Should weight factor into antibiotic dosage?

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Most antibiotics and antimicrobial medications are prescribed to adults based on broad dosage recommendations that do not take individual body mass into account, a system that is outdated, according to an editorial published in the current issue of the British medical journal The Lancet. Whereas children’s antibiotic dosing is generally calculated according to body mass, for adults, no such system is in place, and for those drugs that do have body mass specific guidelines for dosing, adherence is “inadequate,” according to the authors. Drs. Matthew E. Falagas and Drosos Karageorgopoulos of the Alfa Institute of Biomedical Sciences in Athens point out that, under current practices, a 200 lb., 6’2″ man (90kg, 1.9m) diagnosed with pneumonia would receive the same dose of antibiotics as a 124 lb., 5′ woman (56kg, 1.5m) with the same condition, despite their dramatically different body sizes. While dosage according to body mass is standard in anesthetics, pediatrics, oncology and other fields, when it comes to antibiotics and antimicrobials the dosing guidelines are too broad, the authors argue, and may undermine a medications efficacy. What’s more, in the face of both widespread obesity and the increasing prevalence of antibiotic-resistance, tailoring dosage for optimal results is increasingly important.

While people with kidney trouble, children and the elderly are often studied separately during clinical trials used to determine appropriate dosing, the rest of the general population is often lumped together—resulting in broad standards for dosing that may not be optimal for all body types, Falagas and Karageorgopoulos argue. As they highlight, “[s]everal physiological alterations reported in obesity can affect the processes of distribution, protein binding, metabolism, and clearance of antimicrobial agents.” That is, overweight patients may need larger doses for the medication to be effective, in the same way that underweight patients may need lower doses.

Of course, the authors concede, there will be hurdles to achieving this goal. Conducting and—finding funding for—studies to establish dosing guidelines will take time, and once formulas are established, doctors will be charged with the extraordinary challenge of keeping track of different equations for a broad range of medications, a possibility that could introduce frequent errors in dosing. While the authors suggest that those problems might be solved by technology—doctors using doctors using “personal digital assistants” or relying more frequently on computerized pharmacy dosing systems, already used in many hospitals, they aren’t likely to be as accessible in a local doctor’s office or primary care settings. Still, the authors say, if simple, effective guidelines can be routinely applied to children’s antibiotics and antimicrobial drugs, there must be a comparably low-tech way to achieve the same standard for grown ups. With the inescapable prevalence of obesity—34% of Americans are obese, and the problem of antibiotic-resistant super bugs, “a one-size-fits-all strategy for prescribing antimicrobial agents to adults is outdated,” the authors conclude.