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FOOD AND DRUG ADMINISTRATION - page 242 / 263

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certainly T4 is not good.  He alluded to changes that can affect TSH.  All the same things can affect T4.  T4 is affected by upright posture.  It's affected by fluid changes.  It's affected by protein binding.  Many more things than TSH is.  TSH can be measured both sensitively and accurately.  The variation in a good TSH assay is extremely tight.  We have third- and fourth-generation TSH assays that make that irrefutable.

Dr. Johnson, I think, ignored the wealth of the data this morning, the Hennessey data, that showed that T4 levels could be the same but TSH is not.  The pituitary is not sensing those levels as the same, and even if, in his last slide where the confidence intervals in the bioequivalence test between the four preparations did fall between the 80 to 125 standards, that's not being questioned.  It's whether that standard really reflects bioequivalence in the pharmacodynamic sense.  To us physicians, it does not.  It may be good pharmacokinetics, but it's not pharmacodynamics and that's what we're concerned about, not the statistics but the clinical effect.

Thank you for the opportunity to make some

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