It fights HIV! It fights hep B! No icky side effects! Too good to be true? Duh. Just when it seemed that Viread (tenofovir), Gilead’s newish nucleotide analogue, was invincible, a smattering of reports shows it can sometimes reduce kidney function (by trashing cells in the microscopic filters). This ain’t pretty (for more on kidneys, see “Hard Workin’ Beans”), but it’s hardly surprising—an earlier version of the drug, adefovir, failed for this very reason. And Viread includes a warning for the kidney-impaired. Happily, the problem cases improved after stopping the drug.

Kidney risk increases if you’re a woman, underweight or have taken other kidney-bashing meds. So if you’re on Viread—or considering it—make sure your doc knows that Gilead discourages those whose serum creatinine (which indicates kidney health) tops 1.5 and whose calculated creatinine clearance is below 60. All systems go? Make sure doc checks your blood and pee regularly for healthy kidney function.