Dear Dr. Roach: Do you have any information on cytochrome P450 testing for drug sensitivity? — S.S.

Answer: Cytochrome P450 is a family of enzymes that are important for cell metabolism and critical for detoxifying many drugs. Any given person has a particular set of P450 enzymes, and understanding them sometimes can help determine the correct exact drug dosages. In a few cases, people with certain P450 enzymes cannot safely take some drugs. However, the clinical usefulness of P450 testing is currently limited, and there are only a handful of drugs for which testing is recommended (for those who want to see the full current list, it’s available on the Food and Drug Administration website at The majority of the drugs for which P450 testing is recommended are for HIV or cancer treatment. Physicians prescribing these drugs would order the appropriate testing.

I do think that this field, called pharmacogenomics, is going to become increasingly useful.

Dear Dr. Roach: My husband bought a used car about two years ago, and every time I ride in his car — no matter the time of day or where we are going — about 10 minutes into the ride, I begin to yawn uncontrollably. These are deep, shuddering yawns that border on painful. Soon thereafter, my nose begins to run, my eyes water and my throat becomes scratchy. Allergies seem the obvious answer, but I have a lot of allergies that don’t cause yawning. — E.R.

Answer: Well, before today, I’d never heard of yawning being a sign of allergies. Yawns are common with fatigue or poor sleep, where air quality is poor and from excess nervousness. However, the runny nose and watery eyes are very consistent with allergies.

If avoiding the offending agent (i.e., whatever is in the car) isn’t possible, premedicating with an antihistamine or prescription medication may be of benefit.