T Nation

What Is Distributional Half-Life?

I’ve got a question for Cy, or anyone else who can shed some light on this for me. What is the difference between the initial or distributional half-life of a drug and its terminal half-life?

The issue came up because a person was asking whether EOD dosages of Nolva was alright, or if they needed ED dosages. I responded that I thought EOD was fine, as the half-life of Nolva is 5-7 days. Another person then said that Nolva needed to be taken ED, as the initial (or distributional) half-life was only 7-14 hours.

What the hell is the initial or distributional half-life, and how does it figure into proper doseing schedules? This person also said that there are no studies showing the effectiveness of EOD dosages of Nolva.

Thanks for the help,

Crowbar

And while we are at it can someone give a scientific reference to half-life versus active-life. I understand that half-life is the amount of time it takes for half of the dose to be gone. But the active life seems to be in dispute.

Most “in the know” people say that every “X” days their is half of the substance left. This is where saying deca is still in your system for six weeks comes from, even though it’s half-life is only a week. Others like Author Ray imply that the active life is merely 2x the half-life. Obviously their is still some left after this period, but is it enough to be counted or suppressive? If you use something like roidcalculator.com it takes forever for things to clear. But personal experience tells me that I can start recovery far sooner than the drug is cleared according to the traditional way.

What I want is an explaination of drug metabolism. According to the blood panels I have seen, there is a high peak (in days) and then a pretty slow drop off.

I’m no expert, but I think the ‘active life’ is going to be different for different substances. Where some might have pharmacologically relevant effects at some miniscule serum concentration, others may not, so that is going to be very specific to the compound at hand.

Out of curiousity I referred to my Remington’s Pharmaceutical Sciences, already notorius for it’s poor information about AAS, as it has a lengthy discussion of basic pharmacokinetics. As yet I haven’t cracked the code, so to speak, about distributional half life. I’ll also offer that to fully understand the elements of drug action and pharmacokinetics, at least from my readings will require a working knowledge of some pretty heavy mathematics, calculus I and II kind of stuff, so be forewarned.

Conor