For Hospital Pharmacists: Which Vanco/gent kinetics Calculators?

[Me_Gusta_Drugs]

Question for hospital pharmacists that do kinetics...Which vanco/gent calculator do you use and why (what do you like/dislike about them)? GlobalRPH....medcalc.com...other?

Or do you eye ball it based on crcl?
Or do you use a hand calculate it? which Im sure very few people do



I personally have found medcalc to be cleaner and more user friendly than globalRPH but does not have as many options and does not use adjusted body weight if required.

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[spacecowgirl]

I actually do the kinetics by hand (nerd) and then double-check my work using global or freekinetics.

 

[Me_Gusta_Drugs]

I actually do the kinetics by hand (nerd) and then double-check my work using global or freekinetics.

I dont understand how people can calcuate the kinetics by hand on the job. How do you have enough time on your shift to do this. I barely have time to plug and chug the numbers using a calculator. They must give you way too many hours for that shift

 

[spacecowgirl]

I dont understand how people can calcuate the kinetics by hand on the job. How do you have enough time on your shift to do this. I barely have time to plug and chug the numbers using a calculator. They must give you way too many hours for that shift

You should see the FarmVille empire I built during working hours.

Har.

We have CPOE, so no order entry. No 24 hour coverage. We are a very small hospital and we have time to do lots of more "clinical" stuff. Counsel patients, attend rounds, precept students, make chemo, MTM, etc. We wouldn't offer pharmacy dosing services if we didn't have enough time to do it properly. Sounds like you guys don't have enough staff.

ETA: it takes like 2 minutes to calculate doses by hand. Really.

 

[Me_Gusta_Drugs]

You should see the FarmVille empire I built during working hours.

Har.

We have CPOE, so no order entry. No 24 hour coverage. We are a very small hospital and we have time to do lots of more "clinical" stuff. Counsel patients, attend rounds, precept students, make chemo, MTM, etc. We wouldn't offer pharmacy dosing services if we didn't have enough time to do it properly. Sounds like you guys don't have enough staff.

ETA: it takes like 2 minutes to calculate doses by hand. Really.

I'm no expert myself, but I don't see how calculating it by hand is more accurate or better than using an online calculator that plugs and chugs. It seems (but I cant confirm) that the online calculators use much more elaborate, and complex (and therefore likely more accurate) equations than what you can practically do by hand within 2 minutes.

 

[owlegrad]

I'm no expert myself, but I don't see how calculating it by hand is more accurate or better than using an online calculator that plugs and chugs. It seems (but I cant confirm) that the online calculators use much more elaborate, and complex (and therefore likely more accurate) equations than what you can practically do by hand within 2 minutes.

I find this post humorous. Elaborate/complex equations are necessarily more accurate? Really?

I can't speak for practising pharmacists, but I think the danger of only using online calculators is that you forget the assumptions that are being made, what factors go in to the final number and when the results are not necessarily valid. This is what I have heard anyway.

 

[WVUPharm2007]

I was forced to use a calculator that one of the pharmacists made. I had issues with it because it used crazy values like Vd=0.9, but I wasn't allowed to have an opinion. It wound up ok, because they were always way too conservative with their dosing, anyway.

 

[Its Z]

I actually do the kinetics by hand (nerd) and then double-check my work using global or freekinetics.

best way...

Actually, every pharmacist should be able to dose Vanc and Gent in their head.

 

[Me_Gusta_Drugs]

I find this post humorous. Elaborate/complex equations are necessarily more accurate? Really?

I can't speak for practising pharmacists, but I think the danger of only using online calculators is that you forget the assumptions that are being made, what factors go in to the final number and when the results are not necessarily valid. This is what I have heard anyway.

well equations for a 2 compartment model are more complex and more accurate than equations for a 1 compartment model

 

[owlegrad]

well equations for a 2 compartment model are more complex and more accurate than equations for a 1 compartment model

Am I being baited? Just because an equation is complicated doesn't mean it is acurate. Two compartment model equations are only more accurate for two compartment models. The fact that it is complicated doesn't make it accurate.

F=MA - simple equation, very accurate.

Cockcroft-Gault Equation - more complicated, not as accurate (it is only an estimate)

Of course the above is worse than comparing apples to oranges, but the point is complicated doesn't mean accurate. The more I think about the more certain I am that I am being baited here. Or at least I hope so...

 

[rxlea]

Hey, if the Cr is below 1 on an elderly bedridden person, do you guys just round up to 1?

We learned how to calculate CrCl today and do initial dosing on vanco.

 

[WVUPharm2007]

Hey, if the Cr is below 1 on an elderly bedridden person, do you guys just round up to 1?

We learned how to calculate CrCl today and do initial dosing on vanco.

In the real world, its calculated for you already in the computerized lab record...but if I was teleported to Somalia and has to figure it out on my own I'd say 1g q12 and see what happens...er...I mean, yeah, I'd round up... 😏

 

[Praziquantel86]

In the real world, its calculated for you already in the computerized lab record...but if I was teleported to Somalia and has to figure it out on my own I'd say 1g q12 and see what happens...er...I mean, yeah, I'd round up... 😏

See, I never use the MDRD that gets calculated for you. All of my preceptors have said that the Cockcroft-Gault is what was used to determine the dose adjustment cutoffs, and that's what we should use to do the doses in practice.

