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Kanis et al. erroneously state in a recent paper about the diagnosis and management of osteoporosis in postmenopausal women that 100 μg of PTH(1-84) is equivalent to 40 μg of teriparatide, PTH(1-34) [1]. This equivalence was calculated from their respective molecular weights (4,115 for teriparatide [2], 9,426 for full-length PTH [3]) but does not consider bioavailability. The bioavailability of PTH(1-34) and PTH(1-84) are 95% and 55%, respectively [4, 5].
Bioequivalence requires that the number of PTH(1-34) and PTH(1-84) molecules should be the same: N PTH(1-34) = N PTH(1-84)
The clinical dose is based on molecular weight and bioavailability leading to the equation:
(where M is the molecular weight of PTH, P abs the bioavailability, and m the mass of PTH).
Using this calculation, 100 µg of PTH(1-84) is equivalent to 25 μg of teriparatide {100 μg × (55/95) × 4,115/9,426 = 25 μg} and these are the approximate doses used in the treatment of postmenopausal osteoporosis.
References
Kanis J et al (2008) European guidance for the diagnosis and management of osteoporosis in postmenopausal women. Osteoporos Int 19:399–428 doi:10.1007/s00198-008-0560-z
Zhou H et al (2002) Solid phase synthesis of N terminal 1-34 peptide of human parathyroid hormone. Zhongguo Shenghua Yaowu Zazhi 23:109–111
Ishibashi Y et al (1993) Fragmentation of parathyroid hormone, a 9.4 kDa polypeptide, in liquid secondary ion mass spectrometry. Biol Mass Spectrom 22:98–100
EPAR (2004) Forsteo scientific discussion. http://www.emea.europa.eu/humandocs/PDFs/EPAR/forsteo/659802en6.pdf
EPAR (2006) Preotact scientific discussion. http://www.emea.europa.eu/humandocs/PDFs/EPAR/preotact/H-659-en6.pdf
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Clausen, J.O. Comment on Kanis et al.: “European guidance for the diagnosis and management of osteoporosis in postmenopausal women”. Osteoporos Int 20, 1631 (2009). https://doi.org/10.1007/s00198-008-0812-y
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DOI: https://doi.org/10.1007/s00198-008-0812-y