**EP310: Common Cardiac Drugs and Common Interactions**
**Dr. Auric Bishop:** Welcome, my name's Dr. Auric Bishop. I'm a cardiologist, an author, and a keynote speaker. I'm the CEO of the Healthy Heart Network. I'm all about trying to help people live as well as possible for as long as possible. Heart disease is huge in Australia. Every 20 minutes, someone suffers a heart attack. Most of these could probably have been avoided if only we knew what to do. This podcast is all about helping you understand blood pressure, weight, and cholesterol for better health. If you enjoy this podcast, I would be honored for a five-star review. You can share it with your family and friends. It may well save someone you love.
**Dr. Warwick Bishop:** Hi, my name's Dr. Warwick Bishop, and welcome to my podcast and videocast station. As always, I'm delighted that you've found the time to have a listen, and I hope I can share with you something that you find informative, beneficial, interesting, and worth listening to. So I thought today I'd talk about common cardiac drugs and some of their interactions.
Well, why don't we start with probably the most common drug seen in our entire universe, and that is aspirin. So, aspirin, we see it everywhere. Obviously, you know you'd take two aspirin for a headache. You'd take two aspirin for pain if you stubbed your toe because it's terrific as an analgesic. It is terrific for modifying the inflammatory response. But we also take it to thin the blood. So, aspirin is used very commonly in coronary artery disease, where we want to keep the blood thin. In particular, we want to stop the stickiness of platelets. These are non-cellular particles of a cell that come from the bone marrow. These platelets are part of what forms a clot or a thrombus in a blood vessel.
Interestingly, it seems that clotting within a blood vessel is different from clotting within a vein. In particular, within arteries, we tend to use aspirin and other antiplatelet medications. Within the veins and within the chambers of the heart, say in atrial fibrillation, we tend to use anticoagulants such as warfarin or the non-vitamin K oral anticoagulants.
Well, if you think about aspirin, obviously the most common interaction is if it's combined with other drugs that can thin the blood, such as clopidogrel, which is commonly used in association with when we put in a stent, or warfarin, for someone who may have a history of ischemic heart disease or coronary artery disease, who also has atrial fibrillation or a mechanical valve where we use warfarin. So, we do need to be careful with combining other blood-thinning drugs with aspirin. If you are on aspirin, be aware of that and let your doctor know.
Remember that aspirin can also give rise to an upset stomach, and the reason it does that is that it blocks the prostaglandin protection within the lining of the stomach and can lead to an increased risk of ulcer formation. So, having your aspirin with food or milk is recommended. Whether it makes a great deal of difference or not, I'm not quite sure. Watch that space.
The next drug I thought I'd talk about is, again, a blood thinner: warfarin. We've heard of this for years. Warfarin, importantly, is going out of favor a little bit because we've got these new agents called the NOACs or DOACs, which stand for non-vitamin K oral anticoagulants or direct oral anticoagulants. These agents are sort of taking over warfarin, but we do still see it used, particularly in people with mechanical heart valves.
Well, warfarin works through vitamin K, and vitamin K is essential for a number of the factors that combine in a cascade, what we call a coagulation cascade. This cascade of interactions gives rise to fibrin, which then interacts with platelets, and fibrin and platelets together give us a thrombus or a clot and plug a hole in an artery. It's a great thing to have if you've cut yourself, so stopping the bleeding is really important.
Remember though, warfarin acts through vitamin K, so it can be interfered with by particularly dietary things like leafy greens, the so-called cruciferous vegetables, which are fairly high in vitamin K, such as spinach and kale. Importantly though, when we think about warfarin and the advice I give people when they're on warfarin is to realize that when everything stays the same, then warfarin tends to stay the same. The concern is really one about variance and things changing, which can give rise to changes in the warfarin levels.
If you had a very stable warfarin profile for a good long period of time and then, because you happened to have grown some leafy greens in the backyard during spring or summer, you eat lots of leafy greens high in vitamin K, it could certainly throw out your warfarin therapy. This is quite different from if you had leafy greens in the same amount every night, ongoing, all year round.
So while all sorts of things can interact with warfarin food-wise, particularly these vegetables with vitamin K in them, I often advise patients to be aware that foods can make a difference, but try to keep the foods as regular as possible. That way, the adjustments that we make to the blood thinning of warfarin are taken into account by the regular dietary patterns.
It's really important to realize that there are lots of drugs that can interact with warfarin because its metabolism is through the liver, and many other drugs can be metabolized through the liver as well. So if you are on warfarin, particularly if you are being prescribed new drugs, anything from anti-epileptic drugs through to antibiotics, these can interact and cause significant problems with warfarin. So do be aware and always tell your doctor.
The next drug I was going to talk about is clopidogrel, which is an agent that works through the platelets and works synergistically with aspirin to keep particularly the blood thin on the arterial side. We use it in the setting of stenting or in the setting of people with an acute coronary syndrome where they have problems with an artery rupture. This drug generally is used for about a year with aspirin if someone's had a stent in place, but it's important to be aware that proton pump inhibitors such as omeprazole can actually reduce the effectiveness of the drug.