What gets me about vanco dosing is that no one actually knows if what they're doing is right. You'll give 1g q12, others will do 20mg/kg then 15mg/kg, all aiming at the same target that's really only been validated in one patient population. Oh well.

 

[rxlea]

See, I never use the MDRD that gets calculated for you. All of my preceptors have said that the Cockcroft-Gault is what was used to determine the dose adjustment cutoffs, and that's what we should use to do the doses in practice.

What gets me about vanco dosing is that no one actually knows if what they're doing is right. You'll give 1g q12, others will do 20mg/kg then 15mg/kg, all aiming at the same target that's really only been validated in one patient population. Oh well.

That's what our prof said. Also, doesn't it depend on the severity of the infection? Like, if an elderly woman comes in with raging bilateral pneumonia, wouldn't we want to do 20mg/kg and then see whàt happens? And then adjust accordingly with trough levels?

EDIT: what I mean is, if it is a real severe infection or a bone infection, wouldn't you choose the higher dosing in the range (20mg/kg vs 15mg/kg) depending on the CrCl?

 

[WVUPharm2007]

That's what our prof said. Also, doesn't it depend on the severity of the infection? Like, if an elderly woman comes in with raging bilateral pneumonia, wouldn't we want to do 20mg/kg and then see whàt happens? And then adjust accordingly with trough levels?

EDIT: what I mean is, if it is a real severe infection or a bone infection, wouldn't you choose the higher dosing in the range (20mg/kg vs 15mg/kg) depending on the CrCl?

The initial dose isn't really that important because its a usually shot in the dark. It's just based on what you want the trough before the next dose to be. There are some instances where a lower dose given q8 is advantageous to a higher dose given q12. You have to do the math on paper, using a good dosing chart (which is probably the easiest to use), or on a computer (what I'd do) and play around with the numbers to see what gives you the best hypothetical result.

The two ranges you'd shoot for based on "severity" are defined as a trough of 10-15 and 15-20...depending on the diagnosis...and under no circumstance less than 10.

I hate that word "severity."

If the infection is likely to exhibit a higher MIC or if it would likely require deeper tissue penetration...or if you just want to be aggressive because its septic or something...yeah, then you'd go for a trough of 15-20.

But anyway, the important thing is how you deal with this initial estimate after you get your data from the trough.

In the real world, it gets pretty complicated sometimes even though the math is relatively easy. They will give it late...or take the trough early...or somehow the bag will start leaking during administration...the patients renal function will magically improve overnight...etc etc...

One time we had an obese midget with renal stents...that were getting taken out halfway through the vanc regimen...

One of the all-time great WTFDID moments...

If you are really interested in it, go to the ID Society's website and read the guideline paper. It is spelled out clearly and in depth what you need to do.

 

[Its Z]

That's what our prof said. Also, doesn't it depend on the severity of the infection? Like, if an elderly woman comes in with raging bilateral pneumonia, wouldn't we want to do 20mg/kg and then see whàt happens? And then adjust accordingly with trough levels?

EDIT: what I mean is, if it is a real severe infection or a bone infection, wouldn't you choose the higher dosing in the range (20mg/kg vs 15mg/kg) depending on the CrCl?

If we're talking vancomycin, it's better to load at 25-30mg/kg then maintenance dose of 20mg/kg. As far as adjusting based on CrCl, you adjust frequency not the dose.

 

[rxlea]

Cool. Thanks guys. I am just a lowly P1 LOL. Next week we are learning to adjust frequency based on troughs. I just want to get this **** down early so I can ask my prof good questions. I'll probably bug the pharmacists I work with this weekend, too.

Oh and Z, what is the reason for that higher loading dose and would you do the same with impaired renal function?

 

[Its Z]

Cool. Thanks guys. I am just a lowly P1 LOL. Next week we are learning to adjust timing based on troughs. I just want to get this **** down early so I can ask my prof good questions. I'll probably bug the pharmacists I work with this weekend, too.

Find me at the ASHP. I will spend 5 min with you with a piece of paper and a calculator to explain everything you ever need to know about PK.

 

[rxlea]

Find me at the ASHP. I will spend 5 min with you with a piece of paper and a calculator to explain everything you ever need to know about PK.

Sweet. Thanks 🙂

 

[Ackj]

One time we had an obese midget with renal stents...that were getting taken out halfway through the vanc regimen...

That's some straightforward dosing . Amputee patients are also great.

 

[Dalteparin]

Hey, if the Cr is below 1 on an elderly bedridden person, do you guys just round up to 1?

We learned how to calculate CrCl today and do initial dosing on vanco.

I do. Although sometimes these little old ladies can clear vanco pretty rapidly. I had one 90-lb, 90-year-old lady who I was sure would wind up with a trough of 40 on her vanco regimen, and I got all freaked out and bugged the ID doc about it. Her trough came back at... 5. (Yes, it was drawn at the right time.) Felt pretty stupid after that one.

In patients who are para/quadriplegics or as another person mentioned, amputees, Cockcroft-Gault is pretty well useless. For people like this, I usually dig through their old records and see if they've had vancomycin before and use a dose that worked in the past. 🙂 That doesn't always work either, but it's a good starting place.