subutex_suboxone/default.htm) for a complete listing of drug interactions, contraindications, warnings, and precautions.

Abuse Potential
Because of its opioid agonist effects, buprenorphine is abusable, particularly by individuals who are not physically addicted to 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-addicted user.

Naloxone via the parenteral route, however, has good bioavailability. If the sublingual buprenorphine/naloxone tablets are crushed and injected by an opioid-addicted individual, the naloxone effect predominates and can precipitate the opioid withdrawal syndrome.

Under certain circumstances buprenorphine by itself can also precipitate withdrawal in opioid-addicted individuals. This is more likely to occur with higher levels of physical addiction, 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. This point is of such importance that physicians must attest to their capacity to refer patients for counseling when they submit their Notification of Intent to SAMHSA to begin prescribing Suboxone® and Subutex®.

Many different types of behavioral therapies (e.g., Motivational Enhancement Therapy, self-help programs) have been used successfully for substance abuse disorders. The SAMHSA Treatment Improvement Protocol (TIP) series (http://www.treatment.org/Externals/tips.html) includes a number of documents that contain best practice guidelines for the provision of interventions and therapies for individuals with substance abuse disorders.

Opioid Addiction Therapy with Buprenorphine
This section provides a brief overview of the clinical use of buprenorphine (Suboxone® and Subutex®) for opioid addiction therapy. For detailed information on this topic see the Buprenorphine Clinical Practice Guidelines.

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-addicted 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 a patient has discontinued or greatly reduced the use of his or her 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.”