Vancomycin Kinetic dosing question

[28657]

Can you all tell me what is the highest Vanco dose/frequency you have seen ordered?

I have a patient who had a trough of 4 with 1g q 12 hours. So I bumped him up to 1.5g q 8 hours and his trough is only 9. He has MRSA and our facility wants trough levels to be around 15 for MRSA.

(FYI-He has received all of his ordered doses, so the trough isn't low due to missed doses.)

I'm probably going to bump him up to 1.5g q 6 hours since Vancomycin is a time-dependent killer. What do you all think?

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[Epic]

Can you all tell me what is the highest Vanco dose/frequency you have seen ordered?

I have a patient who had a trough of 4 with 1g q 12 hours. So I bumped him up to 1.5g q 8 hours and his trough is only 9. He has MRSA and our facility wants trough levels to be around 15 for MRSA.

(FYI-He has received all of his ordered doses, so the trough isn't low due to missed doses.)

I'm probably going to bump him up to 1.5g q 6 hours since Vancomycin is a time-dependent killer. What do you all think?

No No No.. What's his Volume of distribution? Once you know Vd, then you need to shoot for Cmax of around 40ug/ml. Then in two t1/2, the trough will be 10ug/ml.

What's his age, height, and weight? And Cr?

 

[Requiem]

since Vancomycin is a time-dependent killer.

Don't think I've seen time-dependent killer written before, weird.

I assume you mean since it has very little PAE and almost no CDK, you need continuous levels of antibiotic above the MIC....

Make sure you consider the levels at the actual site of the infection too, compared to just serum.

 

[28657]

No No No.. What's his Volume of distribution? Once you know Vd, then you need to shoot for Cmax of around 40ug/ml. Then in two t1/2, the trough will be 10ug/ml.

What's his age, height, and weight? And Cr?

72", 91kg, SCr = 0.7, 34 year old male.

 

[njac]

I'm seeing 1G Q6H more and more.

Have you considered a continuous infusion? That's en vogue at our hospital right now.

 

[Epic]

Vd = 58 Liters.

1 gram q12 will result in SS peak of 20ug/ml and trough of 4ug/ml.

Estimated t1/2 = 6 hours.

1 gram in 58 Liters will result in increase of approxmately 16ug/ml.

Patient needs 1.75 grams q12h. It will get it up to 10ug/ml trough to 40ug/ml.

Always calculate the size of the bucket... for Vanc, Vd = 0.7L/kg.
Pt's dosing weight = 83kg.

83kg X 0.7L/kg = 58Liters.

1.75 grams in 58 Liters = 30ug/ml.
In 2 half lives, the level = 7.5ug/ml.

Dump another 1.75 grams will raise the level to 37,5ug/ml
In 2 half lives, the level = 9.375ug/ml

Dump another 1.75 grams will raise the level = 40ug/ml...
In 2 half lives, the level = 10ug/ml

Steady State.

Voila!.

 

[28657]

Voila!.

You make it sound so easy, and I am so so confused.....

When you state 1g q12 will result in a trough of 4....I'm assuming you're referring to my specific patient. Which is true, because that's what his trough was after 3 doses.

However, I am confused when you do all of your fancy calculations and arrive at 1.75g q 12 hours with a trough of 10 at steady state. Because I put my guy on 1.5g q 8 hours, and after 3 doses his trough is 9.

I'm not as familiar with the math of kinetic dosing, but I'm experienced with the way things always seem to work with my patients. (e.g., Doubling the dose will double my trough).

What would you do at this point if you were me? The ID doc wants the trough 10-15. With the current dose resulting in a trough of 9, can't I safely assume that the trough will just creep up slightly higher over the next couple of doses, and just leave things alone for now?

What trough does your kinetics calculations estimate with my 1.5g q 8 hours?

 

[SpirivaSunrise]

Amanda,

Epic is the guy when it comes to ID...so I don't want to butt in, but since there's a patient behind this, maybe this will clear up some of your math questions. Hopefully the long calcuations won't confuse you even more...but this is how I'd come up with 1.75 grams q12h.

