Some results from my Depo-T Absorption Calculator

[Ruper]

If that graph were litterally true then injecting every 2-4 weeks would result in zero test levels after 10 days. - Or at least base levels, which since you system is shut down, would be basically zero T after 2 weeks.

In fact that graph shows a strikingly linear decrease with time - so much so that I'm very suspicious. Of course I don't have the whole article in front of me and it is more than 25 years old!

PS. I'm not saying I have evidence for an exactly exponential decay. In fact, the very fact that we cannot come up with a decent amount of real data is somewhat disturbing.

 

[pmgamer18]

Have you all read this link.
http://forum.mesomorphosis.com/attachment.php?attachmentid=6413&d=1139879356

 

[chap]

nice article pmgamer

the graphs in that article look like they basically agree with the graph I posted

and yes, I believe if you inject every 2 to 4 weeks you will be riding a rollercoaster of extremes from zero to high

 

[Ruper]

Have you all read this link.
http://forum.mesomorphosis.com/attachment.php?attachmentid=6413&d=1139879356

Yup, that's where I got my initial guess of 12 days 1/2 life, but my brain wasn't working - 10-2 = 8, not 12!

That is probably the best example I have seen, and supports an 8 day 1/2 life which seems reasonable to me.

The other info I personally know about is John's 'HCG update', where he quotes 5-8 1/2 life for cypionate (I presume from his own experiences?).

I have seen nothing about the HCG response in doses John gives in humans.

 

[chap]

That is probably the best example I have seen, and supports an 8 day 1/2 life which seems reasonable to me.
.

How do you get an 8 day half life out of the graphs there? It shows testosterone returning to basal between 10.5 and 14 days.... if it was an 8 day half life, after 14 days there should still be approx. 1/4 of the depot still active!

The article also plainly states that cypionate and enanthate have virtually identical pharmacokinetics.

 

[Ruper]

How do you get an 8 day half life out of the graphs there?

Figure 1. The peak occurs on ! day 2 at ~1300. So 1/2 of 1300 is 750 which occurs ~ day 10 - Therefore 8 days. Well, OK, maybe 7 days! Also it looks like the decay is levelling off, rather than linear.

 

[chap]

since when did a half life calculation have anything to do with the numbers of days between the peak concentration and half of that peak?

 

[Ruper]

if it was an 8 day half life, after 14 days there should still be approx. 1/4 of the depot still active!
.

There is. As I understand these are the steady-state values. In other words after 5 or more injections - thus the levels will by default decay to 'basal' levels after 14 days.

If the same injections were given every 7 days, they would still fall to basal levels after 7 days - the difference is that the peak and basal levels would be a lot higher. - You are stacking multiple decay curves on top of each other untill you get to a steady-state - i.e. the same peak and trough after each injection.

 

[chap]

The only way to measure a drugs true 'half life' is starting from the initial injection only, the charts in both studies clearly show that levels returned to basal between 10 and 14 days.

'Half life', which isn't a very accurate model to follow in biochemical systems anyway, refers to the time it takes from initial injection for half of the drug to be delivered (or metabolized if it is a metabolism 'half life'). Following the incorrect assumption that drug pharmacokinetics are rigid like the half-lifes of isotopes, you can then wrongly assume that the half life would indicate the next elapsed time until 1/4 more of the drug is delivered, and so on....

This is painful when we are all looking at the same black and white data and somehow it is not entering your brain the same way. Look at the graph, it says "initial injection" and shows a level; betweeen 10.5 to 14 days later the testosterone has returned to that basal level, yet you somehow see that as 1/4 of the depot still being delivered. I can't argue about this anymore when it is there in black and white.

 

[Ruper]

since when did a half life calculation have anything to do with the numbers of days between the peak concentration and half of that peak?

Err, OK. Look, forget the math. I assume from this comment, and your previous ones that you are essentially saying that the description in terms of radioactive decay/1/2 life etc.. is bogus because that is not the same mechanism that is occurring biologically. Fine, that could well be true. We are just trying to mathematically describe the response of T in a person to an injection. It really doesn’t matter what equation we use, IF that represents a close approximation to the curves seen in practice.

But if I want to mathematically describe the curve in that figure as the testosterone levels fall, I can do so using an exponential with a ½ life of ~7-8 days. Although there are reasons to suggest that the action might be close to a radioactive decay type processes, I don’t think anyone has actually said that they know that the process is the same a mineral formation followed by radioactive decay.

If you use that graph (or 8 day 1/2 life) as a response to injection, you can stack up the graphs as if you gave injections every 7 days instead of 14 days, reduce the area under the curve to account for injecting less testosterone and basically get the figures ASaxon quoted - or for that matter in the steroid calculation link.

I do, however, think the time to peak is somewhat important, since it describes when the decay part of the curve occurs , and how many decay days to the next injection.

 

[Ruper]

The only way to measure a drugs true 'half life' is starting from the initial injection only, the charts in both studies clearly show that levels returned to basal between 10 and 14 days.

You just shot yourself in the foot with that comment.

EDIT - you are correct though that the way I describe is poor and probably only worked because of the time between injections (see comment below).

 

[Ruper]

'Half life', which isn't a very accurate model to follow in biochemical systems anyway, refers to the time it takes from initial injection for half of the drug to be delivered (or metabolized if it is a metabolism 'half life'). Following the incorrect assumption that drug pharmacokinetics are rigid like the half-lifes of isotopes, you can then wrongly assume that the half life would indicate the next elapsed time until 1/4 more of the drug is delivered, and so on....

