Benzos Don't fully understand half life

[illmantos]

Could someone help me out a little with this please , for example if I take 4mg of etizolam (which I believe has a half life of 6-8 hours) at sat 9am and another 4 mg at 6pm same day by Sunday morning 9am would I still have a considerable amount of etizolam in my system still, as this is when I start work and don't want to appear or feel still under the inflluence.
Thanks in advance for any replys.

Half life is when the drug or particle has fully disposed of one half of its self, usually used for radioactive items and carbon dating.

 

[Kid Amine]

keep in mind that while many drugs metabolize into inactive metabolites, some drugs, like diazepam, have active metabolites that can have even longer half lives than the parent drug. Diazepam is the example I use for this; it has several active metabolites, one of which I believe has a half life of close to 24 hours. I dont know the pharmokinetics of the drug the the OP mentions but it definitely something to keep in mind.

Also, many drugs have hugely variable half lives depending on individual metabolism, and sometimes based on ROA. Wiki lists the half life of methadone as 15-60 hours, quite a big range. and the half life of fentanyl IV is a matter of minutes vs hours if taken via wearing patches.

 

[NonEuthymicBoy]

ok. this thread is quite old but I couldn't find a newer one about the same thing. My questions:

1. Amphetamine has a ~12 hours half-life, and a single dose of let's say 30 mg dexedrine lasts me only 3-4 hours. So when I take my second dose after 4 hours, I still have ~20 mg in my system, resulting in an increase to 50 mg. Then why it doesn't has a increased effects as it builds up in the blood?
2. I know the drug has a threshold, so if I simple take 60 mg alltogether, shouldn't the effects last the double considering the half-life principle? 60 mg 12hr -> 30 mg.

I'm confused.
thanks guys!

 

[Swimmingdancer]

ok. this thread is quite old but I couldn't find a newer one about the same thing. My questions:

1. Amphetamine has a ~12 hours half-life, and a single dose of let's say 30 mg dexedrine lasts me only 3-4 hours. So when I take my second dose after 4 hours, I still have ~20 mg in my system, resulting in an increase to 50 mg. Then why it doesn't has a increased effects as it builds up in the blood?
2. I know the drug has a threshold, so if I simple take 60 mg alltogether, shouldn't the effects last the double considering the half-life principle? 60 mg 12hr -> 30 mg.

I'm confused.
thanks guys!

That's a really good question and I don't know how to explain it briefly. People have written entire papers on the subject.

The posts above equating half-life with how many milligrams are in your body are misleading. (and unless injecting the drug, you are not getting 100% absorption to the blood from the drug you take anyway). It's not actually accurate to say if you took 20mg of XYZ drug and its half-life was 12 hrs, then at the 12 hr point you would have 10mg left in your body. And it leads to confusion because then people think at the 12 hr point they should be experiencing effects equivalent to if they took 10mg of the drug, which obviously, as you have found, they are often not.

The half-life usually refers to the amount of time (which is a mean from the people studied and can actually vary significantly from person to person) it takes for the blood plasma concentration of the substance to halve its steady state, (or half to be excreted/eliminated from the body, depending on the drug and the way they are measuring its half-life). The relationship between the half-life of a substance and the drug's actual effects is complex, due to various factors including: the relationship of the actual blood concentration to a minimum effective/threshold concentration, the relationship of blood concentration to actual effects of the drug, active metabolites, accumulation in tissues/organs, and the body's response to the drug like receptor and metabolic interactions, (for example, your brain/body can respond to the drug's presence, creating a sort of temporary tolerance).

Having half the drug left in your body or blood is not the same as having half of it in your brain or activating the receptors in your brain. Does that make sense?

Depending on the drug, the dose you take can make a difference in the duration of effects however, since for drugs where the effects do correspond to the blood concentration then you will have a blood concentration that is above the threshold needed for noticeable effects for a longer period of time. But it is rarely strictly as simple as take 2x the quantity get 2x the duration.

 

[laCster]

I agree with mostly everyone, but id like to add that half life does not exactly mean how long the high will last. For example, LSD has a 1-3 hour half life but its effects last around 12 hrs.

 

[Swimmingdancer]

Very true. A few of us did mention that

Half life is when the drug or particle has fully disposed of one half of its self, usually used for radioactive items and carbon dating.

^That is biological half-life which is a different thing from a drug's pharmacological of elimination half-life in the human body.

 

[NonEuthymicBoy]

That's a really good question and I don't know how to explain it briefly. People have written entire papers on the subject.

The posts above equating half-life with how many milligrams are in your body are misleading. (and unless injecting the drug, you are not getting 100% absorption to the blood from the drug you take anyway). It's not actually accurate to say if you took 20mg of XYZ drug and its half-life was 12 hrs, then at the 12 hr point you would have 10mg left in your body. And it leads to confusion because then people think at the 12 hr point they should be experiencing effects equivalent to if they took 10mg of the drug, which obviously, as you have found, they are often not.

The half-life usually refers to the amount of time (which is a mean from the people studied and can actually vary significantly from person to person) it takes for the blood plasma concentration of the substance to halve its steady state, (or half to be excreted/eliminated from the body, depending on the drug and the way they are measuring its half-life). The relationship between the half-life of a substance and the drug's actual effects is complex, due to various factors including: the relationship of the actual blood concentration to a minimum effective/threshold concentration, the relationship of blood concentration to actual effects of the drug, active metabolites, accumulation in tissues/organs, and the body's response to the drug like receptor and metabolic interactions, (for example, your brain/body can respond to the drug's presence, creating a sort of temporary tolerance).

Having half the drug left in your body or blood is not the same as having half of it in your brain or activating the receptors in your brain. Does that make sense?

Depending on the drug, the dose you take can make a difference in the duration of effects however, since for drugs where the effects do correspond to the blood concentration then you will have a blood concentration that is above the threshold needed for noticeable effects for a longer period of time. But it is rarely strictly as simple as take 2x the quantity get 2x the duration.

yeah sure there's the bioavailability, I just wanted to be more direct and forget it ha.

"Having half the drug left in your body or blood is not the same as having half of it in your brain or activating the receptors in your brain. "
This! makes sense, never thought about it, gonna google it.
receptor desensitizasion and receptor internalization are things very complex too. My wuestions were pure mathemathical where in biochemistry is not "2 and 2=4". Thanks you guys, I love this forum.

 

[NonEuthymicBoy]

I agree with mostly everyone, but id like to add that half life does not exactly mean how long the high will last. For example, LSD has a 1-3 hour half life but its effects last around 12 hrs.

uau. LSD always lasted me at least 6 hours. I took infinites times and I needed just half of an original bike (bike 100). The max i took was 2 and things turned blue. awesome. This summer I will do it again (South Hemisfere, Brazil) it's comming! =)

 

[NonEuthymicBoy]

Heroin has 30 min half-life and 3-4 hr half-life for it's Morphine metabolite. I never did heroin but most say it last a long time, so btw half life doesn't precisely show how long effects lasts.