Each year, about 422 million prescriptions are filled in Canada. And each year, countless Canadians are sent to hospital because of problems with these prescriptions.

A study published this past summer in the Canadian Medical Association Journal estimated that more than one in nine of all emergency room visits are medication-related.

Many of the times, the patients are at fault because they skipped doses or ignored warnings on the label. But often, the patient has done everything right; they've simply been the victim of a prescribing error.

Somewhere between a doctor writing a prescription and a patient receiving it, errors can be made with incorrect drug selection, dosage errors, bad medication combinations, or communication problems with the pharmacy.

How serious is the problem in Canada? Startlingly, no one knows. That's because Canada still does not have a decent nationwide system for reporting medication errors.

The systems that do exist focus more on medication side effects or on errors made in hospital. But the problem of prescribing errors made in doctors' offices remains largely unexplored, says Dr. Neil MacKinnon, an associate professor at the College of Pharmacy at Dalhousie University in Halifax, whose primary area or research is studying medication errors.

"If you ask me how many of these errors happen in Canada, I can't tell you. It's a black hole, nobody really knows," he tells CTV.ca.

The U.S. Agency for Healthcare Research and Quality recently published a small study on the problem. They found that of the medication errors that were voluntarily reported, most were prescribing errors.

While none of the errors they found resulted in permanent harm or death,

• 13 per cent required some kind of intervention such as a trip to the ER
• 8 per cent required some kind of follow-up monitoring,
• 3 per cent required hospitalization

Pharmacists intercepted 40 per cent of the errors, while physicians and patients caught 19 per cent and 17 per cent of the mistakes, respectively.

MacKinnon suspects prescribing errors are a big problem. If only one in 10,000 prescriptions leads to a problem for a patient - and most experts would say that's a wildly conservative estimate - that still means there are more than 44,000 incidents in this country a year.

"That a pretty significant number," says MacKinnon. "Even if only a small number of prescription errors are made every year, it still results in huge costs."

Lookalikes and soundalikes

In many cases, the problem lies with the medications themselves. With the number of drugs on the market today, there are lots that look or sound the same. Celebrex, Celexa and Cerebyx, for example, could all be mistaken for another. But the first one is used for arthritis pain, the second for depression and the third for seizures. Mistake one for another and there could be a trip to the ER involved.

Some other examples of brand name soundalikes that can lead to serious errors include:

• Accutane/Accupril
• Lamictal/Lamisil
• Losec/Lasix
• Narcan/Norcuron
• Seroquel/ Serzone
• Taxol/Taxotere
• Zantac/Zyrtec

Doctors, notorious for their poor handwriting, can also run into problems when they write up prescriptions. ISMP Canada is a non-profit organization that regularly alerts health care workers of medication errors. In 2007, it reported an incident in which a doctor had handwritten a prescription for six units of insulin. But when he wrote "6 U" he almost closed the "U" until it looked like an "0," leading to a tenfold overdose for the patient.

MacKinnon says the solution for these mixups already exists: get rid of handwritten prescriptions and bring in electronic prescriptions and electronic health records.

With e-prescriptions, already in use in many parts of the United States, doctors simply type up a prescription into an electronic system and it's sent off to the pharmacy of the patient's choice for immediate pickup. The system alerts the doctor right away if the drug conflicts with anything the patient is already on or any other problems.

Currently, many of those checks happen at the pharmacy, says Dr. Jeff Poston, the executive director of the Canadian Pharmacists Association.

"Part of what the pharmacist does routinely when they take the prescription behind the counter and disappear is they check to make sure the prescription is accurate, that the dose is correct, that there's no interaction between what's being prescribed and what the patient is already on," he tells CTV.ca.

"So the pharmacist actually makes a lot of checks when they get a prescription that patients don't usually see happen."

Electronic health records could also track what medications a patient already takes using the patient's health card number. Currently, B.C. and P.E.I. have such province-wide programs, but in the rest of the country, it's left to drug store chains to track prescription records and they are of no use if a patient decides to use a pharmacy from a different chain.

The Canada Health Infoway, funded by the federal government, is trying to accelerate the adoption of nationwide electronic health record systems, but "it's kind of embarrassing that it's taking so long to implement this across the country," says MacKinnon, who notes the technology has been in place for years.

Monitoring errors

Even if a doctor prescribes the right medication, the pharmacy fills it correctly, and the patient takes the medication as prescribed, there can still be problems.

MacKinnon says he was part of study in Halifax that involved about 22,000 seniors over two years and found that one of every 11 of them experienced something wrong with a medication that sent them to hospital.

"The number one cause of that was lack of monitoring," says MacKinnon.

Patients given new prescriptions need to be monitored to ensure they drug is working as prescribed and not causing side effects that require the patient to stop taking the drug. But too often, doctors do not have their patients come back to ensure that all is well with their prescriptions.

Other times, patients miss out on crucial lab work. For example, 519 of the incidents MacKinnon studied involved patients with thyroid conditions that required them to get regular blood work to adjust their dosage. Many of these patients overdosed simply because they had not gone for the lab work.

Most prescribing errors are not the result of incompetence, MacKinnon says; they're due to what he calls "system errors."

Family doctors in this country are overworked and tired. They sometimes make simple mistakes. They're not properly informed of medication recalls or warnings because of poor reporting systems.

"We know how to fix most of the problems," says MacKinnon. "The technology is there. But we haven't implemented the solutions."

• 10 ways to protect yourself from medication errors