The REAL Future of Partial Agonist Treatment— Pharma are you Listening?
Posted Oct 13 2011 12:58am
I just wrote a note to a friend who works in the molecular sciences– she has been studying opioid receptors since the early 1980′s, when things were just getting started on a molecular level. I’m keeping her name to myself, but I’ll share a few thoughts about what is needed to advance the treatement of opioid dependence– and make a few million dollars along the way (are you listening, RB?)
(private chit chat that would bore everyone)
Anyway, today I realized what is needed in order to take partial agonist treatment of opioid dependence to the next level.
The problem with buprenorphine is that the ‘ceiling effect’ occurs at a relatively high tolerance level, approximately equal to 40 mg of methadone. That causes at least two problems. First, going off Suboxone is a lot of work, as the person still has a great deal of withdrawal to go through. That may be a good thing early in the process, as it may help keep people on Suboxone, but after a year or so, when people want to try going off the medication, it is a major barrier that opens the floodgates to those old memories of using, etched in the emotions associated with withdrawal.
The second problem with the high ceiling/tolerance level is that surgery is a hassle. People needing surgery need HIGH amounts of oxycodone to get any analgesia—I usually give 15-30 mg every 4 hours. Pharmacists shudder to release those doses, and some surgeons and anesthesiologists balk.
The horizontal part of the dose/response curve is the essential part of buprenorphine; that is what tricks the brain into ‘thinking’ that nothing is wearing off, and in that way eliminating cravings. But that flat dose/response relationship could occur at lower tolerance levels and still work the same way.
Since I’m wishing for the moon, a series of molecules with progressively lower ceiling levels would be ideal, with the last molecule in the series being Naltrexone. Although actually, naltrexone doesn’t work—it has NO mu agonism, so there is no tricking of the brain, and no reduction of cravings. We would want something close to naltrexone, but with a tiny bit of opioid activity that does not vary with dose.
A shorter half-life would also be helpful. Preparing for surgery requires weeks to get the buprenorphine out of the system. Of course a shorter half-life means it is easier to get around buprenorphine by people who want to play with agonists, so again, these new molecules would be intended as ‘step down’ meds from early-stage buprenorphine treatment.
Do we know enough about molecular actions at the mu receptor to design molecules with these properties? Or are we still at the point of making somewhat random changes and assaying the result? Do you know of any labs doing this type of work?