An antidepressant taken together with a cholesterol lowering drug, by as many as one million people in the United States, may cause a spike in blood sugar levels, researchers said Wednesday.
Paxil and the anti-cholesterol drug Pravachol do not have this effect when taken independently, said researchers at the Stanford University School of Medicine, Vanderbilt University and Harvard Medical School.
The interaction was uncovered by analyzing voluntary reports of adverse events in a database maintained by the US Food and Drug Administration, and comparing that to electronic medical records held by the three medical institutions.
The study used "data-mining techniques to identify patterns of associations in large populations that would not be readily apparent to physicians treating individual patients," it said.
While none of the patients taking the combination reported having hyperglycemia as a result, researchers found 135 patients who did not have diabetes showed an average increase of 19 milligrams per deciliter in blood glucose after starting treatment.
Among 14 people with diabetes, the effect was greater -- 48 mg/dl after the drug combo was begun.
The blood sugar spikes were significant enough to possibly push a person who is pre-diabetic into full blown diabetes, and to put diabetic patients' health in danger, said the study published in Clinical Pharmacology and Therapeutics.
Then researchers tested the drug combination in laboratory mice who were first fed a high-fat, high-calorie diet which would put them in a state considered pre-diabetic and insulin resistant.
When these pre-diabetic mice were treated with the two drugs for three weeks, their blood glucose soared from about 128 mg/dl to 193 mg/dl. Neither drug alone has such an effect.
"These kinds of drug interactions are almost certainly occurring all of the time, but, because they are not part of the approval process by the Food and Drug Administration, we can only learn about them after the drugs are on the market," said Russ Altman, professor of medicine at Stanford.
"Understanding and mitigating the effect this pair of medications has on blood sugar could allow a person with diabetes to better control his or her glucose levels, or even prevent someone who is pre-diabetic from crossing that threshold into full-blown diabetes," said Altman.
Up to 15 million people in the United States have prescriptions for the two drugs, said the study. Paxil is also known by its generic name, paroxetine, and Pravachol is pravastatin.
The drugs do not currently carry warning against combinations that may increase blood sugar.
"By extrapolating from the electronic medical records at Stanford and elsewhere, we can predict that between 500,000 and one million people are taking them simultaneously," Altman said.