Pharmaceutical Calcultion

Started by Jaguis
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codep1nk said:
u can use a simpler estimate...
cmax = dose/vd

still dont have vd...but if we had a weight...you could estimate that as well with the population parameter...but no weight either. thus i stick to my final answer...b/c u don't generally dose 7mg/kg of an aminoglyc unless its amikacin... Cmax = too high
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watch kidney function, dose adjust from there. no sense in dosing too low if it won't fight the infection. ****ing pseudomonas.

Cmax =28 ug/mL

Tobra has concentration dependent killing (loading dose) and plus if its a 1 time dosing, how much will it affect the kidneys.
 
Quiksilver said:
Cpeak = [Dose/CL*T(infusion time)*(1-e^-kT)*e^-kt2 (1/2 hr in this case)]/1-e^-kt (dosing interval)


I am missing a clearance.
Click to expand...

Granted I've only been out of school for a short while, but I've never seen anyone use these PK equations in practice. Those are great for class, but are too cumbersome for actual pharmacy work.
 
codep1nk said:
u can use a simpler estimate...
cmax = dose/vd

still dont have vd...but if we had a weight...you could estimate that as well with the population parameter...but no weight either. thus i stick to my final answer...b/c u don't generally dose 7mg/kg of an aminoglyc unless its amikacin... Cmax = too high
Click to expand...


Why do you need the weight?
 
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Quiksilver said:
watch kidney function, dose adjust from there. no sense in dosing too low if it won't fight the infection. ****ing pseudomonas.

Cmax =28 ug/mL

Tobra has concentration dependent killing (loading dose) and plus if its a 1 time dosing, how much will it affect the kidneys.
Click to expand...


Thank you.
 
Loading Dose = Vd X Cmax

Cmax = LD/Vd

LD = 7mg/kg
Vd = 0.25L/kg

Cmax = 7mg/kg/0.25L/kg = 28mg/L = 28ug/ml.
 
ItsOverZyvox said:
Loading Dose = Vd X Cmax

Cmax = LD/Vd

LD = 7mg/kg
Vd = 0.25L/kg

Cmax = 7mg/kg/0.25L/kg = 28mg/L = 28ug/ml.
Click to expand...


Now that's useful information. The simplicity is beautiful. I thought the same complicated way before I had applied kinetics and actually used it in practice.
 
ItsOverZyvox said:
Wrong. 0.109375 ug/ml :meanie:

0 hours - 28
3 14
6 7
9 3.5
12 1.75
15 0.875
18 0.4375
21 0.21875
24 0.109375!

:meanie:
Click to expand...

I use your methodology to solve the 2nd question, argh. well certainly its lost all of its killing ability by that point so it might as well be 0.
 
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To whom ever said about making it over complicated -- true. Most hospitals have dosing protocols with just 2, maybe 3 parameters. They are designed for expediency and shooting for a window that's "close enough", not exact number. I see my ER preceptor whip out her deck of cards all the time. I have a feeling if I ask her about a new drug without a card, just a bunch clinical test parameters, she'll be stuck because she won't know how to work the math.

But for us students, that just won't fly on our tests. Professor will give you big fat 0 for it. And if I do the simple approximation route, it would give plenty of excuses for others to say it's not right and it's not close enough. 🙂

Anyone interested in an old exam question of this type? I can dig one up from my old exams, just for fun.
 
ItsOverZyvox said:
You sound so sure.... Have you heard of PAE exhibited by aminoglycosides?
Click to expand...

I have, but is it effective even after 1 dose? How about looking at the AUC/MIC ratio, how high does it stay even after D/C and for how long, does it provide a large enough ratio to effectively cover pseudomonas?
 
Quiksilver said:
I have, but is it effective even after 1 dose? How about looking at the AUC/MIC ratio, how high does it stay even after D/C and for how long, does it provide a large enough ratio to effectively cover pseudomonas?
Click to expand...


You tell me.

How long does the PAE last?
 
xiphoid2010 said:
To whom ever said about making it over complicated -- true.

But for us students, that just won't fly on our tests. Professor will give you big fat 0 for it. And if I do the simple approximation route, it would give plenty of excuses for others to say it's not right and it's not close enough. 🙂

Anyone interested in an old exam question of this type? I can dig one up from my old exams, just for fun.
Click to expand...

Don't worry, I remember these exams quite well. I know it's not useful for you right now, but this simplified approach should prove useful on rotations.
 
xiphoid2010 said:
But for us students, that just won't fly on our tests. Professor will give you big fat 0 for it. And if I do the simple approximation route, it would give plenty of excuses for others to say it's not right and it's not close enough. 🙂
Click to expand...


Your professor can kiss my ass. Ok, so you need to get good grades and I'll give you that. But once you're out of school, saving lives is more important than worrying about tests. You'll thank the simplicity once you're out practicing.
 
Quiksilver said:
no googling, just studying Digoxin PK at the same time as this.


besides outside of you, we weren't born with this knowledge
Click to expand...


I'm not interested in you not knowing it today. But I am interested in you learning it that will benefit patient care in the future.
 
rphello said:
No one has implied that. I certainly didn't know this stuff, but I welcomed the revelation. I'm out of school and still learning.
Click to expand...
Don't take it personally, it was a jab for the google comment (he dishes it so i can assume he can take it, i'm sure he's been practicing long enough to understand a joke😀), I am happy to have the challenge of figuring this **** out. I try to use what i learn instead of just studying from test to test. Although I have probably wasted my night answering this. Thats how you learn.

