QT Prolongation

[Vort3x]

Hey everyone,

I'm a pharmacy student completing my final set of rotations and I'm trying to get as much practice as possible dealing with drug interactions. One grey area I find difficult is QT prolongation. Who's actually at risk of torsades? I found this neat study of of developing a risk score for hospitalized patients (not sure how applicable it is to community patients): http://www.ncbi.nlm.nih.gov/pubmed/23716032

There are "high risk" ones you just wouldn't combine, ie: sotalol + macrolides, etc. but what about SSRIs and other low risk QT prolonging drugs? Is it reasonable to try and consider the risk factors in that study, female, low K/Mg, >=2 QT drugs, etc. before considering switching medications?

Would love to hear how others approach this interaction/your thought process. Thanks!

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[gwarm01]

I don't have any method quite as elaborate as developing a risk score, but I try to use common sense. If a patient is on one or two drugs that prolong the QT interval and a doctor adds PRN Zofran, I'm not going to call. If they add scheduled methadone I'll give them a call.

 

[radio frequency]

I wouldn't say I have a method, but this website can be helpful: http://www.sads.org

 

[Carboxide]

I don't think you can really say that certain drugs are absolute contraindications. We dispense sotalol + azithro inpatient all the time, even to patients not on tele. I mean, tele is preferred, but if the patient has a fine QTc before the azithro, then 5 days of azithro ain't gonna kill em. Plus, what's your alternative for atypical coverage in PNA? A quinolone? Not better.

When I'm working, and I see a QTc contraindication involving very high-risk drugs (sotalol and dofetilide come to mind as major red flags) I start by looking at the QTc and then considering appropriateness of the drug and other options. Sometimes you have no choice.

 

[BidingMyTime]

Yes, in practice, QT prolonging drugs are combined all the time. There aren't any hard and fast guidelines, as with anything else, the prescriber must weigh the risks vs the benefits for the individual patient (and the pharmacist essentially double checks and/or makes recommendations alongside that.) In hospital where there is more monitoring, the risk is less. In outpatient, there is more risk, still hospitalizing people solely because they need a combo of QT prolonging drugs is not reasonable and not reimbursable. Weigh the risks vs benefit, and make sure the patient understands.

 

[cardiacnerd]

Hey everyone,

I'm a pharmacy student completing my final set of rotations and I'm trying to get as much practice as possible dealing with drug interactions. One grey area I find difficult is QT prolongation. Who's actually at risk of torsades? I found this neat study of of developing a risk score for hospitalized patients (not sure how applicable it is to community patients): Development and validation of a risk score to predict QT interval prolongation in hospitalized patients. - PubMed - NCBI

There are "high risk" ones you just wouldn't combine, ie: sotalol + macrolides, etc. but what about SSRIs and other low risk QT prolonging drugs? Is it reasonable to try and consider the risk factors in that study, female, low K/Mg, >=2 QT drugs, etc. before considering switching medications?

Would love to hear how others approach this interaction/your thought process. Thanks!

Curious if you ever came to any conclusion on this. I'd have involved myself in the discussion if I'd been here at the time. Happy to involve myself now if you're still working on it.

 

[lord999]

Billion or zero dollar question in Toxicology. You solve this to a great degree, that's a Nobel winner. Problem is that Homer Simpson regularly gets prescribed a BB and CCB which should trigger this and other fatal arrhythmia patterns, and manages to not notice it.

 

[hye345]

I was told that drug-induced QT prolongation is usually only a problem in those who already have an underlying issue with arrhythmia. So, if a (new) combo happens with 2 or more drugs that can cause it, I usually ask the patient if they have any history of arrhythmia. If they say no, then it's all good. If they say yes, then I give them a warning on what to watch out for, and/or call the prescriber to ask if they are aware, and are gonna monitor the patient.

 

[trailerpark]

I treat QT alerts the same as Serotonin Syndrome alerts.


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[RxPreceptor]

If you read the warning and precautions section of most drug monograms (I.e. Ziprasidone), some will give you a threshold of not to exceed 500ms of the (keyword) Corrected QT interval (QT subscript C). Other drugs (mostly anti arthymia drugs, esp ones started in-hospital) will have dosing ranges based on the QTc range.

