Doctors warn of drug interactions
In mid summer, Health Canada issued a warning about a deadly drug interaction between two anti-cholesterol drugs, Baycol and Lopid. Baycol’s manufacturer, Bayer, pulled the drug off the market after 31 deaths in the United States were linked to its use. (Lopid was not affected by the recall.)
According to several Canadian doctors, drug interactions like this are a growing problem. They say just two medications gives you a six per cent chance of some adverse reaction. If you take five medications, chances are 50 per cent you’ll have some adverse interaction. And for eight medications, it’s 100 per cent sure you’ll have drugs interacting.
And in several instances in recent years, the effects have been so serious patients have died.
But how likely is it that the average person would take five to eight medications? According to Dr. Peter Lin, medical director of the Health and Wellness Centre at the University of Toronto Scarborough campus, the likelihood is increasing as the population ages and the baby boomers head into their ’50s. He says that’s the time of life when illness and medication use traditionally incrse.
“To give you an example of how quickly you can get there: let’s say you have a heart attack. Twenty years ago, you might have got a little bit of morphine, went home with some nitro glycerin, and that would be it,” he says.
“Nowadays, after a heart attack, the big studies are telling us you should be on Aspirin, you should be on a beta blocker, an ace inhibitor, and a statin of some sort to lower your cholesterol. Automatically, after a heart attack, you’re committed to four medications. If you have diabetes, you have to add on those medications. If your blood pressure is not well controlled, you’ll need two to three medications to control it properly. So therefore you can see the number of prescriptions increasing rather significantly,” he says.
Health Canada reports a 29 per cent increase in the number of adverse drug interactions between 1999 and 2000. About 45 per cent of these were considered serious.
Dr. Lin says the public tends to look on drug interaction like a lightning bolt that comes out of the blue. There are examples of the interaction between the allergy drug Seldane and the antibiotic erythromycin, which upset heart rhythms. And a year ago, the heartburn medication Propulsid was taken off the market after several deaths were attributed to its interaction with other medications. Now, the same fate has hit Baycol.
“About 75 per cent of drug interactions can be predicted. By understanding how drugs clear through your body, you can understand that in certain situations, if you combine these two drugs, they’re going to affect each other. So what you do is change the dosing, or select other medication. Then we can prevent many of the drug interactions from occurring. There is evolving science that is teaching us how to avoid these areas,” says Dr. Lin.
He says drug processing in the body is very complex. One part of the system is a group of enzymes found in the intestinal well, the gut and liver. They’re called cytochromes. These cytochromes are pathways for processing and clearing all the chemicals that come through the body. That could be food, herbs, or other sources of chemicals. Different chemicals use the same pathways to clear the body.
Cytochromes can speed up and clear the chemicals more efficiently or they can be slowed down. When that happens, Dr. Lin says you get a rise in levels of certain chemicals in the body and that’s when the trouble starts. He uses a traffic flow analogy to describe how this happens.
“Think of the Don Valley Parkway (in Toronto). People are all driving alongside one another on the freeway, no problem. But if you take a truck and park it sideways, you’ll plug up the highway. Then you’re affecting everyone else using the highway. So if you have drugs that affect cytochromes in that way, then you have drug interactions,” he says.
Keep a list
Dr. Robert Bailey says it’s important that patients and the medical profession, including pharmacists, become more aware about the problem of drug interaction. He’s a gastroenterologist and professor of medicine at the University of Edmonton in Alberta.
“Patients who come to my office now, not all of them, say ‘here’s a typed list of my drugs’-which is great. They may not think about it the same way the medical profession does, but they know it’s important. But you’d be surprised at the number of patients who forget, or say ‘I was taking that blue pill’ or ‘I was taking that over the counter thing’ or ‘I’m on this hormone replacement but that doesn’t count’,” he says.
“So sometimes you say, ‘listen, the next time you come to see me, don’t worry about the list, you just empty the drug cabinet. Put them all in a bag, and bring them in when you come to see me.’ And you line them all up-and there’s an amazing number-and one of your jobs, as a physician, is to say ‘do you really need all of these things’. Because in this day and age, particularly in big cities, they don’t go to the same doctor all the time. They go to a walk-in clinic, or emergency, and everyone is trying to help them. So they say ‘try this’-and pretty soon, there’s a whole bunch of ‘try this’-a bag of them. So doctors have to get them to bring in the pills,” he says.
Dr. Bailey says the Capital Health Authority in Edmonton uses computer link-ups with all the city’s pharmacies to keep a record of the drugs used by individual patients. He says hospital emergency departments can call up the list of drugs and get a complete history on the patient.
“Now that’s a case of technology helping us. It also saves a lot of time. When you try to dig out the history from the patient, you say ‘did you ever have heart disease’ and you get the answer, ‘well, yes’. But when you get this list, you say ‘you’re on these four things’-and they say, ‘oh is that what they’re for?’ When you get into a stressful situation, you can’t remember everything. So as a broader heath care community, using this approach is one of the things we’re doing,” he says.
Manitoba is another jurisdiction using a similar approach. Dr. Lin says in Ontario, the pharmacies are connected for people in the seniors’ drug programme or on social assistance. But the data is used for billing the government, not for medical avoidance of potential drug interactions.
“I love the Alberta approach because I think that’s the right approach in the long term, using technology to help out,” says Dr. Lin.
Pharmacy drug list
“We’ve got simple technology in Toronto. Number one, we tell the patient to go to the same pharmacy. And that way the pharmacist has a computer that checks that new prescription against all the old prescriptions you’ve ever had. And that’s nice, because that old prescription is probably still sitting in the cupboard. So the pharmacist can pick that up and check it for drug interaction with the new prescription,” says Dr. Lin.
“The second thing we tell them to do is to hang onto the little label from the pharmacy with the drug history of the last 10 drugs prescribed. We ask our patients to stick that label on the back of our business card. So now the patient has our name, phone number, and a printed out list of the real names of the drugs-not just blue pill, red pill. So that’s all in one place, and we tell them to keep that in their wallet so wherever they go, they have that information,” he says.
Dr. Lin says patients also need to realize that taking generic and brand names of the same drug is doubling up the amount of the drug in their system. And that can sometimes create a problem with the safe therapeutic “window” for any medication and increase chances for bad interaction with other drugs.
“So you might see a diuretic which says ‘apo’ and then another bottle that says ‘novo’. So chances are they’re taking one of each, because they think apo and novo are two different drugs. So they double dose on that kind of drug regularly. So we worry about that.” He says.
Dr. Lin is also involved in physician education about drugs and potential drug interaction.
“Most doctors use 10 to 15 drugs regularly in a daily practice. What we try and do with them is say ‘just know your 10 to 15 drugs you use daily. Know those inside out.’ There are another 10 drugs you use peripherally. So understand those ones. And for the rest of them, just know where to go and look it up. You don’t have to know the whole drug compendium,” he says.
“The second thing we’re trying to teach is a basic principle that if all drugs in a certain class are the same, they all work equally well, then what you should do is pick the one that’s least likely to offend in terms of drug interactions. And if you do that with every category of medication, then at the end of the day, you’ll end up with a patient at the lowest risk of drug interaction and health complications,” says Dr. Lin.