ItsOverZyvox said:
You tell me.

How long does the PAE last?
Click to expand...

I really don't know, thats why I asked. I don't think we learned it other then the effect does exist and the longer the dosing interval, the shorter the PAE. I didn't think that it would provide sufficient killing just from a single dose to kill Pseudomonas. Especially if you are concerned about developing resistance. From my understanding the longer you can keep AUC/MIC ratio high, the more sucessful a treatment will be. Unfortunately, I am not too sure beyond that. If the drug is eliminated, how long can the effects last? Perhaps I can google it later when I have a little more time🙂
 
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ItsOverZyvox said:
Your professor can kiss my ass. Ok, so you need to get good grades and I'll give you that. But once you're out of school, saving lives is more important than worrying about tests. You'll thank the simplicity once you're out practicing.
Click to expand...

of course in real practice I'll just follow the hospital dosing charts just like my preceptor and go with a 'ball park figure'. But then again, you don't need a pharm.d to flip cards. Hell that preceptor is so old, they might not even have a real PK class in her days. 🙄
 
Quiksilver said:
Don't take it personally, it was a jab for the google comment (he dishes it so i can assume he can take it, i'm sure he's been practicing long enough to understand a joke😀), I am happy to have the challenge of figuring this **** out. I try to use what i learn instead of just studying from test to test. Although I have probably wasted my night answering this. Thats how you learn.



I really don't know, thats why I asked. I don't think we learned it other then the effect does exist and the longer the dosing interval, the shorter the PAE. I didn't think that it would provide sufficient killing just from a single dose to kill Pseudomonas. Especially if you are concerned about developing resistance. From my understanding the longer you can keep AUC/MIC ratio high, the more sucessful a treatment will be. Unfortunately, I am not too sure beyond that. If the drug is eliminated, how long can the effects last? Perhaps I can google it later when I have a little more time🙂
Click to expand...


Why does it have to kill pesudomonas? What does MIC stand for? So how long will the concetration be above MIC and how long will the PAE last? What is the mechanisim of action of Aminoglycoside?
 
leave for just a moment and it's a whole new convo going on...

i wanted wt b/c i wouldve calculated a pop parameter...but yes I see now that 0.25 works just fine (ah, why did not I not remember that!). I still think 28 is high if you're starting a patient...you probably just want them over 20 for your pseudomonal infection if you're using extended interval. Under 30 is apparently okay...but I was on ID under a clinician who was pretty conservative about this.

as for length of PAE...no idea? is this established? i would guess at least up to 48 hours...i've seen patients with intervals extended to Q48 with EIDA
 
codep1nk said:
leave for just a moment and it's a whole new convo going on...

i wanted wt b/c i wouldve calculated a pop parameter...but yes I see now that 0.25 works just fine (ah, why did not I not remember that!). I still think 28 is high if you're starting a patient...you probably just want them over 20 for your pseudomonal infection if you're using extended interval. Under 30 is apparently okay...but I was on ID under a clinician who was pretty conservative about this.

as for length of PAE...no idea? is this established? i would guess at least up to 48 hours...i've seen patients with intervals extended to Q48 with EIDA
Click to expand...


Why is 28ug/ml high? What's wrong with it? Why was your ID clinician conservative? Do you think it will reach 28ug/ml in vivo? Why would drug free period be perferred and help the patient?
 
SpirivaSunrise said:
I thought you had minions and secret agents embedded throughout the industry to collect data for you. Even ones who work for the competitor!
Click to expand...


but sometimes I need the data now...at my finger tips. But I couldn't get though my usual means. It's fixed now.
 
ItsOverZyvox said:
Why is 28ug/ml high? What's wrong with it? Why was your ID clinician conservative? Do you think it will reach 28ug/ml in vivo? Why would drug free period be perferred and help the patient?
Click to expand...

I was told why shoot for 30 when over 20 is fine. I'm not sure if it would reach 28 in vivo...but I'm guessing that it's a possibility. Drug free period in EIDA = still have efficacy...less toxicities.
 
codep1nk said:
I was told why shoot for 30 when over 20 is fine. I'm not sure if it would reach 28 in vivo...but I'm guessing that it's a possibility. Drug free period in EIDA = still have efficacy...less toxicities.
Click to expand...


An hour infusion with short t1/2, I don't believe it will ever hit 30. You say less toxicities. But what's responsible for nephrotoxicity of AG? But there is another benefit of drug free period. What is it?
 
ItsOverZyvox said:
An hour infusion with short t1/2, I don't believe it will ever hit 30. You say less toxicities. But what's responsible for nephrotoxicity of AG? But there is another benefit of drug free period. What is it?
Click to expand...

simple, wash out period. You need Cp < 2 mcg/ml for wash out. Hence the trough needs to be less than 2 for a signficant period of time to reduce nephrotox, which is perfect since AG has long PAE.
 
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xiphoid2010 said:
simple, wash out period. You need Cp < 2 mcg/ml for wash out. Hence the trough needs to be less than 2 for a signficant period of time to reduce nephrotox, which is perfect since AG has long PAE.
Click to expand...


Ok, so what's another major benefit of wash out period?
 
ItsOverZyvox said:
An hour infusion with short t1/2, I don't believe it will ever hit 30. You say less toxicities. But what's responsible for nephrotoxicity of AG? But there is another benefit of drug free period. What is it?
Click to expand...

toxicities = repeated high peaks?

another benefit = minimize adaptive resistance?

hah--i feel like i'm on rotation at sdn 😛
 
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