If doctors could measure drug levels in your blood, they’d be sure you’re getting the right dose. They could monitor drug interactions, adjust doses after severe side effects and figure out why a combo isn’t performing. But the April 15th issue of Clinical Infectious Diseases cut the sprouting science of therapeutic drug monitoring (TDM) down to size. The journal printed a small study suggesting that TDM still can’t track all drug-level variations, since levels changed even when readings were taken at the same time of day. The investigation followed ten people, who were measured three times a week over four months. Readings proved far too diverse to guide drug dosage. So the effort to tailor treatment to drug levels continues.