The truth about drug interactions?

Jules A, MSN · Feb 19, 2015

I think you are showing very good insight to be concerned about the lack of knowledge we receive in school as much of what we do is not black and white. As for the EMRs in my experience they are now so sensitive that they flag every single medication I order to the point where I barely even read them before I click ignore which is unfortunate. There are books on drug:drug interactions as well as online resources such as UpToDate, micromedics etc. I use the last two most often but again it is only a guideline. You need to decide risk vs benefit and much of that comes with experience. There are some meds that I would never prescribe together and much of that I learned as a RN. What I would suggest doing is keep a notebook with the medications that you will see in your specialty that are almost always contraindicated such as Lithium for example with NSAIDs, the MAOIs with most every medication in the world and of course in primary care high alert meds like Coumadin. Good luck.

zmansc, ASN, RN · Feb 19, 2015

I'm a bit confused by what you are looking for. I'm sure your books and classes have discussed the various aspects of pharmacodynamics and pharmacokinetics. These concepts are the key underpinnings of understanding d-d interactions. Have you not discussed protein binding, CYP450 enzymes, etc? What about how different populations (peds, pregos, elderly) impact the pharmacokinetics of the medications?

All of these concepts are the underpinnings of d-d interactions (and for that matter drug to food, etc). I would hope your RN program's pharm class discussed this, your BSN program's pharm class discussed this and then your NP program's pharm class reviewed these concepts. If not, I would suggest finding a pharm book and reviewing the first few chapters (my adv pharm book has 10 chapters at the beginning of the book covering these topics) or doing a little research on these topics on the web. Youtube is great for these general topics.

If you understand those aspects of pharmacology, then d-d interactions is the basic process of applying it. If two drugs are using the same enzyme, you will likely have competition for that enzyme and thus a concern for an increased serum level of one or both medication. If one medication either increases or decreases the speed at which an enzyme works, then other medications that are processed by that enzyme will be metabolized faster or slower. If two medications are highly protein bound, then they will compete for the proteins in the patient's serum, the free level of one or both (depending on bindings) will be increased. So, to understand d-d interactions you have to understand the basic concepts and then apply them.

That's the basics, of course there are many more layers to the onion. When medications affect the ions in the body, and those ions are used somewhere in the process of another drug, then their is a potential for impact. Dig and a diuretic for example. Or one of my personal favorites, increasing synthroid which then speeds up everything, so the patient now has palpitations and their HTN is all the sudden no longer controlled. It's not actually a d-d interaction but a drug-body-drug interaction.

The thing is, I don't believe you could just memorize the list of d-d interactions or get the list from a program, and be able to Rx meds. I think you have to understand it at a deeper level and be able to ask how these two compounds interact with each other and with the body. Only then can you decide how to proceed.

As for guides, I prefer epocrates or up-to-date for giving me the basic information. Epocrates has a great tool where you can see all the interactions between the meds the patient is on. But that just gives you a list, from there you have to figure out which of these interactions are a concern for you with this patient, and the first step in that is figuring out how these two compounds interact with the body and or each other.

nurselove757 · Feb 19, 2015

I think you are showing very good insight to be concerned about the lack of knowledge we receive in school as much of what we do is not black and white. As for the EMRs in my experience they are now so sensitive that they flag every single medication I order to the point where I barely even read them before I click ignore which is unfortunate. There are books on drug:drug interactions as well as online resources such as UpToDate, micromedics etc. I use the last two most often but again it is only a guideline. You need to decide risk vs benefit and much of that comes with experience. There are some meds that I would never prescribe together and much of that I learned as a RN. What I would suggest doing is keep a notebook with the medications that you will see in your specialty that are almost always contraindicated such as Lithium for example with NSAIDs, the MAOIs with most every medication in the world and of course in primary care high alert meds like Coumadin. Good luck.

Ok, so it seems that most of the correct implementation concerning drug to drug interaction is based on clinical judgement. I wonder if someone can sue a Nurse Practitioner (NP) because a drug to drug interaction did harm to a patient. What are your thoughts on this?

Jules A, MSN · Feb 19, 2015

Its a combination of the published research with clinical knowledge. Sort of like with laboratory values, there are some that when out of range are no biggie, and others like K for example where it might be a very big deal.

