For example, a Dartmouth study found that taking the breast cancer drug lapatinib with food instead of on an empty stomach, as currently suggested, could increase the bioavailability of the drug by 167 percent.

If the food had a high fat content, that number jumped to 325 percent.

Since patients currently take five 250 mg lapatinib tablets on an empty stomach at a cost of $2,900 a month, taking the drug with a fatty meal could potentially lower costs by around 40 percent, or $1,740 per month, said oncologists Mark Ratain and Ezra Cohen of the University of Chicago in a commentary on their own research and the study done at Dartmouth.

If the patient washes everything down with grapefruit juice, which increases the amount of drug concentrated in the plasma, Ratain said he thought the savings might increase to 80 percent.

The authors said many more common drugs should be studied this way to increase drug potency and save drug costs. They are currently conducting a phase 1 trial of the effect of grapefruit juice on sirolimus (rapamycin), an antibiotic and immunosuppressant drug used in organ transplants.

The Dartmouth study was presented in June at a meeting of the American Society for Clinical Oncology.

The commentary is published in the July 16 issue of the Journal of Clinical Oncology.