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Re: ALKS-5461

Posted by ed_uk2010 on January 29, 2015, at 9:49:25

In reply to ALKS-5461, posted by hello123 on January 28, 2015, at 21:08:16

Hello :)

Buprenorphine is an opioid with high binding affinity for mu opioid receptors, but it only partially stimulates them; this is responsible for its typical opioid-like pain relieving properties. Buprenorphine also acts on other opioid receptors (kappa and delta), but as an antagonist ie. it blocks them, with no stimulation. Partial agonist activity at mu receptors combined with antagonist activity at kappa receptors may elevate mood in some types of depression, but mu agonist drugs can cause dependence, and bupe is not an exception. Buprenorphine also has an active metabolite called norbuprenorphine, with somewhat different opioid properties.

Buprenorphine is used both for pain relief (for moderately severe pain), and as part of the treatment for opioid dependence. Like methadone, it relieves opioid withdrawal symptoms and reduces the risk of relapse into IV drug misuse. Bupe is generally safer than methadone - which is very dangerous in overdose. Withdrawal symptoms from bupe and methadone can be rather prolonged, especially if high doses have been taken. Bupe withdrawal symptoms are less intense, however.

Bupropion is the generic name for Wellbutrin, an antidepressant. Bupropion has a similar name to buprenorphine but is not related to it in any way.

Buprenorphine is not similar to naltrexone. The fact that bupe stimulates mu receptors whereas naltrexone potently blocks them makes the drugs very different clinically.

Naltrexone and naloxone are different drugs too. They have similar effects but are used differently in practice. Naloxone is a short acting opioid antagonist - it blocks all opioid receptors, but is most potent at blocking the mu receptors, followed by the kappa receptors. It's used a lot by injection to treat opioid overdose, and in combination with buprenorphine to discourage the IV misuse of Suboxone tablets. Naltrexone is a long acting opioid antagonist - it blocks opioid receptors but for a much longer duration than naloxone. Naltrexone is used by mouth for a variety of reasons. It is sometimes used to decrease relapse after opioid detox, and to reduce drinking after alcohol detox. If naltrexone is taken by someone who is physically dependent on opioids, it will rapidly induce severe withdrawal symptoms. As a result, it can only be started once withdrawal is complete - with the aim of preventing relapse by blocking drug effects if opioids are taken. Low dose naltrexone (usually 4.5mg/day), has been recommended by alternative practitioners for a huge range of illnesses.

ALKS-5461 is a combination product containing buprenorphine and samidorphan. It is being studied for TR-depression. The idea is that samidorphan blocks the activity of buprenorphine at the mu receptor, and therefore presumably prevents dependence. In this combination, buprenorphine is still able to block the kappa receptors, which is thought to improve depression. Presumably, this combination will have more antagonist activity at the kappa receptors than naltrexone, while having minimal effect at the mu receptors. Naltrexone is a very strong mu antagonist, which may cause some unpleasant effects except at very low doses....




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