No it just blocks everything and everything there is? If thats not an antagonist I don't know what is?
Well, to use the metaphor from the Reckitt-Benckiser Suboxone patient booklet, think of a door with a lock on it.
For opioids, think of
agonists and
antagonists when it comes to opening that door. An agonist is a key that fits in the lock and opens the door wide open. An antagonist is a key that will fit the lock, but won't open the door. Because it is filling the lock, if an agonist comes along and tries to unlock and open the door, it cannot, because the antagonist is taking up the space in the keyhole.
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses
When it comes to agonists blocking other agonists, this is due to
cross tolerance.
Cross tolerance occurs when a person is dependant on a mu-agonist opioid. Lets say Morphine. The person is taking 100mg Morphine three times a day. Halfway through the day that person comes across 20mg of Oxycodone, and takes it. However, the Oxycodone has no effect. This is not because the Morphine is an antagonist, but because of cross-tolerance. It would take an equi-potent dose of another opioid to have mu-agonist effects (i.e. getting high, miosis, respiratory depression, constipation, sedation/nodding, etc).
If that same person came across say 16mg Hydromorphone, they would most likely feel its effects- because this dose of Hydromorphone is close to or above the tolerance level of the person dependant on Morphine.
This is what happens to people on MMT (Methadone Maintanence Therapy). Due to a high volume of distribution, Methadone has a very long half-life, which increases over time on MMT when high doses and daily administration are involved. The treatment protocol in the United States (and most other nations that use MMT) calls for 2 stages in MMT dose adjustment.
1) Gradually titrate (raise) the Methadone dose until the patient reaches stability (i.e. a single dose keeps them out of withdrawal for a full 24 hours).
2) Raise the Methadone dose to a point where they no longer feel cravings to use other opioids (generally 80mg-120mg+). At these dose levels, cross-tolerance becomes a factor. The Methadone dose is high enough that it would take a very large amount of Heroin or another opioid to go over the top of the cross-tolerance level. Most opioid addicts will not or simply cannot spend several hundred dollars on one high trying to 'breakthrough' their Methadone dose.
There are studies from Holland & Sweden that show some opioids, due to their rapid lipid solubility and high potency, are capable of 'breaking through' cross-tolerant levels of Methadone at lower doses. Trials were conducted using a combination of Hydromorphone & Methadone (Holland) and Dextromoramide & Methadone (Sweden). Dilaudid (Hydromorphone) is often used to treat severe pain in MMT patients hospitalized in the United States.
The ability of Methadone to "block" other opioids for several days without redosing the Methadone is due to its high volume of distribution and thus very long half-life. A person who takes a single dose of Methadone will most likely stop showing it in their urine within 2 - 4 days. An MMT patient who stops taking their Methadone will often test positive for 7- 9 days after their last dose.
It is still cross-tolerance relative to the physiological effects of the particular opioid used.
![:\](https://bluelight.org/xf/BL_Images/Orig_Emoji/wrygrin.gif "wry grin :\")
