Studies presented to a meeting of the American Association of Anesthesiologists have shed some light on the often wide variation in people's response to anaesthetics and other drugs.

Common foods, such as potatoes, tomatoes and aubergines, contain natural insecticide compounds called solanaceous glycoalkaloids. Even in small amounts, these compounds can greatly slow the metabolism of anaesthetic agents and muscle relaxants. Patients with high levels of solanaceous glycoalkaloids may take up to 10 hours to recover from anaesthesia, compared to the usual 40 to 90 minutes.

According to Daniel McGehee of the Department of Anesthesia and Critical Care at the University of Chicago, potatoes are the most common culprit because they are consumed in such large quantities, both as vegetables and as snack foods.

Another problem highlighted at the meeting was the interaction of over the counter drugs with anaesthetic agents. In one study, for instance, 43 per cent of patients were on a psychiatric drug. Commenting on the findings, Dr Corey Scher of Tulane University School of Medicine in New Orleans said: "We really don't know anything about the interaction of drugs our patients are taking and anaesthesia."

In the light of a poor understanding of the mechanisms of food and drug interactions, careful history taking by anaesthetists was proposed as the most sensible precaution currently available (BMJ, 1998, 317: 1102).