So, drug-drug interactions are something to be aware of, and perhaps, as always, carry a list of your medications so that if your doctor is prescribing you something, they can look and see exactly what you're on. Now, proton pump inhibitors are pretty commonly used, and although omeprazole could potentially reduce the effectiveness of clopidogrel, I've not actually seen that clinically. Commonly, I would see patients who are on a proton pump inhibitor in combination with clopidogrel, and they seem to do okay, thankfully.
You may have heard of the beta blockers. These are drugs that block or dampen down the sympathetic nervous system. Interestingly, because of the way beta blockers are metabolized, grapefruit juice can increase the blood levels and potentially lead to side effects. So, a glass of grapefruit juice here and there is probably not such a big deal. But regular grapefruit every morning with a glass of grapefruit juice could play around with the drug levels and push them up.
Interestingly, grapefruit is not just a culprit for beta blockers, but it can also increase the serum levels of calcium channel blockers. You may have heard of the calcium channel blockers, such agents as amlodipine or diltiazem, which go by trade names of Norvasc or Cardizem. Grapefruit can push these levels up as well.
And interestingly, grapefruit can have a bit of a negative impact in terms of increasing levels and therefore leading to some toxicity potential with atorvastatin, a cholesterol-lowering agent, and simvastatin. So, regular grapefruit, if you're on calcium channel blockers, beta blockers, or statins, could be a problem and one that you might just want to have a think about.
The ACE inhibitors are a commonly used blood pressure agent, and taking potassium supplements or using salt substitutes that are high in potassium could lead to elevated potassium levels. This can cause problems of its own, particularly with a rhythmic disturbance. So, be aware that potassium supplements and salt substitutes, which are high in potassium, could be a problem with the ACE inhibitors, such as enalapril, lisinopril, or ramipril. You may be on one of those agents.
The opposite, low potassium, can be seen if we use diuretic therapy, particularly the frusemide or loop-type diuretics, so potassium is lost. In those situations, it may actually be pretty important to replace the potassium.
Well, what's the story here? If you're on such drugs as frusemide and ACE inhibitors, and there's consideration of potassium supplementation or not, it's probably pretty important that you chat with your doctor about regular testing of the kidneys so we can see exactly what's going on. We can do that in a steady state, so if you're taking an ACE inhibitor and a diuretic, you might find that the diuretic loss of potassium is offset by the ACE inhibitors holding on to potassium, and so everything could be fine. But it's really important to be aware that some of these drugs can interact, and the best way to find the path through that is to get regular blood testing.
It's a pretty simple thing to do, and I'm sure any GP you spoke with about it would be more than happy to assist. While we're talking about low potassium, it's quite important for a drug called digoxin, as it can lead to digoxin becoming more toxic and leading to potentially unwanted rhythms. We see digoxin therapy in atrial fibrillation; it's pretty valuable, works really well, it's an oldie but a goodie, and I use it quite a lot. But if we don't look after that potassium and kidney function, we can run into strife.
A couple of other drugs that I'm going to talk about regarding drug interactions just before we wrap up: sublingual GTN spray can interact with the phosphodiesterase inhibitors like sildenafil, which you might know as Viagra. So, sublingual GTN, the spray under the tongue, together with other nitrates, things like isosorbide mononitrate, can interact together and give people a profound blood pressure drop.
So, it's very important that if there is a history of using a Viagra-type preparation, and then the patient develops chest pain, that the ambulance officers, who tend to give routinely sublingual spray under the tongue, are informed of the use of the Viagra-type preparation. A nasty drug interaction can be avoided. Very low blood pressure can be quite a problem, so it needs to be thought of.
Some people end up on a drug called amiodarone, particularly people who have funny rhythms with the heart. Interestingly, this drug is complex; it interacts with other drugs through its metabolism, in particular things like warfarin. One of the interesting things is that a high-fat meal can increase its absorption and therefore change blood levels, and that's because it's a highly fat-soluble drug. It has a huge volume of distribution, which means as you consume it, it gets into the bloodstream and gets into your fat and ends up in fat reserves. So, if you eat it with a high-fat meal, the drug is absorbed into the fat of the meal, and then you absorb the fat with the drug, increasing the levels.
Well, there you go. I ran through some common cardiac drugs and some common potential interactions. I hope you found that informative. If you have any queries or questions, drop us a note at info@drwarwickbishop.online. If you've got any suggestions for other podcasts, equally let us know. For now, I do, of course, wish you the very best. I hope you live as well as possible for as long as possible. Take care and bye for now.
**Dr. Warwick Bishop:** Hi. Ever wondered what your risk of heart attack is? You should. It's the single biggest killer in the Western world. We're talking one death less than every 30 minutes in Australia, one death less than every 60 seconds in the United States, and nine million deaths globally per annum.
Well, how do you check your risk? You can go to www.virtualheartcheck.com.au. You'll find out about your risk and what can be done. Beyond that, to be even more precise.
