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Your Good Health: Generic drugs must meet standards

Dear Dr. Roach: I read that with certain medications, you should never take the generic medicine over the nongeneric. I read this for Synthroid and levothyroxine, as the range varies greatly. Is this true? I have also heard this about heart drugs. K.
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Dr. Keith Roach writes a medical question-and-answer column weekdays.

Dear Dr. Roach: I read that with certain medications, you should never take the generic medicine over the nongeneric. I read this for Synthroid and levothyroxine, as the range varies greatly. Is this true? I have also heard this about heart drugs.

K.A.

Many physicians insist on brand-name Synthroid; however, generic levothyroxine is effective at treating thyroid issues. I treat my own patients with either, depending on their preference.

A 2017 study showed that brand-name Synthroid was about 1.7% better than a generic at keeping patients in the desirable range of thyroid hormone. The clinical value of this is marginal. However, patients who are taking levothyroxine should use the same generic manufacturer, and if they must switch, should have a thyroid blood test afterward to make sure the dose is still appropriate. Your pharmacist can tell you your manufacturer and can try to order the same one consistently.

Other medications, such as some for heart problems and seizures, also have a narrow range of effectiveness: Too little and the drug is ineffective; too much and it is toxic. Some physicians prefer brand names but the U.S. Food and Drug Administration requires that both brand name and generic drugs meet the same standards for exact doing and purity.

Dear Dr. Roach: My 75-year-old uncle was diagnosed with an enlarged prostate some time ago. He tells me that he now has a strong burning sensation shortly before and during urination and would like to know the cause of the burning apart from a possible urinary tract infection. He thinks it is from the urine being too acidic, which encourages bacterial growth. He wants to eliminate acidifying fruits such as oranges and grapes, soft drinks and acidifying foods like fish and eggs. What is your opinion on this?

R.I.

An enlarged prostate and symptoms of burning should absolutely raise the suspicion for a urinary tract infection, which is easily evaluated. If that isn’t the answer, and it very well may not be, then the diagnosis is the catch-all term “lower urinary tract symptoms.” Although your uncle possibly may benefit from changing the pH of his urine through diet, it is not effective for most people, and the changes he is proposing may not have the effects he expects. High-protein foods such as fish and eggs do tend to make the urine more acidic, but an acid food like an orange has the paradoxical effect of making the urine more alkaline (one can also say less acidic). Large amounts of orange juice are necessary to make a significant change in urine pH. Small changes in pH have negligible effect on bacterial growth.

Lower urinary tract symptoms can come from prostate or bladder. If the enlarged prostate is thought to be the underlying cause, a trial of medication to shrink the prostate is reasonable to see whether that helps. In my experience, burning alone is unlikely to be due to prostate enlargement, even if he has that diagnosis. He may have other symptoms, such as a weak urinary stream or a feeling he can’t empty the bladder completely, which would make the prostate a more likely culprit.

In a man who has been shown not to have a urine infection as the cause of the symptoms, failure to respond to appropriate trial of therapy is an indication for evaluation by a urologist.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers can email questions to ToYourGoodHealth@med.cornell.edu