Always mention use of over-the-counter drugs to a doctor or pharmacist when filling a prescription to prevent adverse reactions, medical experts warn. (Adrian Wyld/Canadian Press)

Australian actor Heath Ledger, best-known for Brokeback Mountain, attracted international headlines when he was found dead in his Manhattan apartment in January 2008. His accidental overdose of six prescription drugs — including painkillers, sleeping pills and anti-anxiety medication — highlighted the danger of mixing medications, be they prescription, non-prescription or herbal.

There were over 45,000 adverse reactions to medication reported in Canadian hospitals outside of Quebec in 2006/07, according to the Canadian Institute for Health Information. In other words, about 22 out of every 1,000 people were hospitalized because of such a reaction. These cases included patients who had a reaction due to prescription drugs, over-the-counter medications or herbal medications, with some exceptions including opioids and related analgesics, and bacterial vaccines. The rate of adverse medication reactions due to multiple drugs is unknown, the CIHI said.

Thankfully, most combinations are not fatal. And, according to Dr. Brett Taylor, an emergency pediatrician at the IWK Health Centre in Halifax, more physicians and pharmacists are moving towards prescribing fewer drugs. But people still suffer drug interactions. Taylor said one of the reasons is that patients often take their drugs in an inappropriate manner, or take them with multiple medications that they were prescribed at different times. The results can be toxic.

In an article presented at the 2007 American Pharmacists Association, author Kathryn Hahn identified the 10 drugs most commonly implicated in adverse events requiring a visit to the hospital. These were:

• Insulin (8 per cent).
• Anticoagulants (6.2 per cent).
• Amoxicillin (4.3 per cent).
• Aspirin (2.5 per cent).
• Trimethoprim-sulfamethoxazole (2.2 per cent).
• Hydrocodone/acetaminophen (2.2 per cent).
• Ibuprofen (2.1 per cent).
• Acetaminophen (1.8 per cent).
• Cephalexin (1.6 per cent).
• Penicillin (1.3 per cent).

Patients often take their drugs in an inappropriate manner, or take them with multiple medications that they were prescribed at different times. (CBC)

Hahn pointed out that 40 per cent of the hospital visits due to adverse drug reactions were due to unintentional overdoses, followed by drug side effects and allergic reactions. Tania Antenucci, director of pharmacy programs at the Ontario Pharmacists' Association and a part-time practising community pharmacist, said she frequently sees adverse reactions — largely between different prescription medications, but also between prescription and over-the-counter drugs.

"It would be medications that the patient is taking in their medical profile that would typically interact with each other," she said.

Antenucci said certain antibiotics can interact with calcium and iron supplements — reducing the absorption of the drugs. Cholesterol-lowering drugs can interact with antibiotics, which can result in serious heart problems. And often patients take a mix of prescription and over-the-counter medications without realizing they have the same ingredients. One example she mentions is Percocet, a narcotic pain reliever that contains acetaminophen. When taken with Tylenol (acetaminophen), it leads to a much higher dose of the drug in the body.

"Quite often, we see that type of interaction, where they have a particular substance already in a medication that they're taking that's available over the counter in a different form," said Antenucci.

There's also the issue of multiple physician involvement. "We also see a lot of duplicate therapy as well," said Antenucci. "This may stem from a patient going to see different practitioners or primary care providers across the city."

She said patients often will receive one drug from a family doctor and then be prescribed another very similar medication on the weekend at a walk-in clinic. "Eventually this will increase the levels of the drug in the body."

Common interactions

The U.S. Food and Drug Administration warns consumers on its website of common drug interactions between over-the-counter drugs and prescription medications:

Drug mixes to avoid

Drug category:	Ask your doctor or pharmacist if:	When using this product:
Acid reducers (drugs that relieve heartburn and indigestion)	You are taking theophylline, warfarin or phenytoin.
Antacids	You are taking a prescription drug.
Antiemetics (drugs for prevention or treatment of nausea, vomiting or dizziness associated with motion sickness)	You are taking sedatives or tranquilizers.	Avoid alcoholic beverages.
Antihistamines (drugs that relive allergy symptoms)	You are taking sedatives or tranquilizers. You are taking a prescription drug for high blood pressure or depression.	Avoid alcohol, sedatives and tranquilizers. Avoid alcoholic beverages.
Antitussives (cough medication)	You are taking sedatives or tranquilizers.
Bronchodilators (drugs that relieve bronchial tightness or wheezing brought on by asthma)	You have ever been hospitalized for asthma or are taking a prescription drug for asthma.
Nighttime sleep aids	You are taking sedatives or tranquilizers.	Avoid alcoholic beverages.
Nighttime sleep aids	You are taking sedatives or tranquilizers.	Avoid alcoholic beverages.
Stimulants		Limit the use of foods, beverages and other drugs that have caffeine.
(Source: U.S. Food and Drug Administration)

Health Canada also has an adverse drug reaction monitoring program, where patients can report adverse drug reactions and read about common ones online, created after CBC News won awards for pioneering the idea in 2004.

Health Canada also has a searchable database where you can look up a medication and its monograph to determine what you can and cannot take with it.

Shopper's Drug Mart also has a comprehensive list of drugs and herbal supplements — and common interactions — on its website that can flag problem drugs.

And there are provincial pharmacy drug monitoring programs, such as OPA-sponsored Safe Meds — a program taught by pharmacists in Ontario that teaches patients about correct drug taking and common drug interactions — and MedsCheck, a program launched in April 2007 in which pharmacists oversee patients' prescriptions if they are taking more than three drugs at one time.

Keeping doctors and pharmacists in the loop

Antenucci said many patients "don't understand the disease state itself, how to prevent a flare-up or an illness from progressing versus treating it acutely." She said a good example of this is people who fail to take their antibiotic until it's finished, which is critical in preventing antibiotic resistance.

Another example is when people suffering from asthma resort to drugs that provide quick relief while failing to take drugs that actually work at preventing flare-ups of the illnesses.

The best way to ensure an adverse reaction doesn't occur is to always list all the prescription drugs, over-the-counter medications and herbs you are taking so that your doctor or pharmacist can review them and check for any possible interactions.

"If you're taking St. John's Wort [a herb used to treat depression], tell the pharmacist before you pick up your prescription," said Taylor. "Pharmacists are underutilized."

Antenucci agreed. "In situations where patients have multiple medications and they're not sure, patients have the right and they certainly have the opportunity to reach out to, specifically, pharmacists who are accessible enough — especially now, with 24-hour stores — that they can ask if they're not sure."

Another key thing to remember is to take your medications as directed. The FDA advises people read the directions for use, the active ingredients, the warnings and the uses sections of the label to make sure they're not taking the same drug in another form.

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