LETTER
Three-Year Follow-up on the Effects of Transdermal Estrogen
A.M. Parfitt, MD
1 May 1997 | Volume 126 Issue 9 | Page 742
TO THE EDITOR:
The demonstration by Drs. Lufkin and Riggs [1] of a significant further gain in bone density of the lumbar spine in the second year of transdermal estrogen therapy is a valuable corrective to the view that this phenomenon is unique to bisphosphonate therapy. However, the authors' conclusion that the mechanism must involve something more than a remodeling transient is premature. They cite an old paper of mine [2] to the effect that the transient lasts no more than 6 months, but this estimate has been superseded. When the remodeling process is considered in three dimensions rather than in two-dimensional cross-sections [3], 12 months is a more realistic estimate in normal persons. The duration may be even longer in osteoporotic patients, especially when the remodeling rate is inhibited by treatment [4]. When the completion of secondary mineralization is taken into account, attainment of a new steady state may take as long as 2 years in some patients [5]. Only if this simpler explanation can be convincingly excluded will the continuation of bone gain for several years provide evidence that bisphosphonates (and estrogen) have a genuine anabolic effect. Regrettably, the uncertainty of mechanism has not prevented the U.S. Food and Drug Administration from allowing this unjustified claim by several pharmaceutical companies in their advertisements in the medical press.
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Author and Article Information
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University of Arkansas for Medical Sciences, Little Rock, AR 72205
1. Lufkin EG, Riggs BL. Three-year follow-up on effects of transdermal estrogen [Letter]. Ann Intern Med. 1996; 125:77.
2. Parfitt AM. Morphologic basis of bone mineral measurements: transient and steady state effects of treatment in osteoporosis [Editorial]. Miner Electrolyte Metab. 1980; 4:273-87.
3. Parfitt AM. Osteonal and hemi-osteonal remodeling: the spatial and temporal framework for signal traffic in adult human bone. J Cell Biochem. 1994; 55:273-86.
4. Frost HM. The origin and nature of transients in human bone remodeling dynamics. In: Frame B, Parfitt AM, Duncan H, eds. Clinical Aspects of Metabolic Bone Disease. Amsterdam: Excerpta Medica; 1973:124-40.
5. Heaney RP. The bone-remodeling transient: implications for the interpretation of clinical studies of bone mass change. J Bone Miner Res. 1994; 9:1515-23.
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