Talk:Biological half-life

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Requested move[edit]

(Biphasic half-lives)[edit]

I came here looking for data about biphasic half lives. I'll look elsewhere, perhaps a more informed person will already have contributed info before I'm able to learn and come back. 12:42, 1 March 2006 (UTC)

I certainly hope you find the information you're looking for. When you do, I hope you can summarize it and add it to the article, together with a list of sources it came from. Jonathunder 16:54, 1 March 2006 (UTC)
See one example at PMID 3765661. 22:29, 15 June 2006 (UTC)
I have added a brief section with ref to a detailed external page & a wikilink to Pharmacokinetics. D A Patriarche, BSc (talk) (talk) 00:30, 3 January 2017 (UTC)

Proposed merge[edit]

I don't see why there are three distinct articles on half-life plus an article on exponential decay, when they are all variations of the same concept. So, I am proposing some consolidation. From what I can see, at least half of the material is common to all four articles. At minimum, the half-life articles could be combined into one article with sections. Robert A.West (Talk) 00:11, 26 June 2006 (UTC)

See Talk:Half-life#Proposed merge. --Smack (talk) 22:50, 27 June 2006 (UTC)

Terminal half-life[edit]

This source says "terminal half-life" is a newer name for "Biological half-life". —Preceding unsigned comment added by (talk) 14:48, 5 January 2008 (UTC)

tautology ?[edit]

"First-order elimination This process is usually a first-order logarithmic process..." Jclerman (talk) 08:02, 30 March 2008 (UTC) "

Clinical half life[edit]

The article states: "In clinical practice, this means that it takes just over 4.7 times the half-life for a drug's serum concentration to reach steady state after regular dosing is started, stopped, or the dose changed."

Where does 4.7 come from? I've heard some clinicians use 4, and others 5. At time X half lives, the percent of steady state concentration is 1-0.5^X. So at:
4 HL -- > 93.75%
4.32 HL --> 95%
4.7 HL --> 96.15%
5 HL --> 96.875%

As you can see, the value 4.7 is totally arbitrary. I suggest replacing "just over 4.7 time" with "4 to 5 times." —Preceding unsigned comment added by (talk) 23:04, 11 February 2009 (UTC)

Correct. 4.7 isn't used in pharmacokinetics. Changed according to your suggestion. →Alfie±Talk 00:42, 13 March 2010 (UTC)

Plasma and biologic halflife[edit]

I understand this article uses the MeSH definition of "biological half-life", but perhaps it should be less ambiguous and state other possible meanings. If you take a look at this book, for example, two terms are defined: the plasma half-life and the biologic half-life. The plasma half-life describes the time taken for the blood plasma concentration of a drug to half, and the biologic half-life describes the time taken for the effect of the drug to half (coincident with the current article). I am going to add this ambiguity to the lead of the article. --Oldak Quill 19:22, 2 May 2009 (UTC)

Equation relating half life to clearance and VD[edit]

The equation relating half-life to clearance and VD uses non-standard terminology. There is a dot out of place. —Preceding unsigned comment added by (talk) 19:17, 4 May 2009 (UTC)

Right, but why don't you correct it yourself? →Alfie±Talk 00:52, 13 March 2010 (UTC)

LD50 and ED50[edit]

I have reverted an edit by Miserlou since LD50 and ED50 didn't seem relevant to the article since it does not discuss pharmacology and doesn't come close to discussing either of these properties of a substance. I thought I'd give Miserlou the opportunity to explain why he disagrees. GiftigerWunsch [TALK] 07:06, 10 May 2010 (UTC)

No objection, thank you for bringing this to talk and notifying me on my page. Very cordial of you. Miserlou (talk) 07:13, 10 May 2010 (UTC)

What about half-life in this case (i.e. Methadone)?[edit]

As you can read in the Methadone article (in the Chembox in the upper-left corner) that the half-life of Methadone is 24-36 hours and below under Metabolism section that it can actually range from "... as few as 4 hours to as many as 130 hours". But this is not the main point of my post.

