Medical Matters: Errors of medication: serious side effects and the seven deadly drugs

Many of us will have experienced a case of “the cure is worse than the disease”. It could have been a complication of surgery, such as bleeding or infection, or a side effect of a medication we were taking. Most adverse outcomes are not the result of an error by a healthcare professional; rather they are a known risk of a treatment where a particular individual is regrettably the one in 100 or one in 1,000 when the side effect occurs. But most medication errors do not cause harm.

However, some serious medication errors do occur, as a literature review published this year in the European Journal of Clinical Pharmacology found. The Danish researchers looked at all studies containing information about adverse reactions caused by serious medication errors. This systematic literature review revealed that 47 per cent of all serious medication errors were caused by seven drugs or drug classes: methotrexate, warfarin, non-steroidal anti-inflammatory drugs (NSAIDS), digoxin, opioids, acetyl salicylic acid (aspirin), and beta-blockers.

The chief culprits

Aspirin, NSAIDS and warfarin, which is a blood thinner, are the chief culprits when it comes to unwanted bleeding. Often from the stomach or intestines, this gastrointestinal bleeding does not usually involve a significant haemorrhage; instead a patient who may have been well settled on one of these drugs is suddenly discovered to have a blood count well below normal. The reason is that they have been bleeding quietly and unobtrusively for months from their gastrointestinal system as a direct side effect of the medication.

Methotrexate, which was responsible for a quarter of the serious medication errors in the Danish study, is an immune-system suppressant. Some 80 per cent of patients taking the drug do so for arthritis, while most of the remaining 20 per cent are prescribed methotrexate for skin diseases. About 11,000 people in Ireland take the medication.

Appropriate monitoring

Oral methotrexate is a safe and effective drug if taken at the right dose and with appropriate monitoring. However, it has some unusual characteristics which can lead to problems. For example, it is one of very few medicines taken at a once-weekly dosage; this can easily be misread or misinterpreted as a once-a-day regime.

In addition, because of its mode of action, blood tests to check blood count and liver function must be carried out every three months before a prescription can be repeated. The side effects from methotrexate include mouth ulcers, fever and unexpected bruising and bleeding. These must be investigated promptly.

Narrow therapeutic window

Opioids, the strongest painkillers, can inadvertently suppress the respiratory system, while digoxin, originally derived from the foxglove and used to treat certain heart- rhythm disturbances, has what is called a narrow therapeutic window. This means there is a narrow blood concentration range where it is effective; if the blood level goes too high, the drug is toxic, while if it slips too low, digoxin is ineffective.

What can be done? The Danish study authors concluded that focusing on the seven drugs they identified could reduce hospitalisation, disability and even death by half. And the following tips could protect you from an adverse drug reaction:

Never take medication that

is a different colour, shape or size to your regular tablets without first checking with your doctor or pharmacist.

If you feel a drug is not helping, tell your doctor you would like to stop taking it or discuss an alternative treatment with them.

If you develop new symptoms within days of taking new medication, contact the doctor who prescribed it to discuss stopping the drug.

Read the information leaflets

that come with your medication. These will tell you about potential drug interactions and side effects.

And when it comes to prescribing, Sir William Osler’s advice comes to mind: “The young physician starts life with 20 drugs for each disease; the old physician ends life with one drug for 20 diseases.”

mhouston@irishtimes.com muirishouston.com