A subscriber to our Health After 50 newsletter asks: I'm taller and heavier than the average person. Should I be taking a higher dose of antibiotics? Here’s what we know …
Physicians use height/weight formulas when prescribing antibiotics to children. And body size characteristics figure prominently in prescribing other medications with a narrow therapeutic index -- when the amount of medicine needed to produce a beneficial effect is very close to the amount that causes more harm than good. (Chemotherapy drugs and blood thinners such as warfarin are some examples.) However, as an editorial in The Lancet recently pointed out, a 6 foot, 198-lb male with pneumonia will likely be prescribed the same dose of antibiotics as a 5 foot, 123-lb woman.
Some research suggests that one-size-fits-all dosing of antibiotics poses a distinct disadvantage for heavier people. Why? Large -- especially obese -- people have comparatively larger blood volumes than their normal-weight counterparts. Consequently, the concentration of an antibiotic in the bloodstream is lower in a large, obese individual than in a smaller one, making it harder for the antibiotic to fight infection.
In fact, some experts theorize that insufficient dosing relative to body size may help explain why obese people tend to recover poorly from infections. Insufficient dosing may also push physicians to prescribe more antibiotics for longer durations, thus contributing to the alarming trend of antibiotic resistance.
Ideally, antibiotics should be individualized to age, gender, and liver and kidney function as well as height and weight. But clinical trials on individualized dosing have yet to be conducted. It's not clear if this would be cost-effective, as drug manufacturers would also have to make changes to match individual patients' needs. For now, talk to your doctor about upping your dose if your current one isn't helping.
