Mixing prescription drugs is exceedingly common—one in five Americans take three or more prescription medicines, and one in ten people take five or more. But, every now and then, the results can be unexpectedly harmful—and sometimes deadly. Adverse drug-drug interactions are estimated to put tens of thousands of people in the hospital each year, but they’re difficult to predict and even trickier to track. Only a relatively small number of patients may take a specific, harmful cocktail of drugs, and only a subset of those will have a notable reaction.

To get around the problem, a team of researchers (working with journalists at The Chicago Tribune) created a computer model to create side-effect profiles for prescription drugs. Then, they mined a massive database of drug-reaction complaints sent to the Food and Drug Administration, as well as 380,000 electronic health records. The results of the analysis so far suggest that four drug combinations—including the combination of the common antibiotic, ceftriaxone, with the over-the-counter heartburn medication, Prevacid (lansoprazole)—may cause a potentially fatal heart rhythm. The findings were published Wednesday in the journal Drug Safety.

The results are only preliminary and need to be backed up with more data. But in lab tests with living cells, researchers found that the combination of lansoprazole and ceftriaxone blocked an electrical channel crucial for a heart beat.

The other problematic drug combinations that the data flagged as possibly producing the same heart problem are: cefazolin, an antibiotic, and meperidine, a pain medicine; meperidine and vancomycin, another antibiotic; and metoprolol, a blood pressure medication, and fosphenytoin, a seizure medication.

While the results still need to be validated in more studies, the researchers are hopeful that the new method will identify other potential drug-drug interactions that could avert deadly events.

Drug Safety, 2015. DOI: 10.​1007/​s40264-016-0393-1 (About DOIs).