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Dear Dr. Roach: I am 71 years old, stand 6 feet, 5 inches tall and weigh 325 pounds. The “average” person is half my size, yet when I get medication for various ailments (e.g., gout, pain, flu shots, etc.) I get the standard dose. I assume I have more physical mass, as well as a larger blood supply, which leads me to the conclusion that I am receiving a smaller concentration of medicine than the typical patient. Am I correct?

M.K.

Dear M.K.: All medicines have concentrations at which they work optimally. Too low a dose and they aren’t effective, and too high a dose increases risk of toxicity. Some drugs have a very small range that’s both effective and nontoxic, and these are referred to as having a “narrow toxic to therapeutic ratio.” Others have a very large range where they are effective and nontoxic, such as most over-the-counter pain medicines and flu shots. Penicillin has a very wide toxic to therapeutic ratio, but I use that example precisely because some people will have an allergic reaction. There is no drug, prescribed, over-the-counter or supplement, that is either perfectly safe while being effective, or perfectly effective while being safe, for every person.

The concentration of the drug in the appropriate area of the body (sometimes blood, sometimes the affected organ, sometimes urine) may depend on the dose, as well as characteristics about you. Despite being much larger than average, your blood volume is probably only a little above the average, since the increased bone mass, muscle mass and, in most people your size, fat mass are disproportionate to the blood. Some medicines go to the blood, others to “lean body mass,” and others to fat.

So, while you are correct you are getting a smaller concentration of medicine, it’s still OK most of the time. For meds that need to be dosed precisely, those with a narrow toxic to therapeutic ratio (such as some antibiotics, heart medication and chemotherapy), the dose is based on height, weight, age and sometimes kidney and liver function.

Dear Dr. Roach: I am 76 years of age and have glucose in my urine (113mg/dL, with the normal range being 70-99). Is this a serious condition?

A.

Dear A.: The range you gave is for glucose in the blood, not in the urine. Any amount of measurable glucose in the urine is very likely to represent diabetes mellitus, although there are other rare causes.

A blood sugar of 113 mg/dL is not normal and suggests glucose intolerance or prediabetes — if the blood was drawn fasting; 113 is normal if taken after eating.

An A1c test looks at average blood sugar over three months or so, and a glucose tolerance test remains the most accurate diagnostic test for diabetes.

Email questions to ToYourGoodHealth@med.cornell.edu.

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