Doctors' alert on herb-drug interaction

The spotlight was cast on the safety of Chinese herbal medication last month following the death last year of a 58-year-old woman who took cordyceps the week before an operation to remove a benign brain tumour.

She had failed to inform her doctors about her use of cordyceps, which is believed to lead to the extensive bleeding in her brain.

The case has prompted doctors and traditional Chinese medicine (TCM) physicians to urge the public to be upfront about their use of medications, including herbs and herbal products.

The interaction between a herb or herbal product and a drug in the body "may augment the action of the drug, reduce the effectiveness of the drug or cause unexplained side effects", warned Ms Lim Ching Hui, senior principal pharmacist at Singapore General Hospital.

She gives four examples of herb-drug interactions that people should be aware of:

• Herbs with high mineral content - such as Gypsum fibrosum (shigao), Concha arcae (waleng zi) and Concha ostreae (muli) - may prevent the oral absorption of the fluoroquinolone class of antibiotics.

The oral and intravenous forms of these antibiotics are used to treat bacterial infections of the lungs, respiratory tract, urinary tract, gastrointestinal tract, abdomen, and bones and joints, among other uses.

• Polyphenols in green tea can inhibit the effects of the anti- cancer drug bortezomib, which is used for the treatment of myeloma, a type of blood cancer.

This observation is based on experiments conducted in the test tube and on mice.

It is therefore not advisable for patients receiving bortezomib to consume green tea extracts or drink green tea in large amounts.

• Patients taking a class of drugs called tyrosine kinase inhibitors for the treatment of chronic myeloid leukaemia, lung and kidney cancers are advised to avoid grapefruit.

Grapefruit contains a group of chemical compounds known as furanocoumarins which can inhibit the enzyme CYP3A4 that metabolises this class of drugs, causing accumulation of these drugs in the body.

• Ephedra sinica (mahuang) is the herb from which the drug ephedrine is derived.

Ephedrine is usually used in cough and cold medicines.

Taking Ephedra sinica and other herbs with similar properties has the potential to stimulate the brain, increase heart rate, narrow blood vessels and increase blood pressure, and cause sweating.

joanchew@sph.com.sg

This article was first published on June 21, 2016.
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