Pharmacokinetics Question

[Anon15489878]

Stuck on a question, any help would be great!!!

A novel anabolic steroid was found to be cleared from the plasma via the following routes and at the corresponding rates:
Metabolism km = 0.175 hr
Excretion by kidneys kr = 0.150 hr
Excretion via bile kb = 0.50 hr
Excretion by salivary gland ks = 0.01 hr
(a) What is the plasma half-life of the drug?
(b) What would the plasma half-life be if the metabolism of the drug was completely blocked?
(c) What would the plasma half-life be if the patient suffered from a liver disease such that biliary flow was completely blocked?

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[gwarm01]

Ah, a typical problem presented to your average pharmacist in the course of their daily routine. Certainly something you would need to know to practice in a typical setting.

Sarcasm aside, I am not ashamed to tell you that I have forgotten how to solve a problem like this. Hopefully someone else can help you.

 

[Dred Pirate]

Ah, a typical problem presented to your average pharmacist in the course of their daily routine. Certainly something you would need to know to practice in a typical setting.

Sarcasm aside, I am not ashamed to tell you that I have forgotten how to solve a problem like this. Hopefully someone else can help you.

right there with you - reminds me of when I used to have to look at a beta blocker chemical formula to determine if it crossed the BBB and its half life

 

[Cleaveland]

Stuck on a question, any help would be great!!!

A novel anabolic steroid was found to be cleared from the plasma via the following routes and at the corresponding rates:
Metabolism km = 0.175 hr
Excretion by kidneys kr = 0.150 hr
Excretion via bile kb = 0.50 hr
Excretion by salivary gland ks = 0.01 hr
(a) What is the plasma half-life of the drug?
(b) What would the plasma half-life be if the metabolism of the drug was completely blocked?
(c) What would the plasma half-life be if the patient suffered from a liver disease such that biliary flow was completely blocked?

Hmm without looking anything up, I'm going to attempt at this.

(a) T1/2 = 0.693 / k. So, T1/2 = 0.693/0.175 about 3.96 ~ 4 hours.
May have to look into more details for (b) and (c)? I wasn't sure what it meant as completely blocked?

 

[confettiflyer]

Isn’t the unit of k 1/hr anyway?


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[dingo499]

Hey man I liked PK despite being relevant in clinical practice I think it's still good to know! About the question I'm not 100% sure myself but I had the same thought as Cleaveland on tackling it. Do you have answers?

 

[owlegrad]

I am thinking that for b you should use just the salivary excretion (a route of excretion that I actually do not recall learning about in school but I am thinking that is what is meant by 'totally blocked metabolism' otherwise wouldn't the half-life be infinity?) and that for c you should use just the kidney and salivary excretion rates and exclude the liver.

Sometimes I think it would be fun to ask interns to do the kinetics of vancomycin dosing by hand, but then I remember that I would be expected to review the work for accuracy and since I never do it by hand I am not totally sure I could do it, LOL

 

[Cleaveland]

I am thinking that for b you should use just the salivary excretion (a route of excretion that I actually do not recall learning about in school but I am thinking that is what is meant by 'totally blocked metabolism' otherwise wouldn't the half-life be infinity?) and that for c you should use just the kidney and salivary excretion rates and exclude the liver.

Sometimes I think it would be fun to ask interns to do the kinetics of vancomycin dosing by hand, but then I remember that I would be expected to review the work for accuracy and since I never do it by hand I am not totally sure I could do it, LOL

Lol, double edged sword

 

[Sabril]

Stuck on a question, any help would be great!!!

A novel anabolic steroid was found to be cleared from the plasma via the following routes and at the corresponding rates:
Metabolism km = 0.175 hr
Excretion by kidneys kr = 0.150 hr
Excretion via bile kb = 0.50 hr
Excretion by salivary gland ks = 0.01 hr
(a) What is the plasma half-life of the drug?
(b) What would the plasma half-life be if the metabolism of the drug was completely blocked?
(c) What would the plasma half-life be if the patient suffered from a liver disease such that biliary flow was completely blocked?

a) t1/2 = 0.693/ (km+kr+kb+ks)
b) metabolism completely blocked so no km, t1/2=0.693/ (kr+kb+ks)
c) like b but no kb this time since the bile flow is blocked.

 

[wucool33]

I am thinking that for b you should use just the salivary excretion (a route of excretion that I actually do not recall learning about in school but I am thinking that is what is meant by 'totally blocked metabolism' otherwise wouldn't the half-life be infinity?) and that for c you should use just the kidney and salivary excretion rates and exclude the liver.

Sometimes I think it would be fun to ask interns to do the kinetics of vancomycin dosing by hand, but then I remember that I would be expected to review the work for accuracy and since I never do it by hand I am not totally sure I could do it, LOL

We have an old timer pharmacist that literally doses all vancomycin by hand. He would write down all his equations so that we could check his work if we wanted to... but obviously no one did.

 

[Dred Pirate]

we don

I am thinking that for b you should use just the salivary excretion (a route of excretion that I actually do not recall learning about in school but I am thinking that is what is meant by 'totally blocked metabolism' otherwise wouldn't the half-life be infinity?) and that for c you should use just the kidney and salivary excretion rates and exclude the liver.

Sometimes I think it would be fun to ask interns to do the kinetics of vancomycin dosing by hand, but then I remember that I would be expected to review the work for accuracy and since I never do it by hand I am not totally sure I could do it, LOL

Our residents are told to not use globalrph - they have to do anything by hand -
me "That is silly and a waste of time - on my rotation you can use global rph - just don't tell others I said that"
resident "Sounds good - that is what John said"
me "john said not to tell anyone he told you that"
resident "yes"
me "what did you tell me then?"
resident " uhhhh"

 

[wucool33]

we don

Our residents are told to not use globalrph - they have to do anything by hand -
me "That is silly and a waste of time - on my rotation you can use global rph - just don't tell others I said that"
resident "Sounds good - that is what John said"
me "john said not to tell anyone he told you that"
resident "yes"
me "what did you tell me then?"
resident " uhhhh"

I personally find the ABPK calculator to be more accurate, so I rarely use GlobalRPh unless patient is amputated...

 

[lane one]

Stuck on a question, any help would be great!!!

A novel anabolic steroid was found to be cleared from the plasma via the following routes and at the corresponding rates:
Metabolism km = 0.175 hr
Excretion by kidneys kr = 0.150 hr
Excretion via bile kb = 0.50 hr
Excretion by salivary gland ks = 0.01 hr
(a) What is the plasma half-life of the drug?
(b) What would the plasma half-life be if the metabolism of the drug was completely blocked?
(c) What would the plasma half-life be if the patient suffered from a liver disease such that biliary flow was completely blocked?

Who cares. Give them vanc and zosyn and they shall be cured.