Buprenorphine and methadone, both being opioids, activate the opioid (mu) receptors on nerve cells. And both drugs have long half-lifes, meaning that they’re long-acting medications. The half-life can vary from 24 to 60 hours for buprenorphine, and from 8 to 59 hours for methadone. (The half-life is the amount of time a drug stays in the body before its concentration in the plasma drops by half. A drug’s half-life can vary from patient to patient.)

The long half-lifes of buprenorphine and methadone account for their usefulness in treating opioid dependence. Simply put, these drugs lack the peaks and troughs that are associated with short-term opioids, like heroin—swings in drug plasma levels that can cause overdose and withdrawal symptoms.

But there are key differences between buprenorphine and methadone.

Full Agonist vs. Partial Agonist

Buprenorphine is a partial agonist; methadone, like heroin, is a full agonist. It is by their actions on opioid receptors that opioids achieve their analgesic (pain-killing) as well as their addictive effects.

Methadone, as a full mu opioid agonist, continues to produce effects on the receptors until either all receptors are fully activated, or the maximum effect is reached.

Buprenorphine, as a partial agonist, does not activate mu receptors to the same extent as methadone. Its effects increase until they reach a plateau. At that level, opioid-addicted patients can discontinue opioid use without experiencing withdrawal. Buprenorphine reaches its ceiling effect at a moderate dose, which means that its effects do not increase after that point, even with increases in dosage.

Like all opioids, buprenorphine can cause respiratory depression and euphoria, but its maximal effects are less than those of full agonists. The benefits of this from an overdose perspective constitute the safety profile of buprenorphine—a lower risk of abuse, addiction, and side effects than with full agonists.

For people who are not addicted to or dependent on opioids, the effects of partial (buprenorphine) and full (methadone) agonists are indistinguishable. However, at a certain point, the increasing effects of partial agonists reach maximum levels. For this reason, people who are dependent on high doses of opioids are better suited to treatment with a full agonist, such as methadone.

Buprenorphine, like methadone, has a serious potential for drug-drug interactions. It must be used cautiously with other medications, in particular benzodiazepines, other sedatives, opioid antagonists like naltrexone, and opioid agonists.

Formulations of Buprenorphine

In October 2002, the Food and Drug Administration (FDA) approved the buprenorphine monotherapy product, Subutex, and a buprenorphine/naloxone combination product, Suboxone, for treating opioid addiction.

Subutex is no longer sold in this country. It has been replaced by generic buprenorphine. Suboxone, a sublingual tablet (designed to dissolve under the tongue), comes in two dosage forms. Suboxone film was approved by the FDA in 2010. The sublingual film dissolves faster than the tablet, and is individually wrapped in unit-dose, child-resistant pouches. According to the manufacturer, Reckitt Benckiser, Suboxone film is clinically interchangeable with the tablet.

Last fall, Reckitt Benckiser voluntarily removed its Suboxone tablets from the market, citing a few pediatric overdoses. But it protected its hold on the Suboxone market by retaining the film formulation. The patent on the tablets had long expired; the patent on the film runs until 2023. Patients, of course, had to be switched to the film, unless their physicians wanted to switch them to generic buprenorphine. At the same time that Reckitt pulled the tablets, it filed a Citizen’s Petition with the FDA, calling on all buprenorphine products to be sold in childproof packaging.

The effect of these moves by Reckitt on the buprenorphine marketplace are not clear, said Nicholas Reuter, MPH, who was senior public health analyst with SAMHSA’s Center for Substance Abuse Treatment (CSAT) when this story was written (he retired on January 31, 2013). “Submitting a Citizen’s Petition doesn’t mean the FDA has to accept it,” he said. In addition, in November 2012 the FDA accepted Orexo’s New Drug Application for Zubsolv, a buprenorphine-naloxone combination. Zubsolv could well be the first generic competition to Suboxone. And on December 17, 2012, Titan licensed Probuphine, its buprenorphine implant, to Braeburn Pharmaceutical for exclusive commercialization in the U.S. and Canada. “The buprenorphine marketplace is looking at different formulations,” noted Mr. Reuter. “There could be a generic competitor [for Suboxone] tomorrow.”

Making the Decision: Methadone vs. Buprenorphine

Aside from the dosage issue, there is no “cookie-cutter” approach for deciding what patient gets buprenorphine and what patient gets methadone. Philip L. Herschman, PhD, chief clinical officer of CRC Health Group, pointed out that different patients react differently to different medications. “Some feel better on buprenorphine, some feel better on methadone,” he said. CRC has been using generic buprenorphine in its OTPs on the same basis as methadone. The extent to which CRC will be able to give buprenorphine take-homes will depend in large part on state regulations—just because the federal government has approved the plan doesn’t mean states will.

“Buprenorphine is great, but it’s not for everybody,” said Walter Ginter, CMA, project director of the Medication Assisted Recovery Support (MARS) project. He doesn’t think the final rule is going to make a big difference for most patients. He noted that few patients go to methadone maintenance as their first course of treatment.

In fact, Mr. Ginter can speak as an expert on subjective effects in a personal way: he has been maintained on both medications—buprenorphine during its development in the 1990s, when he was a study subject, and then methadone. He has been on a high dose of methadone for years, and says “I don’t think I’m clouded out.” Indeed, he is one of the most energetic and articulate advocates in the field. It comes down to a matter of personal preference, he said. “With methadone, you’re never sick and you’re never high, but you do get the serum peaking four hours after the dose,” he said. “I think Suboxone is too much the same, with no ups or downs.”

Still, there are OTPs that do switch patients from methadone to buprenorphine, titrating very carefully downward for patients on doses of 80 milligrams or more of methadone before switching to buprenorphine, said Mark Parrino. MPA, president of the American Association for the Treatment of Opioid Dependence (AATOD). In general, if a patient has been using opioids for a longer period, or has a higher tolerance, methadone would be more appropriate. The reason is that buprenorphine’s ceiling limits those higher-dose equivalents.

Publishers Note: Nicholas Reuter, MPH joined Reckitt Benckiser in February 2013 as a Treatment Manager.