We absolutely could be sued if a known drug:drug interaction harmed a patient. As is the case with off label use my best defense is educate the patient and document that the risks vs benefits were considered and the patient verbalized understanding. I usually add the adverse reactions we discussed as ones they should recognize as requiring immediate attention in my documentation also.

nurselove757 · Mar 1, 2015

Hello Zmansc,

Thank you so much for responding to my post. The teacher did not mention anything about the CYP enzymes, but I do remember a couple of students mentioning it in their post. But they did not mention it in depth. I did look over my pharmacology book which is:

Edmunds, M. W., & Mayhew, M. S. (2014). Pharmacology for Primary Care Providers (4th ed.). St. Louis, MO: Elsevier Mosby.

This book does not has a drug interaction section. I did however find information regarding the CYP enzymes. I guess this is a good starting point for me to learn about drug interaction. Actually, thoroughly going over the first few chapters seems essential if I want to prescribe medication. I am usually more focused on mechanisms of action of a drug and side effects, but I should not neglect other parts of the book. These chapters include contents on pharmacokinetics, pharmacodynamics, and special populations such as geriatrics and pregnant women (just as you mentioned). Even though the chapters are in the book and also in the syllabus, we never discussed anything regarding these topics in the class discussions or in the exams. I know that it is up to me to thoroughly know these contents whether I am being asked about it or not. Anyways, I think this is where I should start right now, and dig deeper into drug interaction books later on. Your comments really helped, especially what you said in the last 3 paragraphs. Thank you.

nurselove757 · Mar 1, 2015

I'm a bit confused by what you are looking for. I'm sure your books and classes have discussed the various aspects of pharmacodynamics and pharmacokinetics. These concepts are the key underpinnings of understanding d-d interactions. Have you not discussed protein binding, CYP450 enzymes, etc? What about how different populations (peds, pregos, elderly) impact the pharmacokinetics of the medications?
All of these concepts are the underpinnings of d-d interactions (and for that matter drug to food, etc). I would hope your RN program's pharm class discussed this, your BSN program's pharm class discussed this and then your NP program's pharm class reviewed these concepts. If not, I would suggest finding a pharm book and reviewing the first few chapters (my adv pharm book has 10 chapters at the beginning of the book covering these topics) or doing a little research on these topics on the web. Youtube is great for these general topics.
If you understand those aspects of pharmacology, then d-d interactions is the basic process of applying it. If two drugs are using the same enzyme, you will likely have competition for that enzyme and thus a concern for an increased serum level of one or both medication. If one medication either increases or decreases the speed at which an enzyme works, then other medications that are processed by that enzyme will be metabolized faster or slower. If two medications are highly protein bound, then they will compete for the proteins in the patient's serum, the free level of one or both (depending on bindings) will be increased. So, to understand d-d interactions you have to understand the basic concepts and then apply them.
That's the basics, of course there are many more layers to the onion. When medications affect the ions in the body, and those ions are used somewhere in the process of another drug, then their is a potential for impact. Dig and a diuretic for example. Or one of my personal favorites, increasing synthroid which then speeds up everything, so the patient now has palpitations and their HTN is all the sudden no longer controlled. It's not actually a d-d interaction but a drug-body-drug interaction.
The thing is, I don't believe you could just memorize the list of d-d interactions or get the list from a program, and be able to Rx meds. I think you have to understand it at a deeper level and be able to ask how these two compounds interact with each other and with the body. Only then can you decide how to proceed.
As for guides, I prefer epocrates or up-to-date for giving me the basic information. Epocrates has a great tool where you can see all the interactions between the meds the patient is on. But that just gives you a list, from there you have to figure out which of these interactions are a concern for you with this patient, and the first step in that is figuring out how these two compounds interact with the body and or each other.

Hello Zmansc,

Thank you so much for responding to my post. The teacher did not mention anything about the CYP enzymes, but I do remember a couple of students mentioning it in their post. But they did not mention it in depth. I did look over my pharmacology book which is:

Edmunds, M. W., & Mayhew, M. S. (2014). Pharmacology for Primary Care Providers (4th ed.). St. Louis, MO: Elsevier Mosby.

This book does not has a drug interaction section. I did however find information regarding the CYP enzymes. I guess this is a good starting point for me to learn about drug interaction. Actually, thoroughly going over the first few chapters seems essential if I want to prescribe medication. I am usually more focused on mechanisms of action of a drug and side effects, but I should not neglect other parts of the book. These chapters include contents on pharmacokinetics, pharmacodynamics, and special populations such as geriatrics and pregnant women (just as you mentioned). Even though the chapters are in the book and also in the syllabus, we never discussed anything regarding these topics in the class discussions or in the exams. I know that it is up to me to thoroughly know these contents whether I am being asked about it or not. Anyways, I think this is where I should start right now, and dig deeper into drug interaction books later on. Your comments really helped, especially what you said in the last 3 paragraphs. Thank you.