Misc Half-Life Question

[KidNapster]

I've never actually fully understood half-lives. If a half life of a substance is 24 hours, that means that in 24 hours half the drug has been eliminated, and then another 24 hours half of that half is eliminated correct? The question that ive been wondering is how people usually use the term half life when talking about drugs and how when they say the half life is lets say 12 hours that that means thats how long it lasts. is that a basic explanation to say in 12 hours you wont be feeling the effects anymore?

 

[BrokedownPalace]

The first part of your post is correct - half lives are exponential, not linear.

But the second part, is incorrect. Half life doesn't directly correlate to how long recreational effects are felt.

 

[KidNapster]

ah i see thank you. But do you know why though many refer to a half life being the time to redose? even though there is still the drug remaining. One example i can think of that relates to me is being on 8mg of Suboxone daily. so since i took one 8mg strip today, tomorrow at the same time around it should be down to around 4mgs right? from there another 24 hours would make it down to 2mg. Since the bupe is still in my system for over 24 hours wouldn't that mean that the 4mg tomorrow should be enough for me to hold off for at least another day without having to re-dose?

 

[rollingstoned!]

From wikipedia:

"Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half.

A half-life describes the decay of discrete entities, such as radioactive atoms. In that case, it does not work to use the definition "half-life is the time required for exactly half of the entities to decay". For example, if there is just one radioactive atom with a half-life of 1 second, there will not be "half of an atom" left after 1 second. There will be either zero atoms left or one atom left, depending on whether or not the atom happens to decay"

 

[Captain.Heroin]

Not all drugs have half lives. Drugs are metabolized based on zero order kinetics or first order kinetics. The only drug I could think of that anyone here would use as a recreational drug, and wouldn't have a half life as it would be metabolized based on zero order kinetics, would be ethanol.

I'm sure knowing this is going to further confuse you... but don't let it. Try to take it all in and memorize it.

Why is this not merged into the BA/HL MT?

But do you know why though many refer to a half life being the time to redose?

If someone is using a SSRI to counteract depression/suicidal ideation, they are going to want a steady blood level of the drug; hence dosing on a regular schedule based on its half life is very necessary. When tapering you'll want to switch over to another SSRI with a longer half life so you're not as likely to have brain zaps/"SSRI discontinuation syndrome".

If someone is using heroin/cocaine/methamphetamine, it's more about when they want to re-dose and not so much the half life.

 

[KidNapster]

thanks captain. yes a little confusing but im gonna take it in as you said. Sorry if it was a little too specific of a question or anything; i really like understanding the whole mechanics behind this/how drugs work

 

[Znegative]

ah i see thank you. But do you know why though many refer to a half life being the time to redose? even though there is still the drug remaining. One example i can think of that relates to me is being on 8mg of Suboxone daily. so since i took one 8mg strip today, tomorrow at the same time around it should be down to around 4mgs right? from there another 24 hours would make it down to 2mg. Since the bupe is still in my system for over 24 hours wouldn't that mean that the 4mg tomorrow should be enough for me to hold off for at least another day without having to re-dose?

Not exactly because with drugs with long half life's like methadone and buprenorphine, the daily dose you take is not necesairily the exact amount of how much of the drug is still left in your system. For instance buprenorphine has an approximate half life of 36 hours, so each 8 mg dose that you take builds upon what's left of the last dose. So if you take bupe for the first time, 8 mg, and then dose another 8mg the next day you have a little over 12mg total in yr system. After about twelve days on one dose of buprenorphine, the half life's start to repeat the cycle, or more accurately the total amount of buprenorphine at any given time stays the same, it does not go up or down as long as you keep taking it. I think after 12 days of being on 8mg a day, you actually have approximately 20mg of buprenorphine in your system. This was a real disappointment when I first learned about it haha.

 

[KidNapster]

Znegative i see what youre saying and that does make sense. That kinda goes back to my question which would be since you still have bupe in your system with a half life of 36 hours, wouldnt it be unnecessary to re-dose daily at the same time since youre only adding to whats left of your last dose?

 

[HYDRO_CHRONIC]

or to just dose enough to keep u at intended doseage? 8mg then 36hrs later just 4mg?

confusion!!actually im listenin to AIC -confusion right now

 

[Znegative]

Znegative i see what youre saying and that does make sense. That kinda goes back to my question which would be since you still have bupe in your system with a half life of 36 hours, wouldnt it be unnecessary to re-dose daily at the same time since youre only adding to whats left of your last dose?

Yeah although it depends on what dosage your on. If your under four mg I find it to be increasingly harder to skip days between dosages because you are under the cieling level, and are experiencing ups and downs more as fare as buprenorphine blood levels go, that's one of the reasons you also feel the bupe more when you're on a lower dosage, because while the half life stays the same, the drop in blood levels is felt more intensely because you're dipping below the point at which all the receptors are saturated, so each time you dose there is a more defined lift or relief from the bupe.

If you're on a dose like sixteen mg (with an approximate 40mg buildup) you can probably wait three days between dosing without feeling any negative effects, as after 72 hours you would still have five mg of buprenorphine in you. But you might as well just drop to a low dosage like two mg, which would give you, according to these numbers a buildup of 5mg in your system, after the twelve or so days it would take to skin the half life of your previouse dosage. Sorry if that's a bit confusing hah

 

[KidNapster]

ive heard about the whole low dosage thing allowing you to achieve more profound effects but i think that might also have to do with norbuprenorphine

 

[Znegative]

Yeah, there's that theory too, that lower dosages of buprenorphine allow for the norbuperenorphine to bind to the empty receptors. However I'm not sure if that's really a proven fact, as I think I read that norbuperenorphine has a real hard time crossing the blood brain barrier.

 

[KidNapster]

im guessing that would be something similar to how Loperamide is closely related to fentanyl (which i think i remember reading somewhere about that) but has the same problem and doesnt cross the blood brain barrier as well.

 

[Znegative]

Right exactly, but the difference is that nor buprenorphine is a metabolite of buprenorphine just as oxymorphone is a metabolite of oxycodone. The thing I don't really understand about the norbupe theory is wether buprenorphine actually leaves receptor sites empty at a low dosage, which could then allow for norbupe to fill them in, or if buprenorphine doesn't work that way at all, and still activates the same amount of receptors, just not as strongly, in which case it would antagonize the norbupe. Anyway sorry this is getting off topic