Sir, I read Grapefruit consumption improves vitamin C status in periodontitis patients (BDJ 2005; 199: 213–217) with interest; it is refreshing to see a holistic approach being taken in research topics. However, before we all recommend our patients consume vast quantities of grapefruit in the fight against periodontal disease, a word of warning. There are some well documented interactions of certain drugs with grapefruit juice in particular.1

Grapefruit juice appears to selectively inhibit the CYP3A4 enzyme system found in the liver and in enterocytes in the small intestine, which can increase the bioavailability of a drug. This inhibition can last for up to 24 hours with a maximal effect when the juice is taken with the drug or up to four hours.

Interactions have been found between grapefruit juice and some of the drugs in the following categories: antihypertensive drugs, 'satins' used to reduce blood cholesterol, immunosuppressant drugs, protease inhibitors used to treat HIV/AIDS, some anxiolytics and antihistamine medications.2

It would therefore be prudent for the patient to obtain advice from the prescribing medical practitioner.