nonspecific antibiotic question

[Glowwyrm]

This is probably a really stupid question so please forgive my ignorance. Say John Doe is on X antibiotic. He needs to take his antibiotic Y amount earlier than his regular dose because he's got a business meeting. John calls the pharmacist and she/he tells him sure it's fine to take X antibiotic Y amount of time earlier.

Are there some antibiotics that the dose will be greatly effected (either by overdose or decrease of effectiveness) if you moved the dose back whereas another antibiotic would be fine given the same amount of time the dose was moved back? For example, antibiotic X dose can be moved back Y amount of time. But if you moved antibiotic Z dose back Y amount of time, it would overdose the patient. I'm not really wondering about any family of antibiotics in particular. Just in general. A yes or no would answer the question so we can keep it completely abstract.

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[sdn1977]

Hmmm....well..an answer in an abstract sense only....yes, its ok .

But, to be a bit more specific, which I think is allowed in this circumstance, you can judge the importance of dosing interval & the ability to lengthen or shorten with antibiotics based on the route & the frequency.

Oral antibiotics will have less importance with regard to dosing interval than intravenous. Those antibiotics which are dosed less frequently throughout the day have a longer duration of action therefore the dosing fequency has a bit more "wiggle" room.

So....lets take a few general examples - if you're being given penicillin IV 3 MU q4h vs penicillin VK 250mg qid - its is going to be more important to stay on the q3h regimen than the qid regimen (you're probably sicker as well). Likewise, someone taking erythromycin 250mg po qid can only move these doses so far to get all four in a 24 hour "day" but azithromycin 250mg qd can be given 2 hours one way or another on any given day without disrupting treatment.

There are exceptions to everything & each of us can dredge up those circumstances when the exception is of importance...so what is being treated becomes significant also - which puts the question out of the realm of being answered on here, so its better not to put that out.

Hope this helps!

 

[Glowwyrm]

Hmmm....well..an answer in an abstract sense only....yes, its ok .

But, to be a bit more specific, which I think is allowed in this circumstance, you can judge the importance of dosing interval & the ability to lengthen or shorten with antibiotics based on the route & the frequency.

Oral antibiotics will have less importance with regard to dosing interval than intravenous. Those antibiotics which are dosed less frequently throughout the day have a longer duration of action therefore the dosing fequency has a bit more "wiggle" room.

So....lets take a few general examples - if you're being given penicillin IV 3 MU q4h vs penicillin VK 250mg qid - its is going to be more important to stay on the q3h regimen than the qid regimen (you're probably sicker as well). Likewise, someone taking erythromycin 250mg po qid can only move these doses so far to get all four in a 24 hour "day" but azithromycin 250mg qd can be given 2 hours one way or another on any given day without disrupting treatment.

There are exceptions to everything & each of us can dredge up those circumstances when the exception is of importance...so what is being treated becomes significant also - which puts the question out of the realm of being answered on here, so its better not to put that out.

Hope this helps!

Yes it does help. Thanks for your response. This is what makes pharmacy so interesting to me. You have to take into account not just the medication and dose, but also how that dose is administered. It can be so multidimensional. I don't see how people can find pharmacy boring when you look at it that way.

 

[Moxxie]

I had a test on this this morning!! Without going into too much math, it's possible to calculate what the average Cp, Cpmin & Cpmax (plasma concentration) will be if the dosing interval changes. If the drug has a narrow therapeutic index, then you might exceed the cmax if the dose is taken too early. But like SDN said, oral antibiotics have a wider TI, so it's not as big of a deal.

Here's the powerpoint slide that my professor gave us on this very subject!

 

[sdn1977]

Good job understanding Cp levels!!! But, don't lose sight that unless you're looking at sepsis, which is probably not being treated at the outpt level, the Cp is not as important as the tissue level.

Some antibiotics will concentrate in tissues & some will not, so the Cp may or may not accurately reflect the level in the tissue or organ (if we're looking at bladder infections, for example). So we don't just consider narrow therapeutic windows, we also must consider drug, dx being treated & setting of the pt - all beyond what the OP asked for (in a very "compliant with TOS" way I might add !).

Again - good job!....just don't lose sight of the forest for the trees.

 

[Moxxie]

Good job understanding Cp levels!!! But, don't lose sight that unless you're looking at sepsis, which is probably not being treated at the outpt level, the Cp is not as important as the tissue level.

Some antibiotics will concentrate in tissues & some will not, so the Cp may or may not accurately reflect the level in the tissue or organ (if we're looking at bladder infections, for example). So we don't just consider narrow therapeutic windows, we also must consider drug, dx being treated & setting of the pt - all beyond what the OP asked for (in a very "compliant with TOS" way I might add !).

Again - good job!....just don't lose sight of the forest for the trees.

Sdn - Those are all good points! I should have mentioned that this graph was based on a one-compartment model. I really hope that I didn't bomb this test!

 

[ZpackSux]

Well...levels are important..but some abx have PAE (post antibiotic effect)...where it's not fully associated with levels..

That being said..unless you're doing an aminoglycoside or vanco dosing where timing of dosing is crucial in future dosing regimen... just remember, pharmacy & pharmacology is not an exact science...where few hours here and there in abx regimen will make that much difference.

 

[Glowwyrm]

I see you have a dung beetle avatar. I have a whole new appreciation for dung beetles because of you.

 

[WVUPharm2007]

Then you have Zithromax. Nobody gives a **** when or how much of it you take at a time. The **** is systemically benign and stays in your stream for about 23 bazillion years before it gets metabolized.

 

[ZpackSux]

I see you have a dung beetle avatar. I have a whole new appreciation for dung beetles because of you.

Thank you...that means a lot... really...

 

[All4MyDaughter]

Then you have Zithromax. Nobody gives a **** when or how much of it you take at a time. The **** is systemically benign and stays in your stream for about 23 bazillion years before it gets metabolized.

I thought it hung out in the tissues more than in the bloodstream.

 

[WVUPharm2007]

I thought it hung out in the tissues more than in the bloodstream.

There's a nice ratio at work that is unique for each drug. It "hangs out" everywhere. That's where that whole volume of distribution concept comes from - a means of quantifying where the drug "hangs out."

 

[hpharm07]

I had a test on this this morning!! Without going into too much math, it's possible to calculate what the average Cp, Cpmin & Cpmax (plasma concentration) will be if the dosing interval changes. If the drug has a narrow therapeutic index, then you might exceed the cmax if the dose is taken too early. But like SDN said, oral antibiotics have a wider TI, so it's not as big of a deal.

Here's the powerpoint slide that my professor gave us on this very subject!

nice post...cut and paste? ahh the Cp re