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Author Topic: Phenotypic and Genotypic Testing  (Read 2317 times)

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Offline nvhorseman

  • Member
  • Posts: 14
Phenotypic and Genotypic Testing
« on: December 19, 2007, 01:32:08 PM »
Dear All:  I would like a response from a person with professional credentials to answer this one please (no insult intended). 

If you have an undetectable viral load of a long duration, is it not necessary to stop and HIV medication, regrow the virus(viruses) and then test phenotypically or genotypically ??  Does this not lead to at least a possibility that the new regrown virus will be inactive against your old meds and you will have to start a new drug or drug combo?  Thanks for your reply

Offline newt

  • Member
  • Posts: 3,887
  • the one and original newt
Re: Phenotypic and Genotypic Testing
« Reply #1 on: December 19, 2007, 04:49:18 PM »
I have no professional credentials.  If you want a professional answer ask a doctor.

But my answer to your Q...

...the purpose of combination therapy is to reduce viral load to "undetectable" (ie less than 50 copies/mL of blood).

If your viral load is consistently 50 copies or lower then treatment is working, resistance not occurring and a genotype or phenotype test is of no value -- indeed will not work under this circumstance. 

If your viral load goes above 500 on two consecutive viral load tests then a genotype and sometimes a phenotype resistance test may be of value to determine which drugs will work best next.

There is no need -- and indeed it is undesirable and pointless -- to interrupt treatment just to do one or both of these tests.

- matt

(anyone wanna back me up? Tim H?)
"The object is to be a well patient, not a good patient"

Offline Tim Horn

  • Member
  • Posts: 799
Re: Phenotypic and Genotypic Testing
« Reply #2 on: December 19, 2007, 07:04:52 PM »
Nothing much to add to Newt's sage comments.

I guess it's hard to expand further without more context from you, nv. You raise one question that might warrant additional feedback:

Does this not lead to at least a possibility that the new regrown virus will be inactive against your old meds and you will have to start a new drug or drug combo?

Generally speaking, if someone stops therapy abruptly, drug levels in the blood quickly diminish and the virus rebounds without acquiring drug-resistance mutations along the way. This is usually what happens for folks who choose -- or need -- to abruptly stop treatment with a protease inhibitor-based regimen that also includes nucleoside reverse transcriptase inhibitors (NRTIs). This is NOT the case if someone is on a non-nucleoside reverse transcriptase inhibitor (NNRTI)-based regimen, such as Sustiva or Viramune. These drugs have very long half-lives, meaning that they are very slow in being eliminated from the body. Thus, if you were to abruptly stop, say, Atripla (with its Sustiva, Viread, and Emtriva), the Viread and Emtriva levels would quickly drop, leaving Sustiva lingering all by its lonesome in your body. And this isn't good -- this would be akin to using Sustiva monotherapy for a week or so, which is enough time for the virus to develop the K103N mutation and, consequently, full-on resistance to Sustiva and cross-resistance to other available NNRTIs. In turn, if a Sustiva-based regimen needs to be stopped, it is very important to stop the Sustiva several days before the NRTIs are stopped.

But going back to your original question, no... there's absolutely no reason to stop a virologically effective regimen to "regrow" the virus and then conduct drug-resistance testing. There's simply no need to go looking for something that clearly isn't broken.

Tim Horn
« Last Edit: December 19, 2007, 07:12:36 PM by Tim Horn »

Offline J.R.E.

  • Member
  • Posts: 7,280
  • Joined Dec-2003 Living positive, since 1985.
Re: Phenotypic and Genotypic Testing
« Reply #3 on: December 19, 2007, 08:12:43 PM »


If your viral load is consistently 50 copies or lower then treatment is working, resistance not occurring and a genotype or phenotype test is of no value -- indeed will not work under this circumstance. 

If your viral load goes above 500 on two consecutive viral load tests then a genotype and sometimes a phenotype resistance test may be of value to determine which drugs will work best next.

There is no need -- and indeed it is undesirable and pointless -- to interrupt treatment just to do one or both of these tests.

- matt

(anyone wanna back me up? Tim H?)



I also, do not have professional credentials, but, the above quotes from Matt is precisely what my doctor has told me on several occasions , when I have asked.


Take care-----Ray
Current Meds ; Viramune, Epzicom, 40mg of simvastatin, 25 mg of Hydrochlorothiazide.
Metoprolol tartrate 25mg



http://forums.poz.com/index.php?topic=40802.0

http://forums.poz.com/index.php?topic=45159.0

http://forums.poz.com/index.php?topic=39722.msg495621;topicseen#msg495621

http://forums.poz.com/index.php?topic=46806.0

http://forums.poz.com/index.php?topic=39414.msg491701#msg491701


Diagnosed positive in 1985,.. In October of 2003, My t-cell count was 16, Viral load was over 500,000, Percentage at that time was 5%. I started on  HAART on October 24th, 2003.

 As of 12/10/14,  t-cells are at 350,  Previous 8/25/14--- 402/ Viral load remains <40

 Current % is at 13% / Previous 8/25/14 11%

  
 63 years young.

Offline HIVworker

  • Member
  • Posts: 918
  • HIV researcher
Re: Phenotypic and Genotypic Testing
« Reply #4 on: December 20, 2007, 02:05:56 AM »
One note to add to the good advice above. If you stop meds and do testing it is possible that a resistant virus is created by the mechanisms described above but will be at low enough levels as to not be detected by current standard tests. Going back on meds would reveal it if it were present at low levels. Now don't panic, because it is not certain that a mutation will be generated -- just a note of caution when getting geno/pheno tests after stopping treatment and having the viral load rebound - only the fit viruses will predominate.

R
NB. Any advice about HIV is given in addition to your own medical advice and not intended to replace it. You should never make clinical decisions based on what anyone says on the internet but rather check with your ID doctor first. Discussions from the internet are just that - Discussions. They may give you food for thought, but they should not direct you to do anything but fuel discussion.

Offline nvhorseman

  • Member
  • Posts: 14
Re: Phenotypic and Genotypic Testing
« Reply #5 on: March 15, 2012, 03:04:56 PM »
Thanks to everyone who answered my queries. You were all correct in some way and no one gave an incorrect answer. I went to the NIH and they pretty much said the same thing. So thanks to all and I am sooooo sorry that I have let sooooo much time go by without thanking you. Life just speeds up when you are dealing with all this and trying to take care of the "normal" things in life too. Thanks again.

 


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