You see, in this section there's nothing mentioned about one certain speciality of Methadone, which is that the actual level of the drug in blood (SML - Serum Methadone Level) is increasing for the 4-5 days until the level of Methadone in blood becomes "stable" (i.e. it's not increasing anymore). I mean, after the initial doze is taken, then after 24 hours when a patient takes another doze, he/she still has half of the previous day's doze in his/her blood serum, therefore the half-life on the 1st day is not the same as on 2nd day (and so on until 5th day).

So what I want to point out is that one "type" of half-life if a drug is consumed just once (and then flushed out of the system), compare to if a drug is consumed one day after another (i.e. more than one day would be enough to make a point in this case).

Please for better understanding what I mean (am trying to say), see Figure 1 on the 2nd page in this Dosing and Safety .pdf file. --Wayfarer (talk) 23:56, 22 October 2010 (UTC)

Examples of biological half-lives[edit]

That section needs a lot of adjustments. First, the part on alcohol is more than confusing since it ends up that in the human body, alcohol does not follow an exponential decay. This is more of a counter-example than an example in the end and should be emphasized. Then, the table containing half-lives of some prescription drugs is a bit void and useless. First, we have a very large collection of drugs and their half-lives, why did these drugs get selected in this table? Then, what is the purpose of that table? I think some extra-information could be interesting. Some more explanations on why does the body eliminate these drugs following exponential decay when it doesn't for say alcohol would contain some valuable information. 313.kohler (talk) 19:12, 20 January 2011 (UTC)


Are the references to "alcohol" and "water" reversed in regard to large volume drinkability in Section 1.1? — Preceding unsigned comment added by LSTech (talkcontribs) 18:03, 28 March 2011 (UTC)

Importance of half life[edit]

What about the importance of half-life, such as that shorter half life means increased frequency of administration? — Preceding unsigned comment added by (talk) 15:33, 9 June 2012 (UTC)

Metals - Mercury[edit]

at the other metals it sais "biological half-life", at mercury it only sais "half-life". might this be a lapse or another kind of error?Aracadonic blacksmith (talk) 20:03, 15 December 2013 (UTC)

first order elimination[edit]

Can someone verify that in first order elimination the half-life "is proportional to the initial concentration of the drug A0"? I thought it should be a constant independent of concentration. Yel D'ohan (talk) 22:06, 31 July 2015 (UTC)

That whole section seems confusing and possibly wrong in places. Half-life is only meaningful for first-order kinetics ? Constant elimination rate is zero-order kinetics ? Alcohol, and eg. methotrexate, kinetics could be used in more detail to clarify. - Rod57 (talk) 13:07, 16 October 2016 (UTC)

Solubility Limitation[edit]

Forgive me if this is dealt with in the article but I did not see any discussion of the biological half-life or excretion rate change once the point of a substance's [Solubility] in the body is reached. For example, the biological half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin from the human body is fairly rapid, until its solubility in human adipose tissue is reached at a range of 5-20 parts per trillion, then becomes more less stable at that concentration in body fat. Solubility is an important limitation of the biological half-life concept for substances that are soluble in fat, plasma, etc. It deserves prominent discussion. Marbux (talk) 05:21, 22 October 2015 (UTC)

half-life of alchohol[edit]

Why does this not include the half-life or speed of elimination of alchohol/ethonol? — Preceding unsigned comment added by 2601:540:C001:FFB0:607E:E192:A5D9:3D05 (talk) 19:03, 27 October 2015 (UTC)

There is (now) a discussion of ethanol kinetics. Although technically it doen't belong in this article as ethanol has 0-order (constant-rate) kinetics and therefore half-life does not apply, I'd keep the section as it clarifies a common confusion. D A Patriarche, BSc (talk) (talk) 23:45, 2 January 2017 (UTC)

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