The mixing of treatments can be lethal

MEDICAL MATTERS:Assessing the effects of drug-drug interactions

THERE WILL always be some tension between conventional medicine and complementary/ alternative medicine (CAM). Sometimes the tension is philosophical, of more interest to practitioners than patients. Increasingly, however, it is of practical concern, as we learn more about how both types of medicine interact and discover how certain combinations may even harm patients.

It’s not that all complementary medicines are scientifically unproven. Some herbal remedies are backed by scientific evidence, but there are many conditions, such as cancer and diabetes, for which no proven herbal medicines exist. St John’s Wort works effectively for mild to moderate depression, but it also stimulates enzymes in the liver that cause other drugs in the body to break down more quickly, with the result that these drugs are rendered less effective.

An article in the latest edition of Cancer World points out how some cancer patients are at risk of both under and over treatment because of the interaction of chemotherapy drugs with both conventional and alternative treatments. It’s become a greater problem the more success oncologists are having treating cancer; people are staying on oral cancer drugs for longer. Naturally, they develop other health problems and are as likely as the rest of the population to buy something over the counter without much thought.

According to a study in the Annals of Oncology, herbal medicine is the most commonly used complementary treatment, with homeopathy, medicinal teas, vitamins and mineral supplements also popular among cancer patients.

An article in the same journal found a paucity of studies when the authors searched the medical literature looking for studies of drug-drug interactions in people with cancer. Their best estimate was that about one-third of cancer outpatients were at risk of drug-drug interactions.

How exactly might people suffer where interactions occur? When the effect is to increase the amount of the active drug circulating in the body, the toxic nature of cancer drugs makes a fatal outcome a real possibility. At the very least the interaction will cause an increase in side effects which may result in the person being taken off the cancer drug under the mistaken impression that they cannot tolerate the chemotherapy.

Take the antifungal drug ketoconazole as an example. It causes the blood levels of the cancer drug dasatinib to rise five-fold, with other chemotherapy drugs increasing by a factor of three when used with a commonly used antifungal agent. The antibiotic rifampicin causes the concentration of some cancer drugs to drop by 80 per cent when used in combination. And St John’s Wort, the antidepressant herbal remedy, reduces the level of the chemotherapy agent imatinib by some 30 per cent.

Conventional antidepressants do not mix well with the drug tamoxifen, taken by thousands of women in this country who have had breast cancer.

Partly responsible for the 26 per cent reduction in breast cancer mortality in the Republic, reported in a European study last week, tamoxifen helps prevent the disease recurring.

Many of the SSRI class of antidepressants are known to inhibit the enzyme CYP2D6, which is essential to the effectiveness of tamoxifen.

There is a definite dearth of information for both patients and doctors when it comes to drug-drug and drug-herb interactions. A paper in the current issue of Archives of Internal Medicine describes how a new computer programme has helped reduce drug interactions and medication-related adverse events at a Boston hospital. Using the programme for older patients, it produced a 20 per cent drop in the use of medicines flagged as potentially dangerous.

Of course, you can never replace the value of talking with patients.

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Thanks to all of you who responded to the column on ticks and Lyme disease some weeks back. One reader told me of an effective way to remove ticks from the skin, courtesy of her father who survived the trenches of the first World War. Light a match and blow it out. Apply the still hot head of the match to the protruding tick, which will promptly withdraw its head from under the skin.