In community/retail, you are not going to have access to that info unlike hospital. Intervene when necessary (Usually BS psychiatrists Rx'ing numerous/combos of high dose/off label antipsychotics, SSRIs, TCAs, etc. yet have no baseline EKG).

 

[MatCauthon]

I was told that drug-induced QT prolongation is usually only a problem in those who already have an underlying issue with arrhythmia. So, if a (new) combo happens with 2 or more drugs that can cause it, I usually ask the patient if they have any history of arrhythmia. If they say no, then it's all good. If they say yes, then I give them a warning on what to watch out for, and/or call the prescriber to ask if they are aware, and are gonna monitor the patient.

Problem with this is that a large number of arrhythmia patients are completely asymptomatic. Look at all the AF patients that didn't know about their condition until something else went wrong.

 

[PharmDBro2017]

I treat QT alerts the same as Serotonin Syndrome alerts.


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Meaning... you ignore them or use clinical judgement?


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[farmadiazepine]

^^^^ Just ignore them.

I work in a hospital, and in retail.

It's risk versus benefit. That's it.

 

[PharmDBro2017]

^^^^ Just ignore them.

I work in a hospital, and in retail.

It's risk versus benefit. That's it.

Ignoring to a certain extent, is understandable. But taking the time to actually look at the warnings is important rather than dismissing them after 0.3 seconds of it popping up. I'm not trying to put anyone into Torsades --> coding because I was too lazy to call the doctor and suggest a different therapy than what they were receiving.

 

[Hulkbuster333]

I was told that drug-induced QT prolongation is usually only a problem in those who already have an underlying issue with arrhythmia. So, if a (new) combo happens with 2 or more drugs that can cause it, I usually ask the patient if they have any history of arrhythmia. If they say no, then it's all good. If they say yes, then I give them a warning on what to watch out for, and/or call the prescriber to ask if they are aware, and are gonna monitor the patient.

I remember learning this too about preexisting arrhythmias. When I was an intern at a psych hospital, the pharmacists would ignore this all of the time though.

 

[Sine Cura]

I'm not sure "suggesting" something else (and documenting such) really protects you unless you refuse to fill it when the prescriber won't budge and a board inspector comes by to get your justification for refusal to fill.

And psych polypharmacy is the worst

 

[PharmDBro2017]

I'm not sure "suggesting" something else (and documenting such) really protects you unless you refuse to fill it when the prescriber won't budge and a board inspector comes by to get your justification for refusal to fill.

And psych polypharmacy is the worst

I always i-vent it and explain that the physician wanted it and disregarded dangerous QTc levels. CYA... that way it's on him.


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[Carboxide]

I always i-vent it and explain that the physician wanted it and disregarded dangerous QTc levels. CYA... that way it's on him.


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Same. I put in there that I discussed appropriate targets for K+ and Mg and discussed level of risk with this specific drug combo/dosage regimen (i.e. if the specific drugs are very high risk or low-medium risk). I make sure the MD has all the information I can possibly provide. I also note if I recommended safer alternatives (e.g. doxy for CAP).

 

[PolarPop]

Qtc prolongation really is a 0 or billion dollar question though (most of the time $0). I would suggest being careful if you are only using the admission EKG to make your recommendations. Most of the time the admission EKG will have a prolonged Qtc because of electrolyte abnormalities or tachycardia. Yes the c is supposed to correct for heart rate, but 9/10 probably if you just repeat the EKG when the electrolytes have been corrected and heart rate is at baseline then the Qtc will be normal.

That being said, I'd be lying if I said I don't use any EKG I can find to switch off of a fluoroquinolone. I have only seen torsades from a drug once which was from levofloxacin. Coupled with all the other side effects they have to be one of the worst classes of drugs available.

The billion dollar question is when you really are stuck using a drug that prolongs Qtc in someone with a definite prolonged Qtc. If you keep the Mg > 2.5 and K > 4 it will be pretty difficult for the patient to go into torsades. That and monitoring EKGs will make you sleep better at night, but repeating EKGs may only be possible if you have a good working relationship with the residents or attendings at your hospital. If you page every time you see a drug that can prolong the Qtc 5-10 ms in someone with a Qtc of ~480 or so they are not going to take you seriously when it really matters for the patient with a Qtc >550.