New pharmacogenomics help in guiding dosages


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, and it is likely that it will be used to more precisely guide drug choices and dosages.

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. The yawns are very uncomfortable! Do you have any advice, other than taking my car all the time? I will note that none of my other family members react this way. — 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, in at least one spectacular case I heard of, from excess nervousness. However, the runny nose and watery eyes are very consistent with allergies. I was able to find other case reports of people having yawns as an initial symptom of 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.


DEAR DR. ROACH: I am a 78-year-old male in good health. This past June, my urologist gave me a test, which revealed that I was at very low risk for prostate cancer. Since then, my numbers have gradually crept up, and the most recent test (a month ago) showed a sharp spike upward. The doctor has scheduled a prostate biopsy in two weeks. I am thinking that I would like another blood test prior to the procedure. Obviously, I am hoping the numbers will have at least leveled off and hopefully gone down. I would appreciate your thoughts on this. — R.S.

ANSWER: You likely are talking about the PSA test or a relative. I do think confirming the test results prior to biopsy is reasonable, as there are rare lab errors, but more commonly, men can develop inflammation in the prostate, causing a “spike” in the reading. There are several new tests that may improve the accuracy of the PSA. Perhaps the best-known is the PCA3.

Another increasingly used option is a prostate MRI, which can better define the anatomy and guide biopsy. As I have recently written about the pain some men feel with biopsy, reducing biopsy need would be beneficial. It is not yet accepted treatment to forgo biopsy on someone with (confirmed) high PSA but a normal MRI.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to or request an order form of available health newsletters at 628 Virginia Dr., Orlando, FL 32803. Health newsletters may be ordered from