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Last updated: 21 July 2014
Mixing medicines can be a recipe for disaster. It can be harmful and dangerous to take different types of medicines together, but many people are in the dark about how medicines interact with other pharmaceutical treatments, and which combinations should be avoided.
Adverse drug events account for more than 400,000 GP visits and 190,000 hospital admissions annually. These figures are conservative and don't necessarily include hospitalisations for injuries, such as car accidents or falls, that may have been a result of medication issues.
While it's hard to put a total dollar cost to the health system of medication-related problems, in 2008 hospital admissions alone were estimated at $660 million. Yet about half of these hospitalisations were likely avoidable.
Who is at risk?
The most commonly implicated drugs are cardiovascular medicines, anticoagulants, anti-inflammatories and chemotherapy medicines. People most likely to be affected are those who:
take five or more medications together
use 12 or more doses per day
have had significant recent changes to their treatment regimen
require ongoing monitoring of medication effects
have language difficulties, problems with dexterity, poor eyesight or dementia
attend several different doctors.
Many elderly people are at risk of adverse events from medicines, which can result in hospital admissions. Not only are they more likely to suffer adverse drug events, but their recovery is likely to be poorer.
Why so many drugs?
People these days are relying more heavily on medications than ever before, with the average number of daily drug doses per person more than doubling in the past 20 years. There are several reasons for this:
The trend to treat single conditions with several drugs.
Risk factors for disease are increasingly managed with medication.
Lifestyle-related conditions, which are on the increase (such as heart disease, high cholesterol, high blood pressure and diabetes), are more conveniently treated with medicines than with a better diet or more exercise.
We're living longer and acquiring more health conditions along the way that need treatment.
Prescription medicines, while helpful in treating or preventing relevant health conditions, often have side effects, and sometimes the side-effect costs outweigh the benefits of the drug. A classic example is benzodiazepines – prescribed to help people sleep, they also increase the risk of falls and broken bones in elderly people.
Polypharmacy
Polypharmacy is the term for people taking many medications – with an accepted clinical definition of "many" being five or more. It's estimated that up to 40% of Australians over 65 are on five or more medications, sometimes with dire consequences. If all drugs have a small chance of side effects, taking different medications combined increases the overall risk and introduces the additional danger of interactions between medicines.
One example is warfarin, a commonly prescribed anticoagulant that interacts with some anti-fungal pills and creams, anti-arrhythmic drugs, thyroid drugs and diuretics, among others, to increase the risk of bleeding. Over-the-counter medicines such as aspirin and herbal medicines such as St John’s wort can also interact with prescription medicines.
On the other hand, taking a few different medicines for some conditions can help reduce the dose of each, and therefore reduces the risk of side effects. And when treating infectious diseases, such as tuberculosis and HIV, multiple drugs can reduce the development of drug-resistant strains. However, drug combinations in these sorts of situations have usually been adequately tested.
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When prescribed appropriately, medicine is usually helpful for most people – but that's not always the case. When in doubt about the p