You may well be correct - I don't know much about biochemical systems, I'm a physicist, not a biologist.

 

[Ruper]

This is painful when we are all looking at the same black and white data and somehow it is not entering your brain the same way. Look at the graph, it says "initial injection" and shows a level; betweeen 10.5 to 14 days later the testosterone has returned to that basal level, yet you somehow see that as 1/4 of the depot still being delivered. I can't argue about this anymore when it is there in black and white.

OK, you need to think about what is going on here.

Let me ask you, why is is that John says to wait 5 weeks for weekly injections before taking blood? Because you are stacking one injection on top of another - you don't reach equilibrium for ~5 weeks.

In the example, not only is the patient getting 1/4 of the dose from the injection 14 days before, but a fraction of the dose from the previous injection, and the one before that etc.. etc..

 

[Ruper]

Figure 1. The peak occurs on ! day 2 at ~1300. So 1/2 of 1300 is 750 which occurs ~ day 10 - Therefore 8 days. Well, OK, maybe 7 days! Also it looks like the decay is levelling off, rather than linear.

Actually point taken by chap - this is a very bad way of estimating the 1/2 life.

Actually what I did was to try to replicate the curves using my 1/2 life model with a time-to-peak at 48 hours and came up with 8 days. Chap is correct that in the steady-state, the above is not correct. However, it is not true that you cannot compute the 1/2 life in the steady-state.

However, it is probably close because the 1/2 life is about 1/2 the interval between injections. For weekly, or Q3D shots the above logic would fail.

 

[pmgamer18]

You may well be correct - I don't know much about biochemical systems, I'm a physicist, not a biologist.

I am an retired Quality Control Engineer up on SPC you guys are beating a dead horse. No one is right and no one is wrong you just don't have enough data to do anything. My GOD does my Head hurt.

 

[ASaxon]

nice article pmgamer

the graphs in that article look like they basically agree with the graph I posted

and yes, I believe if you inject every 2 to 4 weeks you will be riding a rollercoaster of extremes from zero to high

I dont mean to pop your bubble but those graphs show a half life of about 7 days (last time I checked thats a lot closer to 8 days than 4.5) and to top it off its for Testosterone enanthate not Testosterone Cypionate. They may slop like your graph the check the days at the bottom!

 

[ASaxon]

OK, you need to think about what is going on here.

Let me ask you, why is is that John says to wait 5 weeks for weekly injections before taking blood? Because you are stacking one injection on top of another - you don't reach equilibrium for ~5 weeks.

In the example, not only is the patient getting 1/4 of the dose from the injection 14 days before, but a fraction of the dose from the previous injection, and the one before that etc.. etc..

That’s a good point. If the drugs were out of the system in 10 to 14 days then your blood work should be stable by the 14th day. Why wait 5 to 6 weeks for bloodwork? The reason is because the injections don't decay like that.

Chad also dosen’t recognize that just because the test subject's T levels have returned to basal doesn’t mean that the injection has fully decayed or been completely absorbed. When people do TRT their natural production of T shuts down. So if someone was at the same basal level in two weeks it’s not because their back to their basal T production, which is a lot lower than when they took the injection, but because the Testosterone injection is still decaying and proping up the measured Testosterone at the basal levels. Why chad can’t see that I’m not sure…

 

[chap]

well, I doubt that testosterone shuts down enough in one injection to account for that, but it may cause a variance, also I believe the studies were done on already hypogonadal men

also, the reason for waiting to do bloodwork might have more to do with the fact that many hormones are disrupted by exogenous testosterone shots, so the extra time is needed for the body to return to a more meaningful testable stasis

 

[Ruper]

Why chad can’t see that I’m not sure…

I'm not sure either because he correctly pointed out that you can't really use that graph in a simplistic manner to get the 1/2 life in the way I initailly described.

However, just from the rate of decay one can see that the 1/2 life is closer to 7-8 days than 4 days and if you model that curve (i.e. decay from the peak) using a radioactive decay equation (with or without an initial ramp-up on each injection), you will get a 1/2 life of about 7-8 days.

He does have a point though, which is that we may not be using the correct model and that the 1/2 life is meaningless. However, for us interested in replicating that graph, the decay model works and I have not seen another model that does as good a job. In addition, any other model could not decay substantially faster than a radioactive decay model with 1/2 life of 7-8 days and still fit those data.

Of course that is only one example. I whould have thought there whould be more available and people like Dr. John would have a ton of results, even if they are individually confidential.

Also I should mention that the time to steady-state is partially contolled by the 1/2 life. For a 4 day 1/2 life one would only have to wait 3 weeks to reach steady-state with weekly injections and not front-loading the first injection. For 8 day 1/2 life it is ~5 weeks (although ~3 weeks with a doubling of the first injection).

Hey I just got a cool result. Try doubling up the first injection and put in a 1/2 life of 4 days with weekly injects - I don't think anyone would do that in practice if they thought the 1/2 life was only 4 days!

Now my head hurts!

 

[ASaxon]

also, the reason for waiting to do bloodwork might have more to do with the fact that many hormones are disrupted by exogenous testosterone shots, so the extra time is needed for the body to return to a more meaningful testable stasis

Even if you were just testing Testosterone levels and nothing else you would still wait 5 to 6 weeks.