Step 1: Determine the patient’s dosing weight:

IBW = 50 + (2.3 x inches over 5’)
IBW = 50 + (2.3 x 12”)
IBW = 77.6 kg

DW = IBW + 0.4(ABW – IBW)
DW = 77.6 kg 0.4(90 kg – 77.6 kg)
DW = 83 kg

Step 2: Estimate the CrCl:

CrCL= [(140 – age) x ABW]/[(72)(SCr)]
CrCL= [(140 – 34) x 83 kg]/(72)(0.7 mg/dL)
CrCL= 174 mL/min

Step 3: Estimate the Vanco clearance:

CLvanco = 0.695 x (CrCL) + 0.05
CLvanco = 0.695 x [(174 mL/min)/90 kg] + 0.05
CLvanco = 1.39 mL/min/kg

Step 4: Estimate the volume of distribution:

V = (0.7 L/kg) x (83 kg)
V = 58 L

Step 5: Estimate the vanco elimination rate constant (ke) and t1/2:

ke = CL/V
ke = [(1.39 mL/min/kg) x (60 min/h)]/[(0.7 L/kg) x 1000 mL/L)]
ke = 0.112 h-1

t1/2 = 0.693/ke
t1/2 = 0.693/(0.112 h-1)
t1/2 = 6 h

Step 6: Determine the desired steady-state serum concentrations:

Cmin,ss = 10 ug/mL
Cmax,ss = 40 ug/mL

Step 7: Compute the vanco dose:

T = (ln Cmax – ln Cmin)/ke
T = [ln(40 ug/mL) – ln(10 ug/mL)]/(0.112 h-1)
T = 12 h

D = Css,max x V x (l – e-kt)
D = (40 mg/mL) x (58 L) x (1 – e-(0.112)(12))
D = 1750 mg q 12 h

 

[SpirivaSunrise]

Don't think I've seen time-dependent killer written before, weird.

Really? Yep, vanco exhibits time-dependent killing (unlike aminoglycosides, which show concentration-dependent killing). So like you said...with vanco, the amount of time the concentration is above the AUC is important. Goal is to keep concentrations about 3 times higher than the MIC.

 

[FruitFly]

so studious

 

[SpirivaSunrise]

so studious

Haha...while I wrap the millionth Christmas present. I'll be the psycho person running through Penn Station monday night with 3 huge bags of gifts...I'm sure it'll be quite the sight.

 

[PharmDstudent]

Amanda,

Epic is the guy when it comes to ID...so I don't want to butt in, but since there's a patient behind this, maybe this will clear up some of your math questions. Hopefully the long calcuations won't confuse you even more...but this is how I'd come up with 1.75 grams q12h.

Step 1: Determine the patient’s dosing weight:

IBW = 50 + (2.3 x inches over 5’)
IBW = 50 + (2.3 x 12”)
IBW = 77.6 kg

DW = IBW + 0.4(ABW – IBW)
DW = 77.6 kg 0.4(90 kg – 77.6 kg)
DW = 83 kg

Step 2: Estimate the CrCl:

CrCL= [(140 – age) x ABW]/[(72)(SCr)]
CrCL= [(140 – 34) x 83 kg]/(72)(0.7 mg/dL)
CrCL= 174 mL/min

Step 3: Estimate the Vanco clearance:

CLvanco = 0.695 x (CrCL) + 0.05
CLvanco = 0.695 x [(174 mL/min)/90 kg] + 0.05
CLvanco = 1.39 mL/min/kg

Step 4: Estimate the volume of distribution:

V = (0.7 L/kg) x (83 kg)
V = 58 L

Step 5: Estimate the vanco elimination rate constant (ke) and t1/2:

ke = CL/V
ke = [(1.39 mL/min/kg) x (60 min/h)]/[(0.7 L/kg) x 1000 mL/L)]
ke = 0.112 h-1

t1/2 = 0.693/ke
t1/2 = 0.693/(0.112 h-1)
t1/2 = 6 h

Step 6: Determine the desired steady-state serum concentrations:

Cmin,ss = 10 ug/mL
Cmax,ss = 40 ug/mL

Step 7: Compute the vanco dose:

T = (ln Cmax – ln Cmin)/ke
T = [ln(40 ug/mL) – ln(10 ug/mL)]/(0.112 h-1)
T = 12 h

D = Css,max x V x (l – e-kt)
D = (40 mg/mL) x (58 L) x (1 – e-(0.112)(12))
D = 1750 mg q 12 h

This looks so exciting! Or maybe I'm just bored, I know I have to work tomorrow so I can't go out tearing up the streets of New Orleans, and we just started going over zero order, first order stuff in pharm school???

Anyway, I never thought I'd see someone use ln. I just thought my Pharmaceutics professor was just too excited about ln. Ha!

I am so ready to learn all of this stuff. Thankfully, the A&P classes are over. Let's see what my schedule looks like for next semester... Pharmacology II, Med Chem II, Biopharm/Basic Pharmacokinetics, Disease State Management I, and a few other tidbits. I can't wait to start. The sooner it's over, the better.

 

[SpirivaSunrise]

This looks so exciting! Or maybe I'm just bored, I know I have to work tomorrow so I can't go out tearing up the streets of New Orleans, and we just started going over zero order, first order stuff in pharm school???

Anyway, I never thought I'd see someone use ln. I just thought my Pharmaceutics professor was just too excited about ln. Ha!

I am so ready to learn all of this stuff. Thankfully, the A&P classes are over. Let's see what my schedule looks like for next semester... Pharmacology II, Med Chem II, Biopharm/Basic Pharmacokinetics, Disease State Management I, and a few other tidbits. I can't wait to start. The sooner it's over, the better.

I personally think Epic's way is easier to understand...bucket/hole. But for others, seeing the math worked out makes it simpler...or "exciting" with the ln's

 

[PharmDstudent]

I personally think Epic's way is easier to understand...bucket/hole. But for others, seeing the math worked out makes it simpler...or "exciting" with the ln's

You're so much fun! I'm thinking about moving to Florida after I graduate, so maybe we could hang out one day. Although, I'll give you fair warning, I've been called a "handful" before . Oh, and maybe I'll have a solid New Orleans accent by then. It's like a Southern + Boston accent if you can imagine that.

Are you still wrapping presents? I don't have time to do that this year. I'm thinking about doing a grab bag. You know, I'll buy several gifts and put them in a big gift bag so people can "grab" what they want .

This guy's a little spacey, but he really digs into the accent.
[YOUTUBE]http://www.youtube.com/watch?v=nukD4xz2tw0[/YOUTUBE]

 

[SpirivaSunrise]

You're so much fun! I'm thinking about moving to Florida after I graduate, so maybe we could hang out one day. Although, I'll give you fair warning, I've been called a "handful" before . Oh, and maybe I'll have a solid New Orleans accent by then. It's like a Southern + Boston accent if you can imagine that.

Are you still wrapping presents? I don't have time to do that this year. I'm thinking about doing a grab bag. You know, I'll buy several gifts and put them in a big gift bag so people can "grab" what they want .

Deal! We'll go out for drinks to celebrate when you graduate. Southern + Bostonian? Wow! And when you throw in some German too, I'm sure everyone's totally confused. I can be a handful too though, so I'm sure it would be lot's of fun...

Yep, still wrapping presents...I shopped all day today. And tomorrow I'll be baking alllll day. Here's the list: buttermilk brownies, ginger cookies, luscious lemon squares, peanut butter temptations, chocolate chip cookies, almond-raspberry meringue bars, and coconut haystacks. I have 35 large cookie tins to fill.

Btw...that flaky guy doesn't have an accent...that's just crazy N'awlins lingo!

 

[PharmDstudent]

Deal! We'll go out for drinks to celebrate when you graduate. Southern + Bostonian? Wow! And when you throw in some German too, I'm sure everyone's totally confused. I can be a handful too though, so I'm sure it would be lot's of fun...

Yep, still wrapping presents...I shopped all day today. And tomorrow I'll be baking alllll day. Here's the list: buttermilk brownies, ginger cookies, luscious lemon squares, peanut butter temptations, chocolate chip cookies, almond-raspberry meringue bars, and coconut haystacks. I have 35 large cookie tins to fill.

Drinks would be fun. I'm not a heavy drinker, but I indulge when I drink.
I have an idea! We can meet up with Caverject too and make him a sandwich, NOT! Haha!

Awwww... I love to cook. The almond-raspberry meringue bars sound really good! If you get a chance, I know you're really busy, but you should take a picture or two. I would love to see the coconut haystacks. I bet they're neat!

 

[PharmDstudent]

Btw...that flaky guy doesn't have an accent...that's just crazy N'awlins lingo!

I can hear the accent. I'm from the other side of the state, so that accent seems very different from my "Cajun" accent. Although, I don't have a "lick" of French in me, so I'm not technically "Cajun". Oh well... I'll always feel out of place, but I really enjoy the differences among cultures.

Have fun wrapping! I gotta go to bed. Dang 10am to 6pm shifts are killer (boring). It's just me and a PharmD tomorrow....

OK! I just spent over an hour searching for a clean video with a "Cajun" accent. There's only one word that might be offensive, at 1:45 minutes, but that's it. So if you're interested, you can compare the "Nawlins" accent with the "Cajun" accent.
Hope you enjoy the movie trailer of Last Man Standing.
[YOUTUBE]http://www.youtube.com/watch?v=N9XdGb1-KkI[/YOUTUBE]

 

[pharmboy30]

1.75gm q8 puts trough ~13-14 (according to globalrph)
our ID wants troughs 15-20 in most cases (actually ID doesn't want us to do anything most of the time, haha)